Vocab

DNA (deoxyribonucleic acid) Long double-stranded chains of nucleotides. The nucleotides consist of the sugar deoxyribose, a phosphate group, and one of four nitrogenous bases: adenine (A), cytosine (C), guanine (G), or thymidine (T).

DNA microarray Asolid substrate containing up to millions of immobilized spots of different oligonucleotides or gene-specific probes. Labeled nucleic acid samples, such as mRNAs extracted from a specific tissue or genomic DNA from an individual, can be hybridized to a DNA microarray to quantify the abundance of different species of nucleic acid molecules in samples. It can be used to determine gene expression patterns or profiles of single- nucleotide and copy number polymorphisms. (Figure 13-16)

DNA shuffling Aprocess by which part or all of the protein- coding sequence of one gene is fused with that of another gene, usually following chromosomal duplication or translocation. The specific type of DNA shuffling that occurs when translocational breakpoints are within introns of two genes is called exon shuffling. (Figure 12-6)

L-dopa The intermediate metabolite between tyrosine and dopamine in the catecholamine biosynthetic pathway. (Figure 11-20)

dopamine Amonoamine neuromodulator derived from the amino acid tyrosine. (Figure 11-20; Table 3-2)

Doppler effect Aphenomenon whereby the sound frequency detected by an observer increases fi the sound-emitting object moves toward the observer and decreases if the sound-emitting object moves away from the observer.

dorsal column pathway An axonal pathway from the spinal cord ot the brainstem, it consists of ascending branches of proprioceptive neurons and Aß-LTMRs, as wel as axons of some dorsal horn projection neurons. (Figure 6-70)

dorsal cortex The evolutionary precursor to the mammalian

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dorsal horn The dorsal part of the spinal gray matter devoted to processing somatosensory information. (Figure 6-70)

dorsal horn projection neuron Aneuron located in the dorsal horn of the spinal cord that projects its axon to the brainstem to relay touch signals. (Figure 6-70)

dorsal root The place where somatosensory axons enter the

spinal cord. (Figure 8-6)

dorsal root ganglia (DRG) Clusters of somatosensory neurons located along an axis parallel to the spinal cord used for sensation of the body (as opposed to the face). (Figure 6-63)

dorsal stream Avisual processing pathway from primary visual cortex to the parietal cortex. It is responsible for analyzing motion and depth; the w' here' stream. (Figure 4-48)

dorsal-ventral Ofabodyaxis,frombacktobelly.

Doublesex (Dsx) ADrosophila gene that encodes sex-specific transcription factors produced by sex-specific alternative splicing. The D s isoform determines sex-specific somatic structures and also regulates sexual behavior. (Figure 9-4)

Down syndrome Asyndrome caused by the presence of an extra copy of Chromosome 21. It is the most common form of intellectual disability with an established genetic etiology.

doxycycline (Dox) Atetracycline analog that readily diffuses across cell membranes and the blood-brain barrier. It is widely used for temporal regulation of gene expression through the tTA/ rtTA/TRE system. (Figure 13-13)

driver transgene In binary expression, it is the transgene that expresses a transcription factor or a recombinase under the

control of a tissue-specific or temporally regulated promoter.

(Figure 13-13)

driving force The force that pushes an ion into or out of a cell, it equals the difference between the membrane potential of the cell and the equilibrium potential of the ion.

drug addiction Compulsive drug use that persists despite long- term negative consequences. It is often associated with loss of self-control and propensity to relapse.

Dscam (Down syndrome cell adhesion molecule) Encoded by a gene on human chromosome 21, which is trisomic in Down

syndrome, it is an evolutionary conserved protein that, in insects, exhibits extraordinary molecular diversity due to alternative

splicing. (Figure 7-20)

T R PA l A Drosophila TRP channel that is activated by high temperature. (Figure 13-43)

dye-coupling The diffusion of a small-molecule dye from one cell to another through gap junctions. It is used as a criterion to identify the presence of gap junctions between two cells.

dynamic range In sensory systems, the ratio between the largest and smallest values of a given dimension of sensory stimuli that can be detected and distinguished.

dynamical state Apoint in a coding space, representing the status of a dynamical system at a given time. See also coding space. (Figure 8-28)

dynamical system Aphysical system whose future state is a function of its current state, its input, and possibly some noise. It can be represented as time-dependent change of neural states in a coding space. See also coding space. (Figure 8-28)

dynein Aminus-end-directed, microtubule-based motor protein. (Figure 2-6)

eardrum Amembrane at the intersection of the mammalian outer ear and middle ear whose vibrations are transmitted

by the bones in the middle ear to the cochlea in the inner ear. (Figure 6-45)

echolocation The ability of certain species to use echoes of their own ultrasonic sound pulses to locate objects.

ectoderm The outer germ layer that gives rise to the skin and nervous system. (Figure 7-2)

efferent An axon that projects from the CNS to peripheral targets. It can also be generalized to describe an output axon from a particular neural center within the CNS.

efficacy of synaptic transmission (synaptic efficacy) The strength of a synaptic connection, it is usually measured by the mean magnitude of the postsynaptic response to a defined presynaptic stimulus.

E-I balance The relative strength of synaptic excitation versus synaptic inhibition.

electrical circuit Connected electrical elements that contain at least one closed current path.

electrical gradient Electrical potential difference between the two sides of the membrane, which contributes to the direction

and magnitude of movement of a charged solute across the membrane. It promotes the movement of a charged solute toward

the side with the opposite charge. (Figure 2-9)

electrical synapse Acell-cell junction enriched in gap junction channels. It transmits (usually bidirectionally) both depolarizing and hyperpolarizing signals between the two cells. See also gap

junction. (Figure 1-14)

electrochemical gradient Acombination of chemical and electrical gradients, which determines the directionand magnitude of movement of a charged solute across the membrane. (Figure 2-9)

electroencephalography (EEG) Amethod for recording the electrical potential differences between surface electrodes placed on specific locations of the scalp. It reports the collective electrical activities of many cortical neurons underneath the surface electrodes. (Figure 8-51; Figure 11-47)

electromotility Aproperty of the cochlear outer hair cells whereby hyperpolarization causes the cells to lengthen, and depolarization causes them to shorten, along their long axis. (Figure 6-52)

electron microscopy Amicroscopic technique that uses beams of electrons to create an image of a specimen. tI has much higher resolution than light microscopy and can resolve structures that are separated by a nanometer or less. See also transmission electron microscopy and scanning electron microscopy.

electroporation Aprocedure in which DNA containing a transgene is introduced into cells by applying electrical current to facilitate the transfer of negatively charged DNA molecules into the cells. In animals, this can be achieved by placing a micropipette containing the DNA near the cells of interest and applying electrical current.

embryonic stem (ES) cells Pluripotent cells derived from early embryos that can be propagated indefinitely in vitro and that can give rise to all cell types of an embryo in vivo. (Figure 11-23)

end-plate current The current that crosses a muscle cell membrane in response to release of acetylcholine from a presynaptic motor neuron.

end-plate potential (EPP) Depolarization produced in a postsynaptic muscle cell by acetylcholine released from a presynaptic motor neuron in response to an action potential. (Figure 3-1)|

endocannabinoids Endogenous cannabinoids, which are lipophilic molecules such as anadamide and 2-arachidonylglycerol. They can be produced in response to a rise of intracellular Ca?+ concentration in certain postsynaptic neurons and diffuse across the synapse to affect presynaptic neurotransmitter release by binding to the CB1 G-protein-coupled receptor.

endocrine Of or related to a form of signaling in which a

recipient cell receives a signal produced by a remote source and delivered through systemic circulation.

endocrine system Asystem consisting of glands that release hormones into the bloodstream, so that those hormones can circulate throughout the body.

endocytosis The process by which cells retrieve, via budding

of intracellular vesicles from the plasma membrane, fluid and proteins from the extracellular space and transmembrane proteins from the cell's plasma membrane. (Figure 2-2)

endoderm The inner germ layer that gives rise to a variety of tissues such as the liver, the inner linings of the gut, and the respiratory tract. (Figure 7-2)

endoplasmic reticulum (ER) Anetwork of membrane- enclosed compartments in eukaryotic cells where secreted and transmembrane proteins are made and into which secreted and transmembrane proteins are translocated. It aso serves as a store for intracellular Ca?+. (Figure 2-2)

endosome Amembrane-enclosed organelle produced by endocytosis. tI carries newly internalized extracellular materials and transmembrane proteins. (Figure 2-2)

engram Physical substrate for memory, ti is also called memory trace.

enteric nervous system Adivision of the autonomic nervous system that is associated with the gastrointestinal tract and that regulates digestion rather independently of the rest of the autonomic nervous system.

entorhinal cortex The part of the temporal cortex overlying the hippocampus. It provides major input to and receives output from the hippocampus. It plays amajor role in representing spatial information. (Figure 10-6)

entrainment The process by which a stimulus, such as light, resets the phase of the circadian clock.

Eph receptors Receptor tyrosine kinases that bind ephrins

with their extracellular domains. Two Eph receptor subtypes, the EphA and EphB receptors, typically bind ephrin-As and ephrin-

Bs, respectively, but this specificity is not absolute. They can also serve as ligands during reverse signaling. (Figure 5-7; Figure 5-12)

ephrins Cell-surface proteins that usually act as ligands for Eph receptors to mediate repulsion during axon guidance. The ephrin family consists of two subfamilies: ephrin-As are attached to the

extracellular face of the plasma membrane by GPI, and ephrin-

Bs are transmembrane proteins. They can also serve as receptors during reverse signaling. (Figure 5-7; Figure 5-12)

epigenetic modifications Molecular modifications to DNA and chromatin, such as DNA methylation and various forms of post- translational modification of histones. They do not modify the DNA sequence but can alter gene expression.

epilepsy Amedical condition characterized by recurrent seizures. See also seizure.

epinephrine Ahormone produced primarily by chromaffin cells in the adrenal gland that mediates systemic responses to extreme conditions, such as the systemic response associated with fright, fight, and flight. It also acts as a modulatory neurotransmitter in a small group of neurons in the brainstem. (Figure 11-20)

epithelialNatchannel(ENaC) AmemberofaclassofNa+ channels involved in Nat reabsorption by epithelial cells, ti is also essential in mammals for the taste of low concentrations of salts.

Its invertebrate homologs participate in mechanotransduction. (Figure 6-41)

EPSC (excitatory postsynaptic current An inward current produced by binding of an excitatory neurotransmitter to its receptor. (Figure 3-23)

EPSP (excitatory postsynaptic potential) Atransient depolarization of a postsynaptic cell associated with an excitatory postsynaptic current (EPSC). (Figure 3-23)

equilibrium potential The membrane potential at which there is no net flow of an ion across the membrane, because the electrical

and chemical forces are equal in magnitude but opposite in direction.

estradiol Asteroid hormone produced by the ovaries of sexually mature females. tI can also be produced outside the ovaries by the actions of aromatase on testosterone. (Figure 9-24)

estrogen Afemale sex hormone, such as estradiol.

estrogen receptor Acytosolic protein that upon binding of an estrogen (such as estradiol) translocates ot the nucleus, where ti acts as atranscription factor. (Figure 9-24)

eukaryote Organism made of cells) with a nuclear membrane that separates the genetic material from the rest of the cellular components.

eumetazoan Ataxon that includes cnidarians, bilaterians, and the most recent common ancestor of cnidarians and bilaterians. (Figure 12-2)

exchanger See antiporter

excised patch Apatch clamp configuration in which the membrane patch underneath the electrode is excised from the cel and placed in a defined medium. tI si often used ot study the biophysical and biochemical properties of the ion channel(s) ni the membrane patch. (Figure 13-37)

excitability Aproperty of aneuron that defines how readily it fires action potentials.

excitable cell Acell that produces action potentials, such as

a neuron or a muscle cell. tI can also refer to any cell that uses electrical signaling to receive, integrate, propagate, and transmit information.

excitation-contraction coupling Aprocess by which action potentials ni muscle cells lead ot muscle contraction. tI involves actin/myosin-mediated contraction triggered by arise of intracellular Ca?* concentration. (Figure 8-5)

excitatory neuron Aneuron that, when activated, depolarizes its postsynaptic target cells and makes them more likely to fire action potentials.

excitatory neurotransmitter Aneurotransmitter that depolarizes postsynaptic target cells and makes them more likely to fire action potentials.

excitotoxicity Toxicity to neurons caused by excessive stimulation by excitatory neurotransmitters such as glutamate, which results in a large or persistent increase in intracellular Ca?+ concentration.

exocrine system Asystem consisting of glands that excrete fluids, such as sweat or tears, locally through specific ducts.

exocytosis The process by which intracellular vesicles fuse with the plasma membrane to release secreted proteins into the extracellular space, and to deliver lipids and transmembrane proteins to the plasma membrane. (Figure 2-2)

exon The part of an RNA molecule that is retained in mRNA after splicing. (Figure 2-2)

exon shuffling See DNA shuffling.

explicit memory Aform of memory that requires conscious recall, such as memory for names, facts, and events. tI is also called declarative memory. (Figure 10-4)

expression cloning A strategy for cloning a gene by transfecting cells with pools of cDNAs and using a functional assay to identify the pool that contains the cDNA of interest. The assay is reiterated with progressively divided pools of cDNAs until a single cDNA is identified. (Figure 6-68)

extensor Amuscle whose contraction increases the angle of a

joint. (Figure 8-8)

extinction In classical conditioning, adecrease in the conditioned response caused by repeated exposure to the conditioned stimulus without the unconditioned stimulus. In operant conditioning, adecrease ni areinforced action or an increase ni a punished action when the action si repeatedly not reinforced or punished, respectively.

extracellular recording Atechnique for recording voltage changes, such as action potentials from a single neuron or synaptic activity from a population of neurons. It utilizes an electrode, often made of metal wire that is insulated except at

the tip, which si placed at close range to a neuronal cel body or a synapse-rich region. (Figure 13-31)

exuberant connection Excess connection made during development that is not retained in adulthood.

Eyeless ADrosophila transcription factor belonging to the Pax family. It contains a homeobox and a paired box and is required

for eye development. Its ectopic expression in other structures,

such as the antenna or the wing precursors, can induce ectopic eye formation. Se also Pax6.

facilitating synapse Asynapse at which successive presynaptic action potentials trigger progressively larger postsynaptic responses. (Figure 3-15)

familial Alzheimer's disease (FAD) Asmall subset of Alzheimer's disease cases that follows a Mendelian (autosomal dominant) inheritance pattern.

fast axonal transport Intracellular transport at a speed of

50-400 m per day; cargos subject ot fast axonal transport include organelles, as well as transmembrane and secreted proteins. (Figure 2-4)

fear conditioning See contextual fear conditioning and auditory fear conditioning.

feedback Inhibition Acircuit motif ni which an excitatory neuron both provides output to and receives input from an inhibitory neuron. (Figure 1-21)

feedforward excitation Acircuit motif in which serially connected excitatory neurons propagate information across multiple regions of the brain. (Figure 1-21)

feedforwardinhibition Acircuitmotifinwhichapostsynaptic neuron receives both direct excitatory input from apresynaptic

neuron and disynaptic inhibitory input from the same excitatory neuron via an inhibitory interneuron. (Figure 1-21)

fertilization The fusion of sperm and egg to create a genetically new organism. (Figure 7-2)

Fezt2 Atranscription factor that specifies subcerebral projection neuron identity. (Figure 7-10)

fibroblast growth factor (FGF) Amember of a family of secreted

growth factors that act as morphogens to pattern early embryos during development.

field excitatory postsynaptic potential (fEPSP) Excitatory postsynaptic potentials recorded from a population of neurons near the tip of an extracellular electrode. fEPSPs evoked by stimulation of axonal inputs to a population are often used as a measure of the strength of synaptic transmission between the stimulated inputs and neurons near the recording electrode. (Figure 10-8)

filamentous actin (F-actin) Amajor cytoskeletal element composed of two parallel helical strands of actin polymers. They are also called microfilaments. (Figure 2-5; Figure 8-3)

filopodia Athin, protruding process of the growth cone made of bundled F-actin. (Figure 5-15)

fissure Adeep invagination of the cortical surface that separates areas of the cerebral cortex.

fitness With respect to an allele (or phenotype), fitness is the ratio of the frequency of the allele (or phenotype) in a population after one generation of selection to the frequency of the allele

(or phenotype) in the same population before the selection.

With respect to an individual, fitness is the number of second- generation descendants the type of individual with a particular genome is expected to have.

fixed (of an allele) The state of an allele when every member of the population si homozygous for the allele.

fixed action pattern An instinctive sequence of behaviors, ti is largely invariant and runs to completion once triggered.

fiavor Asynthesis of taste and olfaction.

fiexor Amuscle whose contraction decreases the angle of a joint. (Figure 8-8)

fioor plate Astructure at the ventral midline of the spinal cord.

FLP recombinase Ayeast-derived enzyme that catalyzes recombination between two sequence-specific DNA elements called FRT (FLP recognition target) sites. (Figure 13-7;

Figure 13-23)

fiuorescence resonance energy transfer (FRET)

Aphenomenon in which energy is transferred between

two fluorophores with an efficiency inversely proportional to the sixth power of the distance between them. It can be used experimentally to determine the distance between two fluorophores. It si also known as Förster resonance energy transfer (FRET).

fiuoxetine Awidely used antidepressant that acts as a selective serotonin reuptake inhibitor. Its brand name is Prozac. (Figure 11-27). See also SSRI.

Fmrl See fragile-X syndrome. FMRP See fragile-X syndrome.

focal selzures Seizures that affect a relatively small, discrete region of the brain.

follicle-stimulating hormone (FSH) See gonadotropins.

forebrain The rostral-most division of the three divisions of

the embryonic brain. It gives rise to the cerebral cortex, basal ganglia, hippocampus, amygdala, thalamus, and hypothalamus. (Figure 1-8; Figure 7-3)

forward genetic screen Aprocedure to identify genes that are necessary for a biological process. It usually involves (1) inducing mutations in a population of experimental animals (such as through radiation, transposon insertion, or treatment with a chemical mutagen) so that each animal carries a different set of random mutations in a small number of genes or a single gene, and (2) identifying mutations that disrupt the biological process of interest based on the phenotypes exhibited by the offspring of the mutagenized animals. (Figure 13-4)

forward signaling See reverse signaling.

