Your body's wiring
Think of your body like a house full of wires. Your brain is the control room. Nerves are the wires that carry messages to and from every room.
Some nerves carry messages in, like 'this cup is hot' or 'that tickles.' Other nerves carry messages out, like 'wiggle your fingers' or 'take a step.'
Nerves are made of nerve cells called neurons. Some are very long. In a tall grown-up, one neuron can stretch from the lower back all the way to the big toe.
The spinal cord, the main cable
Your spinal cord is a thick bundle of nerves. It runs from the bottom of your brain down your back. In a grown-up it is about 18 inches long, about as long as one and a half rulers.
Your backbone, or spine, is a stack of small bones. They wrap around the soft spinal cord and keep it safe, like a tunnel of armor.
Pairs of nerves branch out from the spinal cord between those bones, 31 pairs in all. They reach your arms, legs, belly and back. Twelve more pairs come straight out of your brain and go to places like your eyes, ears, nose and tongue.
The spinal cord is shorter than your backbone. It ends partway down your back, and below it a bundle of nerves keeps going. Scientists named that bundle after a horse's tail, because that's what it looks like.
As fast as a race car
Nerve messages travel as tiny electric signals. The fastest ones zoom along at more than 100 meters a second. That's over 200 miles an hour, about as fast as a race car!
Some messages travel on slower nerves. That's why when you stub your toe, you may feel a quick, sharp OUCH first, and then a slow, achy throb a moment later.
Many nerves are wrapped in a fatty coat called myelin (MY-uh-lin). It works like the plastic coat on a wire and helps signals go faster.
Reflexes: faster than thinking
A reflex is a move your body makes all by itself, before you even think. If you touch something hot, your hand jerks away right away.
Reflexes are quick because the message doesn't have to go all the way up to your brain first. It goes to your spinal cord, which sends a 'move!' message straight back to your muscles. Your brain finds out a split second later, and that's when you feel the ouch.
At a checkup, a doctor might tap just below your knee with a little rubber hammer. Your leg kicks out on its own. That's a reflex too, and it shows your nerves are working well.
Blinking when something flies at your face and sneezing when your nose tickles are reflexes as well.
Feeling, tingling and the funny bone
Nerves in your skin sense touch, heat, cold, pressure and pain. Your fingertips and lips are packed with them, which is why they feel things so well.
When you sit on your foot for too long, its nerves get squished. Your foot 'falls asleep,' and when you move, it tingles with pins and needles. That's the nerves waking back up.
Your funny bone is not a bone at all. It's a nerve that runs close to the skin at your elbow. Bump it and you get a zingy, tingly feeling all the way down to your little finger.