The Human Body: Skeleton and Muscles

The human body is held together and given shape by the skeleton — a framework of 206 bones. The skeleton does several important jobs: it supports the body, allows movement, and protects vital organs. The skull protects the brain, the ribcage protects the heart and lungs, and the spine protects the spinal cord. Bones are connected at joints, and muscles are attached to bones by tough fibres called tendons. Muscles work in pairs — when one muscle contracts (gets shorter and fatter), the opposite muscle relaxes. This is called antagonistic muscle action. The bicep and tricep in your upper arm are a perfect example: bending your arm contracts the bicep and relaxes the tricep; straightening it does the opposite. Exercise, a diet rich in calcium and vitamin D, and plenty of sleep all help keep bones and muscles strong and healthy.