And this is because the sodium channels are inactivated. There's nothing we can do that will activate those inactivated channels. So we have to wait until they recover from that inactivation period. So this is explained in the following diagram. So, as our action potential moves over this way, the region right and back of that action potential is experiencing a refractory period, absolute refractory. And that means our sodium channels on the cell membrane here and here are inactivated.