So let's begin by describing phase number four. So phase number four is shown in brown. And notice that this line has a constant slope of zero, and that means our membrane voltage is not changing. In fact, this is the voltage of the membrane when the cell is resting, when it's not generating any action potential. And this is known as the resting membrane potential. So the brown section describes the resting membrane potential of the cell for a typical cardiac myoside.