neuron

A neuron is a single nerve cell — the tiny living unit that the whole nervous system is built from, the way a wall is built from bricks. But a neuron is no ordinary cell: it is excitable, meaning it can be triggered to fire a quick electrical signal, and it is shaped for talking. From the cell body sprout many short, branching arms called dendrites that act like antennas, collecting incoming messages, plus one long cable called the axon that carries the cell's own message outward to other cells. Picture a tree with a bushy crown of roots gathering signals at one end and a single long trunk delivering the answer at the other.

Here is how one works. The dendrites and cell body add up all the little nudges arriving from neighboring cells; if the total pushes the neuron past a tipping point, it fires a brief electrical pulse that races down the axon. At the axon's far end the signal does not jump directly into the next cell — instead the neuron squirts out chemical messengers across a microscopic gap, and the next neuron's antennas catch them. By wiring up in vast chains and webs and passing signals this way, billions of neurons together let you sense, move, remember, and think.

Neurons come in many shapes and jobs: some carry sensation inward from your skin and eyes, some send commands out to your muscles, and most sit in between, doing the brain's heavy lifting of processing and deciding. They are long-lived and, for the most part, are not replaced if lost, which is why protecting them matters so much.