Now let's move on to phase zero. Phase zero is shown by the red region. So let's suppose we have some type of outside stimulus, either by a neuron or by an adjacent muscle cell. Let's suppose the stimulus basically reaches the threshold potential of around negative 70 millivolts. If this takes place, then we have the opening of our sodium voltage gated channels down on the cell membrane. So these voltage gated sodium channels are known as time dependent channels.