What Is the Major Positive Ion Outside Cells?

The major positive ion outside the cell is sodium, symbolized by "Na+". This is due to the action of the sodium-potassium pump that actively transports sodium ions outside the cell. The number of sodium ions outside the cell is 10 times greater than the number of sodium ions inside.

The sodium-potassium pumps use the hydrolysis of ATP to generate energy used to actively transport three sodium ions outside the cell while simultaneously transporting two potassium ions inside the cell. This maintains proper osmotic balance inside the cell, generates action to run other pumps and establishes a net charge that enables muscle contraction.