Graph plots membrane potential in millivolts versus time. The membrane remains at the resting potential of -70 millivolts until a nerve impulse occurs in step 1. Some sodium channels open, and the potential begins to rapidly climb past the threshold of excitation of -55 millivolts, at which point all the sodium channels open. At the peak action potential, the potential begins to rapidly drop as potassium channels open and sodium channels close. As a result, the membrane repolarizes past the…
