Action Potential

  1. What are the 6 phases?
    • Resting MP
    • Threshold
    • Depolarization phase
    • Repolarization Phase
    • Undershoot
    • Na-K Pump
  2. Part one
    All voltage-gated ion channels are closed
  3. Part Two
    EPSPs summate, making the interior more positive nad causing the activation gates of voltage-gated Na channels to fly open
  4. Part Three
    • Depolarization phase:
    • Na floods into the axon, making the interior more positive (depolarizing the interior) and drives the membrane potential above zero (all the way up to +40)
  5. Part Four
    • Repolarization phase:
    • Voltage gated Na+ channels close and voltage-gated K+ channels open. K floods out of hte axon, carrying out positive charge and making the interior negative again, repolarizing it
  6. Part FIve

    Voltage-gated K channels are slow to close; and so much K leaves the axon/ cell that the membrane voltage falls below the original resting membrane voltage/ potential
  7. Part Six
    • Sodium-Potassium Pumps
    • They are finishing the job. Na-K pumps reaestablish the original ion distribution
    • 3 Na+ kicked out; K+ comes in
    • Pumping against concentration gradient
  8. Resting state
    no channels open
  9. Depolarization phase
    • Na+ activation gates open, allowing influx of sodium
    • Note: Voltage-gated Na+ channnels have 2 gates:
    • a) Activation gate opens rapidly at depolarization
    • b) Inactivation gate closes slowly at depolarization
  10. Repolarizing phase
    • inactivation gates close Na+ channels, and activation gates open K+ channels.
    • Note: Voltage-gated K+ channels have one gate
    • - This gate opens slowly at depolarization
  11. Undershoot phase
    • Membrane potential temperarily more negative than resting state
    • Since K+ gates slow to close
    • Refractory period: Neuron insensitive to depolarizing stimuli
Card Set
Action Potential