Ch. 5 Synaptic Transmission

Gap junctions

6 connexins = 1 connexon; 2 connexons = 1 gap junction

Postsynaptic potential (PSP)

electrical current that passes to the other cell. it’s typically small but when summed, can be meaningful

Synaptic cleft

separates pre- and post- synaptic membrane (20-50 nm)

CNS synapses

vary in size and shape

Axodendritic

axon to dendrite

Axosomatic

axon to cell body

Axoaxonic

axon to axon

Axospinous

axon to dendritic spine

Dendrodendritic

dendrite to dendrite (where neurons feed info back to self)

Membrane differentiation

classified based on the thickness of the membrane differentiations

Gray’s Type I

asymmetrical, excitatory

Gray’s Type II

symmetrical, inhibitory

Neuromuscular junction

synapse between motor neurons in the spinal cord and skeletal muscle (ACh triggers muscular contraction)

3 categories of neurotransmitters

amino acids, amines, peptides

Site of neurotransmitter synthesis

in cell body or axon terminal

Action potential at axon terminal

depolarizes membrane and opens voltage-gated Ca channels which allows Ca2+ to flow into cell and trigger neurotransmitter release by exocytosis very rapidly

SNARE family proteins

mediate exocytosis

Transmitter-gated ion channels

not as selective as voltage-gated ion channels, mediated by amino acid and amine neurotransmitters binding to the channel

Excitatory Postsynaptic Potential (EPSP)

if transmitter-gated channels permeable to Na+, then depolarization of the membrane via Ca2+ inflow

Inhibitory Postsynaptic Potential (IPSP)

if transmitter-gated channels are permeable to Cl-, then hyperpolarization of the membrane

GPCRs

when neurotransmitter binds to receptor, it activates intracellular G-protein which causes signaling cascade in postsynaptic regions

Presynaptic terminal GPCRs

autoreceptors

Autoreceptors

presynaptic receptors sensitive to neurotransmitter released by presynaptic terminal. it commonly inhibits neurotransmitter release when activated, functions as kind of safety valve…regulates!

Neurotransmitter clearance

diffusion, reuptake, uptake by glial cells, or enzymatic destruction. if not cleared, desensitization can occur

Integration

EPSP added together to produce significant postsynaptic depolarization

Spatial summation

EPSP generated simultaneously at different sites

Temporal summation

EPSP generated at same synapse in rapid succession

Action of inhibitory synapses

takes membrane potential away from action potential threshold so exerts powerful control over neuron output

Shunting inhibition

synapse inhibits current flow from soma to axon hillock