What is resting potential?

• A. -70 mV baseline membrane potential
• B. -40 mV
• C. 0 mV
• D. -90 mV

Answer: (A)

Resting membrane potential is the voltage difference across a neuron's membrane when it is not sending a signal. In many neurons this interior negative potential is about -70 mV. This occurs because the membrane is more permeable to potassium than to sodium at rest, so potassium tends to leak out, pulling the inside negative. Sodium ions do want to enter, but the membrane is less permeable to them at rest, so their influence is smaller. The Na+/K+ ATPase pump also helps maintain the gradients by pumping Na+ out and K+ in, helping keep the inside negative. Put together, the resting potential settles around -70 mV rather than at 0 mV or near -40 mV (which would be depolarized) or -90 mV (which is more hyperpolarized than typical resting).