There are three main types of muscle in the human body: skeletal muscle, smooth muscle, and cardiac muscle. Skeletal muscle is attached to bones and is responsible for voluntary movements, such as walking and lifting. It appears striated under a microscope due to its organized structure. Smooth muscle is found in the walls of internal organs, like the stomach and blood vessels. It operates involuntarily, meaning it functions without conscious control. Cardiac muscle is unique to the heart and is also involuntary. It has a striated appearance but is specialized for continuous, rhythmic contractions to pump blood.