The muscular system supports body movement, maintains posture, and circulates blood through the body. According to Live Science, the system consists of 650 skeletal, smooth and cardiac muscles.
Skeletal muscles are voluntary, meaning they direct muscle movement based on actions a person purposely performs. Wikipedia explains that coordinated contractions occur in skeletal muscles when stimulated by an intentional movement. These contractions consist of an overlapping motion of muscle fibers. The majority of skeletal muscles are connected to bones at the joint. This connection works to facilitate the movement of bones close together.
Smooth muscles exist inside of muscles, such as the stomach, intestines or blood vessels. They are not voluntary muscles, meaning they cannot move by purposeful intention, according to Live Science. Instead, they are controlled by the unconscious part of the brain. As their name suggests, smooth muscles have a smooth appearance, as opposed to the banded structure of skeletal or cardiac muscles.
Cardiac muscles are found only in the heart, pumping blood throughout the body. Live Science explains that cardiac muscle also stimulates other cardiac muscles to contract, while the brain and hormones control the rate of contraction. As with smooth muscle, cardiac muscles are not under voluntary control.