And so as a result of this, the voltage will actually begin to increase. Now, if the voltage increases to about negative 40 millivolts, this voltage is known as the threshold voltage. Why? Well, because this is the voltage that is needed to activate the voltage gated on channels. And this includes not only the sodium, but also the potassium voltage gated on channels. So as the voltage increases from the resting membrane potential of about negative 70 millivolts to about negative 40 millivolts, the voltage gated sodium channels begin to open, and they open very quickly.