Muscles whose actions are not controlled by the will of the animal are called involuntary muscles. They are also called visceral muscles because they are present in the walls of various organs (vessels).
Structure of involuntary muscles
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 sheath of muscle is called sarcolemma. In involuntary muscles the sarcolemma is inconspicuous.
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. 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.
Location of involuntary muscles
Involuntary muscles are located in alimentary canal, blood vessels, trachea, urethra, uterus etc.
Function/importance/role of involuntary muscles
1. The contraction-expansion capacity of this muscle is slow and long-lasting.
2. It regulates the rhythmic activity of the organs.
3. It controls the movement of food material in the process of peristalsis.
4. Controls the contraction and expansion of blood vessels, airways, excretory canals etc.