Question

(14) Which statement is correct for muscle
contraction?
A) Length of H-zone decreases
B) Length of A-band decreases
C Length of two Z-line increases
D) Length of l-band remains constant​

Answer 1

Which statement is correct for muscle contraction : -

( A ) Length of two Z-line become increase

( B ) Length of I-band become increase

( C ) Length of A-band remains constant

( D ) Length of H-zone become decreas

Answer : (A)

Both the choices are correct. In contraction, the laterally projecting heads (cross bridges) of the thick myosin myofilaments come in contact with the thin actin myofilaments and rotate on them. This pulls the thin myofilaments toward the middle of the sarcomere past the thick myofilaments. The Z lines come closer together and the sarcomere becomes shorter. Length of the A band remains constant. Myofilaments stay the same length. Free ends of actin myofilaments move closer to the centre of the sarcomere, bringing Z lines closer together. I bands shorten and H zone narrows. A similar action in all the sarcomeres results in shortening of the entire myofibril, and thereby of the whole fibre and the whole muscle