Fos An immediate early gene that encodes a transcription factor. Its expression is commonly used as an indicator of recently activated neurons.

fovea The central part of the primate retina that has a high density of cones. (Figure 4-14)

fragile-X syndrome (FXS) Aleading cause of inherited intellectual disability, it is caused by expanded trinucleotide repeats in the 5' untranslated region of the Fmrl gene, which encodes an RNA binding protein called the fragile Xmental retardation protein (FMRP).

Frazzled See DCC/Unc40.

frequency tuning The property whereby a cell in the auditory system is best activated by sounds of a particular frequency. It si usually represented as a V-shaped curve on a frequency-intensity

frontal eye field (FEF) Aneocortical area that receives extensive feedforward connections from both the dorsal and ventral streams and sends feedback projections to many visual cortical areas. (Figure 4-48)

frontal lobe One of the four cerebral cortex lobes, it is located at the front of the brain rostral to the central sulcus. (Figure 1-23) |

FRT See FLP recombinase.

Fruitless (Fru) ADrosophila gene that regulates al aspects

of male courtship rituals. The splicing of one of its transcripts

is regulated by a hierarchy of sex-determining splicing factors: females express a non-functional splice isoform of the protein while males express a functional form of the protein (FruM) that acts as a transcription factor. (Figure 9-4)

functional architecture The physical arrangement of neurons in a brain region based on their functional properties.

functional magnetic resonance imaging (MRI) Anon-

invasive functional brain imaging technique, it monitors signals originating from changes in blood flow that are closely related to local neuronal activity. It is also called BOLD (blood-oxygen-level dependent) fMRI.

fundamental frequency The frequency of the lowest frequency component of a periodic waveform.

fura-2 Asmall molecule Ca?* indicator whose optimal excitation wavelength shifts from 380 nm to 350 nm when Ca?+ is bound. The ratio of fluorescence intensity measured at excitation wavelengths of 350 nm and 380 nm can be used as a sensitive measure of Ca?+ concentration.

fusiformfacearea Aspecificareaofhumantemporalcortexthat is preferentially activated by images of human faces.

GABA Aglutamate derivative that si the predominant inhibitory neurotransmitter in vertebrates and invertebrates. (Figure 3-16;

Table 3-2)

GABA, receptor An ionotropic receptor that si gated by GABA and mediates fast inhibition. (Figure 3-21; Figure 11-29)

GABA, receptor Ametabotropic receptor that is activated by GABA and that mediates slow inhibition.

gain control Modulation of the slope of a system's input-out function, it is often used to restrict output to a limited dynamic r a n g e .

gain-of-function experiments Experiment in which a specific component is added to the system. They are often used to test whether the added component is sufficient for the system to function in a specific context.

GALA Ayeast transcription factor that binds to a DNA element called a UAS (upstream activation sequence) in the promoter regions of genes to activate the transcription of those genes. (Figure 13-13)

galanin Aneuropeptide with diverse functions, including the promotion of parental behavior.

ganglion Acluster of neurons located in the peripheral nervous system.

ganglionic eminences Developing ventral telencephalon structures that include the medial, caudal, and lateral ganglionic eminences (MGE, CGE, LGE). They are the birthplaces of cortical GABAergic neurons (MGE and CGE), GABAergic interneurons in the basal ganglia and amygdala (MGE and CGE), and olfactory bulb interneurons and most GABAergic projection neurons in the striatum (LGE). (Figure 7-5)

gap junction The morphological correlate of the electrical synapse, which usually contains hundreds of closely clustered channels that bring the plasma membrane of two neighboring cells together and allow passage of ions and small molecules between the two cells. (Figure 3-38)

gastrin-releasing peptide receptor (GRPR) AG-protein-

coupled receptor that is activated by gastrin-releasing peptide and is involved in processing itch signals.

gastrula The product of gastrulation, it is an embryo with a three-layered structure consisting of ectoderm, mesoderm, and endoderm. (Figure 7-2)

gastrulation The process by which an embryo is transformed from a ball of cells into a structure with three distinct layers: ectoderm, mesoderm, and endoderm. (Figure 7-2)

GCaMP AGFP-based genetically encoded Ca?* indicator whose fluorescence increases in response to arise of Ca'+ concentration.

GCAP (guanylate cyclase activating protein) Acalcium- binding protein which in its calcium-free form binds ot and activates guanylate cyclase.

gene Asegment of DNA that carries the instructions for how and when to make specific RNAs and proteins. (Figure 2-2)

gene expression profiling Determining the genes expressed in a sample on a whole-genome scale using methods such sa microarray and RNA-seq.

gene therapy The use of DNA and/or genome modification to treat disease.

generalized seizures Seizures that affect multiple, bilateral regions of the brain.

genetic drift The process in which chance events that result

in death of an organism or failure of an organism to reproduce can lead ot the loss of an allele from a smal population and an increase in the prevalence of the remaining allele(s).

genetic mosale animal An animal that contains cels of more than one genotype. (Figure 5-36; Figure 13-10)

genetic susceptibility locus Agenomic locus with variant(s) that increase the probability of carriers developing a trait (such as a disease).

genetically encoded Ca?+ indicators

Proteins whose fluorescence properties change before and after binding to Ca?+. See also Ca?+ Indicator. (Figure 13-38)

genome engineering The general process of altering the genome at a predetermined locus, such as deleting a piece of endogenous DNA, inserting a piece of foreign DNA, or creating a specific base- pair change.

genome-wide association study (GWAS) Astrategy for identifying genes associated with a specific trait by comparing DNA samples collected from many people with or without the trait. The DNA samples are used to identify single nucleotide polymorphisms throughout the entire genome that are most strongly linked with the trait.

ghrelin Aneuropeptide produced by stomach-associated glands in response to a reduced glucose level. It acts as a hunger signal to stimulate eating. (Figure 8-43)

G, (inhibitory Gprotein) AGa variant that binds to adenylate cyclase and inhibits its activity.

gill-withdrawal refiex Areflex in the sea slug Aplysia in which the gil is withdrawn into the mantle shelf when a tactile stimulus is applied to its siphon. It has been used as a model system to

investigate the mechanisms that underlie simple forms of learning and memory.

glia Nonneuronal cells of the nervous system, they play essential roles for the development and function of neurons.

glomerulus Adiscrete, ball-like structure in the vertebrate olfactory bulb or insect antennal lobe where ORN axons form synapses with the dendrites of their postsynaptic target neurons. (Figure 6-3; Figure 6-17)

GluN1 See NMDA receptor. GluN2 See NMDA receptor.

glutamate An amino acid that is the predominant excitatory neurotransmitter in vertebrates. (Figure 3-16; Table 3-2)

glutamic acid decarboxylase (GAD) An enzyme that converts glutamate into GABA.

glycine An amino acid that is an inhibitory neurotransmitter released by a subset of brainstem and spinal cord neurons in vertebrates. (Figure 3-16; Table 3-2)

glycine receptor An ionotropic receptor that is gated by glycine and mediates fast inhibition. (Figure 3-21)

Goldman-Hodgkin-Katz (GHK) equation An equation that relates the membrane potential at equilibrium to the membrane permeabilities and concentrations of multiple ions on the two sides of a membrane. Avariant of the GHK equation relates the membrane potential at equilibrium to the equilibrium potential and conductance of each ion.

Golgi outpost Fragments of the Golgi apparatus that are located in neuronal dendrites. (Figure 7-18)

Golgi staining Ahistological staining method, it uses solutions of silver nitrate and potassium dichromate, which react to form a black precipitate (microcrystals of silver chromate). This precipitate accumulates stochastically in a small fraction of the nerve cells so that these cells, and most or all of their elaborate extensions, can be visualized against unstained tissue.

gonadotropin-releasing hormone (GnRH) Apre-hormone released by hypothalamic neurons (called GnRH neurons) that stimulates the release of gonadotropins by anterior pituitary endocrine cells. (Figure 9-27)

gonadotropins Afamily of hormones that includes luteinizing

hormone (LH) and follicle-stimulating hormone (FSH). Released by anterior pituitary endocrine cells, these hormones stimulate the maturation of male testes and female ovaries during puberty. In adults, they stimulate the testes to release testosterone and the ovaries to release estradiol. (Figure 9-27)

GPCR (G-protein-coupled receptor) Amember of a receptor family with 7 transmembrane domains that, upon ligand binding, activate trimeric G proteins, which in turn activate intracellular signaling cascades.

GPe (globus pallidus external segment) An intermediate nucleus in the basal ganglia indirect pathway. It contains GABAergic neurons that project to the GPi, SNr, and STN. (Figure 8-22)

GPI (globus pallidus internal segment) One of the two major

output nuclei of the basal ganglia. It contains GABAergic neurons that project to the thalamus. (Figure 8-22)

GPI (glycosylphosphatidylinositol) Alipid anchor that can covalently attach to an extracellular protein to anchor it to the plasma membrane. GPI-anchored protein can be released from the membrane by phosphatidylinositol-specific phospholipase C (PI-PLC), which cleaves the bond between the GPI group and the protein.

G, AGa variant that activates phospholipase C, ni turn leading to activation of the inositol-phospholipid signaling pathway.

(Figure 3-34)

graded potentials (local potentials) Membrane potentials that can change in continuous values, as opposed to the all-or-none property of the action potential. (Figure 2-18)

granule cells Neurons that are granular in appearance because they are densely packed, including three prominent types. The

cerebellar granule cells are the most numerous type of neuron in the brain; their cell bodies and dendrites reside in the granular layer of the cerebellar cortex where they receive mossy fiber input; their axons ascend into the molecular layer, where each bifurcates to become a parallel fiber to send glutamatergic output to Purkinje cells. (Figure 8-20). The granule cells in the hippocampus are

the major cellular constituents of the dentate gyrus; they receive input from the entorhinal cortex via the perforant path and send glutamatergic output to CA3 pyramidal neurons. (Figure 1-12;

Figure 10-6). The olfactory bulb granule cells constitute a large subtype of olfactory bulb interneurons that receive input from the secondary dendrites of mitral cells and send GABAergic output back to mitral cells. (Figure 6-17).

gray matter The parts of the CNS that are enriched with neuronal cell bodies, dendrites, axon terminals, and synapses and that appear gray.

green fiuorescent protein (GFP) Ajellyfish protein that emits green fluorescence when excited by blue light. It is widely used as a marker for gene expression and for live imaging.

grid cell Acel in the entorhinal cortex whose activity depends on an animal's location in an arena, with peak firing rate occurring at the apices of an imaginary hexagonal grid superimposed on the arena floor. (Figure 10-31)

growth cone Adynamic structure at the tip of a developing neuronal process, it enables the extension of the process and guides its direction.

G, (stimulatory Gprotein) AGa variant that binds ot adenylate cyclase and stimulates its activity. (Figure 3-33)

GTPase An enzyme that hydrolyzes GTP, converting it to GDP.

GTPase activating protein (GAP) Aprotein that switches GTPases of by accelerating the GTPases' endogenous activity, which converts GTP to GDP. (Figure 3-32)

guanine nucleotide exchange factor (GEF) Aprotein that switches GTPases on by catalyzing the exchange of GDP for GTP. (Figure 3-32)

guanylate cyclase An enzyme that produces G M P from GTP.

guide RNA In the CRISPR/Cas9 system, an RNA molecule that brings Cas9 to a target DNA sequence, where Cas9 generates a double-strand break. The guide RNA must contain sequences that base-pair with the target DNA. See also CRISPR and Cas9. (Figure 13-8)

gustatory nerve Abundle of axons that originate from the

basal ends of the taste receptor cells. The nerve projects to the nucleus of the solitary tract in the brainstem, and thus relays taste information from the tongue to the brain. (Figure 6-35)

gyrencephalic Of cortex, having gyri and sulci. (Figure 12-5) Ga, Gß, Gy See trimeric GTP-binding protein.

habituation Adecrease in the magnitude of responses to stimuli that are presented repeatedly.

hair cell The primary sensory cell for audition, it converts mechanical stimuli-movement of stereocilia at its apical end — into electrical signals. (Figure 6-47; Figure 6-50)

halorhodopsin Alight-activated inward chloride pump in archaea, it can be used to silence neuronal activity in heterologous system by light. See also optogenetics. (Figure 13-45)

harmonics Sounds with frequencies that are integer multiples of the fundamental frequency.

HCN (hyperpolarization-activated cyclic nucleotide-gated) channels Non-selective cation channels that are activated by hyperpolarization and whose gating is influenced additionally by the concentration of a specific intracellular cyclic nucleotide. (Figure 2-34)

head direction cell Acell that fires when an animal's head is facing a specific direction in space, regardless of the animal's location in the environment.

Hebb's rule Apostulate by Donald Hebb that describes how

learning can be transformed into a lasting memory, ti states: "When an axon of cell Ais near enough to excite a cell Band repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that As' efficiency, as one of the cells firing B, is increased."

Hebbian synapse Asynapse whose strength can be enhanced by co-activation of pre- and postsynaptic partners.

hedonic value The degree to which something is pleasant or unpleasant, which usually correlates with the degree to which something is potentially beneficial or harmful to an animal.

hemispheres The two sides of the brain.

heritability Ameasure of the contribution of genetic differences to trait differences within a population. It can be measured in twin studies as 2 ×(the correlation of the trait between pairs of monozygotic twins - the correlation of the trait between pairs of dizygotic twins).

herpes simplex virus (HSV) ADNA virus used to deliver transgenes into post-mitotic neurons. It has a capacity to include ~150 kb of foreign DNA. (Table 13-1)

heterophilic binding Binding of two different proteins, usually two different membrane proteins expressed from adjacent cells across the cell junction.

hindbrain The caudal-most division of the three divisions

of the embryonic brain. It gives rise ot the pons, medulla, and cerebellum. (Figure 1-8; Figure 7-3)

hippocampus Astructure underneath the cortical surface of the temporal lobe. It has been most studied for its role in the

acquisition of explicit memory and representation of space. (Figure 1-8; Figure 10-6)

histamine Amonoamine neuromodulator derived from the amino acid histidine. (Figure 3-16; Table 3-2)

histological sections Slices of frozen or chemically fixed tissue produced by microtomes, with thicknesses ranging from several to several hundred micrometers. They can be stained using

a number of different methods and examined under a light microscope.

homeodomain Originally discovered in proteins whose disruption causes transformation of one body part into another, it is a DNA-binding domain shared by all Hox proteins and many other transcription factors. It is also called ahomebox.

homeostasis The maintenance of a steady state of a physiological parameter-such as blood pressure, body temperature, or nutritional level-by feedback physiological and behavioral responses. (Figure 8-34)

homeotic transformation Transformation of one body part to another, such as the transformation of a pair of antennae to a pair of legs in Drosophila antennapedia mutants.

homologous recombination Exchange of nucleotide sequences between two identical or highly similar DNA molecules. It occurs

naturally in certain cells due to its role in specific biological processes, such as in germ-line cells during meiotic crossing over.

It is also used experimentally for genome engineering, such as the generation of knockout and knock-in alleles. (Figure 13-6; Figure 13-8)

homophilic binding Binding of two identical proteins, usually two membrane proteins expressed from adjacent cells across the

cel junction.

horizontal cell An inhibitory neuron in the vertebrate retina whose actions influence the signals that are transmitted from the photoreceptors ot the bipolar cells. (Figure 4-26)

horizontal gene transfer Gene transfer from one organism ot another through mechanisms other than reproduction, such as via viral transduction.

horizontal sections Asection plane that is perpendicular to the dorsal-ventral axis.

Hox gene Amember of a family of evolutionarily conserved genes that are arranged in genomes in clusters and that encode homeobox-containing transcription factors. Hox genes define

the anterior-posterior body axes of most invertebrates and al vertebrates and also regulate neuronal fate at later developmental stages. (Figure 12-32)

HTMR (high-threshold mechanoreceptor) Amechanosensory neuron that senses pain caused by strong mechanical stimuli. (Figure 6-64)

huntingtin See Huntington's disease.

Huntington's disease (HD) Adominantly inherited disease that

usually strikes patients during midlife. It si characterized initially by depression or mood swings and subsequently by abnormal movements due ot degeneration of striatal neurons. It si caused by expanded poly-glutamine repeats in the huntingtin protein. (Figure 11-14)

HVC (high vocal center) Adorsal forebrain nucleus in the songbird essential for song production. (Figure 9-21)

hyperpolarization Achange in the electrical potential inside the cel toward amore negative value.

hypocretin (orexin) Aneuropeptide expressed by specific lateral hypothalamus neurons, ti is important for regulating sleep and eating.

hypogonadotropic hypogonadism Adisorder characterized by delayed, reduced, or absent puberty due to reduced gonadotropin

hypothalamus Acollection of nuclei ventral to the thalamus, it controls many bodily functions including eating, digesting, metabolic rate, drinking, salt intake, reproduction, body temperature, emergency response, and circadian rhythms. It executes many of these functions by regulating the autonomic nervous system and neuroendocrine system. (Figure 1-8; Figure 8-34)

identified neuron Aneuron that can be recognized across individuals of the same species due to its stereotyped location, size, and shape.

Ig CAM (immunoglobulin cell adhesion molecule) Acell adhesion molecule that contains immunoglobulin domains on its extracellular side.

