Understanding Action Potentials in The Nervous System - WJEC A Level Biology

Action Potential: The Electrical Signal of Life

Ever wondered how your brain sends messages to your muscles in milliseconds? Action potentials are the answer - they're like electrical waves that zip along your nerve cells at incredible speeds.

Your nerve cell membrane normally sits at resting potential $-70mV$, where more potassium ions $K+$ are outside and more sodium ions $Na+$ are inside. When a stimulus hits, sodium channels open and Na+ floods in, making the inside more positive. This is called depolarisation.

Once the electrical charge reaches the threshold level $-55mV$, it triggers an "all or nothing" response. Every sodium channel opens simultaneously, shooting the voltage up to +40mV - this is your action potential peak. Think of it like a domino effect that can't be stopped once it starts.

The cell quickly recovers through repolarisation - potassium channels open, K+ rushes out, and the Na+/K+ pump restores the original balance. During the refractory period, the cell can't fire again immediately, ensuring signals only travel in one direction.

Quick Tip: Remember "DePoKaRe" - Depolarisation (Na+ in), Potassium out, Repolarisation!