When the
inside of the axon becomes sufficiently positive, about 30 mV is
given as an average value, the sodium channels close. This
closing of the sodium channels will greatly limit the
ability of sodium ions to enter the axon. In addition to the
sodium channels closing, the potassium (K+) channels open. Now
potassium is free to cross the axon.
The next page will now show the action potential moving down the axon.