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Neural Communication: Action Potential

Neural Communication: Action Potential. Lesson 9. Neural Signaling: Axon. Action Potentials propagated electrical signal regenerated Large & rapid changes in E m depolarization repolarization ~. Action Potentials. Electrically-gated channels or voltage-gated Characteristics

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Neural Communication: Action Potential

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  1. NeuralCommunication: Action Potential Lesson 9

  2. Neural Signaling: Axon • Action Potentials • propagated electrical signal • regenerated • Large & rapid changes in Em • depolarization • repolarization ~

  3. Action Potentials • Electrically-gated channels • or voltage-gated • Characteristics • all-or-none • relatively slow • non-decremental ~

  4. Threshold of Excitation • also: threshold potential • Triggered at axon hillock • point of decision • integration • Threshold potential • Depolarization; • approximately 10 mV • EPSPs  AP ~

  5. +40 0 -60 -70 -80 Time Em

  6. +40 C & E gradients drive Na+ into cell Depolarization Na+ influx 0 Em -60 -70 -80 Time

  7. + - Na+ K+

  8. + - Na+ K+

  9. +40 Repolarization K+ efflux 0 Em -60 -70 -80 Time

  10. + - Na+ K+

  11. + - Na+ K+

  12. After- hyperpolarization +40 0 Em -60 -70 -80 Time

  13. Refractory Period • After AP • time-out • prohibits or resists AP • absolute & relative ~

  14. Refractory Period • Absolute refractory period • Na+ channels deactivate • will not trigger AP • must reset • one-way transmission of signal • Ball & Chain Model ~

  15. Na+ channel deactivation

  16. Na+ channel deactivation

  17. Refractory Period • Relative refractory period • during after-hyperpolarization • requires greater depolarization to reach threshold ~

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

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

  20. Saltatory Conduction • Myelinated neurons • oligodendrocytes & Schwann cells • Long distances transmission • 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 • no myelin • Myelinated portions • passive current • decremental but triggers AP at next node ~

  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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