The generation of electrical signals in neurons requires both selective membrane permeability and specific ion concentration gradients across the plasma membrane. The membrane proteins that give rise to these two essential conditions are called ion channels and pumps, respectively. Ion channels have pores that allow particular ions to diffuse across the neuronal membrane. Some channels also have specialized domains that sense the electrical potential across the membrane. Such channels open or close in response to the level of membrane potential, allowing the membrane permeability to be voltage-sensitive. Pumps are membrane proteins that produce and maintain ion concentration gradients. The Na+ pump, which regulates the intracellular concentrations of Na+ and K+ by hydrolyzing ATP to fuel the movement of these ions across the plasma membrane, is the best-known example.

From the perspective of neural signaling, pumps and channels are complementary: pumps create the concentration gradients that impel ions to diffuse through open channels, thus generating electrical signals.

Neuroscience, Sinaur Associates (QP355.2.N487 1997)