Imipramine Atricyclic antidepressant that inhibits the plasma membrane monoamine transporters. (Figure 11-27)

immediate early genes (IEGs) Aclass of genes whose transcription is rapidly induced by external stimuli without requiring new protein synthesis.

immuno-EM Acombination of immunostaining and electron microscopy used to visualize the distribution of individual

proteins at an ultrastructural level. (Figure 13-24)

immunostaining Astaining method that uses antibodies to visualize the distributions of proteins in fixed tissues. The most common form uses sequential application of two antibodies: a primary antibody that binds the protein of interest and a fluorescence- or enzyme-conjugated secondary antibody that binds to the primary antibody. Protein distribution can be visualized by fluorescence or a color substrate produced by the enzyme conjugated to the secondary antibody.

implicit memory Aform of memory in which previous experience aids in the performance of a task without conscious recall. It is also called non-declarative memory or procedural memory. (Figure 10-4)

in situ hybridization Amethod for determining mRNA distribution in tissues by hybridizing labeled gene-specific nucleic acid probes to fixed histological sections or whole-mount tissues.

in vitro mutagenesis Amolecular biology technique used to alter the sequence of agene in atest tube.

inactivation (of ion channels) Adecrease of ion conductance

through a channel after an initial increase. The ion channel when inactivated is in a distinct state from when it is closed.

indirect pathway (in basal ganglia) An axonal projection from a subset of spiny projection neurons that terminate in the GPe and STN. (Figure 8-22)

induced pluripotent stem (IPS) cells Pluripotent cells produced experimentally from differentiated cells by a variety of means, such as forced expression of key transcription factors involved

in maintaining the pluripotency of embryonic stem cells. (Figure 11-23)

induction Amechanism for determining cell fate in which a

cell is born with the same potential to develop into different cell types as its sibling or cousins, and its fate is acquired by receiving external signals (i.e. the cell's fate is 'induced' by external cues).

inferior colliculus A midbrain nucleus that integrates auditory signals from brainstem nuclei. It sends auditory output to the thalamus and to the nearby superior colliculus/ tectum. (Figure 6-54)

Inferior olive Anucleus in the medulla containing neurons whose axonal projections to the cerebellum form climbing fibers. (Figure 8-20)

inhibitory neuron Aneuron that, when activated, hyperpolarizes its postsynaptic target cells and makes them less likely to fire action potentials.

inhibitory neurotransmitter Aneurotransmitter that hyperpolarizes postsynaptic target cells and makes them less likely to fire action potentials.

Initial segment of the axon

The segment of the axon closest to the neuronal cell body, it is usually the site of action potential

initiation.

Innate Atrait or behavior that is genetically programmed and that is thus with an organism from birth rather than acquired by experience.

Innate song The song a songbird would sing fi raised in acoustic isolation during the sensory stage of song learning.

innexins Aprotein component of gap junctions in invertebrates.

Inositol 1,4,5-triphosphate (IPs) Asecond messenger that binds ot the IP, receptor on the endoplasmic reticulum (ER) membrane to trigger the release of ER-stored Ca?+ into the cytosol.

(Figure 3-34)

Input specificity (of LTP) Aproperty of long-term potentiation (LTP) whereby LTP occurs only at synapses that have experienced an LTP-inducing stimulus and not at unstimulated synapses on the same postsynaptic neuron. (Figure 10-9)

insular cortex Apart of the cerebral cortex that represents taste, pain, and interception. (Figure 6-35; Figure 8-33)

insulator An object or substance that does not allow electric current to pass. It is equivalent to a resistor with infinite resistance.

insulin Apeptide hormone produced by the pancreas in response to a rise in blood glucose level after meals. It regulates carbohydrate metabolism throughout the body, and also regulates food intake through its actions on target neurons in the brain. (Figure 8-43)

intellectual disability Acondition characterized by deficits in general mental abilities such as reasoning, problem-solving, planning, abstract thinking, judgment, and learning.

interaural level difference (ILD) The level difference of a sound that is received in the left ear and the right ear, used for sound localization.

interaural time difference (ITD) The difference in the arrival time of a sound at the left ear and the right ear, used for sound localization.

HTMR (high-threshold mechanoreceptor) Amechanosensory neuron that senses pain caused by strong mechanical stimuli. (Figure 6-64)

huntingtin See Huntington's disease.

Huntington's disease (HD) Adominantly inherited disease that

usually strikes patients during midlife. It si characterized initially by depression or mood swings and subsequently by abnormal movements due ot degeneration of striatal neurons. It si caused by expanded poly-glutamine repeats in the huntingtin protein. (Figure 11-14)

HVC (high vocal center) Adorsal forebrain nucleus in the songbird essential for song production. (Figure 9-21)

hyperpolarization Achange in the electrical potential inside the cel toward amore negative value.

hypocretin (orexin) Aneuropeptide expressed by specific lateral hypothalamus neurons, ti is important for regulating sleep and eating.

hypogonadotropic hypogonadism Adisorder characterized by delayed, reduced, or absent puberty due to reduced gonadotropin

hypothalamus Acollection of nuclei ventral to the thalamus, it controls many bodily functions including eating, digesting, metabolic rate, drinking, salt intake, reproduction, body temperature, emergency response, and circadian rhythms. It executes many of these functions by regulating the autonomic nervous system and neuroendocrine system. (Figure 1-8; Figure 8-34)

identified neuron Aneuron that can be recognized across individuals of the same species due to its stereotyped location, size, and shape.

Ig CAM (immunoglobulin cell adhesion molecule) Acell adhesion molecule that contains immunoglobulin domains on its extracellular side.

Imipramine Atricyclic antidepressant that inhibits the plasma membrane monoamine transporters. (Figure 11-27)

immediate early genes (IEGs) Aclass of genes whose transcription is rapidly induced by external stimuli without requiring new protein synthesis.

immuno-EM Acombination of immunostaining and electron microscopy used to visualize the distribution of individual

proteins at an ultrastructural level. (Figure 13-24)

immunostaining Astaining method that uses antibodies to visualize the distributions of proteins in fixed tissues. The most common form uses sequential application of two antibodies: a primary antibody that binds the protein of interest and a fluorescence- or enzyme-conjugated secondary antibody that binds to the primary antibody. Protein distribution can be visualized by fluorescence or a color substrate produced by the enzyme conjugated to the secondary antibody.

implicit memory Aform of memory in which previous experience aids in the performance of a task without conscious recall. It is also called non-declarative memory or procedural memory. (Figure 10-4)

in situ hybridization Amethod for determining mRNA distribution in tissues by hybridizing labeled gene-specific nucleic acid probes to fixed histological sections or whole-mount tissues.

in vitro mutagenesis Amolecular biology technique used to alter the sequence of agene in atest tube.

inactivation (of ion channels) Adecrease of ion conductance

through a channel after an initial increase. The ion channel when inactivated is in a distinct state from when it is closed.

indirect pathway (in basal ganglia) An axonal projection from a subset of spiny projection neurons that terminate in the GPe and STN. (Figure 8-22)

induced pluripotent stem (IPS) cells Pluripotent cells produced experimentally from differentiated cells by a variety of means, such as forced expression of key transcription factors involved

in maintaining the pluripotency of embryonic stem cells. (Figure 11-23)

induction Amechanism for determining cell fate in which a

cell is born with the same potential to develop into different cell types as its sibling or cousins, and its fate is acquired by receiving external signals (i.e. the cell's fate is 'induced' by external cues).

inferior colliculus A midbrain nucleus that integrates auditory signals from brainstem nuclei. It sends auditory output to the thalamus and to the nearby superior colliculus/ tectum. (Figure 6-54)

Inferior olive Anucleus in the medulla containing neurons whose axonal projections to the cerebellum form climbing fibers. (Figure 8-20)

inhibitory neuron Aneuron that, when activated, hyperpolarizes its postsynaptic target cells and makes them less likely to fire action potentials.

inhibitory neurotransmitter Aneurotransmitter that hyperpolarizes postsynaptic target cells and makes them less likely to fire action potentials.

Initial segment of the axon

The segment of the axon closest to the neuronal cell body, it is usually the site of action potential

initiation.

Innate Atrait or behavior that is genetically programmed and that is thus with an organism from birth rather than acquired by experience.

Innate song The song a songbird would sing fi raised in acoustic isolation during the sensory stage of song learning.

innexins Aprotein component of gap junctions in invertebrates.

Inositol 1,4,5-triphosphate (IPs) Asecond messenger that binds ot the IP, receptor on the endoplasmic reticulum (ER) membrane to trigger the release of ER-stored Ca?+ into the cytosol.

(Figure 3-34)

Input specificity (of LTP) Aproperty of long-term potentiation (LTP) whereby LTP occurs only at synapses that have experienced an LTP-inducing stimulus and not at unstimulated synapses on the same postsynaptic neuron. (Figure 10-9)

insular cortex Apart of the cerebral cortex that represents taste, pain, and interception. (Figure 6-35; Figure 8-33)

insulator An object or substance that does not allow electric current to pass. It is equivalent to a resistor with infinite resistance.

insulin Apeptide hormone produced by the pancreas in response to a rise in blood glucose level after meals. It regulates carbohydrate metabolism throughout the body, and also regulates food intake through its actions on target neurons in the brain. (Figure 8-43)

intellectual disability Acondition characterized by deficits in general mental abilities such as reasoning, problem-solving, planning, abstract thinking, judgment, and learning.

interaural level difference (ILD) The level difference of a sound that is received in the left ear and the right ear, used for sound localization.

interaural time difference (ITD) The difference in the arrival

time of a sound at the left ear and the right ear, used for sound localization.

intermediate progenitor Aprogenitor cell produced by division of a radial glial cell. It divides further to give rise to post-mitotic neurons. (Figure 7-4)

interneuron Aneuron with the axon confined to the specific CNS region that houses the neuron's cell body, it is also called local neuron in this context. It may also refer to any neuron that is not a motor or a sensory neuron.

Interception The sense of the state of internal organs.

intersectional methods (in genetics) Strategies that use two orthogonal binary expression systems to refine patterns of transgene expression. (Figure 13-14)

interstitial branching Extending a collateral from the side of a growing process. (Figure 7-19)

Intracellular recording Aprocedure for measuring the membrane potential of a cell using an electrode inserted into or continuous with the cytoplasm. (Figure 13-31)

Intracellular vesicle A small, membrane-enclosed organelle in the cytoplasm of a eukaryotic cell. (Figure 2-2)|

intrinsic properties The electrophysiological properties of a neuron determined by the composition, concentration, subcellular distribution, and biophysical properties of ion channels it expresses.

Intrinsic signal imaging Amethod for measuring neuronal activity based on changes in the optical properties of tissue surrounding active neurons, primarily as a result of changes in blood oxygenation in those regions. (Figure 4-42)

Intrinsically photosensitive retinal ganglion cell (IpRGC) Atype of RGC that expresses melanopsin and that can be directly depolarized by light. (Figure 4-36)

intron The part of an RNA molecule that is removed during splicing. (Figure 2-2)

Inward-rectifier K+ channels Asubfamily of K+ channels that preferentially pass inward currents over outward currents: i.e. these channels pass current at membrane potentials more hyperpolarized than E, but allow minimal outward currents at membrane potentials more positive than Ex- (Figure 2-34)

ion channel Achannel that allows the passage of one or more specific species of ion.

ionotropic receptor A neurotransmitter receptor that functions as a neurotransmitter-gated ion channel to allow rapid (within

a few milliseconds) membrane potential changes in response to neurotransmitter binding. (Figure 3-21)

lontophoresis Atechnique by which ions or charged chemicals are locally applied from a micropipette via a current pulse.

IP, receptor An IP,-gated Ca?* channel on the ER membrane. (Figure 3-34)

iproniazid The first antidepressant discovered serendipitously in the 1950s. It is an inhibitor of monoamine oxidase.

(Figure 11-27)

IPSC (inhibitory postsynaptic current) An outward current produced by binding of an inhibitory neurotransmitter to its receptor. The fast component is usually mediated by Cl influx

through the GABA, receptor or glycine receptor.

ipsilateral Of the same side of the midline. For example, an

ipsilateral axonal projection is an axon that does not cross the midline and therefore terminates on the same side of the nervous system as the soma.

IPSP (Inhibitory postsynaptic potential) Atransient hyperpolarization of a postsynaptic cell associated with an inhibitory postsynaptic current (IPSC).

I-V curve Agraphical representation of the relationship between the current that passes through a piece of ion-channel-containing membrane (I) and the voltage across the membrane (V).

(Figure 3-17)

K* channels Ion channels that allow selective passage of K*, they constitute the most diverse channel family. (Figure 2-34)

K+-Cl- cotransporter Atransporter that couples K+ and C-I export to help maintain the Cl gradient across the membrane. (Figure 2-12)

kainate receptor Aglutamate-gated ion channel that conducts Nat and +K and that can be selectively activated by the drug kainate (kainic acid).

kinesins Afamily of microtubule-based motor proteins that are

mostly plus-end-directed. (Figure 2-6; Figure 2-7)

KissIR AG-protein-coupled receptor for kisspeptins, ti is also called GPR54.

kisspeptins Afamily of neuropeptides encoded by the Kis 1 gene that play an important role in activating GRH neurons. (Figure 9-27)

knee-jerk refiex The involuntary forward movement of the

lower leg due to the contraction of the quadriceps femoris

muscle (an extensor) and relaxation of the hamstring muscle

(a flexor). Atap of the knee (patellar ligament) stretches the muscle spindle in the quadriceps muscle and activates the proprioceptive sensory neurons. Sensory neuron activation initiates the reflex through monosynaptic excitation of motor neurons that excite the quadriceps femoris muscle and disynaptic inhibition of motor neurons that excite the hamstring muscle. (Figure 1-19)

knock-in Avariation of the knockout procedure in which an

in vitro engineered gene-either a transgene or a variant of an endogenous gene-is inserted into a specific chromosomal locus; the procedure can produce changes to endogenous genes as small as a single base pair.

knockout Agenetic engineering procedure that inactivates a specific gene. In the mouse, ti is usually achieved by homologous recombination in embryonic stem cells to create a mutation in the target gene. The resulting mutant mouse is called a knockout mouse for that particular gene. (Figure 13-6)

kuru See prion diseases.

lamellipodia Aveil-like meshwork of the growth cone made of branched F-actin. (Figure 5-15)

lamina (in Insect visual system) The first neuropil layer underneath the retina in the insect compound eye. (Figure 5-35)

landmark-based strategy A navigational strategy in which animals use external cues to determine their locations.

laser-scanning two-photon imaging See two-photon

microscopy.

late LTP Along-lasting phase of long-term potentiation (LTP),

usually lasting longer than 3 hours and requiring new protein synthesis and likely new gene expression.

lateral geniculate nucleus (LGN) Athalamic nucleus that receives visual input from retinal ganglion cell axons and sends output to the primary visual cortex. (Figure 4-35; Figure 4-37)

lateral horn Asecond-order olfactory center for odor-mediated innate behavior in the insect brain. It and the mushroom body are the two major output sites for projection neuron axons. (Figure 6-27)

lateral inhibition (in cell fate determination) The process by which neighboring cells are prevented from adopting identical

GLOSSARY G:15

G : 1 6 GLOSSARY

fates through cell-cell interactions, such as those mediated by Notch/Delta. (Figure 7-7)

lateral inhibition (in information processing) Acircuit motif in which an inhibitory neuron receives excitatory input from one or several parallel streams of excitatory neurons, and sends inhibitory output to many or all of the postsynaptic targets of these excitatory neurons. It is widely used in sensory systems. (Figure 1-21)

lateral intraparietal area (LIP) Acortical area in the primate parietal lobe implicated in making the decision to move eyes in a particular direction. (Figure 4-48)

length constant (space constant, 1.) Akey parameter that defines the passive electrical properties of electrical signaling. It

is equal to the distance along a neuronal process over which the amplitude of a membrane potential change decays to 1/e or about 37% of its original value.

lentivirus Aretrovirus that can infect post-mitotic neurons. It has a capacity to include 8- kb foreign DNA. (Table 13-1)

leptin Ahormone secreted by the fat tissues that negatively regulates food intake through its actions on specific neurons in the brain. (Figure 8-38)

Lewy bodies Intracellular inclusions that are a defining pathological feature of most forms of Parkinson's disease.

lidocaine An anesthetic that blocks action potential propagation by inhibiting voltage-gated Nat channels.

ligand Amolecule that binds to its receptor.

ligand-gated ion channel Atransmembrane protein complex that directly conducts ions in response to the binding of a neurotransmitter or other ligand.

light microscopy The most widely used microscopic technique in biology. tI uses beams of visible light (photons) to create an image of a specimen and, with the exception of some methods for super-resolution fluorescence microscopy, can only resolve structures greater than 200 nm apart.

light-sheet fluorescence microscopy A fluorescence microscopy technique in which only the focal plane (i.e. a single plane in the z-dimension) is illuminated with a thin sheet of a laser beam from

the side. Al fluorescence emissions in the focal plane are collected simultaneously by a detector. (Figure 13-19)

lissencephalic Of cortex, being smooth. (Figure 12-5)

LKB1 Aprotein kinase essential for determining axon fate during the establishment of neuronal polarity.

LMAN (lateral magnocellular nucleus of the anterior nidopallium) Aforebrain nucleus in the songbird that is essential for song learning but not for song production. (Figure 9-21)

lobula complex Neuropil underneath the medulla in the insect compound eye. (Figure 5-35)

high-frequency signals, ti reflects collective dendritic and synaptic activities of many neurons near the electrode. (Figure 10-8)

local interneuron (LN) (in insect olfactory system) A neuron whose processes are restricted to the antennal lobe. (Figure 6-27)

local neuron See interneuron.

local protein synthesis Translation of mRNA into protein in a neuron's cytoplasmic extensions (usually dendrites) rather than in the cell body.

locus coeruleus Abrainstem nucleus consisting of norepinephrine neurons that project widely across the brain. (Figure 8-54)

long-range cue (in axon guidance) Asecreted protein that can act at a distance from its cell of origin. (Figure 5-9)

long-term depression (LTD) Along-lasting decrease of synaptic efficacy that can be induced experimentally by specific stimulus conditions.

long-term memory Memory that lasts hours to years. (Figure 10-4)

long-term potentiation (LTP) A long-lasting enhancement of synaptic efficacy. tI can be induced experimentally under a variety of conditions, such as high-frequency stimulation of input axons. (Figure 10-8)

long-term synaptic plasticity Achange in the efficacy of synaptic transmission that lasts hours to the lifetime of the animal.

loose-patch recording A technique in which a patch electrode is placed against the cell membrane without forming a gigaohm seal. tI can only be used to record spiking activity (not sub- threshold activity), but, unlike whole-cell recording, does not affect the intracellular content of the recorded cell.

lordosis Aposture that female rodents assume when sexually aroused. It facilitates sexual intercourse.

loss-of-function experiment An experiment in which a specific

component is disrupted, often used to determine fi the missing component is necessary for the system to function.

loss-of-function mutation Amutation that disrupts the function of a gene.

lower envelope principle The idea that the limits of psychophysical performance are determined by the sensitivities of the most sensitive individual neurons. (Figure 6-72)

loxP See Cre combinase.

