"[A] change in the electrical state of the nerve cell... hurries along the axon in advance of the impulse... partnered by an alteration in the permeability of the membrane... permitting sodium ions to pour into the cell... [T]he more... ions rush in the more channels are opened to increase this torrent. Suddenly, with a change in the membrane potential from negative to positive... sodium channels close. Another group... opens, permitting potassium ions to flow out... until the... minus seventy millivolts is achieved again."