sodium pump (sodium-potassium pump)

n. Within the neuron, an electrolytic balance must be attained for normal neural transmission to occur. To obtain this electrical (ionic) and chemical balance, some sodium ions (Na⁺) must be relocated through the cell membrane from the intracellular portion of a neuron to the extracellular space by an active mechanism, the sodium-potassium pump. The pump obtains energy to supply this transport from the breakdown of adenosine triphosphate (ATP) produced by the mitochondria in the cell. The sodium-potassium pump exchanges intracellular sodium ions for extracellular potassium ions (K⁺), to 
obtain the necessary cellular balance. This transport is expensive, requiring up to 40% of the neuron's metabolic resources, indicating the importance of this active transport for neural transmission. – VS