The action potential is the temporary local reversal of the resting potential that occurs when the axon is stimulated.
When a neurone receives an impulse it depolarises. Molecularly what this means is that there is an influx of positive charge inside the cell. This is caused by the Na+ channels becoming permeable and the K+ becoming impermeable.
This means that Na+ ions flow rapidly inside the cell due to the steep concentration gradient. K+ is unable to leave due to its channels being closed. The positive charge therefore builds up…