<P> The course of the action potential can be divided into five parts : the rising phase , the peak phase , the falling phase , the undershoot phase , and the refractory period . During the rising phase the membrane potential depolarizes ( becomes more positive ) . The point at which depolarization stops is called the peak phase . At this stage , the membrane potential reaches a maximum . Subsequent to this , there is a falling phase . During this stage the membrane potential becomes more negative , returning towards resting potential . The undershoot , or afterhyperpolarization , phase is the period during which the membrane potential temporarily becomes more negatively charged than when at rest ( hyperpolarized ) . Finally , the time during which a subsequent action potential is impossible or difficult to fire is called the refractory period , which may overlap with the other phases . </P>
<P> The course of the action potential can be divided into five parts : the rising phase , the peak phase , the falling phase , the undershoot phase , and the refractory period . During the rising phase the membrane potential depolarizes ( becomes more positive ) . The point at which depolarization stops is called the peak phase . At this stage , the membrane potential reaches a maximum . Subsequent to this , there is a falling phase . During this stage the membrane potential becomes more negative , returning towards resting potential . The undershoot , or afterhyperpolarization , phase is the period during which the membrane potential temporarily becomes more negatively charged than when at rest ( hyperpolarized ) . Finally , the time during which a subsequent action potential is impossible or difficult to fire is called the refractory period , which may overlap with the other phases . </P>
the rising phase of the action potential is due to
the rising phase of the action potential is due to
the membrane potential depolarizes ( becomes more positive ) .
the membrane potential depolarizes ( becomes more positive ) .