The membrane potential when a neuron is at rest and not firing is called the

• A. Resting potential
• B. EPSP
• C. Graded potential
• D. Action potential

Answer: (A)

Resting membrane potential is the voltage difference across a neuron's membrane when it is not signaling. It’s typically around -70 mV, with the inside of the cell negative relative to the outside. This steady state is established and maintained by ion gradients and membrane permeability: K+ leaks out more readily through open channels, and the Na+/K+ pump moves Na+ out and K+ in, keeping the inside negative.

This state is distinct from other events. An EPSP is a local depolarization caused by neurotransmitter binding that can contribute toward reaching threshold, a graded potential refers to small, variable changes at a site that can summate, and an action potential is a rapid, all‑or‑none spike that travels along the axon once threshold is reached. The resting potential is simply the cell’s baseline voltage when it’s not firing.