In
physiology, an
action potential is a short-lasting event in which the electrical
membrane potential of a
cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of
animal cells, called
excitable cells, which include
neurons,
muscle cells, and
endocrine cells, as well as in some
plant cells. In neurons, they play a central role in cell-to-cell communication. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, 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. Action potentials in neurons are also known as "
nerve impulses" or "spikes", and the temporal sequence of action potentials generated by a neuron is called its "
spike train". A neuron that emits an action potential is often said to "fire".