What changes occur in the sarcomere during muscle contraction?

• A. The H zone widens and the I band lengthens.
• B. The A band shortens and the I band remains the same length.
• C. The I band shortens and the A band remains the same length.
• D. Both the A band and I band lengthen.

Answer: (C)

Verified step by step guidance

1. Understand the structure of the sarcomere: The sarcomere is the functional unit of a muscle fiber, composed of thick (myosin) and thin (actin) filaments. It includes regions such as the A band, I band, H zone, and Z lines.
2. Identify the components of the sarcomere: The A band contains the entire length of the thick filaments and remains constant during contraction. The I band contains only thin filaments and is the region that changes length during contraction.
3. Recognize the process of muscle contraction: During contraction, the actin filaments slide over the myosin filaments, causing the sarcomere to shorten. This sliding filament mechanism results in the shortening of the I band.
4. Analyze the changes in the sarcomere: As the muscle contracts, the I band shortens because the actin filaments are pulled towards the center of the sarcomere. The A band remains the same length because it is defined by the length of the myosin filaments, which do not change.
5. Conclude the changes during contraction: The correct observation during muscle contraction is that the I band shortens while the A band remains the same length, reflecting the sliding filament theory of muscle contraction.