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

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During the falling phase of the action potential, the permeability to potassium (K⁺) increases greatly, and the permeability to sodium (Na⁺) decreases. This leads to an efflux of potassium ions, causing repolarization of the cell membrane.

Which Is Most Directly Responsible for the Falling (Repolarizing) Phase