PSY 2710 Chapter 3: Neurons and Synapses

Neurons

A cell in the nervous system specialized for quickly transmitting electrical signals to other neurons via connections known as synapses; networks of neurons can coordinate their activity to process information and to serve specific functions in guiding the behavior of the organism.

Cell Membrane

Membrane that separates the cell’s components from the external environment.

Dendrites

Branching projections from the cell body of the neuron that are specialized for conveying information into the neuron.

Soma

The largest part of the neuron, the soma contains the nucleus and most of the specialized organelles of the cell.

Nucleus

A collection of neuron cell bodies within the central nervous system, with multiple nuclei typically gathered together to perform similar functions, such as control of a specific motor function or processing of a specific type of sensory information. [2] Regarding cells, a specialized part of the cell that contains the DNA.

Axon

The long projection from the cell body of the neuron that is specialized for conveying information away from the neuron.

Axon Terminals

Branches at the end of the axon, from which neurotransmitters are released.

Synapses

A structure that serves as a point of connection and communication between one neuron and another; it includes the presynaptic cell membrane, the synaptic cleft between the two neurons, and the postsynaptic cell membrane.

Afferent (Sensory) Neurons

A neuron that conveys sensory information into the nervous system.

Efferent (Motor) Neurons

A neuron that conveys information out of the nervous system.

Multipolar Neurons

Neurons with a single large axon and multiple branches of dendrites providing input to the cell body.

Bipolar Neurons

Neurons with just one dendrite and one axon connected to the cell body.

Monopolar Neurons

Neurons with just one connection to the cell body; this connection branches to form both the axon and the dendrite.

Glial Cells

A class of nonneuron cells within the nervous system that perform a range of supporting functions to ensure an optimal environment for the neurons themselves.

Golgi Staining

A tissue-staining method developed by the neuroanatomist Golgi in the late 19th century; turns the entire membrane of a neuron dark, allowing the entire structure of the neuron to be seen under a microscope.

Nissl Staining

A method of tissue staining that binds to the RNA in the cell bodies of neurons.

Autoradiology

A technique in which a radioactive substance is taken up by some specific cells, allowing the location of those cells to be identified when a photographic emulsion is placed over the tissue.

Immunocytochemistry

A technique in which antibodies are used to bind to specific proteins on a cell’s surface, allowing researchers to identify where in the cell or the brain those proteins are found.

in situ hybridization

A technique that uses radioactive or fluorescent compounds to label a “probe” sequence of DNA or RNA; the probe can then bind to a complementary sequence of DNA or RNA in a sample of tissue, to identify cells where a gene of interest is expressed.

DNA

Deoxyribonucleic acid; a molecule found in the nucleus that encodes genetic information in living organisms.

Optogenetics

From the Greek optikós, meaningvisible. Technique of genetically putting light-responsive proteins into neurons, allowing researchers to turn neurons on or off by shining light on them.

CLARITY

Technique of making tissue optically transparent while preserving structural details.

Oligodendrocytes

Glial cells that wrap myelin around the axons of neurons in the central nervous system.

Schwann Cells

Glial cells that wrap myelin around the axons of neurons in the peripheral nervous system.

Myelin

A fatty material wrapped around the axons of neurons that provides electrical insulation of the membrane and thereby increases the speed of conduction of action potentials along the axon.

Myelin Sheaths

Collections of myelin, each of which is wrapped around the length of the axon to speed up neuronal conduction.

Nodes of Ranvier

Gaps in the myelin sheath that enable ions to cross the neuronal membrane in order to propagate the action potential along the axon.

Astrocyte

A star-shaped glial cell that regulates the chemical concentration gradient around the neurons.

Microglia

A subtype of glial cells that provide immune system functions for the central nervous system.

Neurotransmitters

Chemical substances, released when a neuron is active, that transmit signals to another neuron, changing that second neuron’s activity.

Synaptic Cleft

The space between the pre- and postsynaptic neurons across which the neurotransmitters diffuse.

Synaptic Vesicles

Membrane-bound sacs of neurotransmitters stored in the presynaptic terminal of the axon.

Acetylcholine

A neurotransmitter used in both the central and the peripheral nervous system.

Monoamines

A class of neurotransmitters playing an important role in sleep, appetite, mood, anxiety, and other homeostatic, motivational, and emotional functions; includes dopamine, epinephrine, serotonin, and melatonin.

Catecholamines

A subtype of monoamine neurotransmitters, including dopamine, epinephrine, and norepinephrine.

Amino Acids

Molecules that are the building blocks of proteins.

Glutamate

A molecule that is both an amino acid and the most common excitatory neurotransmitter in the nervous system.

Gamma-aminobutyric acid (GABA)

The major inhibitory neurotransmitter of the central nervous system in vertebrate organisms.

Peptide Neurotransmitters

Neurotransmitters that are built from short chains of amino acids.

