Action potential

What is action potential?

An action potential is the rapid voltage change across a neurone membrane that propagates an electrical signal. Resting potential (~−70 mV) is maintained by the Na⁺/K⁺ pump. A stimulus opens voltage-gated sodium channels → depolarisation (up to ~+40 mV) → potassium channels open → repolarisation → temporary hyperpolarisation → return to resting potential. The all-or-nothing principle: action potentials only fire above a threshold (~−55 mV), and all action potentials in a given neurone have the same amplitude.