---
title: "Resting Membrane Potential | General Biology I"
description: "Resting membrane potential is the voltage difference across a cell membrane at rest, usually about -70 mV in neurons, set by ion gradients and pumps."
canonical: "https://fiveable.me/college-bio/key-terms/resting-membrane-potential"
type: "key-term"
subject: "General Biology I"
unit: "Unit 5"
---

# Resting Membrane Potential | General Biology I

## Definition

Resting membrane potential is the voltage across a neuron’s membrane when it is not sending a signal. In General Biology I, it is the starting electrical state that makes nerve signaling possible.

## What It Is

Resting membrane potential is the electrical difference across a cell membrane when a neuron is not firing. In General Biology I, it usually means the inside of the neuron is more negative than the outside, often around -70 mV.

That negative value does not come from one single ion sitting in place. It comes from uneven ion distributions on the two sides of the membrane, especially potassium (K+) being higher inside the cell and sodium (Na+) being higher outside. Because the membrane is selectively permeable, ions do not move equally. Some ions cross more easily than others, so the charge difference stays in place instead of flattening out.

The biggest reason the resting membrane potential stays negative is that K+ leak channels let potassium move out of the cell more easily than sodium can move in. As K+ leaves, it carries positive charge away, leaving the inside relatively negative. That charge difference builds until electrical attraction starts pulling K+ back in, which balances the diffusion of K+ outward.

The sodium-potassium pump keeps the gradients from disappearing. It uses ATP to move 3 Na+ out of the cell and 2 K+ into the cell. That pump does not create every bit of the resting membrane potential by itself, but it maintains the ion gradients that make the resting state possible.

This matters because the resting membrane potential is the baseline from which a neuron can respond. If the membrane is at rest and then a stimulus changes the voltage enough, the neuron may reach threshold and fire an action potential. If the resting membrane potential shifts too far in either direction, the cell becomes less able to signal normally.

A helpful way to think about it is this: the neuron is not electrically “empty” at rest. It is actively maintaining a charged state so it is ready to communicate the moment a signal arrives.

## Why It Matters

Resting membrane potential sits at the center of neuron function in General Biology I because it explains how cells turn ion movement into electrical signaling. Without a stable resting state, a neuron could not respond quickly or predictably to a stimulus.

It also connects two big course ideas at once: membrane transport and cell communication. The voltage across the membrane depends on selective permeability, ion gradients, and active transport. That makes resting membrane potential a good checkpoint for understanding how passive diffusion and ATP-driven transport work together.

Once you know the resting state, action potentials make sense. Depolarization, threshold, and repolarization all start from the resting membrane potential. If you do not know what the membrane looks like before the signal, the later steps in the signal are just memorized labels.

It also shows up in questions about what happens when membrane proteins are altered. If leak channels, pumps, or ion gradients change, the neuron’s excitability changes too. That is why this term is often used to explain why some cells fire easily, why others stay quiet, and why nerve signaling depends on tightly controlled ion balance.

## Connections

### Ion Channels

Ion channels are the membrane proteins that let specific ions cross the plasma membrane. Resting membrane potential depends heavily on which channels are open at rest, especially potassium leak channels. If the channel mix changes, the voltage across the membrane changes too, because ions no longer move with the same ease or in the same direction.

### Sodium-Potassium Pump

The sodium-potassium pump maintains the Na+ and K+ gradients that make the resting membrane potential possible. It uses ATP to move sodium out and potassium in, which keeps the cell ready for repeated signaling. Without this pump, the gradients would fade and the membrane potential would slowly collapse.

### Action Potential

An action potential starts from the resting membrane potential. The resting value gives the neuron its baseline, and a stimulus must shift the membrane far enough to reach threshold. That means resting membrane potential is not the signal itself, but the starting point that makes the signal possible.

### [Graded potentials](/college-bio/key-terms/graded-potentials)

Graded potentials are small, variable changes in membrane voltage that can move a neuron closer to or farther from threshold. They are measured relative to the resting membrane potential, so you need the resting value to know whether a cell is depolarizing or hyperpolarizing. These small shifts can add up near the axon hillock.

## On the AP Exam

A quiz question will often give you ion concentrations, a membrane diagram, or a change in pump activity and ask what happens to the membrane potential. Your job is to trace the direction of ion movement and decide whether the cell becomes more negative, less negative, or stays near -70 mV. In a lab or problem set, you might compare normal neurons with cells treated with a pump blocker or a channel blocker. If potassium leak channels are reduced, the membrane potential will not stay as negative as usual. If the sodium-potassium pump fails over time, the ion gradients weaken and the resting state becomes unstable. For short-answer questions, use the vocabulary directly: selective permeability, ion gradients, ATP, and excitability.

## resting membrane potential vs Action Potential

Resting membrane potential is the steady electrical state of a neuron when it is not firing. An action potential is the rapid change in membrane voltage that happens after a stimulus reaches threshold. One is the baseline, the other is the signal.

## Key Takeaways

- Resting membrane potential is the voltage across a cell membrane when a neuron is not firing, and it is usually around -70 mV.
- The inside of the neuron is negative relative to the outside because potassium and sodium are distributed unevenly and the membrane is selectively permeable.
- Potassium leak channels and the sodium-potassium pump work together to maintain the resting state.
- This membrane voltage is the starting point for action potentials, so changes in it affect how easily a neuron can signal.
- If ion channels or pumps change, the resting membrane potential changes too, which can alter excitability.

## FAQs

### What is resting membrane potential in General Biology I?

It is the electrical charge difference across a cell membrane when the neuron is not actively sending a signal. In most neurons, the inside is about -70 mV compared with the outside. That resting voltage comes from ion gradients and selective permeability.

### Why is the inside of the neuron negative at rest?

More potassium can leave the cell than sodium can enter, so positive charge moves out more easily than it moves in. The sodium-potassium pump also maintains the concentration differences that make that voltage possible. The result is a net negative interior.

### How is resting membrane potential different from action potential?

Resting membrane potential is the stable baseline voltage, while an action potential is the rapid spike that occurs when the cell is stimulated enough to reach threshold. The resting state sets the starting point for the spike. Without it, the neuron would not have a normal signaling range.

### What happens if the sodium-potassium pump stops working?

The Na+ and K+ gradients slowly weaken, so the resting membrane potential becomes less stable over time. The cell may not stay as negative inside, which makes signaling harder. Short-term changes may be small, but continued failure disrupts excitability.

## Related Study Guides

- [5.3 Active Transport](/college-bio/unit-5/3-active-transport/study-guide/EhowRViJi1g4aycv)
- [35.2 How Neurons Communicate](/college-bio/unit-35/2-neurons-communicate/study-guide/Qy9hYvFLfwyGUrWj)
- [35.1 Neurons and Glial Cells](/college-bio/unit-35/1-neurons-glial-cells/study-guide/nKLFaHbdmfM6wyi7)

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