1. Synaptic Transmission Lesson 12

2. Synapses n Communication b/n neurons n Electrical l Electrotonic conduction n Chemical l Ligand / receptor ~

3. Electrical Synapses n Tight junctions l Connexons l Passive current l & larger molecules (e.g., ATP) n Synchronous activity l Breathing l Hormone release from hypothalamus ~

4. Synaptic Events n Action Potential reaches axon terminal n Chemical substance released l Neurotransmitter (NT) n Diffuses across synapse n Binds to receptor protein l EPSP or IPSP ~

5. 1. Precursor transport 2. NT synthesis 3. Storage 4. Release 5. Activation 6. Termination ~ Synaptic Transmission Model

6. Presynaptic Axon Terminal Postsynaptic Membrane Terminal Button Dendritic Spine

7. 1. Precursor Transport

8. E 2. Synthesis Enzymes & cofactors ~

9. 3. Storage E

10. Synapse Terminal Button Dendritic Spine 3. Storage In vesicles

11. Synapse Ca++ AP 4. Release via exocytosis diffusion

12. Exocytosis: Membrane Fusion n Ca 2+ influx l 2 d messenger l Ca 2+ -Calmodulin n SNAPs l soluble-NSF- attachment proteins n SNAREs l SNAP receptors ~

13. 5. Activation l NT binds to receptor

14. Activation n NT binds to postsynaptic receptor l opens ion channel l EPSP u Na+ into cell l or IPSP u K+ out of cell ~

15. 6. Termination n 4 Basic methods l Diffusion l Enzymatic degradation l Presynaptic reuptake u active transport l Autoreceptors ~

16. 6. Termination l autoreceptors A

17. Autoreceptors n On presynaptic terminal n Binds NT l same as postsynaptic receptors l different receptor subtype n Decreases NT release & synthesis ~

18. Termination n Must have discrete signal n What if ion channels continually open? l ions move toward equilibrium l membrane no longer polarized l no EPSPs or IPSPs n Disrupts neural communication n Termination ---> neuron repolarizes ~

19. Axoaxonic Synapses n Modulation of NT release l *via  or  Ca 2+ influx n Presynaptic Facilitation l Increases NT release n Presynaptic Inhibition l decreases NT release n Via modulation of E m l Ca 2+, K +, and Cl - ~

20. Drug Interaction Terms n Drug’s effect on synaptic transmission l Direct  at postsynaptic receptor l Indirect  at any other step n Agonist (AG) mimics or  NT effects n Antagonist (ANT) blocks or  NT effects ~