Question

How does the z line, m line, i band, zone of overlap change when the muscle contracts?

A) They shorten
B) They lengthen
C) They remain the same
D) They disappear

Answer 1

During muscle contraction, the Z lines and I band shorten, the zone of overlap increases, the H zone shortens, while the A band remains the same width.

Step-by-step explanation:

Changes in Muscle Structures During Contraction

When a muscle contracts, specific structural changes occur within the sarcomere, the basic unit of a muscle. Specifically:

• The Z lines (Z discs) move closer together, indicating that the sarcomere has shortened.
• The I band, which contains only thin filaments, becomes smaller.
• The zone of overlap, where thin and thick filaments overlap, increases as the contraction pulls thin filaments inward.
• The H zone, which is the central part of the A band with only thick filaments, shortens.
• However, the A band itself, which consists of the full length of the thick filaments, remains the same width even as the A bands of different sarcomeres move closer to each other.

Thus, during muscle contraction, the answer to how the Z line, M line, I band, and zone of overlap change is A) They shorten, except for the A band, which C) remains the same.