transmitting an impulse - action potential and hyperpolarisation

First, sodium gated channels open

[blank_start]Sodium[blank_end] ions flow [blank_start]down[blank_end] the concentration gradient into the axon through the gated channels

The build up of positive ions inside the axon [blank_start]open[blank_end] more gated channels

The potential difference across the membrane is now +[blank_start]40[blank_end]mV

The axon is now [blank_start]depolarised[blank_end]

During [blank_start]repolarisation[blank_end], the [blank_start]sodium[blank_end] gated channels close and the sodium permeability returns to its usual [blank_start]low[blank_end] state

[blank_start]potassium[blank_end] gated channels [blank_start]open[blank_end] and potassium ions move out of the axon down the electrochemical gradient and potassium concentration gradient, [blank_start]attracted[blank_end] by the negative charge outside of the axon.

This makes the inside of the cell more [blank_start]negative[blank_end] than the outside as a lot of sodium and potassium ions are [blank_start]outside[blank_end] of the cell. The cell is now [blank_start]repolarised[blank_end].

The membrane is [blank_start]highly[blank_end] permeable to potassium ions at this stage so too [blank_start]many[blank_end] move out of the cell. This makes the potassium gated channels close and the potassium diffuse back [blank_start]into[blank_end] the axon in order to restore the resting potential. If there has been a build up of sodium inside the cell due to many successive action potentials then the [blank_start]sodium-potassium[blank_end] start working once more.