Sodium and potassium ions are pumped out of and into of the body's
cells (respectively) to help maintain water balance, move glucose
(sugar) around, and to facilitate nerve impulses. This process is the
"sodium-potassium pump" about which there should be a lot of
information in your biology textbooks. Here are some websites:
The Free Dictionary - NAKATPase:
The Free Dictionary - NA-K Pump:
Estrella Mountain Community College: Online Biology Book - The Nervous System
"The plasma membrane of neurons, like all other cells, has an unequal
distribution of ions and electrical charges between the two sides of
the membrane. The outside of the membrane has a positive charge,
inside has a negative charge. This charge difference is a resting
potential and is measured in millivolts. Passage of ions across the
cell membrane passes the electrical charge along the cell. The voltage
potential is -65mV (millivolts) of a cell at rest (resting potential).
Resting potential results from differences between sodium and
potassium positively charged ions and negatively charged ions in the
cytoplasm. Sodium ions are more concentrated outside the membrane,
while potassium ions are more concentrated inside the membrane. This
imbalance is maintained by the active transport of ions to reset the
membrane known as the sodium potassium pump. The sodium-potassium pump
maintains this unequal concentration by actively transporting ions
against their concentration gradients."
Transport Across Cell Membranes: Direct Active Transport
"the same transporter, called the Na+/K+ ATPase, does both jobs. It
uses the energy from the hydrolysis of ATP to
actively transport 3 Na+ ions out of the cell
for each 2 K+ ions pumped into the cell.
This accomplishes several vital functions:
It helps establish a net charge across the plasma membrane with the
interior of the cell being negatively charged with respect to the
exterior. This resting potential prepares nerve and muscle cells for
the propagation of action potentials leading to nerve impulses and
The accumulation of sodium ions outside of the cell draws water out of
the cell and thus enables it to maintain osmotic balance (otherwise it
would swell and burst from the inward diffusion of water).
The gradient of sodium ions is harnessed to provide the energy to run
several types of indirect pumps.
The crucial roles of the Na+/K+ ATPase are reflected in the fact that
almost one-third of all the energy generated by the mitochondria in
animal cells is used just to run this pump."
Here's the Google search I did to find these sites: "sodium potassium
pump human". As always, let me know if you need more or different