LRP4 (low-density lipoprotein receptor-related protein-4)

Along with MuSK, it is an agrin receptor in muscle. It also signals back to motor axons to trigger presynaptic differentiation in a MuSK-independent manner. (Figure 7-24)

LTMRs (low-threshold mechanoreceptors) Touch sensitive somatosensory neurons that innervate hair follicles, specialized epithelial cells, and encapsulated corpuscles in the skin. They respond to vibration, indentation, pressure, and stretch of the skin, as well as to the movement or deflection of hairs. (Figure 6-63)

luteinizing hormone (LH) See gonadotropins.

lysosome A membrane-enclosed organelle that contains enzymes for protein degradation. (Figure 2-2)

M pathway A visual processing pathway from the retina to the visual cortex that originates from retinal ganglion cells with

large receptive fields and engages lateral geniculate nucleus cells in the magnocellular layers. It carries information about luminance and has excellent contrast and temporal sensitivity. (Figure 4-48)

macular degeneration Adisease that causes photoreceptors in the fovea to die, impairing high-acuity vision.

major depression Amood disorder characterized by persistent feelings of sadness, emptiness, and worthlessness.

major urinary protein (MUP) A highly stable protein found in the urine, which is used by some species to mark an individual's territory for a long duration.

MARCM (mosaic analysis with a repressible cell marker) Agenetic mosaic method in Drosophila used to label individual neurons or groups of neurons that share the same lineage and at the same time to delete an endogenous gene or express a transgene specifically in these labeled neurons. (Figure 13-23)

Martinotti cell Atype of GABAergic neuron in the cerebral cortex that forms synapses onto the distal dendrites of cortical pyramidal cells. (Figure 3-46)

massively parallel processing An information processing method, it utilizes a large number of units to perform a set of coordinated computations in parallel. It is a key feature of the

nervous system.

maximum parsimony A means of generating phylogenetic predictions by selecting the interpretation of the experimental data that posits the fewest number of evolutionary changes among all the potential interpretations.

MC4R AG-protein-coupled receptor that is activated by a-MSH. (Figure 8-42)

mechanosensory neurons Somatosensory neurons that are activated by mechanical force and are responsible for proprioception, touch, and a subset of pain sensations.

mechanotransduction The process in sensory cells by which mechanical stimuli are converted to electrical signals.

mechanotransduction channel An ion channel that is gated by mechanical force.

MeCP2 (methyl-CpG-binding protein 2) Anuclear protein that binds to DNA at methylated CpG sites (i.e. adjacent cytosine and guanine nucleotides). It is highly expressed in developing and adult neurons. (Figure 11-36) See also Rett syndrome.

medial amygdala Part of the olfactory amygdala complex that receives direct input from accessory olfactory bulb mitral cells. It is sexually dimorphic and regulates male courtship behavior. (Figure 9-32)

medial geniculate nucleus Athalamic nucleus that processes and relays auditory signals to the auditory cortex. (Figure 6-54)

medial-lateral Of a body axis, from midline to side.

medial preoptic area (MPOA) Asexually dimorphic nucleus in the anterior hypothalamus that regulates male courtship behavior. (Figure 9-28; Figure 9-32)

medulla The caudal-most part of the brainstem between the pons and the spinal cord.

medulla (in insect visual system) Aneuropil that lies beneath the lamina in the insect compound eye. (Figure 5-35)

Meissner corpuscle A specialized structure closely associated with the peripheral ending of the rapidly adapting type I (RAI) LTMR. (Figure 6-64)

melanopsin An opsin expressed by vertebrate intrinsically photosensitive retinal ganglion cells (ipRGCs). It is a member of the c-opsin subfamily, whose members are most widely used in invertebrate visual systems.

membrane potential The electrical potential difference between the inside of the cell and the extracellular environment.

memory The process in which information is encoded, stored, and retrieved. It can also be defined as the lasting changes in the brain that retain the learned information.

Merkel cell Aspecialized epithelial cell at the junction of the dermis and epidermis. It is closely associated with the peripheral ending of the slowly adapting type I(SAI) LTMR. (Figure 6-64)

mesencephalic locomotor region (MLR) Amidbrain region where electrical stimulation evokes locomotor activity.

mesoderm The middle germ layer that gives rise to the skeletal system, connective tissues, muscle, and the circulatory system. (Figure 7-2)

messenger RNA (mRNA) Amature RNA molecule that has undergone 5' capping, 3' polyadenylation, and splicing to remove

introns and that is exported to the cytoplasm to direct protein synthesis. (Figure 2-2)

metabotropic receptor Aneurotransmitter receptor that regulates ion channel conductance indirectly through intracellular signaling cascades, modulating membrane potential over a timescale of tens of milliseconds to seconds. (Figure 3-22)

microglia Aglial cell that functions as the resident immune cell of the nervous system. It engulfs damaged cells and debris. (Figure 1-9)

microneurography Aneurophysiological technique used to record neuronal activity in the peripheral nerves of awake human subjects.

microRNA Ashort, noncoding RNA (21-26 nucleotides ni length) widely used ni eukaryotic organisms ot regulate gene expression. It triggers the degradation and inhibits the translation of mRNAs with complementary sequences. Se also RNA Interference.

microstimulation Delivery of small currents through an extracellular electrode with the goal of activating a limited number of nearby neurons.

microtubule Amajor cytoskeletal element composed of hollow cylinders of 13 parallel protofilaments made of -a and ß-tubulin. (Figure 2-5)

midbrain The rostral-most part of the brainstem, ti includes the tectum (superior and inferior colliculus in mammals) dorsally and the tegmentum ventrally. tI is also the middle part of the three divisions of the embryonic brain caudal to the forebrain and rostral to the hindbrain. It is also called the mesencephalon. (Figure 1-8; Figure 7-3)

middle temporal visual area (MT) Ahigh-order visual cortical area in the dorsal stream specialized for analyzing motion signals. (Figure 4-48)

midget ganglion cell An Aretinal ganglion cell with a small receptive field used for high-acuity vision and green-red color vision. (Figure 4-33)

miniature end-plate potential (mEPP) Small depolarization

of the muscle cell in response to spontaneous neurotransmitter release from the motor neuron. (Figure 3-2)

mitogen-activated protein (MAP) kinase cascade Akinase cascade that acts downstream of the small GTPase Ras and

other signaling molecules. The cascade consists of three serine/ threonine kinases represented by Raf, Mek, and Erk (also

called mitogen-activated kinase). Ras-GTP activates Raf, which phosphorylates and activates Mek, which in turn phosphorylates and activates Erk. (Figure 3-39)

mitotic recombination Exchange of a portion of homologous maternal and paternal chromosomes during mitotic cell division. It can create daughter cells homozygous for alleles on portions

of the paternal or maternal chromosomes. (Figure 13-10;

Figure 13-23)

mitral cell A second-order neuron in the vertebrate olfactory bulb, it receives input from ORNs and sends output to the olfactory cortex. It differs from a tufted cell, also a second-order neuron in the vertebrate olfactory bulb, in its cel body location in the olfactory bulb and axon termination pattern in the olfactory

cortex. (Figure 6-17)

modulatory neurons Neurons that release modulatory neurotransmitters. They can act on both excitatory and inhibitory neurons to up- or down-regulate their excitability or synaptic transmission.

GLOSSARY G:17

G : 1 8 GLOSSARY

modulatory neurotransmitter (neuromodulator) Aneurotransmitter that can bidirectionally change the membrane potential, excitability, or neurotransmitter release of its postsynaptic target neurons.

molecular clock Atechnique that utilizes the rates of sequence changes, calibrated against fossil records, to estimate the times at which two species diverged.

monoamine neurotransmitter Aneurotransmitter, such as serotonin, dopamine, norepinephrine, and histamine, derived from an aromatic amino acid.

monoamine oxidase An enzyme that oxidizes dopamine, norepinephrine, and serotonin, leading to their degradation. (Figure 11-24)

T o n g e a t e t y s h a r e w n i s o r d e r f r o m h t e a ms e

morphine The active ingredient of opiates.

morphogen Adiffusible signaling protein that can cause cels located at different distances from the source to adopt different fates.

Morris water maze Anavigation task in which rats and mice learn to locate a hidden platform in a pool of milky water using distant cues in the room.

Mosaic analysis Amethod for analyzing the cell types in which the function of a gene is important by creating genetic mosaic animals containing both wild-type and mutant cells that are usually differentially marked.

mossy fiber An axon that has elaborate terminal arborizations. The two most prominent types are found in the cerebellum

and hippocampus. The cerebellar mossy fiber is an axon that terminates in the granular layer of the cerebellar cortex, where it synapses onto granule cells. It originates from a neuron residing in the pons, medulla, or spinal cord. (Figure 8-20). The hippocampal mossy fiber is an axon of a dentate gyrus granule cell, which synapses onto CA3 pyramidal neuron dendrites.

motor homunculus Amap in the primary motor cortex that corresponds to movement of specific body parts. Nearby areas in the motor cortical areas represent movement control of nearby body parts. (Figure 1-25)

motor neuron Atype of neuron that extends dendrites within the CNS (the spinal cord or brainstem in vertebrates) and projects its axon out of the CNS to innervate a muscle. (Figure 1-15;

Figure 8-9)

motor pool Acluster of motor neurons that innervate the same muscle. (Figure 8-6)

motor protein Aprotein that converts energy from ATP hydrolysis to movement along the cytoskeletal polymers.

motor system The collected parts of the nervous system that control the contraction of skeletal muscles and thereby enable movement and maintain body posture.

motor unit Amotor neuron and the set of muscle fibers it innervates. (Figure 8-6)

motor unit size The number of muscle fibers a motor neuron innervates.

mount A posture that male rodents assume when sexually aroused. It facilitates sexual intercourse.

MrgprA3 AG-protein-coupled receptor that is activated by the pruritogen chloroquine.

a-MSH (a-melanocyte-stimulating hormone) A neuropeptide

released by POMC neurons in the arcuate nucleus that reduces food intake.

mTOR (mammalian target of rapamycin) Akey protein in intracellular signaling pathways that plays an important role in regulating protein translation. (Figure 11-45)

Muller glia Aglial cell in the retina where the conversion of al-

trans retinal to 11-cis retinal occurs to assist the recovery process in cones.

multi-electrode array Adevice used to record the spiking activities of many individual neurons. The electrodes can be arrayed either horizontally or vertically. (Figure 4-47; Figure 13-33)

multiple sclerosis (MS) Acommon adult-onset CNS demyelinating disease, ti is characterized by inflammatory plaques in the white matter caused by immune cell attack of myelin. The cause is still mostly unknown.

multipolar Having more than two processes leaving the cell body.

muscarinic AChR See acetylcholine receptor (AChR).

muscimol Amushroom-derived toxin that is a potent activator of

the GABA, receptor.

muscle fiber Amuscle cell.

muscle spindle Aspecial apparatus in muscle cells that sense muscles stretches. It has embedded endings of peripheral branches of the proprioceptive somatosensory neurons.

(Figure 1-19; Figure 6-63)

mushroom body Asecond-order olfactory center for odor- mediated learning and memory in the insect brain, it and the lateral horn are the two major output sites for projection neuron axons. (Figure 6-27; Figure 10-29)

MuSK Amuscle-specific receptor tyrosine kinase, ti acts together with LRP4 as an agrin receptor to promote acetylcholine receptor clustering. (Figure 7-24)

mutation Achange in DNA, including the insertion, deletion, or alteration of one or more base pairs.

myelin sheath Cytoplasmic extensions of oligodendrocytes and Schwann cells, they wrap around the axons with multi-layered glial plasma membrane to increase resistance and decrease capacitance for action potential propagation. See also axon myelination. (Figure 2-26; Figure 2-27)

myofibril Athread-like longitudinal structure in muscle cells composed of repeating sarcomeres and responsible for muscle contraction. (Figure 8-3)

myosin An F-actin-based motor protein. (Figure 8-3)

Nat-K+ ATPase Apump that uses energy derived from ATP hydrolysis to pump Nat out of a cell and K+ into a cell against their respective electrochemical gradients. It helps maintain the Nat and K+ concentration differences across the membrane.

32 nAChR Asubunit of nicotinic acetylcholine receptors that, among other functions, is essential for cholinergic retinal wave propagation. See also acetylcholine receptor (AChR).

narcolepsy Adisorder characterized by difficulty staying awake during the day, especially following moments of happiness or excitement. It is caused either by a deficiency of the neuropeptide hypocretin or by dysfunction of hypocretin-expressing neurons.

nasal (in retinal map) In the direction of the nose.

natural selection Akey mechanism of evolution, it is the process by which genetic variations that confer individuals a better chance of reproductive success become more common in a population over time. (Figure 12-1)

nature In the context of nature versus nurture, 'nature' is the contribution of genetic inheritance to brain function and behavior.

nematocin C. elegans ortholog of vertebrate oxytocin and vasopressin. (Figure 9-45)

neocortex The largest part of the mammalian cerebral cortex, it typically contains six layers and is evolutionarily the newest part of the cerebral cortex.

Nernst equation An equation that relates the equilibrium potential of an ion to the concentrations of the ion on the two sides of a membrane.

nerve A discrete bundle of axons in the peripheral nervous

system.

nerve growth factor (NGF) Aprototypical neurotrophin, ti is a target-derived secreted protein that supports the survival and axon growth of sensory and sympathetic neurons. (Figure 7-31; Figure 7-32)

nerve impulse Historical name for transient changes in membrane potential that propagate along axons, it is the same as

action potential.

netrin/Unc6 Homologous secreted proteins originally identified by biochemical purification (netrins in vertebrates) and genetic screen (Unc6 in C. elegans). They are widely used axon guidance cues first discovered in the context of midline guidance in both

C. elegans and vertebrates. (Figure 5-10)

neural circuit An ensemble of interconnected neurons that act together to perform specific functions.

neural crest cells Aspecial group of cells at the junction of the dorsal neural tube and the overlying epidermal cells. They migrate away from the neural tube ot produce diverse cell types, including cells of the peripheral nervous system. (Figure 7-2)

neural plasticity Changes of the nervous system in response to experience and learning.

neural plate The layer of ectodermal cells overlaying the notochord that invaginates and gives rise to the neural tube during neurulation. (Figure 7-2)

neural progenitor Adividing cell that gives rise to neurons and glia. In vertebrates, it is usually located near the ventricle in the developing vertebrate CNS. (Figure 7-4)

neural prosthetic device Adevice that can substitute a sensory or motor function that has been disrupted due to an injury or

a disease. For example, population activity of neurons in the motor cortex can be used to control an external device such as a

robotic arm or a computer cursor to help patients who suffer from paralysis or motor neuron diseases. (Figure 8-29)

neural tube Ahollow tube surrounded by layers of neuroectodermal cells, it is the embryonic precursor to the vertebrate CNS. (Figure 7-2)

neuraxis Axis of the CNS. The rostral-caudal neuraxis follows the curvature of the embryonic neural tube; the dorsal-ventral neuraxis is perpendicular to the rostral-caudal neuraxis. (Figure 1-8)

neurexin Aprotein on the presynaptic membrane that mediates synaptic adhesion. Amajor binding partner is neuroligin.

(Figure 7-25)

neuroblast Aneuronal progenitor.

neurodegenerative disorders Disorders characterized by progressive neuronal dysfunction, including loss of synapses, atrophy of dendrites and axons, and death of neurons.

neuroendocrine system The collected parts of the nervous system that control the secretion of hormones to regulate an animal's physiology and behavior in response to sensory stimuli and brain states.

neurothology Abranch of science that emphasizes the study of animal behavior in the natural environment.

neurofascin An immunoglobulin superfamily molecule that, among other functions, serves as a cue in Purkinje cells to instruct targeting of basket cell axons and presynaptic terminals to the correct subcellular domain.

neurofibrillary tangle An intracellular fibril consisting of an abnormal accumulation of hyper-phosphorylated tau, a microtubule-binding protein. (Figure 11-2)

neurofilament An intermediate filament (a cytoskeletal polymer with a diameter between F-actin and microtubules) in vertebrate neurons. It is concentrated in axons and provides stability to axons.

neurogenic inflammation Inflammation triggered by release of neuropeptides such as substance P and calcitonin gene-related peptide from the peripheral terminals of sensory neurons.

neuroligin Aprotein on the postsynaptic membrane that mediates synaptic adhesion. Amajor binding partner is neurexin.

(Figure 7-25)

neuromuscular junction The synapse between a motor neuron's presynaptic terminals and a skeletal muscle cell. (Figure 3-1; Figure 7-28)

neuron (nerve cell) An electrically excitable cell that receives, integrates, propagates, and transmits information as the working unit of the nervous system.

neuron doctrine The principle that individual neurons are the working units of the nervous system.

neuronal polarity The distinction between axons and dendrites. neuronal process Cytoplasmic extension of a neuron.

neuropeptide Apolypeptide a few to a few dozen amino acids in length that acts as a neurotransmitter.

neuropil Astructure composed mostly of synapses. neuropilin-1 (Nrpl) Aco-receptor for semaphorin.

neurotransmitter reuptake The process by which neurotransmitters in the synaptic cleft are transported either into nearby glial cells or back into the presynaptic cytosol and into synaptic vesicles. (Figure 3-12)

neurotransmitters Molecules that are stored in synaptic vesicles (or dense-core vesicles in the case of neuropeptides)

in the presynaptic terminals, are released into the synaptic cleft triggered by presynaptic depolarization, and activate ionotropic or metabotropic receptors on a postsynaptic target cell. (Figure 3-16; Table 3-2)

neurotrophic hypothesis The idea that the survival of developing neurons depends on neurotrophins produced by the neurons' postsynaptic targets.

neurotrophin-3 (NT3) See neurotrophins.

neurotrophin-4 (NT4) See neurotrophins.

neurotrophins Afamily of secreted signaling proteins that regulate the survival, morphology, and physiology of target neurons through binding to specific receptors on those neurons. Mammalian neurotrophins include nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT3), and neurotrophin-4 (NT4). (Figure 3-39; Figure 7-32). Se also Trk receptors, p75NTR.

neurulation The developmental process in vertebrate embryos leading to formation of the neural tube, which gives rise to the nervous system. (Figure 7-2)

nicotinic AChR See acetylcholine receptor (AChR).

