Each muscle is similar to an instrument in an orchestra where the brain is the master conductor. The conductor speaks to each instrument through the movement of his baton. Each swing of the conductor's baton could be compared to nerve impulses directing the activity of the muscle. Muscle is the only type of body tissue that has the ability to contract. It actually becomes shorter and thicker at contraction.
Some muscles work in pairs or as antagonists.
This means when a muscle contracts, the opposing muscle relaxes. The muscles, along with the supporting system of ligaments, control the spine's ability to maintain balance and stability when a person stands or moves. Without the muscular system, the body would be motionless. This site uses Flash media extensively.