The blue region is phase two, and the green region is phase number three. So, before we actually examine each one of these phases, let's discuss what this dashed line is. So the dashed line basically is our threshold potential. This is basically the voltage difference that must exist across the membrane of the cell for our action potential to actually generate. So if our stimulus does not reach this value, no action potential is generated. But if the stimulus reaches or exceeds this value, our action potential is generated.