Bones and Muscles: Your Body's Framework and Movers

Hi, I'm Atlas! Let's talk about the strong team inside you: your bones and your muscles. Right now, inside your body, you have more bones than a grown-up does — somewhere between 270 and 300! As you get older, some of those bones slowly join together, and by the time you are a grown-up they will have fused down to about 206. How cool is that? Your skeleton is what holds you up, like the poles that hold up a tent. Without bones you would flop down like a beanbag! Bones also protect the soft parts inside you. Feel your head — that hard shell is your skull, a helmet for your brain. Press your chest gently and feel your ribs, a bony cage that guards your heart and lungs. But bones cannot move by themselves. That's where muscles come in. On our diagram you can see muscles attached to bones. When a muscle gets shorter — scientists say it contracts — it PULLS on the bone and moves it. Muscles only pull; they never push. So how do you bend AND straighten your arm? Muscles work in pairs! One muscle pulls to bend your elbow, and a different muscle on the other side pulls to straighten it back. If you can, try this: bend your arm and feel the muscle on top get firm. If you'd rather watch, ask someone nearby to do it and look for the shape change under the skin as the muscle contracts. Together, your bones and muscles let you walk, wave, and jump.