1. What happens when action potential reaches axon terminal?
Forms a synapse with another neuron or muscle
Two types: Electrical and Chemical

2. Chemical Synapse

4. 1. action potential arrives at terminal 2. voltage-gated Ca
channels open
3. Ca triggers exocytosis
of vesicles
4. neurotransmitter is re-
leased, binds to re-
ceptor
5. ligand-gated Na or K
6. neurotransmitter broken
down, taken up
7. synaptic vesicles re-
constituted
8. neurotransmitter stored,
awaits next impulse
Action
potential
Synaptic
vesicle
active
uptake
Ca2+
voltage-
gated Ca
channel
Ca2+
docking
protein K+
Postsynaptic
cell
Na+

6. Neuromuscular Junction
acetylcholine X
botulinum
toxin X
curare (antagonist)
nicotine (agonist)
acetylcholinesterase
Nicotinic cholinergic synapse

7. Muscarinic cholinergic synapse
acetylcholine X
atropine (antagonist)
muscarine (agonist)

8. Post-Synaptic Events Graded vs Action Potentials
Excitatory vs. Inhibitory PSPs
Pre- vs. Post-Synaptic Inhibition
Divergence vs. Convergence

9. Receptor binding results in opening of agonist-gated K and Cl channels
e.g. muscarinic acetylcholine receptor of
heart

10. Receptor binding results in opening of agonist-gated Na channel
e.g. nicotinic acetylcholine receptor of
neuromuscular junction

12. One synapse is generally not sufficient to
generate a threshold stimulus at the axonal
hillock.
Most neurons receive thousands of synaptic endings -
each of which contributes a postsynaptic potential
(EPSP or IPSP) of less than 1 mV.
Each of these PSPs are conducted to the axonal
hillock with decrement (decay).
An action potential will only be generated if the
sum of the IPSPs and EPSPs reaching the axonal
hillock at any time exceed the threshold voltage.

13. Dendrite of
postsynaptic
neuron
Axon terminals
of presynaptic
neuron
Dendrite of
postsynaptic
neuron
Glial cell
processes
Axon

14. Spatial
summation

17. excitatory inhibitory A D E B C electrode threshold A A+B A+B+C D D+E
A+B+C+E

18. Postsynaptic Inhibition

19. Presynaptic Inhibition

20. Divergent
circuit
Allows for
amplification
of a signal:

21. single pyramidal cell in the motor cortex of the brain
15-20 internuncial cells in CNS
each stimulates several hundred motoneurons
each of these stimulates muscle fibers
Divergence results in 50,000-fold amplification

22. Important for summing, correlating and sorting information in the CNS
Convergent circuit
Important
for
summing,
correlating
and sorting
information
in the CNS