■Another property of an excitable cell is its ability to conduct an action potential when adequately stimulated. ■An adequate stimulus is one that brings about a depolarization in a membrane that is sufficient to exceed the threshold potential of the membrane and thereby elicit an all-or-none action potential that travels in an unattenuated fashion at a constant velocity along the membrane of the excitable cell■Because of the steady resting potential, the cell membrane is said to be polarized. A lessening of the magnitude of this polarization is called depolarization; an increase in its magnitude is referred to as hyperpolarization