GLOSSARY G : 1 9

G : 2 0 GLOSSARY

Nissl stain Astain that labels RNA and thus highlights the rough endoplasmic reticulum in cytoplasm. Nissl stains are basic (that is, proton-accepting, positively charged) dyes such as cresyl

violet that bind to RNA molecules (which are negatively charged). (Figure 13-18)

NMDA receptor Aglutamate-gated ion channel that conducts Nat, K+, and Ca'* and can be activated by the drug NMDA

(N-methyl-D-aspartate). Its opening requires both binding of glutamate and postsynaptic depolarization. It is a heterotetramer of two GluN1 subunits encoded by a single gene, and two GluN2 subunits, of which there are four variants (GluN2A, GluN2B, GluN2C, GluN2D) each encoded by separate genes. (Figure 3-24; Figure 3-25)

nociception The sense of pain.

nociceptive neuron Asomatosensory neuron that senses pain.

nodes of Ranvier Periodic gaps in the myelination of an axon, usually 200 um to 2 mm apart, where the axon surface is

exposed to the extracellular ionic environment. They contain high concentrations of voltage-gated Nat and K+ channels that regenerate action potentials. (Figure 2-26)|

nonhomologous end joining An endogenous DNA repair system, ti re-joins the two ends of a DNA molecule with a double-strand break. It often creates a small deletion or duplication at the breakpoint as a result of the repair process. (Figure 13-8)

non-spiking neuron Aneuron that uses graded potentials rather than action potentials to transmit information.

non-synonymous substitutions Nucleotide changes in DNA that result in corresponding amino acid changes in the protein encoded by that DNA.

norepinephrine Amonoamine neuromodulator derived from dopamine. (Figure 11-20; Table 3-2)

northern blot Amethod for determining the amount of aspecific RNA in an RNA mixture. RNAs are separated by gel electrophoresis and are then transferred to a membrane; labeled nucleic acid

probes are then hybridized to the membrane to visualize specific RNA molecules that hybridize to the probe. It can be used to determine RNA expression patterns. (Figure 6-9)

Notch Atransmembrane receptor widely involved in diversifying cell fate during development. Binding of a ligand to Notch triggers proteolytic cleavage of Notch in the transmembrane domain to release the Notch intracellular domain, which can then enter the nucleus to regulate gene expression. (Figure 7-7)

notochord Amidline mesodermal structure in vertebrate

embryos ventral to the spinal cord that produces secreted cues for patterning the spinal cord. (Figure 7-2; Figure 7-8)

NREM sleep Non-rapid eye movement (NREM) sleep, or sleep stages other than REM sleep. (Figure 8-51)

nucleus accumbens The major part of the ventral striatum, it receives input preferentially from the prefrontal cortex, thalamus,

hippocampus, and amygdala. (Figure 11-31)

nucleus laminaris (NL) Abrainstem nucleus in the barn owl that

analyzes interaural time differences. It is analogous to the medial superior olivary nucleus in mammals.

nucleus of the solitary tract (NTS) Anucleus in the brainstem that receives input from the taste system as well as sensory information from internal organs. (Figure 6-35)

null direction The direction of stimulus motion that elicits the lowest firing rate of a direction-sensitive visual system neuron.

Numb ADrosophila protein that is segregated asymmetrically to daughter cells during sensory organ precursor and neuroblast

divisions. It is essential for conferring different fates to the two daughter cels of an asymmetric division. (Figure 7-6)

nurture In the context of nature versus nurture, 'nurture' is

the contribution of environmental factors to brain function and behavior.

occipital lobe One of the four cerebral cortex lobes; ti is located at the back of the brain. (Figure 1-23)

octopamine Aneurotransmitter in some invertebrate nervous systems that is chemically similar to norepinephrine in vertebrates.

ocular dominance Preference for receiving and/or representing visual input from one eye over the other eye. In the primary visual cortex of some mammals, such as cats and monkeys, cells in the same vertical columns share the same ocular dominance, thus producing ocular dominance columns. (Figure 4-43)

ocular dominance column See ocular dominance.

odds ratio In genetics, a measure of the effect of a genetic variant on the likelihood of having a particular trait, such as a disease. It

is calculated by dividing the probability of having the trait among people with the genetic variant by the probability of having the trait among people without the genetic variant.

odorant Amolecule that elicits olfactory perception, it is usually volatile.

odorant receptor Areceptor on the surface of olfactory cilia that binds odorants. (Figure 6-9)

OFF bipolar Abipolar cell that expresses ionotropic glutamate receptors and is depolarized by glutamate release from photoreceptors. Its membrane potential changes follow the

sign of photoreceptors such that it is hyperpolarized by light. (Figure 4-25)

Ohm's law An equation that relates current (I) to voltage (V) and resistance (R); I = V/R.

olfactory bulb The first olfactory processing center in the vertebrate brain. (Figure 6-3; Figure 6-17)

olfactory cilium Adendritic branch of an olfactory receptor neuron enriched for odorant receptors. (Figure 6-3)

olfactory cortex Brain regions that receive direct input from

mitral/tufted cells, including the anterior olfactory nucleus, piriform cortex, olfactory tubercle, cortical amygdala, and entorhinal cortex. (Figure 6-19)

olfactory epithelium The epithelial layer in the nose that houses the olfactory receptor neurons. (Figure 6-3)

olfactory processing channel Adiscrete information processing unit in the olfactory system consisting of olfactory receptor neurons (ORNs) that express a given odorant receptor, the glomerular target of those ORNs, and second-order neurons that send dendrites to the same glomerulus.

olfactory receptor neuron (ORN) The primary sensory neuron in the olfactory system, it converts odorant binding to odorant receptor proteins into an electrical signal that is relayed to the brain via its axon. (Figure 6-3)

oligodendrocyte Aglial cell in the CNS that wraps axons with its cytoplasmic extension to form myelin sheath. (Figure 1-9)

ommatidium Arepeating unit of the arthropod compound eye. In Drosophila, each ommatidium contains eight photoreceptors.

(Figure 5-35)

ON bipolar Abipolar cell that expresses metabotropic glutamate receptors and is inhibited by glutamate release from photoreceptors. Its membrane potential changes are opposite in sign to those of the photoreceptors such that it is depolarized by light. (Figure 4-25)

open probability The proportion of time that an individual ion channel is open and able to conduct current.

operant conditioning Aform of learning in which a subject associates performance of a specific action (e.g. pressing a lever) with a particular outcome, such as delivery of a reinforcer (e.g. food) or a punishment (e.g. an electrical shock).

opioid receptors Asubfamily of G-protein-coupled receptors that serve as receptors for opioids, including morphine and endogenous opioid neuropeptides. They are widely distributed across the nervous system.

opioids Molecules that have effects similar to opiates such

as morphine. They include opiates from opium poppy and endogenous neuropeptides such as encephalin, endorphin, and dynorphin.

opsin Amember of a family of G-protein-coupled receptors expressed in photoreceptors of multicellular organisms, it is associated with retinal and converts photon absorption to the activation of a trimeric GTP-binding protein. In microbes, it si a member of light-induced channels or pumps, which are not G-protein-coupled receptors.

optic chiasm The midline structure where a fraction of retinal ganglion cell axons cross to the side of the brain contralateral to the eye of origin. (Figure 4-35)

optic lobe The part of the insect brain that consists of the retina, lamina, medulla, and lobula complex and that is used to analyze visual signals. (Figure 5-35)

optic nerve The bundle of retinal ganglion cell axons, ti sends visual information from the eye to the brain. (Figure 4-35)

optic tract The bundles of retinal ganglion cell axons distal to the optic chiasm. (Figure 4-35)

optical imaging An approach that uses changes of fluorescence or other optical properties as indicators of neuronal activity.

optogenetics The set of methods used to manipulate neuronal activity by using light to activate agenetically encoded effector, most commonly microbial opsins (e.g. channelrhodopsin-2, archaerhodopsin, halorhodopsin). (Figure 13-45)

organ of Corti An organ in the cochlea that consists of hair

cells, the surrounding support cells, and the basilar membrane. (Figure 6-45)

organization-activation model Acentral principle in endocrinology, it proposes that sex hormones have two different types of effects: 'organizational' effects during development, which configure the brain in a sex-typical manner, and 'activational' effects in adults, which stimulate male- or female- typical sexual behaviors. (Figure 9-25)

otolith organ Asensory organ in the vestibular system that senses linear acceleration and stationary head tilts. (Figure 6-59)

outer radial glia (oRG) Atype of radial glia whose cell bodies are located in the subventricular zone. They serve along with

ventricular zone radial glia as neural progenitors. They are greatly expanded in number in human neocortex compared with mouse neocortex and likely contribute to increased neuronal production in mammals with large neocortices. See also radial glia. (Figure 12-37)

outer segment Acytoplasmic extension of a rod or a cone, it contains a highly specialized photon detection apparatus made of tightly stacked membrane disks enriched in opsins. (Figure 4-2)

outgroup Agroup of organisms that is closely related to but falls outside of a set of organisms of interest. It is used as a reference

group in determining the phylogenetic relationships among aset of organisms.

ovarietomized female Afemale from which the ovaries have been removed.

oxytocin Ahormone secreted by hypothalamic neurons in the posterior pituitary and aneuropeptide released by some CNS neurons. tI regulates maternal and social behavior.

Ppathway Avisualprocessingpathwayfromtheretinatothe visual cortex that originates from retinal ganglion cells with small receptive fields and engages lateral geniculate nucleus cells in the parvocellular layers. tI carries information about high-acuity and color vision. (Figure 4-48)

p75NTR A75 kilodalton neurotrophin receptor that has a low affinity for al neurotrophins and is also a receptor for al proneurotrophins. (Figure 7-32)

pacemaker Acell that can produce rhythmic output in the absence of input.

Pacinian corpuscle An encapsulated structure closely associated with the ending of the rapidly adapting type I (RAI) LIMR.

(Figure 6-64)

PALM See super-resolution fiuorescence microscopy.

parablosis The joining of the circulatory systems of two animals

so that they have limited exchange of substances in systemic circulation.

parabrachial nucleus Abrainstem nucleus that transmits ascending signals from the visceral sensory system and

pain somatosensory system to the thalamus, amygdala, hypothalamus, and brainstem autonomic centers. (Figure 6-70; Figure 8-33)

paracrine Of or related to a form of signaling in which a recipient cell receives asignal produced by nearby cells.

parallel fiber The portion of the axon of a cerebellar granule cell that runs in parallel to the pial surface and crosses Purkinje cell dendrites at a right angle. (Figure 8-20)

parasympathetic nervous system Abranch of the autonomic

nervous system that facilitates energy conservation. Activation of the parasympathetic nervous system slows down the heart rate, decreases blood flow, constricts airways in the lung, and stimulates salivation and digestion. (Figure 8-31; Figure 8-32)

paraventricular hypothalamic nucleus (PVH) Ahypothalamic nucleus involved in multiple physiological functions, including the release of oxytocin and vasopressin into the bloodstream through axonal projections in the posterior pituitary and the descendingcontrolofautonomicnervoussystemfunctions. (Figure 8-43)

parietal lobe One of the four cerebral cortex lobes, it is located behind the frontal lobe and above the occipital lobe. (Figure 1-23)

Parkinson's disease (PD) A common neurodegenerative

disease caused by death of substantia nigra dopamine neurons. It primarily affects movement control, with symptoms that include shaking, rigidity, slowness, and difficulty walking. (Figure 11-16)

parthenogenesis Areproductive process in which embryos develop from unfertilized eggs and which therefore does not involve exchange of genetic materials.

passive electrical properties Membrane properties in the

absence of voltage-dependent conductance. Two salient examples are: (1) a sharp change of electrical signal (e.g. a current pulse) becomes more spread temporally as the signal travels along a neuronal process because of membrane capacitance; (2) the magnitude of electrical signal becomes attenuated across a distance because of membrane conductance. They are also called cable properties. (Figure 2-16)

GLOSSARY G:21

G : 2 2 GLOSSARY

passive transport Movement of a solute across a membrane down its electrochemical gradient via achannel or atransporter. (Figure 2-8)

patch clamp recording An electrophysiological recording technique that utilizes a glass electrode (patch pipette) to form a high-resistance seal with the membrane. It has several variants, including cell-attached patch, excised patch, and whole-cel recording. (Figure 13-37)

patch pipette See patch clamp recording.

path-integration strategy A navigational strategy in which animals use the speed, duration, and direction of their own movement to calculate their current position with respect to their starting position.

Pax6 Amember of the Pax family of transcription factors, it contains ahomeobox and a paired box. It regulates the patterning of the cerebral cortex and spinal cord and si required for eye development in mammals. Its Drosophila homolog is Eyeless. See

also Eyeless.

PDZ domain Acronym for a domain shared by PSD-95, Discs large (a Drosophila protein implicated in cell proliferation and associated with postsynaptic density), and ZO-1 (an epithelial tight junction protein). tI is a protein-protein interaction domain that binds to a specific protein sequence motif that is present at the C-terminal end of many transmembrane receptors.

percept Aspecifically perceived object or the brain representation of the object.

perforant path Axons of neurons in the superficial layer of the entorhinal cortex that project to the hippocampus. (Figure 10-6)

peri-stimulus time histogram (PSTH) Agraph that plots firing rates of neurons as a function of time after stimulus onset.

perlaqueductal gray (PAG) Amidbrain gray matter structure surrounding the cerebral aqueduct. It serves many functions including the descending control of pain and the execution of defensive behavior such as freezing. (Figure 6-70)|

periglomerular cell Amember of diverse types of interneurons that receive direct input from olfactory receptor neuron (ORN) axons or from apical dendrites of mitral cells and that send (mostly inhibitory) output to targets within the same glomerulus, or in nearby glomeruli. (Figure 6-17)

Period Afruit fly gene discovered based on mutations that speed up, slow down, or disrupt circadian rhythms. tI encodes a protein that participates in the negative regulation of its own transcription, and its mammalian homologs serve a similar function. (Figure 8-45)

permeability The ability of a membrane to conduct specific ions, determined principally by the number of open channels capable of conducting those ions.

perturbation experiment An experiment in which key parameters ni a biological system are altered, usually under the experimenter's control, ni order ot study the consequences.

pharmacodynamics The effects of adrug in the body, including the intended effects on target molecules and processes as wel as the unintended side effects.

pharmacokinetics The effects of the body's biological processes on a drug, including the drug's absorption, distribution, metabolism, and excretion.

phase locking Aproperty whereby the spikes of auditory neurons occur at a specific phase of each cycle of a sound wave.

(Figure 6-51)

phasic Of a neuronal firing pattern, bursts of action potentials in response to specific stimuli.

pheromone Asubstance produced by an individual to elicit a specific reaction from other individuals of the same species.

phosphodiesterase (PDE) An enzyme that hydrolyzes cyclic AMP (cAMP) to AMP, or GMP to GMP.

phospholipase C (PLC) Amembrane-associated enzyme that

(Figure 3-34)

photoreceptor A cell that converts light into electrical signals. (Figure 4-2; Figure 12-23)

phototaxis Movement toward or away from a light source.

phototransduction The biochemical reactions triggered by photon absorption. (Figure 4-10)

phrenology Adiscipline created by Franz Joseph Gal with the goal of mapping the functions of brain areas by studying the shape and size of bumps and ridges on the skull, which were thought

to be correlated with an individual's talents and character traits. (Figure 1-22)

phylogenetic tree A branching diagram showing the relationships among different organisms. tI is constructed based on the similarities and differences of different organisms' traits, such as nucleotide and protein sequences. (Figure 12-2)

picrotoxin Aplant toxin that is apotent blocker of the GABA, receptor.

Plezo A mechanotransduction channel with over 30 transmembrane segments for each subunit. (Figure 6-66)

pigment cell Acell in the pigment epithelium layer of the retina adjacent to the outer segments of photoreceptors that reflects light and converts all-trans retinal back to 11-cis retinal to assist the recovery process in rods.

piriform cortex The largest olfactory cortical region, ti is a three- layered cortex separated from more dorsally located neocortex by the rhinal sulcus. (Figure 6-19)

pituitary The endocrine center of the brain, it is located ventral

to the hypothalamus. The posterior pituitary contains axon terminals of hypothalamic neurons that directly release hormones into the bloodstream. The anterior pituitary contains endocrine cells that release hormones into the bloodstream in response

to prehormones originated from hypothalamic neurons and transmitted by specialized portal vessels. (Figure 8-35)

place cell Ahippocampal cell that fires maximally when the animal is at a particular place in an environment.

place field The physical location in an environment that elicits maximal firing of a particular place cell.

placebo effect In the context of pain perception, the phenomenon whereby the perception of pain can be reduced in some patients by the mistaken belief that they have received a treatment thought to reduce pain.

plasma membrane dopamine transporter (DAT)

See plasma

membrane monoamine transporters.

plasma membrane monoamine transporters (PMATs) Afamily of proteins on the presynaptic membrane that transport serotonin [serotonin transporter (SERT)], dopamine [dopamine transporter (DAT)], or norepinephrine [norepinephrine transporter (NET)] from synaptic cleft into the presynaptic cytosol. (Figure 11-24). See also plasma membrane neurotransmitter transporter.

plasma membrane neurotransmitter transporter A transmembrane protein on the presynaptic or glial plasma membrane that transports neurotransmitters from the extracellular space into the cell using energy from the co-transport of Nat down its electrochemical gradient. (Figure 3-12)

plexin Amember of a class of proteins that serve as receptors for the axon guidance cues, semaphorins.

pluripotent cell Acell that has the potential to develop into al cell types of an embryo.

PNS (peripheral nervous system) Neural tissue and cells outside the central nervous system (CNS), including the nerves that connect the CNS with the body and internal organs as well as isolated ganglia outside of the CNS.

