Without muscles, humans would not be able to live. Muscles have a big part in a human's body. The muscles main job in the human's body is to move the bones of the skeleton. Muscle also helps the heart beat and helps other organs work in the body. Muscles don't only do this though. The muscles in a human body help maintain posture and circulate blood and other substances throughout the body. There are three types of muscle tissue: skeletal, smooth, and cardiac. The skeletal muscle is in charge of movement in the body. Cardiac muscle makes up the walls of the heart and creates and calm pulsing that pumps the blood through the body from signals from the brain. Smooth muscle are the walls of the hollow organs, blood vessels, and respiratory passages.