Muscles are the part of our body that allow us to move. They make up almost half of the weight of our bodies. They are made up of special tissues.When brain gives muscles a signal, those tissues can contract, or shorten. The muscles are attached to bones by stendons. Tendons pull on the bones and cause our limbs to move. There are more than 640 muscles in our body.They work in pairs.. Muscles can get shorter and pull, but they cannot push.  One muscle pulls the body part one way, then the other team pulls it back again.