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Synaptic Transmission

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

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Synaptic Transmission

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  1. Synaptic Transmission Lesson 12

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

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

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

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

  6. Postsynaptic Membrane Presynaptic Axon Terminal Dendritic Spine Terminal Button

  7. 1. Precursor Transport

  8. 2. Synthesis Enzymes & cofactors ~ E

  9. 3. Storage E

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

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

  12. Exocytosis: Membrane Fusion • Ca2+ influx • 2d messenger • Ca2+ -Calmodulin • SNAPs • soluble-NSF-attachment proteins • SNAREs • SNAP receptors ~

  13. 5. Activation • NT binds to receptor

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

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

  16. 6. Termination • autoreceptors A

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

  18. 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 ~

  19. Axoaxonic Synapses • Modulation of NT release • *via  or  Ca2+ influx • Presynaptic Facilitation • Increases NT release • Presynaptic Inhibition • decreases NT release • Via modulation of Em • Ca2+, K+, and Cl- ~

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

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