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Synaptic Transmission: From Electrical Signals to Neurotransmitter Release

Explore the intricate process of synaptic transmission, from electrical synapses to chemical signaling between neurons. Learn about the nature of signals across synapses, Sherrington's work, Otto Loewi's experiment with frog hearts, and the different methods of neurotransmitter termination.

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Synaptic Transmission: From Electrical Signals to Neurotransmitter Release

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  1. Synaptic Transmission Lecture 12

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

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

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

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

  6. electrical stimulation - • Stimulate Vagus • Heart rate slows ~

  7. - • Stimulate A • Collect fluid ~ B A

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

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

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

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

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

  13. Postsynaptic Membrane Presynaptic Axon Terminal Dendritic Spine Terminal Button

  14. 1. Precursor Transport

  15. 2. Synthesis Enzymes & cofactors ~ E

  16. 3. Storage E

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

  18. AP Ca++ 4. Release diffusion

  19. 5. Activation • NT binds to receptor

  20. Activation • NT binds to postsynaptic receptor • opens ion channel • EPSP • Na+ into cell • or IPSP • K+ out of cell ~

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

  22. 6. Termination • autoreceptors A

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

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

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