Use the diagram of an action potential to answer the following questions.

-Phase 2, the plateau phase, of the action potential shown

Question

Use the diagram of an action potential to answer the following questions.
 
-Phase 2, the plateau phase, of the action potential shown

Quizplus · Accepted Answer

[Chapter 3, III B $1 \mathrm{c}$ ]. Because the plateau phase is a period of stable membrane potential, by definition, the inward and outward currents are equal and balance each other. Phase 2 is the result of opening of $\mathrm{Ca}^{2+}$ channels and inward, not outward, $\mathrm{Ca}^{2+}$ current. In this phase, the cells are refractory to the initiation of another action potential. Phase 2 corresponds to the absolute refractory period, rather than the effective refractory period (which is longer than the plateau). As heart rate increases, the duration of the ventricular action potential decreases, primarily by decreasing the duration of phase 2 .

Use the Diagram of an Action Potential to Answer the Following