Action potentials occur in several types of animal cells called excitable cells. These include neurons, muscle cells, and endocrine cells, as well as in some plant cells. The 'action potential' is the name of an event during which the electrical membrane potential of a cell rapidly rises and falls - 'exciting' the cell.

In neurons, they play a central role in cell-to-cell communication. Action potentials in neurons are sometimes called 'nerve impulses' or 'spikes'. A neuron that emits an action potential is often said to 'fire'.

In other types of cells, their main function is to activate intracellular processes.

e.g. in muscle cells an action potential is the first step in the chain of events leading to contraction.

in beta cells of the pancreas, they provoke release of insulin.

For A level Physics you have to know the potential/time graph for such events and know the ion movement that is associated with the changes of potential. See the links below:

Action Potential

Biopotentials

E.C.G.

Heart Action Potential

Neurons

PQRST Trace