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Neural Communication

Neural Communication. Action Potential Lesson 11. Action Potentials. Large and rapid change in membrane potential electrically-gated channels EPSPs threshold potential Occurs in axon triggered at axon hillock ~. axon hillock. AP Characteristics. Voltage-gated channels

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Neural Communication

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  1. NeuralCommunication Action Potential Lesson 11

  2. Action Potentials • Large and rapid change in membrane potential • electrically-gated channels • EPSPs • threshold potential • Occurs in axon • triggered at axon hillock ~

  3. axon hillock

  4. AP Characteristics • Voltage-gated channels • All or none • Slow • Non-decremental • Self Propagated • regenerated ~

  5. +40 0 -55 -65 -75 Time Vm

  6. +40 0 -55 -65 -75 Time Vm

  7. +40 0 -55 -65 -75 Time Vm

  8. +40 0 -55 -65 75 Time Vm

  9. +40 C & E gradients drive Na+ into cell Depolarization Na+ influx 0 Vm -55 -65 -75 Time

  10. +40 = 105 mV Amplitude Depolarization Na+ influx 0 - 65 mV to +40 mV Vm -55 -65 -75 Time

  11. +40 Repolarization K+ efflux 0 Vm -55 -65 -75 Time

  12. After- hyperpolarization +40 0 Vm -55 -65 -75 Time

  13. Refractory Period • after AP • won’t fire again • relative & absolute • Relative • during after hyperpolarization • requires greater depolarization ~

  14. +40 0 Time Relative Refractory Period Vm -55 -65 -75

  15. Absolute refractory period • Na+ channels deactivate • will not trigger AP • must reset • Ball & Chain Model ~

  16. Na+ channel deactivation

  17. Na+ channel deactivation

  18. Frequency Code • Pattern = Intensity of stimulus • frequency of APs • Place = type of stimulus • Visual, auditory, pain, etc. • Brain area that receives signal • Doctrine of Specific Nerve Energies ~

  19. 1. 2. 3. FREQUENCY CODE Weak stimulus Moderate stimulus Strong stimulus

  20. Saltatory Conduction • Myelinated neurons • oligodendroglia & Schwann cells • Transmit long distances • APs relatively slow, regenerates • EPSPs - fast, decremental • Saltatory: combines both types of current • speed without loss of signal ~

  21. Saltatory Conduction • Nodes of Ranvier • action potentials • Myelinated • like electricity through wire • decremental but triggers AP at next node • Safety factor - trigger AP across 5 nodes • .2 - 2 mm apart • larger neurons  farther apart ~

  22. Saltatory Conduction Nodes of Ranvier

  23. Graded Summation longer duration *10-100 msec chemical-gated passive spread instantaneous decremental All-or-none short 1-2 msec voltage-gated propagated slow nondecremental PSPs vs APs

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