And eventually, if that voltage reaches the threshold voltage, it causes the rapid opening of the voltage gated sodium ion channels. At the same time, it causes a slow opening of those potassium voltage gated ion channels. And so, because we have the rapid opening of these voltage gated sodium ion channels, these sodium ions move into the cell and that makes the inside positive with respect to the outside. And that's why it shoots up. And this is known as the depolarization period, because we change the charge values on that cell membrane. So before, during the resting memory potential, the inside was negative, the outside was positive, and now it essentially reverses.