The three small sodium ions are bound inside the pump (violet spheres to the left), whereas there is not sufficient room for the larger potassium ions (green spheres to the right).

However, up to 40 per cent of your body's energy goes into supplying the microscopic sodium-potassium pump with the energy it needs. It's not visible to the naked eye and you can't feel it.

Energy is provided by the breakdown of ATP inside the cell ... The proteins pump sodium out of the cells and potassium into the cells. This helps nerve cells to transmit nerve impulses.