The complex protein in plasma membranes that is responsible for primary active transport; it pumps sodium ions out of the cell and potassium ions into the cell, both against their concentration gradients.

A mechanism of the neuron that keeps the resting membrane potential at a constant --70 mV, which sets the stage for electrical action. go to glossary index

a protein complex that acts as an active transport system (one that requires energy) 3 sodium ions out; simultaneously drawing 2 potassium ions in. Both carry a +1 charge, but 3 sodium ions are ejected to every 2 potassium in so the net effect is positive ions out of cell (i.e. inside slightly more negative) maintains resting potential.