axon hillock

The axon hillock is a small, cone-shaped bump on the body of a neuron — the cell that carries signals in your brain and nerves. Picture the neuron's main body as a round hub with many short branches reaching in; on one side, the hub narrows into a little ramp, and from the bottom of that ramp the single long output cable, called the axon, sets off. That tapering ramp is the axon hillock: the spot where the cell body hands off to the wire that carries its message away.

This little hump matters because it is the decision point. A neuron collects countless tiny nudges from its neighbors — some pushing it toward firing, some holding it back — and all of those nudges spread across the cell and pile up at the hillock. Here the membrane is unusually crowded with voltage-gated sodium channels, tiny gates that pop open when the electrical charge crosses a threshold. If the combined push is strong enough, the gates fly open and a full nerve signal, the action potential, ignites and races down the axon. So the axon hillock is the neuron's trigger: the place that adds up the votes and decides, moment by moment, whether to fire.