Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

SECTIONTHE MUSCULARLSYSTEMThe muscular system is composed of specialized cells called muscle fibers. Their predominantfunction is contractibility. Muscles, where attached to bones or internal organs and blood vessels, areresponsible for movement. Internal movement involves the contraction and relaxation of muscleswhich are a part of the viscera; external movement is accomplished by the contraction and relaxationof muscles which are attached to bones.MuscleTypesIn the body are found three types of muscle: skeletal, smooth, and cardiac.• Skeletal muscle, attached to bones, is responsible for skeletal movements. Theperipheral portion of the central nervous system (CNS) controls the skeletalmuscles. Thus, these muscles are under conscious, or voluntary, control. The basicunit is the muscle fiber with many nuclei. These muscle fibers are striated (havingtransverse streaks) and each acts independently of neighboring muscle fibers.• Smooth muscle, found in the walls of the hollow internal organs such as bloodvessels, the gastrointestinal tract, bladder, and uterus, is under control of theautonomic nervous system. Smooth muscle cannot be controlled consciously andthus acts involuntarily. The nonstriated (smooth) muscle cell is spindle-shaped andhas one central nucleus. Smooth muscle contracts slowly and rhythmically.• Cardiac muscle, found in the walls of the heart, is also under _ontrol of theautonomic nervous system. The cardiac muscle cell has one central nucleus, likesmooth muscle, but it also is striated, like skeletal muscle. The cardiac muscle cellis rectangular in shape. The contraction of cardiac muscle is involuntary, strong,and rhythmical.Muscle tissue receives a rich supply of blood which is carried by the arteries into the verysubstance of the muscle. Most of the arterioles run parallel with muscle fibers and branch off intocapillaries at right angles into the fibers.Muscle tumors tend to spread by way of the blood stream rather than to the lymphatics. Lymphnode metastasis does not often occur.Smooth and cardiac muscle are discussed in more detail with respect to their appropriate systems.This section explains mainly the skeletal muscular system.377