Explain the formation of an action potential.

The change from resting potential to action potential is caused by the stimulation of a recpetor, this causes a chain reaction which eventually leads to a positive environement inside the cell.

1. An change in permiability of the cell surface membrane to Na+ and K+ ions leads to Na+ flooding into the cytoplasm through newly opened Na+ membranes, down the concentration gradient. 

2. This causes the membrane to depolarise, this depolarisation has to reach a certain level, known as threshold, before action potential is thought to be reached. (This is about -50 to -55mV) If this is reached, an impulse will be fired.

3. This impulse creates a local current between itself and a resting area next to it, some Na+ will move towards the resting area, causing Na+ channels to open and depolarisation occurs there, moving the action potential down the neruone. 

4. Na+ channels close and K+ open in a process called repolarisation, so K+ floods out of the cytoplasm.

5. The K+ channels then close, the sodium potassium pump restarts and the ion balance is restored back to a level of resting potential.