Whenever you see, hear, and feel — and whenever you think, move, and even breathe — your brain buzzes with the activity of neurons.

Neurons are tiny cells that are the building blocks of the nervous system. They come in many shapes and sizes. Some stretch from the spinal cord all the way to the toes and can be more than 3 feet (1 meter) long!

Neurons send messages from different parts of your body to your brain, all around your brain, and from your brain out to the muscles in your body.

They can send more than 100 signals a second, at speeds up to 400 kilometers (250 miles) an hour. That's four times faster than a moving car on the highway!