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5.8.3 – The Action Potential

Sequence of events in an action potential;

 

  1. Nerve is at resting membrane potential (-70mV)
  2. A stimulus depolarises the nerve to threshold (-50mV)
  3. Voltage-gated Na+ Channels open
  4. Sodium floods  into  the  cell  and  the  membrane  potential  depolarises to +30mV
  5. Voltage-gated K+ Channels open
  6. Potassium floods out of the cell and the membrane potential falls to -90mV
  7. The nerve is in the refractory period and cannot conduct another action potential.
  8. The 3Na+/2K+ ATPase (Na+/K Pump) restores the ion
  9. The nerve is ready to fire

As one part of the nerve fires off, Na+ diffuses into the next section of the nerve, which depolarises the nerve to threshold. This sequence is repeated like a tiny Mexican wave down the axon of the nerve.

Nodes of Ranvier speed this conduction process up. When one node depolarises it induces the next section of the nerve to depolarise by forming a mini-circuit  between nodes. This causes the action potential to “jump” between nodes of ranvier, making conduction speed much faster.