Poisson distribution Adiscrete probability distribution in which the frequency (f) that k events occur can be determined by a single parameter ?. (the mean frequency of occurrence, which equals the product of n and p in the binomial distribution).f (k; 2) = (2k / k!) e-*. It is an approximation of the binomial distribution when n is large and p is small. (Box 3-1)|

polyadenylation The process by which a long sequence of adenosine nucleotides is added to the '3 end of the mRNA. (Figure 2-2)|

polymerase chain reaction (PCR) Ahighly sensitive DNA amplification technique that uses a pair of oligonucleotide primers to amplify the DNA segment between the sequences

corresponding to the primers through cycles of DNA replication.

polymodal neuron In the somatosensory system, a neuron that responds to stimuli of more than one sensory modality.

polymorphism In the context of genetics, a DNA sequence variation among individuals of the same species.

POMC neuron Aneuron in the arcuate nucleus that expresses pro-opiomelanocortin (POMC), a precursor protein for multiple

peptides including the anorexigenic peptide a-melanocyte- stimulating hormone (a-MSH). (Figure 8-42)

pons The middle part of the brainstem caudal to the midbrain and rostral to the medulla. (Figure 1-8)

population vector (in movement control) The sum of the preferred direction vectors of a population of neurons weighted by the firing rate of each neuron. The preferred direction of a neuron is a vector in a three-dimensional space pointing in the direction towards which movement elicits the highest firing rate of the neuron. (Figure 8-27)

positional cloning Amolecular genetic technique that uses molecular and genetic markers on specific chromosomes to identify a gene that causes a particular phenotype or disease.

positive selection The process by which an allele that is beneficial to an organism becomes more prevalent in a population.

positron emission tomography (PET) Anon-invasive three- dimensional imaging technique for measuring the distribution of positron-emitting probes introduced into the body.

posterior pituitary See pituitary.

postganglionic neuron Aneuron whose cell body is located in a sympathetic or parasympathetic ganglion in the peripheral nervous system and whose axon innervates effectors such as smooth muscle, cardiac muscle, and glands. (Figure 8-32)

postsynaptic specialization Astructure on a postsynaptic target cel that is adjacent ot apresynaptic terminal, ti is enriched for neurotransmitter receptors as wel as signaling and scaffolding molecules. It is also called postsynaptic density because ti is electron dense in electron microscopic images.

Potocki-Lupski syndrome Aneurodevelopmental disorder characterized by mild intellectual disability and autistic symptoms. It is caused by duplication of a chromosome segment (that includes Rail and many other genes) reciprocal to the common deletion that causes Smith-Magenis syndrome.

power stroke The process by which myosin and actin filaments move relative to each other. It involves the conversion of chemical

energy from ATP hydrolysis into mechanical force by the myosin motor. (Figure 8-4)

precedence effect The ability of a first-arriving sound to suppress the perception of later-arriving sounds.

preferred direction The direction of stimulus motion that elicits the highest firing rate of a direction-sensitive visual system neuron.

prefrontal cortex Aneocortical area anterior to the motor cortex, it is an executive control center that integrates multisensory information, mediates working memory, and performs complex executive functions such as goal selection and decision making.

preganglionic neuron Aneuron whose cell body is located within the CNS and whose axon synapses onto the postganglionic neurons in the sympathetic or parasympathetic ganglion.

(Figure 8-32)

premotor cortex Areas of motor cortex anterior to the primary motor cortex. Its neurons send axons primarily to primary motor cortex.

premotor neuron Aspinal cord or brainstem neuron that is presynaptic to motor neurons and thereby participates directly in controlling the firing of the motor neurons. (Figure 8-10)

presenilin One of two members of a family (consisting of presenilin-1 and presenilin-2) of multi-pass transmembrane

proteins that function as subunits of the y-secretase complex. They were originally identified based on mutations that cause familial Alzheimer's disease. (Figure 11-5)

prestin Aprotein that mediates electromotility in the cochlear outer hair cells.

presynaptic facilitation The process by which neurotransmitter release from cell Aonto the presynaptic terminal of cell Bleads to an increase in neurotransmitter release from cell B.

presynaptic inhibition The process by which neurotransmitter release from cell Aonto the presynaptic terminal of cell Bleads to a decrease in neurotransmitter release from cell B.

presynaptic terminal Astructure at the end (or along the trunk) of an axon that is specialized for releasing neurotransmitters onto target cells. (Figure 1-9)

pretectum Abrainstem structure that receives retinal ganglion cell axon input and regulates pupil, lens, and eye movement

reflexes. (Figure 4-35)

primary antibody An antibody that selectively recognizes a specific protein.

primary auditory cortex (Al) The part of the cerebral cortex that first receives auditory sensory information. (Figure 6-54)

primary cilium Ashort, single, non-motile cilium that projects from the surface of many animal cell types and is used often as a

signaling center.

primary motor cortex (M1) The part of the cerebral cortex that sends descending axons directly to motor neurons to control

muscle contraction. (Figure 1-25)

primary somatosensory cortex The part of the cerebral cortex that first receives somatosensory information from the body. (Figure 1-25)

primary visual cortex (V1) The visual cortical area that receives direct input from the lateral geniculate nucleus. (Figure 4-38; Figure 4-45)

principal component analysis (PCA) Astatistical method used to reduce the dimensionality of a dataset. The axes of the reduced

GLOSSARY G:23

G : 2 4 GLOSSARY

dataset are called principal components and their orientations in the non-reduced space are selected to maximize the spread of the data along each principal component-data are most spread along the axis of the first principal component, followed by the axis of the second principal component, and so forth.

prion diseases Diseases characterized by the propagation

across the brain of prion protein (PrP) that adopts a specific conformation (PrpS), which aggregates and causes massive neurodegeneration and neuronal death. PrpS spreads by interacting with PrP in its innocuous cellular conformation (PrPC) to induce a conformational change and convert it into PrPSc. Prion diseases include scrapie in sheep and goats, mad cow disease in cows, kuru (a human disease that occurred in certain tribes that observed ritual cannibalism), and Creutzfeldt-Jakob disease (CJD, a human disease in which mutations in the Prp gene make PrPC more prone to adopt the Prps conformation spontaneously). (Figure 11-13)

prion hypothesis The idea that the infectious agent in scrapie is

solely proteinaceous in nature.

programmed cell death (apoptosis) Aform of cell death in which a cell kills itself by initiating a cell-death program.

projection neuron Aneuron with an axon that projects outside the CNS region that houses the neuron's cell body. In the insect olfactory system, it is a second-order neuron (PN) that receives input from olfactory receptor neuron (ORN) axons and sends output to higher olfactory centers, analogous to a vertebrate mitral/tufted cell. (Figure 6-27)

prokaryote Asingle-cell organism without a nucleus. Prokaryotes are members of one of two domains of life: eubacteria or archaea.

proprioception The sense of body position and movement.

proprioceptive neurons Somatosensory neurons that

have peripheral endings embedded in the muscle spindles, tendons, and joints for sensation of muscle stretch and tension.

(Figure 6-63)

prostaglandin Alipid released during inflammation, it binds to specific G-protein-coupled receptors on the peripheral terminals of nociceptive neurons. (Figure 6-71)

protein Aspecific sequence of amino acids linked by peptide bonds to form a chain.

protein kinase A(PKA) See cAMP-dependent protein kinase.

protein kinase C(PKC) Aserine/threonine kinase with diverse substrates that is activated by binding of both diacylglycerol and Ca?*. (Figure 3-34)

proteinphosphatase Anenzymethatremovesphosphates from phosphorylated proteins, thus counteracting the actions of kinases.

proteinopathy Adisease caused by altered protein conformations, interactions, and homeostasis.

protocadherin Amember of a class of cell adhesion molecules in vertebrates whose structures and biochemical properties resemble those of cadherins.

protostomes Animals in which the mouth appears before the anus during development. They include most invertebrate phyla. See also deuterostomes. (Figure 12-2) |

pruriception The sense of itch.

pruritogen Achemical that causes the sensation of itch.

PSD-95 (postsynaptic density protein of 95 kllodalton) Apostsynaptic scaffolding protein highly enriched at the glutamatergic synapse. (Figure 3-27; Figure 7-25)

pseudogene Agene that has been rendered nonfunctional

by stop codons in the coding sequences or by other disrupting mutations. Such disrupting mutation(s) is prevalent in agiven species.

psychometric function The quantitative relationship between a parameter of a physical stimulus and the response or perception of a s u b j e c t .

psychophysical study An experimental approach that characterizes the relationship between physical stimuli and the sensations or behaviors they elicit.

psychosis The mental state characterized by hallucinations and/ or delusions.

psychostimulant Adrug that transiently produces euphoria and suppresses fatigue.

pump Atransporter that uses external energy, such as ATP hydrolysis or light, to actively move a solute across a membrane against its electrochemical gradient. (Figure 2-10)

Purkinje cell GABAergic neuron of the cerebellar cortex with highly branched planar dendritic trees. It receives excitatory input from parallel fibers (axons of cerebellar granule cells) and climbing fibers from inferior olive neurons, and sends output ot the deep cerebellar nuclei. (Figure 1-11; Figure 8-20)

pyramidal neuron Atype of glutamatergic neuron that has a pyramid-shaped cell body with an apical dendrite and several basal dendrites that further branch. It is abundant in mammalian cerebral cortex and hippocampus. (Figure 1-15)

quantal hypothesis of neurotransmitter release The idea that neurotransmitters are released in discrete packages of relatively uniform size.

quantal yeld The number of synaptic vesicle exocytosis events in response to a single action potential.

R-C circuit Acircuit that contains both resistors and capacitors. (Figure 2-14)

RA (robust nucleus of the arcopallium) Adorsal forebrain nucleus in the songbird essential for song production. It functions downstream of the HVC. (Figure 9-21)

Rab Amember of a family of small monomeric GTPases involved in intracellular vesicle trafficking.

rabies virus A neurotropic RNA virus that spreads within the nervous system of its host naturally by crossing synapses. It has been modified for the use of retrograde trans-synaptic tracing. (Figure 13-30)

radial glia Progenitor cell in the ventricular zone that extends two radial processes-one to the ventricle and the other to the pial surface of the developing cortex. These radial processes serve as substrates for neuronal migration. (Figure 7-4)

random mutagenesis See forward genetic screen.

random X-Inactivation Aprocess in which one of the two X chromosomes in female mammals is randomly inactivated in each cell during early development.

raphe nuclel Brainstem nuclei enriched for serotonin neurons that project widely across the brain. (Figure 8-54)

Ras A member of a family of small monomeric GTPases involved in signaling pathways necessary for cel growth and differentiation.

readily releasable pool Asmall subset of synaptic vesicles that are docked at the active zone, primed by an ATP-dependent process to achieve a high-energy configuration that includes pre- assembled SNARE complexes.

receptive field In the visual system, the area of the visual field that influences the activity of a given neuron. In the somatosensory system, the area of the body where stimuli can influence the firing of a neuron.

receptor Aprotein that binds and responds to a specific signaling molecule.

receptor potential Atype of graded potential induced at the peripheral endings of sensory neurons by sensory stimuli.

receptor tyrosine kinase (RTK) Atransmembrane protein with an N-terminal extracellular ligand-binding domain and a C-terminal intracellular tyrosine kinase domain. Upon ligand binding, receptor tyrosine kinases add phosphates to tyrosine residues of target proteins.

recording electrode An electrode used to measure membrane potential changes.

recovery (photoreceptor) The process by which light-activated photoreceptor cells return to the dark state. (Figure 4-11)

recurrent (cross) Inhibition Acircuit motif in which two parallel excitatory pathways mutually inhibit each other via inhibitory interneurons. (Figure 1-21) |

refractory period Atime window after an action potential during which another action potential cannot be initiated. (Figure 2-25)

regeneration (axon) Re-extension of axon after injury, including formation of synaptic connections with their original partners.

regenerative Having the property of propagating without attenuation in amplitude, it applies to action potentials. (Figure 2-25)

regulator of G protein signaling (RGS) Aprotein that acts as a GTPase activating protein for a trimeric GTP-binding protein.

release probability The probability that an active zone will release one or more synaptic vesicles following an action potential.

releasers The essential features of a stimulus that activate a fixed action pattern.

REM sleep Astage of sleep that is characterized by rapid eye movement. (Figure 8-51)

repellent Amolecular cue that guides axons away from its source. (Figure 5-9)

reserpine Afirst-generation antipsychotic drug, ti is an inhibitor of monoamine oxidase.

reserve pool Alarge subset of vesicles in the axon terminal available to replenish the readily releasable pool.

resistance (R) The degree to which an object or substance opposes the passage of electrical current, ti is the inverse of conductance: R= 1/g.

resistor An electrical element through which passage of current is limited. Current flow through a resistor produces a voltage difference across its two terminals. (Figure 2-13)

responder transgene In binary expression, ti is the transgene containing the coding sequence for the protein or RNA of interest, along with binding or recombinase sites for the transcription factor or recombinase, respectively, encoded by the driver transgene. (Figure 13-13)

resting potential The membrane potential of a neuron at

rest (i.e. in the absence of action potentials or synaptic input), which is typically between -50 and -80 millivolts relative to the extracellular fluid. (Figure 2-11)

reticular theory The idea that the processes of nerve cells fuse and form a giant net that constitutes the working unit of the nervous system. It has been mostly disproven (with the exception of electrical synapses, that allow limited exchange of ions and small molecules between partner neurons).

retina Alayered structure at the back of the vertebrate eye made of five major neuronal types (photoreceptors, horizontal

cells, bipolar cells, amacrine cells, and retinal ganglion cells)

and support cells. Collectively, these cells convert light into electrical signals, extract biologically relevant signals from the outputs of photoreceptors, and transmit these signals to the brain. (Figure 4-2)

retinal A chromophore covalently linked with an opsin, it

changes its configuration after photon absorption. (Figure 4-6; Figure 12-20)

retinal ganglion cell (RGC) The output cell of the retina that transmits information from the eye to the brain. (Figure 4-2; Figure 4-28)

retinal wave The spread of spontaneous excitation of retinal neurons, including retinal ganglion cells and amacrine cells, across the developing retina. (Figure 5-21)

retinotopy The topographical arrangement of cells in the visual

pathway according to the position of the retinal ganglion cells that transmit signals to them.

retrieval (of memory) The recall of a memory.

retrograde From the axon terminal to the cell body.

retrograde flow The flow of F-actin from the leading edge of the growth cone to its center powered by the myosin motor.

tI contributes to dynamic changes of growth cone shape. (Figure 5-15)

retrograde tracer Amolecule used to trace axonal connections. tI is taken up primarily by axon terminals and transported back to the cell bodies. (Figure 13-27)

retrograde trans-synaptic tracing See trans-synaptic tracing.

Rett syndrome Aneurodevelopmental disorder in girls caused by disruption of an X-linked gene encoding methyl-CpG binding protein 2(MeCP2). Patients usually develop normally for the

first 6-18 months. Their development then slows, arrests, and regresses, with severe deficits that include social withdrawal, loss of language, and motor symptoms. See also MeCP2.

reversal potential (Erev) The membrane potential at which the current flow through an ion channel changes direction.

reverse genetics The strategy or process of disrupting a pre-

designated gene to identify its loss-of-function phenotypes. (Figure 13-4)

reverse signaling The process by which a protein that 'normally' functions as aligand functions as areceptor and aprotein that 'normally' functions as a receptor functions as a ligand. The originally discovered ('normal') signaling mode is referred to as forward signaling. (Figure 5-12)

reward prediction error Atheoretical value representing the difference between a received reward and the predicted reward. It is represented by a population of midbrain dopamine neurons.

rhabdomeric type Atype of photoreceptor in which the apical surface folds into microvilli that house opsins. (Figure 12-22)

Rho A member of a family of small monomeric GTPases involved in actin cytoskeleton regulation.

rhodopsin Aphotosensitive molecule in the rod consisting of opsin covalently attached to retinal, a chromophore derived from vitamin A. (Figure 4-6)

GLOSSARY G:25

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RNA editing Apost-transcriptional modification that alters a nucleotide sequence of an RNA transcript after ti is synthesized.

RNA splicing The process by which introns are removed from RNA molecules. In the case of alternative splicing a subset of exons is removed as well. (Figure 2-2)

RNA-seq Atechnique ni which RNA molecules from a given tissue are sequenced one by one in a massively parallel fashion using next generation sequencing methods. It si used to obtain information about which genes are expressed and at what level in

agenome-wide scale.

RNAI (RNA Interference) Agenetic technique for knocking down the expression of a gene of interest by producing a double- stranded RNA with a sequence corresponding to that of the gene

of interest. (Figure 13-9)

Robo (Roundabout) Areceptor for Slit. (Figure 7-13)

rod Arod-shaped photoreceptor in the vertebrate retina, it is a very sensitive photon detector specialized for night vision. (Figure 4-2)

rostral-caudal (anterior-posterior) Of a body axis, from head to tail.

rtTA SeetTA.

Ruffini ending An encapsulated structure closely associated with the ending of the slowly adapting type I (SAII) LTMR. (Figure 6-64)

ryanodine receptor ACa?* channel on the ER membrane that

is activated by an increase in intracellular Ca?+ concentration and that thus amplifies cytosolic Ca?* signals. It is also activated by the plant-derived agonist ryanodine. (Figure 3-41)

saccade Arapid movement of the eyes between fixation points.

sagittal section Asection plane that is perpendicular to the medial-lateral axis.

saltatory conduction The process by which an action potential

in a myelinated axon 'jumps' from one node of Ranvier to the next. (Figure 2-26)

salty Ataste modality that functions primarily to reveal the salt content of food. It is usually appetitive at a low concentration and aversive at a high concentration.

sarcomere The contractile element of a myofibril composed of

overlapping F-actin (thin filaments) and myosin (thick filaments). (Figure 8-3)

sarcoplasmic reticulum Aspecial endoplasmic reticulum derivative that extends throughout muscle cels. Ca?+ released from the sarcoplasmic reticulum mediates the excitation- contraction coupling. (Figure 8-5)

Satb2 Atranscription factor that specifies callosal projection neuron identity. (Figure 7-10)

savings Aphenomenon whereby less effort is required for an

animal to re-learn something it has previously learned and then forgotten.

scanning electron microscopy (SEM) Aform of electron microscopy that produces images by scanning the surface of a biological specimen, collecting information regarding the interaction of the electron beam with the surface areas.

