And when they open up, they allow the flow of our ions. So these voltage gated ion channels can open if the voltage changes. Now, let's suppose that we have our neuron, the axon hillock of the neuron, that is at the resting membrane potential. So at negative 70 millivolts. Now, let's suppose we apply a stimulus onto the cell membrane of the neuron. And this stimulus is equal to, or it exceeds the threshold value, which is around, usually around negative 45 millivolts.