Nervous impulses

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  • Created by: Anon
  • Created on: 06-04-15 12:07
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  • Nervous impulses
    • Resting potential
      • Na+ channels are shut
      • K+ channels are open, so the axon membrane is more permeable to potassium ions
      • A sodium-potassium pump is constantly moving the ions by active transport
        • Na+ is pumped out of the axon
        • K+ is pumped into the axon
        • For every 3 sodium ions that are pumped 2 potassium ions are pumped
      • After being pumped into the axon membrane the potassium ions diffuse back out again
        • This causes the outside of the axon to be more positive
        • Resting potential is about 65mV
    • Action potential
      • The stimulus causes Na+ channels to open and sodium diffuses into the axon membrane
      • Na+ channels open exponentially: the influx of sodium ions causes yet more channels to open
      • When the action potential reaches +40mV the Na+ channels shut and K+ channels open
    • Repolarisation
      • The K+ channels opening causes potassium ions to diffuse out of the axon membrane
      • This causes resting potential to resume and repolarises the axon membrane
    • Hyperpolarisation
      • During repolarisation there is a temporary overshoot in the electrical gradient
      • This overshoot causes K+ channels to shut and resting potential to resume

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