Schaffer collateral An axonal branch of a hippocampal CA3

pyare dal neuorn htat synapses ont CAl pyramdial neurons.

schizophrenia Apsychiatric disorder characterized by aset of positive symptoms (those not present in control people, such as hallucinations and delusions), negative symptoms (those, such as social withdrawal and lack of motivation, that reflect an absence

of some characteristic that is normally present), and cognitive impairment (such as deficiencies in memory, attention, and executive functions).

Schwann cell Aglial cell in the PNS that wraps axons with its cytoplasmic extension to form myelin sheath. (Figure 2-27)

s c a t i c nerve A nerve consisting of sensory and motor axons that innervates the leg.

scraple See prion diseases.

secondary antibody An antibody that recognizes selectively primary antibodies made by specific animal species. tI is usually conjugated to a fluorophore or to an enzyme that produces a color substrate.

secondary dendrite Amitral cell dendrite that extends laterally, ti is used to form reciprocal synapses with granule cells and other olfactory bulb interneurons to spread information across different olfactory processing channels. It is distinct from the primary (apical) dendrite of mitral cells that extends to the glomerulus. (Figure 6-17)

a-secretase An extracellular protease that cleaves amyloid precursor protein (APP) in the middle of the amyloid ฿(AB) peptide and prevents the production of pathology-associated Aß. (Figure 11-3)

B-secretase An extracellular protease that cleaves amyloid precursor protein (APP) at the N-terminus of amyloid B(Aß)

to produce, along with y-secretase, the intact Aß peptide. (Figure 11-3)

y-secretase An intra-membrane protease that cleaves -a or ß-secretase-processed amyloid precursor protein (APP) at the C-terminus of amyloid ฿(Aß). (Figure 11-3)

secreted protein Aprotein that is destined for export from the cell. (Figure 2-2)

selzure An episode involving abnormal synchronous firing of large groups of neurons. (Figure 11-47)

selective sweep The reduction or elimination of nucleotide variations as a result of strong positive selection of a nearby chromosome locus.

selectivity filter The part of an ion channel pore that is responsible for discriminating between the different ionic species so that only some species can pass through the channel. (Figure 2-33)

self-avoldance The process in which different axonal or dendritic branches from the same neuron are repelled by each other ot avoid overlap of processes from a single cell.

SemalA, Sema2A, Sema2B (Semaphorins-1A, -2A, -2B) Axon guidance molecules of the semaphorin family in invertebrates; SemalA is a transmembrane isoform, whereas Sema2A and Sema2B are secreted isoforms.

Sema3A (Semaphorin-3A) Asecreted axon guidance molecule of the semaphorin family in vertebrates.

semaphorins Evolutionarily conserved and widely used axon guidance cues, they consist of secreted and transmembrane variants and mostly act as repellents. Some transmembrane variants can also act as receptors. (Figure 5-9)

semicircular canal Asensory organ in the vestibular system that senses angular acceleration in a specific plane. (Figure 6-59)

sensitization An increase in the magnitude of a response to a stimulus after a different kind of stimulus, often noxious, has been applied.

sensorimotor stage The period of song learning in birds when a young bird starts ot produce his own immature song, which he compares with the tutor song template he has memorized. He

then adjusts his own song until it closely matches the tutor's song. (Figure 9-21)

sensory homunculus Amap in the primary somatosensory cortex, it corresponds to sensation of specific body parts. Nearby

somatosensory cortical areas represent sensation from nearby body surface. (Figure 1-25)

sensory neuron Aneuron that directly responds to external

stimuli, such as light, sound, chemical, thermal, or mechanical stimuli.

sensory organ precursor (SOP) In Drosophila, a progenitor cell whose asymmetric divisions give rise to different cells (a socket cell, hair cell, sheath cell, and sensory neuron) in the external sensory organ. (Figure 7-6)

sensory rhodopsin Type I rhodopsin used in prokaryotes for phototaxis. (Figure 12-20)

sensory stage The period of song learning in birds when a young bird hears and memorizes the song of atutor. (Figure 9-21)

serial electron microscopic (EM) reconstruction Amethod in which consecutive electron micrographs of thin sections are aligned to produce a three-dimensional volume. (Figure 13-29)

serial processing An information processing method in which processing units are arranged in sequential steps.

serine/threonine kinase An enzyme that adds a phosphate onto specific serine or threonine residues of target proteins.

serotonin Amonoamine neurotransmitter derived from the amino acid tryptophan that primarily acts as neuromodulator. tI is also called 5-HT for 5-hydroxytryptamine. (Figure 3-16; Table 3-2)

Sevenless Originally identified from a mutation in Drosophila that lacks photoreceptor R7, ti is a gene that acts cel- autonomously in R7 to specify the R7 fate. It encodes a receptor tyrosine kinase. (Figure 5-36)

sex chromosome The chromosome whose presence or number determines the sex of an organism.

Sex lethal (Sxl) A Drosophila gene that encodes a splicing

factor which acts at the top of the sex-determination hierarchy. (Figure 9-4)

sex-linked Of a mutation, having a Mendelian inheritance pattern characteristic of genes located on a sex chromosome. (Figure 11-34)

sex peptide In Drosophila, a peptide transferred with sperm from males to females during mating. It reduces female receptivity to courtship.

sexually dimorphic Of a trait, differing between females and males.

SH2 (Sc homology 2) domain Adomain present in many signaling proteins, ti binds phosphorylated tyrosines ni the context of specific amino acid sequences.

Shaker Identified as a mutation in Drosophila that causes defects in a fast and transient K+ current in muscles and neurons. Its corresponding gene encodes a voltage-gated K+ channel.

short-range cue (in axon guidance) Acell-surface protein that can exert its guidance effects only when axons contact the cell that produces it. (Figure 5-9)

short-term memory Memory that lasts seconds to minutes. (Figure 10-4)

short-term synaptic plasticity Achange in the efficacy of synaptic transmission that lasts milliseconds to minutes.

sign In sensory physiology, the direction in which a neuron's activity or membrane potential is changed by a stimulus (for example, the sign is positive fi a neuron is depolarized by a

stimulus, and the sign is negative fi a neuron is hyperpolarized by astimulus).

signal transduction The process by which an extracellular signal is relayed via intracellular pathways to varied effectors to produce specific biological effects.

silent synapse Aglutamatergic synapse that contains NMDA but not AMPA receptors on the postsynaptic membrane. tI can be activated by presynaptic glutamate release that coincides with postsynaptic depolarization but not by presynaptic glutamate release alone.

simple cell Afunctionally defined neuronal type enriched in layer 4 of the primary visual cortex. It si best excited by a bar of light in aspecific orientation, and it has separate ON and OFF regions that, when stimulated together, cancel each other's effect. (Figure 4-39)

single channel conductance (y)

Conductance of a single ion channel when open.

single nucleotide polymorphism (SNP) Asingle nucleotide of DNA in the genome that varies between members of a species.

single-unit recording Extracellular recording of the firing pattern of an individual neuron. See also extracellular recording. (Figure 13-31)

sIRNA (short interfering RNA) Double-stranded RNA with a length similar to microRNA (21-26 nucleotides). It directs a protein complex to degrade the target mRNA through base pairing. See also RNA interference.

size principle The idea that within a motor pool, motor neurons that have smaller motor unit sizes (with smaller axon diameters

and cell bodies) fire before neurons with larger motor unit sizes during muscle contraction. (Figure 8-7)

Slit Asecreted protein best studied as a repulsive ligand involved in midline axon guidance in many species, from insects to vertebrates. (Figure 7-13)

slow axonal transport Intracellular transport at a speed of 0.2-8 mm per day. Cargos subject to slow axonal transport mostly include cytosolic proteins and cytoskeletal components. (Figure 2-4)

SM protein Aprotein related to yeast Secl and mammalian Munc18, it binds SNAREs and is essential for vesicle fusion.

small bistratified RGC Ablue-yellow color opponent retinal ganglion cel. Se also color-opponent RGC. (Figure 4-33)

Smith-Magenis syndrome Aneurodevelopmental disorder characterized by mild-to-moderate intellectual disability, delayed speech, sleep disturbances, impaired impulse control, and other behavioral problems. tI si caused by mutations that disrupt the function of one copy of a single gene called Rail (retinoic acid induced 1) or by loss of one copy of a chromosome segment that includes Rail.

smooth muscle Muscle that controls movement of tissue within the digestive, respiratory, vascular, excretory, and reproductive systems.

SNAP-25 At-SNARE attached to the plasma membrane via lipid modification. (Figure 3-8)

SNARES (soluble NSF-attachment protein receptors) Proteins on intracellular vesicles and target membranes that form a complex and mediate membrane fusion. (Figure 3-8)

SNc (substantia nigra pars compacta) Amidbrain nucleus containing dopamine neurons that project mainly to the dorsal striatum. (Figure 8-22)

SNr (substantia nigra pars reticulata) One of the two major output nuclei of the basal ganglia, it contains GABAergic neurons

GLOSSARY G:27

G : 2 8 GLOSSARY

that project to the thalamus, superior colliculus, and brainstem motor control nuclei. (Figure 8-22)

solute Awater-soluble molecule such as an inorganic ion, nutrient, metabolite, or neurotransmitter.

soma Cell body of a neuron or any cell.

somatic mutation Amutation that occurs in a progenitor cell and that thus affects only the cells derived from that progenitor. somatosensory system The collected parts of the nervous system that provide bodily sensation.

somatostatin Aneuropeptide whose transcription is regulated by asignaling cascade involving cAMP, PKA, and CREB. tI si amarker for a subset of cortical GABAergic neurons.

Sonic Hedgehog (Shh) Amorphogen that determines cell fate by regulating the expression of specific transcription factors in many developmental contexts. For instance, floor-plate-derived Shh si responsible for determining the different fates of neuronal progenitors located at different positions along the dorsal- ventral axis of the ventral spinal cord. It is also used as a midline attractant for commissural axons. (Figure 7-8)

sour Ataste modality that functions primarily to warn the animal of potentially spoiled food. It is usually aversive.

Southern blotting Amethod for determining the amount of a specific DNA in a DNA mixture. DNA molecules are separated

by gel electrophoresis and are then transferred to a membrane; labeled nucleic acid probes are then hybridized to the membrane to visualize specific DNA molecules that hybridize to the probe.

spatial integration (in dendrites) The summation of postsynaptic potentials produced by synchronous activation of synapses located at different spatial locations on the postsynaptic neuron. (Figure 3-43)

spectral sensitivity The relationship between a response (e.g. of a photosensitive cell or molecule) and the wavelength of the stimulus light.

spike See action potential.

spike-timing-dependent plasticity (STDP) A change of

synaptic efficacy induced when pre- and postsynaptic neurons repeatedly fire within a restricted time window: synaptic efficacy is potentiated fi the presynaptic neuron fires prior to the postsynaptic neuron, and synaptic efficacy is depressed fi the presynaptic neuron fires after the postsynaptic neuron.

spinal cord The caudal part of the vertebrate CNS enclosed by the vertebral column. (Figure 1-8)

spinocerebellar ataxia One of a collection of neurodegenerative diseases, which share motor defects such as ataxia and are

caused by poly-glutamine expansion in a number of proteins. (Table 11-1)

spinocervical tract pathway An axonal pathway from the dorsal spinal cord to the lateral cervical nucleus that relays a subset of touch signals, particularly from hairy skin.

spiny projection neuron The most numerous type of neuron in the striatum, it is a GABAergic neuron that projects either directly or indirectly to the output nuclei of the basal ganglia. It is also called medium spiny neuron. (Figure 8-22)

spiral ganglion neuron Abipolar neuron whose peripheral axon receives auditory information from a hair cell in the cochlea and whose central axon transmits information to the brainstem as part of the auditory nerve. (Figure 6-49)

spontaneous neuronal activity Firing of neurons in the absence

of environmental stimuli.

sporadic Of a human disease, occurring in a patient without an identifiable family history of the disease.

Sry (Sex determining region Y) Agene located on the Y

chromosome in mammals, ti encodes a transcription factor that determines testes differentiation and other male-specific characteristics.

SSRI (selective serotonin reuptake inhibitor) An inhibitor of the plasma membrane serotonin transporter. It prolongs the action of serotonin in the synaptic cleft.

starburst amacrine cell (SAC) Aclass of GABAergic inhibitory neurons in the retina that also release acetylcholine. It is acrucial

cell type that shapes the responses of direction-selective retinal ganglion cells. tI also participates ni generating retinal waves essential for activity-dependent wiring of the visual system. (Figure 4-31)

starter cell See trans-synaptic tracing.

STED See super-resolution fluorescence microscopy.

stereocilium Arigid bundled F-actin-based cylinder located on the apical surface of a hair cell. Stereocilia on the same hair cell are arranged in rows of increasing height like a staircase. (Figure 6-47; Figure 6-50)

stereotactic injection The use of a three-dimensional coordinate system to inject substances such as viruses into a small target region of tissue in an animal.

stereotyped axon pruning The pruning of exuberant axons with an invariable outcome.

stereotypy Atrait or behavior that is largely invariant in different

individual organisms.

stimulating electrode An electrode used to pass current into a

neuron, usually with the goal of changing the membrane potential of a neuron or its processes.

stomatogastric ganglion (STG) Acrustacean ganglion that controls stomach contraction. It has been used as a model system

to study central pattern generators and rhythmic activity in neuronal circuits. (Figure 8-13)

storage (of memory) Astep in between acquisition and retrieval, in which a memory is encoded as a persistent representation somewhere in the nervous system.

STORM See super-resolution fluorescence microscopy.

striatum The part of the basal ganglia that receives convergent input from the cerebral cortex and thalamus. Also called caudate- putamen because in some species, the striatum has two separate regions called caudate and putamen, respectively. (Figure 8-22)

subcerebral projection neuron (SCPN) Acortical neuron, found in layer 5, that projects its axon to subcortical targets, such as the pons, superior colliculus, and spinal cord. (Figure 7-10)

substance P Aneuropeptide that promotes inflammation

when released by the peripheral terminals of sensory neurons. (Figure 6-71)

substantia nigra Amidbrain structure named after the high levels of melanin pigments present in the dopamine neurons of healthy human subjects. (Figure 11-16). See also SNc and SNr.

subthalamic nucleus (STN) An intermediate nucleus in the basal ganglia indirect pathway, it contains glutamatergic neurons that project to the GPi and SNr. These neurons receive GABAergic input from the GPe and glutamatergic input from the cerebral

cortex. (Figure 8-22)

sub-threshold stimulus Astimulus that is insufficient to cause a neuron to generate an action potential. (Figure 2-18)

super-resolution fluorescence microscopy Aset of fluorescence microscopy techniques capable of imaging specimens at resolutions below the diffraction limit of light.

For example, STED (stimulated emission depletion microscopy)

achieves super resolution by exciting fluorophores in a region

of tissue smaller than the diffraction limit through depletion of fluorescence in an annulus surrounding a central focal spot. STORM (stochastic optical reconstruction microscopy) and PALM (photoactivated localization microscopy) achieve super resolution by photoactivating a random small subset of photo-switchable fluorophores at any one time, such that the position of each fluorophore can be localized to a precision much finer than the resolution limits set by diffraction; repeated rounds of imaging and deactivation enable the reconstruction of the entire imaging field. (Figure 13-25)

superior colliculus Amulti-layered midbrain structure in mammals that receives retinal ganglion cell axonal input, as well as input from other sensory systems. It regulates head orientation and eye movement and is analogous to the tectum in non- mammalian vertebrates. (Figure 4-35)|

superior olivary nuclel Brainstem nuclei in mammals where auditory signals from the left ear and right ear first converge. The medial superior olivary nucleus (MSO) analyzes interaural time differences, whereas the lateral superior olivary nucleus (LSO) analyzes interaural sound level differences. (Figure 6-57)

suprachiasmatic nucleus (SCN) Ahypothamalic nucleus that is the master regulator of circadian rhythms and light entrainment in mammals. (Figure 8-34; Figure 8-49)

supra-threshold stimulus Astimulus that can cause a neuron to generate an action potential. (Figure 2-18)

sweet Ataste modality that functions primarily to detect the sugar content of food. It is usually appetitive.

sympathetic nervous system Abranch of the autonomic nervous system that facilitates energy expenditure, such as in the case of an emergency response. Activation of the sympathetic nervous system speeds up the heart rate, increases blood flow, relaxes airways in the lungs, inhibits salivation and digestion, and stimulates the production of the hormone epinephrine (adrenaline) from the adrenal glands. (Figure 8-31; Figure 8-32)

symporter Acoupled transporter that moves two or more solutes in the same direction. (Figure 2-10)

synapse Asite at which information is transferred from one neuron to another neuron or a muscle cell. It consists of a

presynaptic terminal and a postsynaptic specialization separated by a synaptic cleft.

synapse elimination The process by which extra synapses are removed during development. It is best described at the vertebrate neuromuscular junction where the innervation of muscle cells

by multiple motor neurons is refined during early postnatal development so that each muscle cell is innervated by a single motor neuron in adults. (Figure 7-27)

synaptic cleft A20-100 nm gap that separates the presynaptic terminal of a neuron from its target cel. (Figure 1-14; Figure 3-3)

synaptic efficacy See efficacy of synaptic transmission.

synaptic failure An event in which an action potential in a presynaptic neuron does not produce a postsynaptic response.

synaptic plasticity The ability to change the efficacy of synaptic transmission, usually in response to experience and neuronal activity.

synaptic potential Atype of graded potential produced at postsynaptic sites in response to neurotransmitter release by presynaptic partners.

synaptic tagging The hypothesis that induction of LTP at a synapse causes the production of a 'tag' at the synapse and that newly synthesized macromolecules necessary for stabilization of LTP are selectively captured by the tag. The hypothesis explains how the input specificity of LTP is maintained despite the cel-

wide distribution of newly synthesized macromolecules required for LTP.

synaptic transmission The process of neurotransmitter release from the presynaptic neuron and neurotransmitter reception by the postsynaptic neuron.

synaptic vesicle Asmall, membrane-enclosed organelle (typically about 40 nm in diameter) enriched at the presynaptic terminal. They are filled with neurotransmitters and, upon stimulation, fuse with the plasma membrane to release

neurotransmitters into the synaptic cleft. (Figure 3-4; Figure 3-7)

synaptic weight matrix Anetwork of synapses between ensembles of input neurons and output neurons, where the strength (weight) of each synapse can vary between 0 (no connection) and 1(maximal strength connection). (Figure 10-5)

synaptobrevin Atransmembrane SNARE on the synaptic vesicle (i.e. a v-SNARE), ti is also named VAMP. (Figure 3-8)

synaptotagmin ACa?+-binding transmembrane protein er on the synaptic vesicle that serves as a Ca?* sensor ot trigg neurotransmitter release.

syndromic disorder Adisorder characterized by a defined constellation of behavioral, cognitive, and physical symptoms.

synonymous substitutions Nucleotide changes in DNA that do not result in amino acid changes in the protein encoded by that DNA. They are used in calculations of genetic drift.

syntaxin Atransmembrane SNARE on the target plasma membrane (i.e. a t-SNARE). (Figure 3-8)

a-synuclein Aprotein normally enriched in the presynaptic terminal. tI is a major component of Lewy bodies, a defining pathological feature of most forms of Parkinson's disease.

