Action Potential

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  1. What is an action pontential?
    • a sudden temporary depolarizing deviation from the normal resting potential.
    • Allows cells to transmit informtaion through nervous system.
  2. Typical action potentials characteristics
    • Each successive one looks the same
    • Have a threshold--once cell is depolarized to this level, AP is generated
    • Typical threshold is ~ -55mV
    • All or nothing
    • In crease in stimulus will not change amp of AP
    • have refractory period, absolute refractory, relative refractory, self-generating
    • Propagate with decrement
  3. Action potential in relation to membrane potential
    • -transient change in emebrane potential
    • -Equilibrum potential stays the same
    • -Tranferences change--so conductances have changed

    Em = TKEK + TNaENa

  4. Membrane potential for EK
    about -90mV
  5. Membrane potential for ENa
    About +60mV
  6. What happens in the AP:
    • sudden and temporary increase in the Na+ conductance
    • Increase Na+ conducdance= increase Na+ Tranference (decreases K+ tranference)
    • Em moves closer to ENa+ so the cell depolarizes (less negative)
    • Em becomes positive and aproaches ENa+ at overshoot
    • At peak of AP, the sodium conductance(gNa) is at its peak
    • Sodium conductance spontaneously decreases at inactivation of the sodium channels
    • Decrease in sodium transference and membrane potential begins to return towards resting value
    • Increase in K+ conductance--increases K+ tranference and brings membrance potential closer to resting value
    • So many K+ channels are open, K+ Transference is large enough to make the membrane potential even more negative than normal resting potential: hyperpolarization (undershoot!)
  7. Relationship between AP and ion gates
    Image Upload 1
  8. Why does the Refractory period need more voltage to produce an AP?
    • a. there are not as many Na+ channels
    • available as normal to trigger another AP because many are inactivated.

    • b.   Also, many more K+ channels are open,
    • so it is more difficult to depolarize the membrane to threshold.
  9. Current of an ion
    • iNa = gNa (Em - ENa)
Card Set
Action Potential
Neuroscience Exam 1
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