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Bio 168 Synaptic Transmission
Fall Semester 2004

Learning Objectives, Topics, Key Words



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Recommended Readings: Martini (6th ed) 388 - 389; 411 - 422.

1. Review basic principals of neuron structure and function

information flow is in one direction only

synaptic inputs:

onto dendrites

onto soma (neuron cell  body)

output: initial segment (where AP is triggered)

axon

axon collaterals

axon terminals

where synapse is made with next cell

where neurotransmitter is released

 

2. Review basic principles of membrane potentials

membrane potential

potential = voltage

difference in potential between inside and outside of cell (transmembrane)

resting potential (usually about —70 mV)

ionic equilibrium potentials (Eion) (ionic batteries)

size depends of magnitude of concentration gradient

sign depends on direction of concentration gradient

sodium ion battery (ENa is about +55 mV)

potassium ion battery (EK is about —100 mV)

 

relative permeability to sodium and potassium ions controls membrane potential

depolarization if permeability to sodium ion increases

cations enter cell (membrane potential approaches ENa)

hyperpolarization if permeability to potassium ion increases

cations leave cell (membrane potential approaches EK)

ions permeate through channels

voltage-gated channels (make action potential)

chemically-gated channels (make synaptic potentials)

action potential is all-or-nothing if threshold is reached

synaptic potentials are graded in size

 

3. Understand principals of chemical synapse structure and function

presynaptic neuron

synaptic knob

vesicles (membrane-enclosed packets of neurotransmitter)

release mechanism (depends on inward Ca++ movement into synaptic knob)

neurotransmitter released when vesicle fuses with presynaptic membrane (exocytosis)

synaptic cleft

postsynaptic neuron

receptor in membrane = chemically-gated ion channel

ionic currents --> postsynaptic potential

transmitter removal

hydrolysis (add water across a bond)

re-uptake (by axon terminals and glia)

covalent modification (add a group)

diffusion

 

4. Understand synaptic transmission in the CNS

types of synapses

axodendritic

axosomatic

axoaxonic (presynaptic)

excitatory synapses (depolarizing)

EPSPs

excitatory transmitters

glutamate, aspartate

inhibitory synapses (hyperpolarizing)

IPSPs

inhibitory transmitters

GABA (gamma-aminobutyric acid), glycine

synapses named for transmitter (e.g., gabaminergic)

presynaptic inhibition and facilitation (axoaxonic synapses)

spatial summation

temporal summation

 

 

5. Recognize how synaptic transmission can be modified by external agents

transmitter release (e.g., tetanus toxin)

transmitter degradation (e.g., nerve gas inhibits acetylcholinesterase)

transmitter re-uptake (e.g. Prozac® inhibits serotonin re-uptake, "SSRI")

transmitter substitutes (bind to receptor)

agonists (e.g., nicotine activates cholinergic receptors in CNS and PNS)

agonists produce same action as transmitter

antagonists (e.g., curare binds to neuromuscular ACh receptor)

block binding of transmitter but don’t activate receptor


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Durham Technical Community College
Durham, NC 27703
Last updated 26 October 2004