Question

The H-Zone in the skeletal muscle fiber is due to

• A. The central gap between the actin filaments extending through myosin filaments in the A- band
• B. Extension of myosin filaments in the central portion of the A- band
• C. the absence of myofibrils in the central portion of A- band
• D. the central gap between the myosin filaments in the A-band

Answer 1

The correct option is A The central gap between the actin filaments extending through myosin filaments in the A- band

Each myofibril has many parallelly arranged myofibrils. Each myofibril contains many serially arranged units called sarcomere which is the functional unit. Each sarcomere has a central 'A' band made of thick myosin and two half 'I' bands made of thin filaments on either side of it marked by 'Z' lines. In a resting state, the edges of thin filaments on either side of the thick filaments partially overlap the free ends of the thick filaments leaving the central part of the thick filaments. This central part of thick filament, not overlapped by thin filaments is called the H - Zone