What are the structural and functional differences between skeletal, cardiac, and smooth muscle tissues?

Skeletal muscle has long, cylindrical, multinucleate fibers with obvious striations; it is voluntary and moves the skeleton. Cardiac muscle has branching, striated, generally uninucleate cells joined at intercalated discs; it is involuntary and pumps blood from the heart. Smooth muscle has spindle-shaped cells with one central nucleus and no striations; it is involuntary and propels substances through hollow organs.

The three muscle tissues share the ability to contract because their cells contain actin and myosin myofilaments, but they differ in structure, location, and control. Skeletal muscle cells are long, cylindrical fibers with many nuclei located near the periphery, and they show prominent striations caused by the precise alignment of myofilaments. These cells are packaged into skeletal muscles attached to bones or occasionally to skin, and because their contraction is consciously controlled, skeletal muscle is voluntary. Cardiac muscle cells are found only in the heart wall. They are also striated, but unlike skeletal fibers they generally have a single central nucleus, they branch, and they fit tightly together at specialized junctions called intercalated discs. Cardiac muscle contracts involuntarily to propel blood into the circulation. Smooth muscle cells appear unstriated because the myofilaments are not aligned in visible bands. They are spindle shaped with one centrally located nucleus and are arranged closely to form sheets. Smooth muscle is located mainly in the walls of hollow organs other than the heart, such as digestive and urinary tract organs, uterus, and blood vessels, and its involuntary contractions squeeze substances along internal passageways.