The Muscles - Smooth muscle

There are two other general types of muscle. One is called smooth muscle because, under the microscope, it lacks the clearly defined stripes of skeletal muscle. Smooth muscle has another name, involuntary muscle , so called because the brain does not voluntarily control its actions. Smooth muscle is responsible for movements such as the muscular action that moves food and waste along the digestive tract, or the contraction and dilation of the pupil of the eye, as well as countless other involuntary movements of the sense and internal organs—with the exception of the heart.