Retrograde Neurotransmitters

Neurotransmitters that transmit signals in the opposite direction of most neurotransmission (i.e., backward from the postsynaptic cell to the presynaptic cell).

Receptors

Proteins embedded in the cell membrane that are specialized to interact with neurotransmitters and exert signaling effects on the cell, via mechanisms such as ion channels or metabolic signaling pathways.

Ions

Electrically charged atoms or molecules.

Metabotropic Receptors

Receptors that, when activated by a neurotransmitter, exert their effects on neural activity via cell-signaling pathways such as G-proteins or tyrosine kinases; in contrast, ionotropic receptors contain ion channels and exert their effects directly by altering the membrane potential of the neuron.

Ionic Receptors

Receptors that, when activated by a neurotransmitter, open a channel through the cell membrane to allow ions to enter or leave the cell.

G protein-coupled receptor

A common type of metabotropic receptor that acts through a G-protein on the surface of the postsynaptic cell; some types of receptors for dopamine, serotonin, and norepinephrine fall into this class.

G proteins

Molecules located on the inner surface of the cell membrane that carry the signal from the G-protein coupled receptor to the metabolic cellular machinery that is the ultimate target of the signaling pathway.

Second Messengers

Molecules used by metabotropic receptors as part of the signaling cascade to trigger physiological changes in target processes in the cell; examples of second messengers include intracellular calcium, cyclic AMP, and nitric oxide.

Ion Channels

Proteins embedded in the cell membrane that allow ions to cross between the inside and outside of the cell.

Degradation

In the context of neurotransmission at the synapse, the process through which neurotransmitters are inactivated by being broken down by enzymes or other molecules.

Reuptake

The process through which neurotransmitters are inactivated by being transported back into the presynaptic neuron, where they can be reused.

Transporters

Proteins that move neurotransmitter molecules from the synapse across the cell membrane and back into the axon terminal as part of the reuptake process.

Membrane Potential

The difference in electrical potential between the inside and outside of the cell.

Excitatory Postsynaptic Potential (EPSP)

A change in the membrane potential of the postsynaptic membrane such that the inside of the cell becomes less negative, normally because of positively charged ions entering the cell; usually results from the release of excitatory neurotransmitters at the synapse.

Inhibitory Postsynaptic Potential (IPSP)

A change in the membrane potential of the postsynaptic membrane such that the inside of the cell becomes more negative, because of positively charged ions exiting the cell or negatively charged ions entering the cell; usually results from the release of inhibitory neurotransmitters at the synapse.

Electrical Synapses

Structures that connect neurons and allow direct transmission of the electrical signal from one neuron to the next, without requiring chemical neurotransmission across a physical gap between the cells as in a chemical synapse.

Agonists

Molecules that mimic or extend the activity of a neurotransmitter.

Antagonists

Molecules that decrease the activity of a neurotransmitter.

Action Potential

A rapid change in the neuron’s membrane potential that is used to transmit information from the cell body to the presynaptic terminal.

Temporal Summation

The process by which EPSPs and IPSPs that occur at slightly different times can combine to change the cell’s membrane potential.

Spatial Summation

The idea that EPSPs and IPSPs that occur at different locations along the cell’s membrane at approximately the same time can combine to change the cell’s membrane potential.

Depolarized

A state in which the electrical charge across the cell membrane is reduced during the course of an action potential or during communication across a synapse.

Threshold

The membrane potential at which a neuron will generate an action potential; typically, this is about –60 mV.

Axon Hillock

The portion of the axon that connects to the cell body.

Voltage-Gated Ion Channels

Ion channels that change from a closed to an open state when the membrane potential reaches a certain value. These types of channels play an important role in triggering and propagating action potentials along the axon.

Concentration Gradient

The difference in concentration between ions outside versus inside the cell; ions move down the gradient, from an area of higher concentration to an area of lower concentration.

Electrical Gradient

The difference in electrical charge between two regions, such as the inside and outside of the cell; ions will move down the gradient toward the area with the opposite charge.

Refractory Period

The time following the action potential when the voltage-gated ion channels are inactivated and unable to generate another action potential.

Saltatory Conduction

The propagation of an action potential along a myelinated axon, in which the action potential “jumps” along the axon from one node of Ranvier to the next.

Rate Coding

A system in which neurons encode information about the stimulus by changing the number of action potentials they generate within a short window of time. For example, a mechanoreceptor may use higher firing rates to encode stronger tactile stimuli.

Optogenetics

From the Greek optikós, meaningvisible. Technique of genetically putting light-responsive proteins into neurons, allowing researchers to turn neurons on or off by shining light on them.

Local Coding

A term describing a system of neural representation in which each feature of the outside world is encoded by a different neuron specialized to detect that particular feature, with no overlap in representation among neurons.

Population Coding

A property of neural representation in which a given stimulus or motor action is represented not by the activity of any single neuron but by the collective activity of a group of neurons.

Coalition

A group of neurons working together to encode a particular stimulus.