TIRI AG-protein-coupled receptor and asubunit (along with TIR3) of the mammalian umami taste receptor. (Figure 6-41)

TIR2 AG-protein-coupled receptor and a subunit (along with T1R3) of the mammalian sweet taste receptor. (Figure 6-41)

T1R3 AG-protein-coupled receptor and a shared subunit of the mammalian umami and sweet taste receptors. (Figure 6-41)

2 R s Afamily of G-protein-coupled receptors that are the mammalian bitter taste receptors. (Figure 6-41)

tamoxifen See CreER.

tastant Anonvolatile and hydrophilic molecule in saliva that elicits taste perception.

taste bud Acluster of tens of taste receptor cells, with their apical endings facing the surface of the tongue. (Figure 6-35)

taste pore Collected apical endings of taste receptor cells in a taste bud. (Figure 6-35)

taste receptor cell Asensory neuron on the surface of the

tongue and oral cavity, it converts tastant binding to taste receptor proteins to an electrical signal that is transmitted to the peripheral terminals of the gustatory nerve. (Figure 6-35)

tau Amicrotubule binding protein that is highly enriched in axons.

tauopathies Neurodegenerative diseases characterized by the presence of neurofibrillary tangles, which consist of aggregates of hyperphosphorylated tau.

Tbrl A transcription factor that specifies corticothalamic projection neuron identity. (Figure 7-10)

tectorial membrane Amembrane on the apical side of hair cells

apposed to the stereocilia. (Figure 6-50)

tectum The major target of retinal ganglion cells in the brains of amphibians and lower vertebrates. It is a midbrain structure

analogous to the mammalian superior colliculus. (Figure 5-5)

GLOSSARY G:29

G : 3 0 GLOSSARY

telencephalon The anterior part of the forebrain, including the

olfactory bulb, cerebral cortex, hippocampus, and basal ganglia. (Figure 7-3)

temporal (in retinal map) In the direction of the temple.

temporal integration (in dendrites) The summation of postsynaptic potentials produced by activation of synapses within a finite time window. (Figure 3-43)

temporal lobe One of the four cerebral cortex lobes, it is located at the side of the brain. (Figure 1-23)

testosterone Asteroid hormone that promotes the development of the male reproductive system (masculinization) and

inhibits the development of the female reproductive system (de-feminization). In adults, it stimulates sexual behaviors. (Figure 9-24)

tetanus toxin Aprotease produced by Clostridium tetani

that cleaves synaptobrevin at a specific site, thereby inhibiting neurotransmitter release.

tetraethylammonium (TEA) Achemical that selectively blocks voltage-gated K* channels.

tetrode An extracellular electrode containing four wires that

enable four independent recordings of spiking activities of

neurons nearby the electrode tip. The firing patterns of up to ~20 neurons can be resolved based on their different action

potential amplitudes and waveforms.

tetrodotoxin (TTX) Atoxin that potently blocks voltage-

gated Nat channels across animal species and is widely used experimentally to silence neuronal firing. It is produced by symbiotic bacteria in puffer fish, rough-skinned newt, and some octopi. (Figure 2-29)

thalamocortical axons (TCAs) Axons of thalamic neurons that project to the cortex.

thalamus Astructure situated between the cerebral cortex and

the midbrain, ti relays sensory and motor signals to the cerebral

cortex through its extensive bidirectional connections with cortex. (Figure 1-8)

theory of dynamic polarization The idea that every neuron has (1) areceptive component, the cel body and dendrites; (2) a transmission component, the axon; and (3) an effector

component, the axon terminals. According to this theory, originally proposed by Ramón y Cajal, neuronal signals flow from dendrites and cell bodies to the axon.

thermosensation The sense of temperature.

thermosensory neuron Asomatosensory neuron that senses temperature.

threshold (of action potential) The membrane potential above

which an action potential is generated. (Figure 2-18)

thrombospondin (TSP) Amember of a family of secreted proteins with diverse functions. tI can be produced by astrocytes to stimulate synapse formation.

time constant (7) The product of resistance and capacitance in an R-C circuit, it is a measure of the rate at which both a capacitor charges or discharges and the voltage across a resistor changes ni response to changes in current. In neurons, t corresponds ot the time required for the membrane potential change to reach 63%

1( - 1/e) of its maximal value in response to a sudden change of current flow.

Timeless Afruit fly gene discovered based on mutations that affect circadian rhythms. It encodes a protein that participates in the negative regulation of its own transcription. (Figure 8-46)

Timothy syndrome Characterized by cardiac arrhythmia and autistic symptoms, ti is caused by mutation in the gene encoding a voltage-gated Ca?+ channel, Ca, 1.2. (Figure 11-45)

tip link The connection between adjacent stereocilia, it consists of cadherin-23 on the taller stereocilium and protocadherin-15 on

the shorter stereocilium. (Figure 6-47)

tonic Of a neuronal firing pattern, regularly timed and repetitive.

tonic-clonic selzure Aseizure associated with loss of

consciousness and a predictable sequence of motor activity:

patients first stiffen and extend al extremities (tonic phase) and then undergo full-body spasms during which muscles alternately flex and relax (clonic phase).

tonotopic map The ordered arrangement of cells in the auditory system in physical space according ot their frequency tuning.

The cochlea and multiple brain regions contain tonotopic maps. (Figure 6-49)

topographic map An ordered representation in the brain of features of either the external world or the animal's interaction with the world. For examples, see retinotopy, sensory homunculus, and motor homunculus.

touch sensory neurons Se LTMRs.

transcription The process by which RNA polymerase uses DNA as a template to synthesize RNAs. (Figure 2-2)

transcription factor ADNA-binding protein that regulates transcription of target genes.

transcription unit The part of the gene that serves as a template for RNA synthesis. (Figure 2-2)

transcytosis The process by which transmembrane or extracellular proteins are first retrieved by endocytosis in one cellular compartment and then delivered for exocytosis at another cellular compartment.

transducin Atrimeric GTP-binding protein that links light- activated rhodopsin (or cone opsin) to phosphodiesterase activation in vertebrate photoreceptors. (Figure 4-8)

Transformer (Tra) ADrosophila gene that encodes a splicing factor which acts downstream of Sex lethal (Sx/) but upstream of Doublesex (Dsx) and Fruitless (Fru). (Figure 9-4)

transgene An in vitro engineered gene that is introduced into somatic cells or the germ line of an organism. (Figure 13-11)

transgenic organism An organism that contains a transgene, usually in the germ line.

translation The process by which an mRNA is decoded by ribosomes for protein synthesis. (Figure 2-2)

transmembrane protein Aprotein that is destined to span the lipid bilayer of a membrane. (Figure 2-2)

transmission electron microscopy (TEM) Aform of electron microscopy in which high voltage electron beams transmitted through ultra-thin (typically under 100 nm) sections of biological specimens are used to create images.

transporter Atransmembrane protein or protein complex that has two separate gates that open and close sequentially to allow solutes to move from one side of the membrane to the other. (Figure 2-8)

trans-synaptic tracing Amethod that labels the synaptic partners of a given neuron or a population of neurons of interest (starter cell or cells). A retrograde trans-synaptic tracer labels

presynaptic partners of starter cells, whereas an anterograde trans-synaptic tracer labels postsynaptic partners of starter cells. (Figure 13-30)

transverse tubules (T tubules) An invagination of the plasma membrane that extends into the muscle cell interior, bringing the plasma membrane close to the sarcoplasmic reticulum, such that depolarization effectively triggers Ca?* release from the sarcoplasmic reticulum throughout the entire large muscle cell.

TRE (tetracycline response elements) The DNA sequences to which tTA or rtTA bind. (Figure 13-13). See also tTA.

trichromat Organisms that have three different cones for color vision-the S-cone, M-cone, and L-cone.

trigeminal ganglia Clusters of somatosensory neurons near the brainstem involved in sensation of the face.

trimeric GTP-binding protein (G protein) AGTP-binding protein complex composed of a Ga, a Gß, and a Gy subunit with an intrinsic GTPase activity in Ga. It has many variants, which

couple diferent GPCRs ot diverse signaling pathways. Se also G, G, and Gai

Trk receptors Afamily of neurotrophin receptors that are receptor tyrosine kinases. It includes TrkA, TrkB, and TrkC. (Figure 3-39; Figure 7-32)

TRP channels Non-selective cation channels that share sequence similarities with the Drosophila transient receptor potential (TRP) protein. (Figure 2-34)

TRPM8 Anon-selective cation channel that is activated by menthol and by temperatures <26°C. (Figure 6-68)

TRPV1 Anon-selective cation channel that is activated by capsaicin and by temperatures >43°C. (Figure 6-68)

Tscl, Tsc2 See tuberous sclerosis.

t-SNARE ASNARE located on the target membrane, such as syntaxin.

tTA (tetracycline-repressible transcriptional activator) Abacterial transcription factor widely used in heterologous systems, including transgenic mice, to control expression of a transgene. It drives expression of target genes whose promoters contain a tetracycline response element (TRE), but its activity

is repressed by tetracycline or its analog doxycycline. Avariant called rtTA (reverse TA) activates TRE-driven transgenes in the presence but not the absence of doxycycline. (Figure 13-13)

tuberomammillary nucleus Ahypothalamic nucleus rich in histamine neurons. (Figure 8-52)

tuberous sclerosis Characterized by non-malignant tumors

in the brain and other organs as well as by symptoms of autism spectrum disorders, ti is caused by mutations in genes encoding Tscl or Tsc2, the products of which are negative regulators of mTOR-mediated translational control. (Figure 11-45)

tufted cell See mitral cell.

two-photon microscopy Amicroscopy technique that relies on simultaneous absorption of two long-wavelength photons in order to excite a fluorophore. Compared with confocal microscopy, it produces less photo-damage because only at the focal plane is the density of photons high enough to cause substantial fluorescence emission. Like confocal microscopy, it relies on laser scanning

of imaging spots across a plane to produce an optical section. (Figure 13-39)

type III neuregulin-1 (Nrgl-III) An axonal cell-surface protein, the expression level of which determines the degree of axon

myelination by Schwann cels.

tyrosine hydroxylase An enzyme that converts L-tyrosine to L-dopa, it is the rate-limiting enzyme in the catecholamine

biosynthetic pathway. (Figure 11-20) UAS See GAL4.

ubiquitin-proteasome system

Aprotein degradation system present in all eukaryotes.

umami Ataste modality that functions primarily to detect the amino acid content of food. It si usually appetitive.

Unc5 Aco-receptor for netrin/Unc6 that acts together with DCC/ Unc40 to mediate repulsion.

Unc6 See netrin/Unc6.

Unc40 See DCC/Unc40.

unconditioned response (UR) Se classical conditioning.

unconditionedstimulus(US) Seclassicalconditioning.

unipolar Having one process leaving the cel body that gives rise ot both dendritic and axonal branches. (Figure 1-15)

Vl Se primary visual cortex.

vagus nerve Acranial nerve in the parasympathetic nervous system that connects the brainstem with internal organs. (Figure 8-32)

variations Differences in genes or inheritable traits.

vasopressin Ahormone secreted by hypothalamic neurons in the posterior pituitary and a neuropeptide released by certain CNS neurons. It regulates water balance and social behavior.

V-ATPase Aproton pump on the synaptic vesicle that pumps protons (H*) into the vesicle against their electrochemical gradient using energy derived from ATP hydrolysis. (Figure 3-12)

ventral horn The ventral part of the spinal gray matter where motor neurons reside. (Figure 8-6)

ventral nerve cord An invertebrate CNS structure posterior to the brain. It is analogous to the vertebrate spinal cord. (Figure 7-11; Figure 7-12)

ventral pallidum Abasal ganglia region that is a major target

of GABAergic projection neurons from the nucleus accumbens. (Figure 9-44)

ventral root The place where motor axons exit the spinal cord. (Figure 8-6)

ventral stream Avisual processing pathway from the primary visual cortex to the temporal cortex. tI is responsible for analyzing form and color; the 'what' stream. (Figure 4-48)

ventral tegmental area (VTA) Amidbrain nucleus containing dopamine neurons that project mainly to the ventral striatum (nucleus accumbens) and prefrontal cortex. (Figure 8-22; Figure 11-31)

ventricle A cavity derived from the lumen of the neural tube. It is filled with cerebrospinal fluid. (Figure 7-5)

ventricular zone Alayer of cells adjacent to the ventricles. (Figure 7-4)

ventromedial hypothalamic nucleus (VMH) Ahypothalamic nucleus whose best characterized roles include regulating female lordosis and male mounting and aggression.

(Figure 9-32)

vesicular monoamine transporter (VMAT)

Atransmembrane protein on synaptic vesicles that transports dopamine, norepinephrine, and serotonin from the presynaptic cytosol

into synaptic vesicles. (Figure 11-24). See also vesicular

neurotransmitter transporter.

vesicular neurotransmitter transporter Atransmembrane protein on the synaptic vesicle that transports neurotransmitters from the presynaptic cytosol into the vesicle using energy from the transport of protons down their electrochemical gradient. (Figure 3-12)

vestibular ganglion neuron Abipolar neuron whose peripheral axon receives vestibular information from a cell in an otolith organ or a semicircular canal and whose central axon transmits information to the brainstem as part of the vestibular n e r v e .

vestibular nerve Acollection of axons from vestibular ganglion neurons that transmits vestibular information to the brainstem. (Figure 6-59)

GLOSSARY G:31

G : 3 2 GLOSSARY

vestibular nuclel Brainstem nuclei where the vestibular nerve terminates. They also receive input from other sensory systems such as the somatosensory systems. (Figure 6-60)

vestibular system The collected parts of the nervous system that sense the movement and orientation of the head and use this

information to regulate a variety of functions including balance, spatial orientation, coordination of head and eye movements, and

perception of self-motion.

vestibulo-ocular reflex (VOR) Areflexive eye movement

that stabilizes images on the retina during head movement by moving the eyes in the direction opposite to the head movement. (Figure 6-61)

viral transduction The process by which a virus infects a host cell, introducing its genome. It is widely used for transgene expression in somatic cells.

visceral motor neurons Pre- and postganglionic neurons in the autonomic nervous system.

visceral motor system See autonomic nervous system.

visceral sensory neuron Asensory neuron whose peripheral branch innervates an internal organ and whose central branch extends ot the spinal cord or brainstem. (Figure 8-33)

visual cortex The part of the cerebral cortex that is dedicated to analyzing visual information.

visual field The portion of external world that can be seen at a given time.

voltage clamp An experimental technique used to measure the ion currents through the membrane while holding (i.e. 'clamping') the membrane potential at a set level. (Figure 2-21)

voltage-gated Ca?+ channel An ion channel that allows selective passage of Ca?* and whose conductance is regulated by the membrane potential. (Figure 2-34)|

voltage-gatedlonchannel Anionchannelwhoseconductance changes as a function of the membrane potential. At a single channel level, a channel is either open or closed; membrane potential change alters its open probability. (Figure 2-30)

voltage-sensitive dye Amolecule whose optical properties change in response to membrane potential changes.

volume transmission The secretion of neurotransmitters (usually neuromodulators) into the extracellular space outside the confines of morphologically defined synapses, where they can affect multiple nearby target cells.

vomeronasal organ (VNO) Aspecial structure located at the front of the nose that houses sensory neurons of the accessory olfactory system. (Figure 6-22)

vomeronasal system See accessory olfactory system. -SNARE ASNARE located on a vesicle, such as synaptobrevin.

VOR gain The ratio of rotation of the eyes to the rotation of the head in the vestibulo-ocular reflex.

Wallerian degeneration The process by which distal axons are eliminated after they are severed from the somata.

Weber's Law In sensory perception, the property that the just- noticeable difference between two sensory stimuli is proportional to the magnitude of the stimulus.

Wernicke's area An area in the left temporal lobe involved in language comprehension. Patients with lesions in this area have difficulty understanding language. (Figure 1-23)

western blot Amethod for determining the amount of aspecific protein in a protein mixture. Proteins are separated by gel electrophoresis and are then transferred to a membrane; labeled antibodies are then used to visualize specific proteins bound by the antibody. It can be used to determine protein expression patterns.

white matter The parts of the CNS that are enriched with oligodendrocytes and myelinated axons and that appear white because of the high lipid content of the myelin.

whole-cell patch recording (whole-cell recording) Aform of intracellular recording in which a glass electrode forms a high- resistance seal with the plasma membrane of the recorded cell.

After formation of the seal, the membrane underneath the patch electrode is ruptured, such that the interior of the patch electrode and the cytoplasm form a single compartment. See also patch clamp recording. (Figure 13-37)

whole-mount Atissue specimen that has not been sectioned.

Wnts A family of secreted proteins that act as morphogens to pattern embryonic tissues, such as the tissues along the anterior-

posterior axis of vertebrates and C. elegans. They can also serve as cues for axon guidance and for directing where synapses form along an axon.

working memory Short-term explicit memory, such as temporary retention of facts. (Figure 10-4)

zygote Afertilized egg. (Figure 7-2)