Week 6 Neurobiology

Synaptic Terminals

Chemical synaptic transmission

Neuron-to-neuron communication using neurotransmitters released into a synaptic cleft

Presynaptic neuron

The neuron that releases neurotransmitter

Postsynaptic neuron

The neuron that receives the neurotransmitter signal

Synapse

The junction between a presynaptic neuron and a postsynaptic cell

Synaptic cleft

The small gap between presynaptic and postsynaptic cells

Neurotransmitter

Chemical messenger released from synaptic vesicles

Synaptic vesicle

Membrane-bound structure that stores neurotransmitter

Exocytosis

Process where vesicles fuse with membrane to release neurotransmitter

Endocytosis

Process that retrieves vesicle membrane after neurotransmitter release

SNARE proteins

Proteins that mediate vesicle docking and fusion

v-SNARE

SNARE protein located on synaptic vesicles

t-SNARE

SNARE protein located on presynaptic membrane

Synaptotagmin

Ca²⁺-sensing protein that triggers vesicle fusion

Voltage-gated Ca²⁺ channel

Channel that opens during depolarization to allow Ca²⁺ entry

Calcium (Ca²⁺)

Triggers neurotransmitter release by activating synaptotagmin

Kiss-and-run exocytosis

Partial vesicle fusion with rapid neurotransmitter release

Full fusion exocytosis

Complete vesicle fusion with membrane

Clathrin-coated vesicle

Vesicle formed during endocytosis

Dynamin

Protein that pinches vesicles off during endocytosis

Postsynaptic potential (PSP)

Local, graded change in membrane potential

Synaptic delay

Time between presynaptic action potential and PSP

Excitatory postsynaptic potential (EPSP)

Depolarization that moves membrane toward threshold

Inhibitory postsynaptic potential (IPSP)

Hyperpolarization that moves membrane away from threshold

Depolarization

Membrane potential becomes more positive

Hyperpolarization

Membrane potential becomes more negative

Spatial summation

Addition of PSPs from different synapses at the same time

Temporal summation

Addition of PSPs from the same synapse over time

Axon hillock

Integration site where action potentials are initiated

Passive current

Current that decays with distance along the neuron

Downstream inhibition

Inhibitory synapse that reduces excitatory signal spread

Terminal boutons

Synaptic terminals at the end of axons

En passant boutons

Synaptic terminals located along the axon shaft

Dense-core vesicles

Vesicles containing neuropeptides

Small clear vesicles

Vesicles containing small-molecule neurotransmitters

Low-frequency stimulation

Releases small vesicles with localized Ca²⁺

High-frequency stimulation

Releases dense-core vesicles with widespread Ca²⁺

Ion channel

Protein pore that allows ions to cross membrane

Ion selectivity

Which ions can pass through a channel

Gating

Mechanism that opens or closes an ion channel

Voltage-gated channel

Channel activated by membrane potential changes

Ligand-gated channel

Channel activated by neurotransmitter binding

Stretch-gated channel

Channel activated by mechanical deformation

Ionotropic receptor

Ligand-gated ion channel producing fast responses

Metabotropic receptor

G-protein–coupled receptor producing slower responses

Neuromuscular junction (NMJ)

Synapse between motor neuron and muscle fiber

End plate potential (EPP)

Evoked postsynaptic potential at the NMJ

Acetylcholine (ACh)

Neurotransmitter at vertebrate NMJs

Choline acetyltransferase (ChAT)

Enzyme that synthesizes acetylcholine

Acetylcholinesterase (AChE)

Enzyme that breaks down acetylcholine

Nicotinic ACh receptor

Ionotropic ACh receptor at skeletal muscle NMJ