neurobiology exam 2

Synapse

The functional contact between neurons.

Presynaptic neuron

The neuron sending a signal from its axon terminal.

Postsynaptic neuron

The neuron receiving a signal at its dendrite.

Electrical Synapse

Quick, bidirectional, direct, and passive flow of current through connexons.

Connexon

Ion channel proteins that align to form a pore connecting two cells.

Connexin

Transmembrane domain protein; six assemble to form a single connexon.

Chemical Synapse

Indirect, slower information flow via neurotransmitters and synaptic vesicles.

Synaptic Cleft

The physical gap between presynaptic and postsynaptic neurons.

Synaptic Vesicles

Membrane-bound structures containing neurotransmitters for transfer between neurons.

Neurotransmitter

Information-containing molecules synthesized and released by the presynaptic neuron.

Neuropeptide

Large neurotransmitter protein synthesized in the soma and transported in large dense-core vesicles.

Small molecule neurotransmitters

Small amino acid derivatives synthesized in the axon terminal and stored in clear-core vesicles.

Small Clear-Core Vesicles

Synaptic vesicles that store small molecule neurotransmitters.

Large Dense-Core Vesicles

Synaptic vesicles that store neuropeptide neurotransmitters.

Quantal release

Neurotransmitter release in discrete packages corresponding to individual vesicle fusion.

Quanta

A single synaptic vesicle containing many neurotransmitters.

SNARE proteins

Proteins including synaptobrevin, SNAP-25, and syntaxin that mediate vesicle fusion.

Three steps of neurotransmitter release

1. Ca²⁺ binds synaptotagmin 2. SNAREs intertwine 3. Vesicle fuses with membrane.

Synaptic vesicle cycle

The process of recycling synaptic vesicle membranes to generate new vesicles.

Lambert-Eaton myasthenic syndrome (LEMS)

Autoimmune disease targeting presynaptic Ca²⁺ channels, blocking muscle movement.

Neuromuscular junction (NMJ)

The specialized synapse between a neuron and a muscle cell.

Tetanus

Toxin blocking inhibitory neurotransmitters (GABA, glycine), causing spastic paralysis.

Botulism

Toxin cleaving SNARE proteins, blocking acetylcholine release and causing flaccid paralysis.

Clathrin

Coat protein facilitating vesicle budding during endocytosis.

Dynamin

Protein that cleaves the lipid stalk of clathrin-coated vesicles.

Hsc70

The primary protein that uncoats clathrin from newly budded vesicles.

Ionotropic receptor

Fast, ligand-gated ion channel that opens directly upon neurotransmitter binding.

Metabotropic receptor

Slower G-protein coupled receptor that activates intracellular signaling cascades.

Three steps of G-protein transmission

1. Neurotransmitter binding 2. G-protein activation 3. Effector system activation.

Excitatory postsynaptic potential (EPSP)

A depolarizing potential that increases the likelihood of an action potential.

Inhibitory postsynaptic potential (IPSP)

A hyperpolarizing potential that decreases the likelihood of an action potential.

Spatial Summation

Integration of EPSPs generated simultaneously at different synapses.

Temporal Summation

Integration of EPSPs generated at the same synapse in rapid succession.

Tripartite synapse

Synaptic structure consisting of presynaptic and postsynaptic neurons plus surrounding astrocytes.

Transmitter-Gated Channels

Pentameric ion channels that mediate fast, sensitive synaptic transmission.

Protein motifs

The membrane-spanning portion of a protein shared among ion channel receptors.

G-Protein Operation (Step 1)

Inactive: Alpha, beta, and gamma subunits float in membrane; alpha binds GDP.

G-Protein Operation (Step 2)

Active: Interaction with receptor triggers exchange of GDP for GTP.

G-Protein Operation (Step 3)

Active G-alpha-GTP and G-beta-gamma subunits separate to influence effector proteins.

G-Protein Operation (Step 4)

Inactivation: G-alpha slowly converts GTP back to GDP.

G-Protein Operation (Step 5)

Reassociation: G-alpha and G-beta-gamma recombine to restart the cycle.

Acetylcholine synthesis

Synthesized from acetyl CoA and choline.

Acetylcholinesterase

Enzyme that breaks down acetylcholine in the synaptic cleft.

Nicotinic acetylcholine receptor

Excitatory, 5-subunit nonselective cation channel involved in motor control.

Muscarinic acetylcholine receptor

7-domain GPCR involved in sleep-wake cycles, sweat glands, and cognition.

Glutamate

The primary excitatory neurotransmitter, used in over 50% of brain synapses.

EAAT

Excitatory amino acid transporters that clear excess glutamate from the cleft.

Glutamate receptors (decreasing excitation)

AMPA, Kainate, NMDA.

