1. Synaptic Transmission Lecture 12

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

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

4. Synaptic Transmission n Nature of signal across synapse? n Sherrington l electrotonic transmission n Most neural conduction too slow l Delay in spinal reflexes ~

5. Synaptic Transmission n Otto Loewi had a dream l Chemical Signal? l How can it be demonstrated? n Frog Heart Preparation ~

6. n Stimulate Vagus l Heart rate slows ~ electrical stimulation -

7. n Stimulate A l Collect fluid ~ A B -

8. A B n Perfuse heart B n Heart B slows l chemical = vagusstoff ~ -

9. B n Repeat w/ accelerator nerve l HR increases l Acceleransstoff ~ A +

10. The Chase Is On n Search for chemical neurotransmitters (NT) n Criteria n Synaptic Model ~

11. 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 ~

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

13. Presynaptic Axon Terminal Postsynaptic Membrane Terminal Button Dendritic Spine

14. 1. Precursor Transport

15. E 2. Synthesis Enzymes & cofactors ~

16. 3. Storage E

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

18. Ca++ 4. Release diffusion AP

19. 5. Activation l NT binds to receptor

20. 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 ~

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

22. 6. Termination l autoreceptors A

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

24. 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 ~