1. Section C: Synapses Section D: Structure of the Nervous System
7 October 2008
Section C: Synapses
Section D: Structure of the Nervous System

2. Fates of neurotransmitters: 1) Diffusion away from synapse,
Vesicle release proportional to Ca++ influx (High f AP leads to residual Ca++ in terminal)
Figure 6.27
Fates of neurotransmitters:
1) Diffusion away from synapse,
2) Enzymatic degradation (e.g. AChE and MAO)
3) Reuptake into presynaptic terminal (e.g. SSRI)
SSRIs: Lexapro, Prozac, Paxil, Zoloft
Tetanus toxin & Botulinum toxin disrupt SNARE function.

3. Figure 6.28
Some ion Channels that allow flux of Na+ and K+ simultaneously
e.g. nicotinic Acetylcholine Receptor (nAChR)
EPSPs :which ion moving in which direction?
Duration of PSP vs AP
Synaptic delay

4. EK+ IPSPs :which ion moving in which direction?
Figure 6.29
IPSPs :which ion moving in which direction?
Some IPSPs result in no change in membrane potential by opening Chloride channels that stabilize membrane potential at resting value (Nernst Potential for Cl- = -70mV) or in cells that actively transport Cl- out.
EK+

5. Summation and Synaptic Integration
Figure 6.31
Summation and Synaptic Integration
Different times
Different locations
Each IPSP hyperpolarizes by 5 mV. Each EPSP depolarizes by 5 mV.
If 4 inhibitory synapses are active at the same time, how many excitatory synapses must be active simultaneously to exceed threshold (-55 mV) if the resting membrane potential is -70mV?

6. Priority by proximity
Demo: Eunice is the axon hillock!
Diagram on Board: Degree of depolarization above threshold is proportional to frequency of action potentials.

7. Figure 6.33 Who Cares? Presynaptic Facilitation Presynaptic Inhibition
Diagram of descending pathway from periaqueductal gray matter to suppress afferent pain via presynaptic inhibition. Example: cut to abdomen.
Mechanism: vary Ca++ entry in presynaptic terminal B.

8. Figure 6.34 Recall AChE and MAO & SSRI
Most neurotransmitters are synthesize in the axon terminal.
Exceptions: Peptide NTs originate in cell body, move in vesicles by fast orthograde axonal transport to axon terminal.
Figure 6.34
Recall AChE and MAO & SSRI