AMPA Receptor

Glutamate-gated ion channel; generates the largest EPSP by passing Na+ and K+.

NMDA Receptor

Glutamate-gated channel permeable to Ca2+; blocked by Mg2+ when hyperpolarized.

Co-agonist

A receptor requiring two different transmitters to bind for activation.

Metabotropic Glutamate Receptors

G-protein coupled receptors; Group 1 is excitatory, Groups 2 and 3 are inhibitory.

GABA

The main inhibitory neurotransmitter, regulating about one-third of brain synapses.

VIAAT

Vesicular inhibitory amino acid transporter that loads GABA into vesicles.

GAT

GABA co-transporters that remove GABA and convert it to succinate.

GABAA Receptor

Ionotropic Cl- channel with 5 domains; target for anti-anxiety drugs.

GABAB Receptor

Metabotropic GPCR; activation blocks K+ and Ca2+ channels.

Catecholinergic Amines

Dopamine, norepinephrine, and epinephrine; all derived from tyrosine.

Dopamine

Catecholamine coordinating movement, motivation, reward, and reinforcement.

Norepinephrine

Catecholamine regulating sleep, wakefulness, arousal, attention, and feeding.

Epinephrine

Catecholamine regulating respiration and cardiac function; counters histamine.

Adrenergic Receptors

GPCRs (alpha and beta types) that bind catecholamines.

Serotonergic Amines

Histamine and serotonin; regulate mood, emotional behavior, and sleep.

Serotonin (5-HT)

Amine derived from tryptophan; regulates sleep and mood; targeted by SSRIs.

Purinergic Receptors

Receptors that bind ATP to excite neurons.

Signal Divergence

One neurotransmitter activating multiple receptor types to amplify the response.

Signal Convergence

Multiple different transmitters converging to affect the same effector system.

Paracrine Signaling

Chemical signaling acting over short distances on neighboring cells.

Endocrine Signaling

Hormones secreted into the bloodstream to act on distant target cells.

Ligand

A signaling molecule that binds to a specific receptor.

Receptor

A protein that detects chemical signals and transduces information.

Signal Amplification

Process where a single signaling molecule generates thousands of downstream responses.

Cell-Impermeant Molecules

Signaling molecules that must bind to extracellular transmembrane receptors.

Cell-Permeant Molecules

Lipophilic signaling molecules that cross the plasma membrane to intracellular receptors.

Channel-Linked Receptors

Ligand-gated ion channels that open or close upon signal binding.

Enzyme-Linked Receptors

Receptors whose extracellular binding activates intracellular enzymatic activity, like tyrosine kinases.

Heterotrimeric G-Proteins

Proteins with ɑ, β, and ɣ subunits; active when ɑ binds GTP.

GEF (Guanine Exchange Factor)

Protein that activates monomeric G-proteins by exchanging GDP for GTP.

GAP (GTPase Activating Protein)

Protein that inactivates monomeric G-proteins by driving GTP hydrolysis.

Most Common Second Messenger

Calcium ions (Ca²⁺).

cAMP and cGMP

Cyclic nucleotide second messengers that activate PKA and PKG.

IP₃ (Inositol Trisphosphate)

Lipid-derived second messenger that releases Ca²⁺ from the endoplasmic reticulum.

DAG (Diacylglycerol)

Lipid-derived second messenger that activates protein kinase C (PKC).

Protein Kinases

Enzymes that add phosphate groups to Ser, Thr, or Tyr residues.

Protein Phosphatases

Enzymes that remove phosphate groups from proteins.

CaMKII Activation

Activated by Ca²⁺/calmodulin; autophosphorylation sustains its activity over long periods.

CREB

cAMP Response Element-Binding Protein; Transcription factor activated by phosphorylation, critical for learning and memory.

c-fos

An immediate early gene synthesized within 30-60 minutes of cellular stimulation.

NGF (Nerve Growth Factor)

Neurotrophin that binds TrkA receptors to promote cell survival and differentiation.

Long-Term Synaptic Depression

synaptic weakening in response to activity patterns; small signal alone → minimal change; large signal alone → minimal change; small + large signals → second messengers (Ca2+ ↑, DAG produced, PKC activated)

Neuroanatomy

The study of nervous system structure to understand brain function.

Central Nervous System (CNS)

Consists of the brain and spinal cord.

Peripheral Nervous System (PNS)

Consists of cranial nerves, spinal nerves, and motor neurons.

Information Processing Flow

Information → PNS → CNS → response.

Superior

Directional term meaning above.

Anterior

Directional term meaning in front of.

Posterior

Directional term meaning behind.

Inferior

Directional term meaning below.

Caudal

Down the longitudinal axis of the brainstem, spinal cord, or forebrain.

Rostral

Up the longitudinal axis of the brainstem, spinal cord, or forebrain.