How does the brain send messages around the body?

1. Your brain is your body's control center. It connects to the spinal cord, a thick bundle of nerves down your back, and nerves branch out from there to every part of you.
2. Nerves are made of nerve cells called neurons. Each one has little branches to catch messages and a long tail called an axon that carries a tiny electrical signal.
3. Neurons don't touch each other. At the end of one, tiny chemical messengers float across a very small gap, called a synapse, and start a new signal in the next neuron.
4. When you touch a feather, sensors in your skin start a message. It races up the nerves in your arm, into your spinal cord and up to your brain, and you feel: soft!
5. To wave, your brain decides and sends a message down the spinal cord and out along a motor nerve to your arm muscles. The muscles pull, and your hand waves!
6. If you touch something too hot, the message reaches your spinal cord, which sends a 'move!' message straight back to your arm. Your hand jumps away before you even feel the heat. That's a reflex.

Tap each part of the body's message system. Watch the messages move!

• Brain. The big wrinkly part of your brain (the cerebrum) lets you think, remember, see, hear and decide what to do. It sends commands to your muscles.
• Cerebellum. The cerebellum, at the back of your brain, helps you balance and makes your movements smooth and well timed, like when you ride a bike or catch a ball.
• Brainstem. The brainstem joins your brain to your spinal cord. It runs the things you don't think about, like breathing, heartbeat and swallowing.
• Spinal cord. The spinal cord is a thick bundle of nerves inside your backbone. It carries messages between your brain and body, and it can handle reflexes on its own.
• Sensory nerve. Sensory nerves carry messages from your senses (skin, eyes, ears, nose and tongue) toward your spinal cord and brain.
• Motor nerve. Motor nerves carry messages out from your brain and spinal cord to your muscles, telling them when to pull.
• Neuron. A neuron is a nerve cell. Its branches (dendrites) catch messages, and its long axon passes them on. Some axons in your legs are about a meter long!
• Myelin coat. Many axons wear a fatty coat called myelin, like the plastic on an electric wire. It helps messages travel much faster.
• Synapse. A synapse is a tiny gap between two neurons. The message crosses it as a puff of chemical messengers, then carries on as electricity.

Choose an action and send the message. Watch where it travels, and compare the times in the race chart.

Experiment: Which is faster: pulling your hand away from something hot (a reflex) or deciding to wave?

1. Choose Hot mug! and send the message. Watch where it turns around.
2. Now choose Wave hello and send it.
3. Compare the two bars in the race chart.

What we found: The reflex wins easily. The message turns around in the spinal cord instead of going all the way to the brain and waiting for a decision. Your hand moves before you even feel the heat!

Turn on JavaScript to try it yourself.

Send each message along the right path. Tap the stops in order, from start to finish.

Your nervous system is made of your brain, your spinal cord and lots of nerves. Nerves are bundles of nerve cells called neurons. A neuron has branches called dendrites that catch messages and a long, thin axon that sends them on. Messages travel along neurons as tiny electrical signals.

Neurons don't touch. Between them is a tiny gap called a synapse. When a message reaches the end of one neuron, chemical messengers float across the gap and start a new message in the next neuron. That's how messages hop from cell to cell.

Sensory nerves carry messages from your senses to your brain, so you can see, hear, taste, smell and feel. Motor nerves carry messages from your brain to your muscles, so you can move. Thinking about what to do takes a little time, about a quarter of a second to react to something you see.

Reflexes are faster. If you touch something too hot, the message only goes as far as your spinal cord, which sends a 'move!' message straight back to your arm. Your hand jumps away before your brain has even felt the heat. Reflexes protect you from getting hurt.

Key words

Neuron

A nerve cell that carries messages.

Synapse

The tiny gap between two neurons, crossed by chemical messengers.

Reflex

A very fast, automatic response that doesn't wait for your brain to decide.

Spinal cord

The thick bundle of nerves inside your backbone that links your brain to your body.

Myelin

A fatty coat on some nerve fibers that makes messages travel faster.

Action potential

The tiny electrical signal that travels along a neuron.

Check your thinking

1. Which two parts make up the central nervous system?

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   The brain and the spinal cord. The brain and spinal cord are the center of the network; nerves branch out from them.

2. Why is a reflex faster than deciding to move?

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   The message turns around in the spinal cord instead of waiting for the brain. Skipping the brain's decision saves the most time.

3. What carries a message across the gap between two neurons?

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   Chemical messengers. Chemical messengers float across the synapse and start a new signal.

4. Which kind of nerve carries messages from your brain to your muscles?

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   Motor nerves. Motor nerves carry commands out; sensory nerves carry information in.

5. When you see a ball coming, where does the message from your eyes go first?

   Show the answer

   Straight to the brain. The eyes connect directly to the brain by the optic nerves.