Excitable cells of the nervous system (i.e., neurons) generate nervous impulses. Nervous impulses are the electrical signals by which neurons talk to one another and also to other cells of the body. The nervous impulse is referred to as the action potential. An action potential is a brief (only a few milliseconds) reversal of the membrane potential (V_m). At rest, the V_m of a neuron is around −70 mV (closer to the equilibrium potential for potassium, V_K), but during an action potential, V_m transiently approaches +50 mV (closer to the equilibrium potential for sodium, V_Na). The membrane potential then rapidly returns to the resting potential and even briefly goes beyond the resting potential to approach V_K before finally returning to the resting value of about −70 mV. The entire process takes about 3-5 ms. This potential reversal of more than 100 mV is responsible for electrical signaling in the nervous system, and is the basis of information transmission in the nervous system.

Test your basic knowledge of the neuronal action potential by taking this simple quiz below. For more information about the neuronal action potential, see the Neuronal Action Potential lecture notes.