Question

During muscle contraction in humans, the

• A. sarcomere does not shorten
• B. A band remains same
• C. A, H and I bands shorten
• D. actin filaments shorten.

Answer 1

The Correct Option is B

To solve this question, we need to understand the process of muscle contraction and the changes that occur in the different bands of a sarcomere during contraction.

A sarcomere is the basic functional unit of muscle fibers and is composed of several structural proteins. Key components of a sarcomere include the A band, I band, and H zone, which are characterized based on the arrangement of thick (myosin) and thin (actin) filaments.

During muscle contraction:

• The A band refers to the length of the myosin filaments and remains the same as the filaments themselves do not shorten during contraction.
• The I band contains only thin filaments and shortens as the actin filaments slide inward towards the center of the sarcomere.
• The H zone is the region of the A band where there are no actin filaments overlapping the myosin and it shortens as well because the actin filaments slide inward.
• Actin filaments do not shorten; rather, they slide over the myosin filaments towards the middle of the sarcomere.

Given these points, we can conclude that during muscle contraction in humans:

• The sarcomere does shorten because the I band and H zone decrease in width, but the correct phrase to describe this is that the A band remains constant in length.
• A band remains same, which aligns with the role of the myosin filaments in contraction.
• A, H and I bands shorten is incorrect because the A band does not change in length.
• Actin filaments shorten is incorrect because they do not physically shorten but slide over myosin filaments.

Thus, the correct answer is: A band remains same.