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Understanding Synaptic Transmission: Communication Between Neurons

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This lesson covers the intricacies of synaptic transmission, exploring the communication between neurons through both electrical and chemical mechanisms. Topics include electrotonic conduction, ligand-receptor interactions, and the steps involved in synaptic events such as neurotransmitter release and binding. Learn about electrical synapses, the roles of connexons, calcium influx, and the modulation of neurotransmitter release. The lesson also addresses drug interactions and their effects on synaptic transmission, enhancing the understanding of neural communication in both health and disease.

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Understanding Synaptic Transmission: Communication Between Neurons

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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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