Question

Select true or false
i. Shortening of sarcomere occurs when Z lines attached to actin filaments are pushed outwards.
ii. During contraction, I bands retain their lengths.
iii. During contraction, A bands get reduced in length.

• A. I- True, ii- False, iii-False
• B. I- False, ii- True, iii-True
• C. I- False, ii- False, iii-False
• D. I- True, ii- True, iii-False

Answer 1

The correct option is C I- False, ii- False, iii-False

The A band contains thick and thin filaments overlapping with each other. The I band is formed only of thin actin filaments. The H zone is formed only of thick myosin filaments. The region between consecutive Z lines is a single sarcomere.
During muscle contraction, the I band is reduced in size as the overlap between the thick and thin filaments increases. Consequently, the H zone also decreases in length. As the Z lines come closer together, the sarcomere shortens. So, the sarcomere, the I band, and the H zone decrease in length during muscle contraction. However, the A band does not change length during muscle contraction, since its length is the same as the length of the thick filaments.