How a neuron works: one neuron, every part

Tap a part to see what it does, or fire it and watch one signal travel through.

Dendrites: catch incoming signals

The branches. They catch signals from other neurons and carry them in to the cell body.

Spines: where inputs land

Tiny bumps all along the branches. Each one is where an excitatory input from another neuron's axon arrives.

Cell body: adds it all up

Every incoming signal is added up here, and if together they push the cell past its threshold, it fires.

Nucleus: holds the chromosomes

Inside the cell body sits the nucleus, the enclosed core that holds the cell's chromosomes.

Axon initial segment: where it fires

Where the decision becomes a signal. At the base of the axon, this short stretch generates the action potential. Sodium channels open, sodium rushes in, and the charge across the membrane swings up.

Axon: the way out

The cable out. The action potential travels along it all the way to its ends, and on to the next cells.

Myelin: insulation for speed

A wrapping of many layers of membrane, made in the brain by glial cells called oligodendrocytes. It insulates the axon, so the signal races along: up to 150 metres a second, against 0.5 to 10 without it. In multiple sclerosis, it's lost.

Nodes of Ranvier: where it leaps

Gaps in the myelin, packed with sodium channels. The signal is rebuilt at each gap and flows to the next, so it leaps from node to node instead of crawling.

Axon terminals: pass it on

The axon's ends. Here the electrical signal becomes a chemical one: messenger molecules are released across a synapse to the next neuron.

One signal, start to finish

  1. Signals arrive. Other neurons' signals land on the dendrites: some push toward firing, some hold it back.
  2. They add up. The cell body adds them all up. This time, they push it past its threshold.
  3. It fires. The axon initial segment fires an action potential.
  4. It leaps. Down the axon it goes, rebuilt at each gap in the myelin, leaping node to node.
  5. It's passed on. At the terminals it becomes chemical: messengers cross to the next neuron.