So we have voltage gated sodium channels, which allow the passage of sodium ions. And we have voltage gated potassium channels that allow the passage of potassium ions when these voltage gated channels are open. Now, when our cell is at the resting membrane potential, which is around negative 70 millivolts, our channels, the voltage gated ion channels, are closed. Now, why exactly do we call these channels voltage gated ion channels? Well, they're called this because they basically respond to changes in voltage. So when the voltage changes across our cell membrane, these voltage gated ion channels can basically open up.