4.4

Skeletal Muscle

• Description: Long, cylindrical, multinucleated cells (muscle fibers) with peripherally located nuclei and obvious striations caused by the precise alignment of myofilaments.

• Function: Responsible for voluntary movement, locomotion, facial expression, voluntary control, and manipulating the environment by contracting and pulling on bones or skin.

• Location: Organized into organs attached to bones or occasionally to skin.

Cardiac Muscle

• Description: Branching, striated, generally uninucleate cells with centrally located nuclei that fit together tightly and interdigitate at specialized junctions called intercalated discs.

• Function: Propels blood into circulation and through blood vessels under involuntary control.

• Location: Exclusively located in the walls of the heart.

Smooth Muscle

• Description: Spindle-shaped cells with tapered ends, a single centrally located nucleus, no visible striations, and closely arranged in sheets.

• Function: Propels substances or objects (e.g., food, urine, a baby) along internal passageways through involuntary, alternating contraction and relaxation.

• Location: Located primarily in the walls of hollow organs (excluding the heart), such as the digestive tract, urinary tract, uterus, and blood vessels.