Describe the process of action potentials occurring.

Stimulus occurs. Membrane potential reaches -50mV and action potential is triggered. Depolarisation: Na+ channels open, Na+ begins to enter cell. K+ channels open, K+ begins to leave cell. Na+ channels become refractory, no more Na+ enters cell. Repolarisation: K+ continues to leave cell, causes membrane potential to return to resting level. K+ channels close, Na+ channels reset. Hyperpolarisation: Extra K+ outside become more -ve diffuse away.