Sodium is required by our nerves and muscles. It is present in almost
everything which we eat. Table salt is Sodium Chloride.
Potassium is also required by nerves and muscles. It is also present
in almost everything we eat.
Cells can pump sodium ions, potassium ions and chloride ions across their membranes.
This is called the "sodium pump", it requires energy from ATP. When nerve cells
and muscle cells pump these ions an and out of their cells they generate a membrane
potential. When a nerve cell stops pumping ions for a fraction of a second, a nerve
impulse travels along the nerve. A similar thing happens when a muscle contracts.
