Bio 168 Synaptic Transmission
Fall Semester 2004
Learning Objectives, Topics, Key Words
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
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 dont activate receptor
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Durham Technical Community College
Durham, NC 27703
Last updated 26 October 2004