The+Muscular+System+By+Natalia+Gavranic

 **Muscular system** Underneath our skin there are muscles. Muscles move our body. They are joined onto the bones. Tendons keep the muscles joined to the bones. There are more than 600 muscles in the human body. Most muscles work together in pairs. One muscle pulls while the other muscle relaxes. When you bend your arm the biceps muscle pulls and the triceps muscle relaxes. When you make your arm straight, the biceps muscle relaxes and the triceps muscle pulls. **Do you know?**  You use 17 muscles when you smile. You use 43 muscles when you frown. **Which muscles in the human body move the most often during the day?** Skeletal muscles, such as those in your arms and legs, only work when you think about making them work. For example, when you want to lift something or go for a run, your brain sends and receives signals through your nervous system to make the muscles work. These muscles are called the voluntary muscles. So the amount of work they do will depend on how active you are. Other muscles, such as the diaphragm, the heart and the intestines work without you having to think about them. You breathe, your heart pumps and your food is digested automatically, all controlled by the brain and the nerves. These automatically operating muscles are called involuntary muscles. Because they work 24 hours a day and seven days a week, they are probably the most worked muscles.

By Natalia Gavranic