What is the typical resting membrane potential of a neuron and what maintains it?

• A. About -60 mV; maintained by voltage-gated calcium channels.
• B. About -50 mV; maintained by passive diffusion alone.
• C. About -70 mV; maintained by Na+/K+ ATPase and leak ion channels generating ion gradients.
• D. About -90 mV; maintained by chloride ion pumps.

Answer: (C)

The resting membrane potential is the neuron's baseline voltage when it's not firing. It sits around -70 mV in many neurons. This negative interior arises because the membrane is more permeable to potassium at rest, so K+ tends to leak out, pulling the inside toward its own equilibrium potential for K+. The gradients that let this leak occur—and stay in place—are maintained by the Na+/K+ ATPase, which pumps 3 Na+ out and 2 K+ in using ATP, and by leak channels that allow a small, continuous flux of ions. These combined actions keep the resting potential stable and near -70 mV.