Action potential
MCAT glossary · Biological & Biochemical Foundations of Living Systems
Definition
Na⁺ influx depolarization (~+30 mV) → K⁺ efflux repolarization → Na⁺/K⁺ pump restores resting (-70 mV); refractory period prevents back-propagation.
Action potential in plain English
An action potential is the electrical 'spike' a nerve cell fires to send a message — it's basically how your brain and body text each other at lightning speed. A resting neuron sits slightly negative inside (about -70 mV); when triggered, sodium ions (Na^+) rush in and flip it sharply positive (~+30 mV), which is the signal firing. Then potassium ions (K^+) flow out to reset it back toward negative, and a tireless little pump shoves the ions back to their starting sides. Right after firing there's a brief 'refractory' recovery moment when the cell can't fire again — like a toilet that must refill before the next flush — and this cleverly forces the signal to travel one direction only.
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