Cell physiology · BEGINNER LESSON
Resting membrane potential
The resting membrane potential is the electrical potential difference across a cell’s plasma membrane when the cell is not actively excited. It is usually described as the voltage inside the cell relative to the outside.
What it is and what is measured
The resting membrane potential is a measured voltage across the plasma membrane, the thin boundary around a cell. “Potential difference” means a difference in electrical charge between two places, here the inside and outside of the cell. In many cells, especially neurons and muscle cells, this voltage is negative on the inside compared with the outside. Sodium (Na+) and potassium (K+) are the main ions involved, and negatively charged proteins and phosphate molecules trapped inside the cell also help shape the charge difference. [0,1,2]
[1] Physiology, Resting Potential - StatPearls - NCBI Bookshelf - NIH [2] Physiology, Resting Potential - StatPearls - NCBI Bookshelf [3] Physiology, Membrane - StatPearls - NCBI Bookshelf - NIH
How the voltage is created
The membrane does not treat all ions equally. At rest, it is much more permeable to potassium (K+) than to sodium (Na+), mostly because K+ leak channels are open. Permeability means how easily something crosses the membrane. Because K+ is more concentrated inside the cell, it tends to diffuse out down its concentration gradient, leaving behind relatively more negative charge inside. That charge separation helps create the resting voltage. [0,2]
[1] Physiology, Resting Potential - StatPearls - NCBI Bookshelf - NIH [3] Physiology, Membrane - StatPearls - NCBI Bookshelf - NIH
How gradients are maintained
The sodium/potassium pump, also called the Na+/K+ ATPase, uses ATP, which is the cell’s main energy-carrying molecule, to move 3 Na+ out of the cell and 2 K+ into the cell. This maintains the concentration gradients that make continued ion movement possible. The membrane potential is therefore not a static balance: ions still move, but pump activity and leak channels keep the overall resting state stable. [0,1,2]
[1] Physiology, Resting Potential - StatPearls - NCBI Bookshelf - NIH [2] Physiology, Resting Potential - StatPearls - NCBI Bookshelf [3] Physiology, Membrane - StatPearls - NCBI Bookshelf - NIH
How scientists estimate it
Because several ions contribute at the same time, the resting membrane potential is not calculated with a single-ion equation alone. The Goldman-Hodgkin-Katz equation is used instead of the Nernst equation when multiple ions matter. In neurons, the resting value is often near −70 millivolts (mV), and one source gives about −73 mV under physiological conditions. Millivolt means one-thousandth of a volt. [1,2]
[2] Physiology, Resting Potential - StatPearls - NCBI Bookshelf [3] Physiology, Membrane - StatPearls - NCBI Bookshelf - NIH
Limits and related behavior
The ions involved usually do not reach electrochemical equilibrium, which is the point where chemical and electrical forces exactly balance. Most ions cannot cross the membrane freely, so the resting membrane potential reflects partial permeability, ongoing diffusion, and active transport rather than a stopped system. In excitable cells such as neurons, a change from this resting level can open voltage-gated channels and produce an action potential. [0,2]
[1] Physiology, Resting Potential - StatPearls - NCBI Bookshelf - NIH [3] Physiology, Membrane - StatPearls - NCBI Bookshelf - NIH
SEE THE IDEA
How the resting membrane potential is built
Uses ATP to move 3 Na+ out and 2 K+ in, maintaining gradients.
Always-open channels let K+ diffuse out more easily than Na+ enters.
K+ leaving leaves the inside relatively negative.
Stable voltage across the membrane in a non-excited cell.
Pump maintains gradients; leak channels use those gradients; charge separation produces the resting membrane potential.
A stable resting voltage comes from maintained ion gradients plus greater K+ permeability at rest.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.