Depolarisation

• Stimulation:

  • Na+ ion channels in the cell membrane open when a neurone is stimulated
  • Na+ ions flood into the neurone
  • The potential difference across the membrane changes to become more positive inside the neurone
• Depolarisation:

  • If the action potential increases above the threshold value (-55mV) then the membrane will become depolarised.
  • More sodium channels open and there is a sharp increase in potential difference t about +30mV.
• All-or-nothing:

  If the potential difference reaches the threshold, depolarisation will always take place and the change in potential difference will always be the same
• All-or-nothing:

  If the stimulus is stronger, action potentials will be produced more frequently but their size doesn't increase.
• Repolarisation:

  After the neurone membrane has depolarised to +30mV, the sodium ion channels close and potassium ion channels will open.
• Repolarisation:

  Na+ ions are transported back out of the neurone and the potential difference becomes more negative. This is known as repolarisation.
• Hyperpolarisation:

  There is a short period of time after depolarisation of a neurone where the potential difference becomes slightly more negative than the resting potential, known as hyperpolarisation.
• Hyperpolarisation will prevent the neurone from being restimulated instantly, this is then known as the refractory period.