Which is most directly responsible for the falling (repolarizing) phase of the action potential?
A. The permeability to Na+ increases greatly.
B. The Na+, K+ pump restores the ions to their original locations inside and outside of the cell.
C. ATPase destroys the energy supply that was maintaining the action potential at its peak.
D. Voltage-gated Na+ channels are opened.
E. The permeability to K+ increases greatly while that to Na+ decreases.
Answer: E
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