Functions of the Muscular System
Vertebrate muscle has only one function: contraction. “Relaxation” is a passive process, a lack of contraction. Thus, the varied functions of the muscular system are all based on contraction (or shortening) of muscle fibers.
Layers of smooth muscle in the walls of the stomach and intestines contract to mix and propel food along the gastrointestinal tract; smooth muscle layers in the walls of blood vessels control the distribution of blood, which is propelled by the contraction of the cardiac muscle of the heart. in the eye, smooth muscle fibers adjust the diameter of the pupil and thickness of the lens for optimal vision, while in the skin, contraction of smooth muscles causes the hair to stand up. skeletal muscles permit locomotion by contracting to change the relative positions of bones during movement and by maintaining joint angles against the pull of gravity during support. The skeletal muscles of respiration move air into and out of the lungs by contracting to change the volume of the thoracic cavity. in addition, heat production through shivering is the result of brief repetitive contractions of skeletal muscle throughout the body.The remainder of this chapter describes the locations, attachments, and actions of the major skeletal muscles. Figures 7-1 through 7-3 illustrate many of these muscles of the horse and ox.
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