Question

H-zone in skeletal muscle fibre is due to

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

Answer 1

Answer: (D)

Central gap between actin filaments extending through myosin filaments in A-band.

• Myofibril is made up of two types of filaments. They are thin filament(actin) and thick filament(myosin).
• The light bands contain actin and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin. The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils.
  
• 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.
  
• Hence H-zone in skeletal muscle fibre is due to Central gap between actin filaments extending through myosin filaments in A-band.
• So, the correct answer is 'Central gap between actin filaments extending through myosin filaments in A-band'.