By Janet Rae-Dupree, Pat DuPree

When studying histology you should know that muscle tissue is made up of fibers known as myocytes. The cytoplasm within the fibers is called sarcoplasm, and within that sarcoplasm are minute myofibrils that contain the protein filaments actin and myosin. These filaments slide past each other during a muscle contraction, shortening the fiber.

Following are the three types of muscle tissue:

  • Smooth muscle tissue: This type of tissue contracts without conscious control. Made up of spindle-shaped fibers with large, centrally located nuclei, it’s found in the walls of internal organs, or viscera. Smooth muscle gets its name from the fact that, unlike other muscle tissue types, it is not striated.

  • Cardiac muscle tissue: This tissue is composed of cylindrical branching fibers, myocardiocytes, each with a central nucleus and alternating light and dark striations. Between the fibers are dark structures called intercalated discs that hold the fibers together. As with smooth muscle, cardiac muscle tissue contractions occur through the autonomic nervous system (involuntary control).

  • Skeletal, or striated, muscle tissue: Biceps, triceps, pecs — these are the muscles that bodybuilders focus on. As the name implies, skeletal muscles attach to the skeleton and are controlled throughout by the conscious (voluntary) control function of the central nervous system for movement. Muscle fibers are cylindrical with several nuclei in each cell (which makes them multinucleated) and cross-striations throughout.