Potassium, a major electrolyte and an essential mineral, can be found in all cells of the human body. The concentrations of potassium found outside of the body's cells are lower than those within. The differences in the levels of both potassium and sodium across cell membranes influence the osmotic balance and the actions of the sodium-potassium pump in animals and humans.
Positive potassium ions, or cations, play an important role in nerve and brain functions, and they are vital to the transmission of all nerve impulses. Potassium is one of the 10 most common elements found in the human body by mass, with only the major minerals phosphorus and calcium found in greater abundance.