MUSCLE LABORATORYElectron Micrographs- 7-1, 7-2, 7-3, 7-4, 7-5, 9-3, 12-4
INTRODUCTIONMuscle tissue is one of the four basic tissues of the body. It is formed of elongated cells in which the major physiological function is contraction. The muscle cells, or muscle fibers, are usually found in bundles or sheets bound together by varying amounts of connective tissue.
The basic cellular unit of muscle tissue is the muscle fiber. The term "fiber" is used here in contrast to a connective-tissue fiber which is noncellular and to a nerve fiber which is a cell process. Every muscle fiber is surrounded by a basement membrane. Its cell or plasma membrane (which is not visible with the light microscope) is called the sarcolemma and its cytoplasm also is given a special name, sarcoplasm. Within the sarcoplasm are cytoplasmic contractile elements, the myofilaments.
On both a structural and a functional basis, muscle is classified as smooth, skeletal, or cardiac. Smooth muscle fibers are structurally unstriated and functionally involuntary (i.e. contract independently of voluntary control). Skeletal and cardiac muscle fibers have a characteristic striated appearance (longitudinal section). However, whereas cardiac muscle is involuntary and contracts automatically and rhythmically, skeletal muscle is usually subject to voluntary control (except for the muscles of the diaphragm, the upper esophagus, and the middle ear).
LEARNING OBJECTIVESYou are expected to be able to distinguish these three muscle types both in cross section and longitudinal section. You are also expected to identify structures which are underlined in the following sections.