action potential

• • to initiate a nerve impulse, the membrane must be depolarised
  • depolarisation=reversal of electrical potential difference
  • -70mV to +40mV
  • action potential=potential electrical difference produced across axon membrane when neurone is stimulated
• Generating an AP

  neurone is stimulated...

  1)small number of sodium channels in the axon membrane are open

  2)NA+ begin to move into axon, down the conc gradient-decreasing PD across axon membrane as inside of neurone becomes more positive

  3)if PD reaches 55mV(threshold period)voltage gated sodium ion channels open=influx of NA+

  4)charge from -70mV to +40mV=membrane is depolarised and action potential is generated
• repolarisation

  1)after AP generated all voltage gated NA+ channels in membrane close

  2)voltage gated potassium ion channels in the axon now open

  3)allowing diffusion of K+ out of the axon and down concentration gradient(pump still working thus gradient still present)

  4)causes inside of axon to be negatively charged again
• hyperpolarisation

  • short period of time when membrane potential is more negative than resting potential- membrane unresponsive to stim during this so no new AP can be generated
  • means impulse can only travel in one direction
  • voltage gated K+ channels then close and pump works to restore resting potential
  • membrane can then be stimulated again