- Resting membrane potential is -70 mV (reason: proteins are negatively charged, outweighs potassium inside, despite outside having negatively charged sodium). In this state, the nerve cell is said to be polarised.

- Na+ in extracellular, K+ intracellular. Ion channels exist that can open and close depending on various other factors (e.g. voltage gated, so when electrochemical potential reaches threshold, it opens, or can open due to other stimuli like ligand)

- Stimuli can cause the electrochemical potential to rise above its resting level (-70mV) If it goes up a bit (doesn’t reach threshold), this is the graded potential. If it does reach threshold (usually around +15mV over resting potential) then these channels open, ions exchange; i.e., Na+ rushes in (influx). It goes up and depolarisation occurs (due to the voltage-gated Na channels opening). This allows a large amount of sodium ions to flow in, and the potential suddenly goes up to ~+30 mV.

- Each neuron has many ion channels, so in this way when each open in a certain area, the local current is strong enough to change the voltage around them. This triggers their neighbouring channels, which goes on in a chain reaction down the axon along the Nodes of Ranvier in myelinated neurons – this is a highly efficient process.

- When this +30 mV is hit, the voltage-gated K channels open up, allowing a lot of K+ out of the cell (efflux). Na+ channels close and are inactivated. This causes the electrochemical gradient to lower and attempt to return to its resting potential. This is repolarisation. However, it goes further than the -70 mV (overshoot) to prevent the action potential from going in the opposite direction. Thus it undergoes hyperpolarisation.

- At this point, most of the K+ channels close, but some remain leaky. Na+-K+ pump uses ATP to exchange 3 sodium ions and 2 potassium ion to rebalance the membrane to the resting potential of -70 mV, during the refractory period. After resting potential is restored, the Na+ and K+ channels are then ready to be stimulated again for the next action potential.