Bones and Muscles

Core Idea

Your body has a skeleton made of over 200 bones. Bones give your body its shape, protect your organs, and help you stand up straight. Muscles are attached to your bones, and when muscles pull on bones, you move. Bones are the frame; muscles are the movers.

How It's Best Learned

Feel your own bones — your skull, elbows, kneecaps, ribs. Flex your arm and feel the muscle get hard. Look at a picture or model of a human skeleton. Try to move your arm without bending at the elbow to understand what joints do.

Common Misconceptions

• Children may think bones are dead and dry (living bones are alive, with blood flowing through them).
• Some children think muscles only exist in your arms (muscles are everywhere in your body).
• Children may not understand that bones meet at joints, which is what lets you bend.

Explainer

Put your hand on the top of your head. Feel that hard shell? That is your skull, and it is made of bone. Now feel your elbow, your kneecap, your ribs. Those are all bones too. Your body has over 200 bones, and together they make up your skeleton — the hard frame inside you that gives your body its shape.

Bones do three important jobs. First, they give you shape and support. Without bones, you would be floppy like a jellyfish. Your skeleton is what lets you stand up tall. Second, bones protect your important organs. Your skull protects your brain. Your ribs make a cage that protects your heart and lungs. Your spine (the line of bones down your back) protects the nerves that connect your brain to the rest of your body. Third, bones help you move — but they cannot move by themselves. That is where muscles come in.

Muscles are soft, stretchy body parts attached to your bones. When your brain tells a muscle to work, the muscle gets shorter (this is called contracting) and pulls on the bone it is attached to. That pull is what makes the bone move. Try this: bend your arm at the elbow. Feel the front of your upper arm — that bump is your biceps muscle squeezing tight and pulling your forearm up.

Muscles work in pairs because they can only pull, not push. To bend your arm, one muscle on the front pulls the bone up. To straighten your arm, a different muscle on the back pulls the bone down. Your whole body works like this — muscles pulling bones in different directions to let you walk, run, jump, wave, chew, and even smile. You have over 600 muscles in your body, and every movement you make is a muscle pulling on a bone.