What is cramp?

Cramp is when a muscle suddenly feels tight and painful. It stops moving properly and it feels like it's stuck. No one is quite sure why cramp happens, but it goes away if you rest the sore part. Rubbing it can also help.

[Have you ever had a stitch after running? It's a pain in your middle, just under your ribs. It means you've got cramp in the breathing muscle below your lungs.]

Why do strong people have big muscles?

Muscles get bigger and stronger if they are used a lot. That's why sportswomen and sportsmen practise hard and do lots of exercises.

[Many tennis players have bigger muscles in the arm they use to hold their racquet.]

How do I move?

Muscles make you move, by pulling your bones about. When you smile or cry, speak or eat, walk or skip, muscles are doing the work.

[Your biggest muscles are the ones you sits on!]

[A muscle can only make itself shorter. It needs another muscle pulling the other way to stretch it out again.]

[To make a bone move, a muscle gets shorter. This pulls the bone one way. To pull the bone back again, another muscle gets shorter. Muscles are fixed to your bones by strong white strings called tendons.]

What are goose bumps?

When a cat is cold, its fur fluffs up. This traps a blanket of air next to its skin to keep it warm. Your hair also stands up when you are cold and shivery, and goose bumps are made by tiny hair muscles tightening. This doesn't keep you very warm, though, because you're not hairy enough!

How thick is my skin?

In most places, your skin isn't much thicker than cardboard. But although it is so thin, lots of things happen inside it. Hair grows in skin, and sweat is made there. Skin also has blood vessels, and nerves to send messages to your brain.

[This is what skin looks like through a microscope.]

[Whether your skin is light or dark, too much sun can burn you. Wear a hat and put on a layer of sun protection cream.]

[Sweat is salty water that your body makes when it's hot.]

What is my skin for?

Skin is the stretchy bad you live in. It covers your whole body, holding your insides in and protecting them from the outside world.

[Your skin gets its colour from something called melanin. People with dark skin have more melanin that people with light skin.]

What is my funny bone?

The funny thing about your funny bone is that it isn't a bone at  all. It's a nerve that runs just under your skin over each elbow. If you bang your elbow, the nerve is banged, too. It sends a message to your brain and you feel pain!