The human body, skeleton, muscles and nervous system

The skeleton is the support of our body. An adult has more than 200 (about 206) bones. The skull protects the brain, the ribs protect the heart and lungs, and the spine holds the body upright. Bones meet at joints, so we can bend, walk and sit. Muscles (over 600) are attached to bones; they contract and relax to move the bones. The walls of the heart, stomach and intestines also have muscles that keep working. Muscles are controlled by the brain: the brain, spinal cord and nerves together make up the nervous system. If a needle pricks a finger, a nerve sends the message to the brain, the brain orders the hand to pull away, and the muscles contract. For good posture: sit straight at the desk, carry a bag evenly on both shoulders, take a short exercise break every 15–20 minutes and sleep on a firm bed.