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Introduction to Neurochemistry II

Introduction to Neurochemistry II. Presentation by Josh Morrison February 23, 2005. Action potential termination. VG Na C. VG K C. Lecture #5 From Dr. James A. Murray’s Website http://faculty.uca.edu/%7Ejmurray/BIOL4425/lec/lectures.asp. Ig loop (H-gate). Role of S4 helix in gating.

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Introduction to Neurochemistry II

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  1. Introduction to Neurochemistry II Presentation by Josh Morrison February 23, 2005

  2. Action potential termination VGNaC VGKC Lecture #5 From Dr. James A. Murray’s Website http://faculty.uca.edu/%7Ejmurray/BIOL4425/lec/lectures.asp

  3. Ig loop (H-gate)

  4. Role of S4 helix in gating http://wilkes-fs1.wilkes.edu/~terzaghi/BIO-226/lectures/13.html

  5. Activation of sodium channel through S4 movement (opening of the M-gate) Outside depol Cytosol Ready state: No Na entry (Vm= -70 mV) time Active State: Na enters (Vm≥threshold)

  6. H-gate inactivates sodium channel once Vm becomes positive Inactive Ready Active No sodium flow, but able to respond to depolarizing stimulus Sodium flow present Impossible for sodium to flow through Na+ H-gate M-gate Lecture #5 From Dr. James A. Murray’s Website http://faculty.uca.edu/%7Ejmurray/BIOL4425/lec/lectures.asp

  7. Refractory period depends on state of VGNa and VGK Channels http://www.biology.eku.edu/RITCHISO/301notes2.htm

  8. http://www.biology.eku.edu/RITCHISO/301notes2.htm

  9. Refractory Period • Inability of neuron to fire after producing an Action Potential • Prevents backward conduction of AP (towards soma) • Allows neuron to “rest”

  10. Absolute Refractory Period • Approx. 1 ms duration • Voltage-gated Potassium channels open • H-gate of VGNaC closed (inactive sodium channel), though M-gate still open • Impossible for new AP to form at this site

  11. Relative Refractory Period • 1-2 ms duration (post-absolute refractory period) • VGKC open • M-gate of VGNaC closed, though H-gate is open (ready state) • Strong stimulus needed for AP formation because flow of Na into cell must be much greater than K flowing out of cell

  12. The Electrical Synapse (Gap Junction) http://www.phd.msu.edu/trosko/lectures/gapjunction/GAP.html

  13. The chemical synapse

  14. Gap vs. Chemical • Gap—heart, CNS • Chemical—PNS, neuromuscular junction • Speed of transmission: Gap > chemical • Discovery of Chemical: Otto Loewi and frog heart (1921)

  15. Common Neurotransmitters (NTs) http://faculty.washington.edu/chudler/chnt1.html

  16. Chemical Synaptic Steps Presynaptic Postsynaptic Synaptic current (in or out) Lecture #7 From Dr. James A. Murray’s Website http://faculty.uca.edu/%7Ejmurray/BIOL4425/lec/lectures.asp

  17. Synaptic Transport Overview • AP invades synapse, causing influx of Ca2+ in presynaptic neuron (due to opening of VGCaC) • Vesicle binds to membrane; releases NT • NT diffuses across synaptic cleft, binds to receptor on postsynaptic neuron • Receptor/channel opens, ions flow into and out of postsynaptic neuron • Ex. Acetylcholine receptor/channel

  18. ACh receptor/channel Lecture #7 From Dr. James A. Murray’s Website http://faculty.uca.edu/%7Ejmurray/BIOL4425/lec/lectures.asp

  19. Both Na and K ions flow through the Ach receptor Lecture #7 From Dr. James A. Murray’s Website http://faculty.uca.edu/%7Ejmurray/BIOL4425/lec/lectures.asp

  20. The change in Vm caused by NT-induced ion flow is dependant on the Vm of the postsynaptic neuron Ach receptor conductance GK > GNa GK = GNa GNa > GK Lecture #7 From Dr. James A. Murray’s Website http://faculty.uca.edu/%7Ejmurray/BIOL4425/lec/lectures.asp

  21. ACh recycling Lecture #7 From Dr. James A. Murray’s Website http://faculty.uca.edu/%7Ejmurray/BIOL4425/lec/lectures.asp

  22. Uptake of Ach by vesicles in presynaptic neuron

  23. The Cycle of the NT Vesicle http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=bnchm.figgrp.636

  24. Proteins involved in vesicle fusion with membrane Ca-sensor SNARE family (vSNARE and tSNARE) Dissociates vesicle/membrane complex http://www.neuro.wustl.edu/neuromuscular/pathol/snare.htm#vsnare

  25. Synaptic Vesicle Stages + Proteins involved in each stage Augustine, GJ et al “Proteins involved in synaptic vesicle trafficking” Journal of Physiology (1999) 520.1:33-41

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