That means the charge on the membrane will basically be the same for a short period of time. And this is shown by the phase number two, the blue region. So once the cell reaches a voltage difference of about zero millivolts, the rate of influx of the calcium is equal to the rate of e flux. It leaves the cell of potassium, and this extends our depolarization period and is known as our plateau phase. So this is our plateau phase because we essentially reach a point on the action potential where the membrane potential is not changing, it remains around zero millivolts. Now, some people say that this is an extension of depolarization, because what depolarization does is it basically maintains a positive concentration on the inside of the cell.