So the threshold's value is basically the value of the stimulus that has to be just right so that the action potential is generated. So once we reach our threshold value, this threshold voltage of about negative 45 millivolts will signal the voltage gated sodium channels to actually open up. And as soon as they open up, our sodium ions will begin to flow. The question is in which direction will the sodium ions travel? So let's take a look at the following diagram, which describes what I just said. So before the stimulus, we have our cell membrane of the neuron that is basically at the resting membrane potential.