~DB12 synaptic transmission.ppt

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~DB12 synaptic transmission.ppt

  1. 1. Synaptic Transmission Lecture 12
  2. 2. Synapses <ul><li>Communication b/n neurons </li></ul><ul><li>Electrical </li></ul><ul><ul><li>Electrotonic conduction </li></ul></ul><ul><li>Chemical </li></ul><ul><ul><li>Ligand / receptor ~ </li></ul></ul>
  3. 3. Electrical Synapses <ul><li>Tight jucnctions </li></ul><ul><ul><li>Connexons </li></ul></ul><ul><ul><li>Passive current </li></ul></ul><ul><ul><li>& larger molecules (e.g., ATP) </li></ul></ul><ul><li>Synchronous activity </li></ul><ul><ul><li>Breathing </li></ul></ul><ul><ul><li>Hormone release from hypothalamus ~ </li></ul></ul>
  4. 4. Synaptic Transmission <ul><li>Nature of signal across synapse? </li></ul><ul><li>Sherrington </li></ul><ul><ul><li>electrotonic transmission </li></ul></ul><ul><li>Most neural conduction too slow </li></ul><ul><ul><li>Delay in spinal reflexes ~ </li></ul></ul>
  5. 5. Synaptic Transmission <ul><li>Otto Loewi had a dream </li></ul><ul><ul><li>Chemical Signal? </li></ul></ul><ul><ul><li>How can it be demonstrated? </li></ul></ul><ul><li>Frog Heart Preparation ~ </li></ul>
  6. 6. <ul><li>Stimulate Vagus </li></ul><ul><ul><li>Heart rate slows ~ </li></ul></ul>electrical stimulation -
  7. 7. <ul><li>Stimulate A </li></ul><ul><ul><li>Collect fluid ~ </li></ul></ul>A B -
  8. 8. <ul><li>Perfuse heart B </li></ul><ul><li>Heart B slows </li></ul><ul><ul><li>chemical = vagusstoff ~ </li></ul></ul>A B -
  9. 9. <ul><li>Repeat w/ accelerator nerve </li></ul><ul><ul><li>HR increases </li></ul></ul><ul><ul><li>Acceleransstoff ~ </li></ul></ul>B A +
  10. 10. The Chase Is On <ul><li>Search for chemical neurotransmitters (NT) </li></ul><ul><li>Criteria </li></ul><ul><li>Synaptic Model ~ </li></ul>
  11. 11. Synaptic Events <ul><li>Action Potential reaches axon terminal </li></ul><ul><li>Chemical substance released </li></ul><ul><ul><li>Neurotransmitter (NT) </li></ul></ul><ul><li>Diffuses across synapse </li></ul><ul><li>Binds to receptor protein </li></ul><ul><ul><li>EPSP or IPSP ~ </li></ul></ul>
  12. 12. <ul><li>1. Precursor transport </li></ul><ul><li>2. NT synthesis </li></ul><ul><li>3. Storage </li></ul><ul><li>4. Release </li></ul><ul><li>5. Activation </li></ul><ul><li>6. Termination ~ </li></ul>Synaptic Transmission Model
  13. 13. Presynaptic Axon Terminal Postsynaptic Membrane Terminal Button Dendritic Spine
  14. 14. 1. Precursor Transport
  15. 15. E 2. Synthesis Enzymes & cofactors ~
  16. 16. 3. Storage E
  17. 17. Synapse Terminal Button Dendritic Spine 3. Storage In vesicles
  18. 18. 4. Release diffusion Ca++ AP
  19. 19. <ul><ul><li>NT binds to receptor </li></ul></ul>5. Activation
  20. 20. Activation <ul><li>NT binds to postsynaptic receptor </li></ul><ul><ul><li>opens ion channel </li></ul></ul><ul><ul><li>EPSP </li></ul></ul><ul><ul><ul><li>Na+ into cell </li></ul></ul></ul><ul><ul><li>or IPSP </li></ul></ul><ul><ul><ul><li>K+ out of cell ~ </li></ul></ul></ul>
  21. 21. 6. Termination <ul><li>4 Basic methods </li></ul><ul><ul><li>Diffusion </li></ul></ul><ul><ul><li>Enzymatic degradation </li></ul></ul><ul><ul><li>Presynaptic reuptake </li></ul></ul><ul><ul><ul><li>active transport </li></ul></ul></ul><ul><ul><li>Autoreceptors ~ </li></ul></ul>
  22. 22. <ul><ul><li>autoreceptors </li></ul></ul>6. Termination A
  23. 23. Autoreceptors <ul><li>On presynaptic terminal </li></ul><ul><li>Binds NT </li></ul><ul><ul><li>same as postsynaptic receptors </li></ul></ul><ul><ul><li>different receptor subtype </li></ul></ul><ul><li>Decreases NT release & synthesis ~ </li></ul>
  24. 24. Termination <ul><li>Must have discrete signal </li></ul><ul><li>What if ion channels continually open? </li></ul><ul><ul><li>ions move toward equilibrium </li></ul></ul><ul><ul><li>membrane no longer polarized </li></ul></ul><ul><ul><li>no EPSPs or IPSPs </li></ul></ul><ul><li>Disrupts neural communication </li></ul><ul><li>Termination ---> neuron repolarizes ~ </li></ul>

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