Which must happen in order for an action potential to begin? A) The membrane potential must be at the Na⁺ equilibrium potential. B) Na⁺ influx must exceed K⁺ efflux. C) The membrane must be out of the relative refractory period. D) Na⁺ channels must all be inactivated. E) Multiple inhibitory postsynaptic potentials (IPSPs) must summate.

Question

Quizplus · Accepted Answer

In order for an action potential to begin, the influx of Na+ ions must exceed the efflux of K+ ions, causing depolarization of the membrane potential. This is represented by choice B, where Na+ influx exceeds K+ efflux. The membrane potential does not need to be at any specific equilibrium potential (choice A), and the membrane does not need to be out of the relative refractory period (choice C) or have all Na+ channels inactivated (choice D) for an action potential to begin. Multiple inhibitory postsynaptic potentials (IPSPs) would actually prevent an action potential from occurring, so choice E is incorrect.

Which Must Happen in Order for an Action Potential to Begin