Now, when we reach about negative 40 millivolts. When it becomes greater than negative 40 millivolts, we also have the opening of these special Ltype calcium channels, and we'll see what those are in just a moment. So as these sodium channels, as these sodium ions rush in, they create a positive charge on the inside and a negative charge on the outside. And that's exactly why we have this positive charge and increase in our membrane voltage potential. So we see that this will cause the movement of sodium ions into the cell, which will lead to the depolarization of that membrane. So depolarization simply means our polarity of the cell membrane switches.