Involuntary muscles are squash-shaped in appearance. That is, it is wide in the middle and narrow at both ends. Its length is 15-200 micrometers and diameter is 8-10 micrometers.
- Sarcolemma: The sheath of muscle is called sarcolemma. In involuntary muscles the sarcolemma is inconspicuous.
- Sarcoplasm: Cytoplasm of muscle is called sarcoplasm. Cytoplasm contains mitochondria. Its cytoplasm is called sarcoplasm. Each cell has a nucleus and numerous fibers called myofibrils.
- Nucleus: Each muscle cell has a nucleus. It performs biological functions of cells.
- Myofibrils: Myofibril fibers run along the length of the cell. Myofibril fibers are composed of actin and myosin filaments. Actin and myosin filaments together are called sarcomere.