Now, if the stimulus is high enough, if it is equal to or exceeds the threshold value, then what that basically causes is the opening of the sodium voltage gated channels. And as soon as our stimulus is applied to a certain region, let's say this region, our channels, the sodium channels on the membrane open up and the sodium travels down its electrochemical gradient and from the outside and into that cell. So we have an influx of sodium into our cell. Now, as soon as our sodium ions rush inside the cell, they will reverse the polarity of the cell. And this is known as the depolarization period. So that basically means because we have positively charged sodium ions flowing into the cell, that will make the inside of the cell momentarily positive and the outside of the cell will become momentarily negative in the region where the stimulus is applied.