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

Action potentials are initiated when the influx of positively charged Na+ ions into the cell exceeds the efflux of positively charged K+ ions out of the cell. This happens because Na+ channels open in response to membrane depolarization, allowing Na+ to rapidly move into the cell. Once a certain threshold is reached (typically around -55mV), an action potential is triggered. Choice A is incorrect because the membrane potential must actually be more positive than the Na+ equilibrium potential for Na+ channels to open. Choice C is incorrect because the relative refractory period occurs after an action potential, not before. Choice D is incorrect because if Na+ channels were all inactivated, this would prevent an action potential from being initiated. Choice E is incorrect because IPSPs actually have an inhibitory effect on membrane depolarization and would therefore make it less likely for an action potential to be initiated.

Which Must Happen in Order for an Action Potential to Begin