Classification of Muscle Tissues

Classification of Muscle Tissues

The three types of muscle tissue are: skeletal, cardiac, and smooth (TABLE 9-1). Of these, skeletal and smooth muscle cells are elongated, and are known as muscle fibers.

Skeletal Muscles

Skeletal muscles are composed mainly of skeletal muscle tissues. The fibers are the longest muscle cells and are striated. Skeletal muscle attaches to bones and is the only type of muscle that is consciously controlled. It is, therefore, referred to as voluntary muscle. Skeletal muscle can, however, also be activated by reflexes. Individual skeletal muscles are separated from other mus-cles and held in position by layers of fibrous connective tissue known as fascia. They are the only cells in the body that are always multinucleated. Skeletal muscle controls overall body mobility. Although contractions may be rapid, skeletal muscle tires easily and requires rest after short amounts of activity.

Cardiac Muscle

Cardiac muscle tissue is found only in the heart and is made up of striated cells that are connected into three-dimensional networks (FIGURE 9-1). Cardiac muscle cells are the only type that commonly branch.

Stimulation to one portion of the cardiac muscle network passes to the other parts of the network, with the entire heart contracting as one functional unit. This type of muscle is self-exciting and rhythmic, repeating contraction and relaxation to cause the heart’s rhyth-mic contractions. Cardiac muscle contracts at a rela-tively stable rate, controlled by the heart’s pacemaker, but increased physical activity causes neural controls to speed up the heart as needed.

Smooth Muscle

Smooth muscle tissue is similar, but not identical, to skeletal muscle. It is not under voluntary control and has slow, sustained contractions. Smooth muscle cells have elongated, spindle-like shapes with tapered ends, but lack striations. They have a single, centrally located nucleus. Smooth muscle, along with skeletal and cardiac muscle, is shown in Figure 9-1.