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Synaptic Transmission

Synaptic Transmission. Lecture 12. Synapses. Communication b/n neurons Electrical Electrotonic conduction Chemical Ligand / receptor ~. Electrical Synapses. Tight jucnctions Connexons Passive current & larger molecules (e.g., ATP) Synchronous activity Breathing

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Synaptic Transmission

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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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