Question

Muscle band that remains unchanged during contraction and relaxation of skeletal muscle is

• A. I
• B. H
• C. A
• D. Z-line
• E. H and Z lines

Answer 1

The correct option is C A

• The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils. The light bands contain actin(thin filament) and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin(thick filament).y. In the centre of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line.
  
• Utilizing the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge.
• This pulls the attached actin filaments towards the centre of ‘A’ band.
  
• The ‘Z’ line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction. Hence ‘I’ bands get reduced, whereas the ‘A’ bands retain the length.
• Hence muscle band that remains unchanged during contraction and relaxation of skeletal muscle is A.
• So, the correct answer is 'A'.