depolarization

Depolarization is the moment a neuron's electrical mood shifts from gloomy to excited. At rest, the inside of a nerve cell is slightly more negatively charged than the outside, a bit like a battery holding a small stored voltage — typically around seventy thousandths of a volt, with the inside being the negative end. Depolarization simply means that this inside becomes less negative, drifting up toward zero and sometimes even past it. The name is a little counterintuitive: the cell is not gaining polarity but losing it, shrinking the charge gap across its outer skin, the membrane.

This shift happens when tiny gates in the membrane, called ion channels, swing open and let positively charged particles — most often sodium atoms — rush into the cell. Each wave of positive charge pulls the inside voltage upward. Think of it like the first guests arriving at a quiet, empty room: the mood lifts a notch with every one who walks in. If enough of them pour in to push the voltage past a tipping point called the threshold, the neuron fires a full action potential, the brief electrical pulse it uses to send a message down its length. So depolarization is the build-up, the rising tension that decides whether the cell will speak or stay silent.