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.
1. Sarcolemma: The muscle sheath is called sarcolemma. The sarcolemma is indistinct in involuntary muscles.
2. 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.
3. Nucleus: Each muscle cell has a nucleus. It performs biological functions of cells.
4. Myofibril: Myofibril fibers are present along the length of the cell. Myofibril fibers are composed of actin and myosin filaments. Actin and myosin filaments together are called sarcomere.