Answer:
B. M line
Explanation:
Sarcomere is the unit of muscle contraction. The muscle fiber is composed of smaller unit called myofibrils. Myofibrils are composed of contractile proteins called actin and myosin. These myofibrils are arranged in a contractile unit called sarcomere. Sarcomere contains the following (please see the attached image, reference: lumen learning):
- A band or anisotropic band: It contains both mysoin and actin filaments. It has a central H band where only thick filament i.e myosin is present and an O band which is overlapping of both actin and myosin. During contraction O band increase and H band reduces in its length. At the center of H band there is the M line.
- I band or isotropic band: It contains only thin filament i.e actin filament. In the center of I band, there is a band of dense amorphous material, the Z line (line of krause). The structure between two Z lines is termed as sarcomere.
The thick filaments lie parallel to one another and thin filaments are present in an orderly manner between the thick filaments.
