Question

based on the sliding filament theory of sarcomere shortening (contraction), which of the following remains unchanged?

a.) i-band distance
b.) z-band to z-band distance
c.) a-band distance
d.) h-zone distance

Explanation:

Analyze sarcomere changes during contraction

During muscle contraction, actin (thin) filaments slide past myosin (thick) filaments.

• The distance between Z-discs (Z-band to Z-band distance) shortens.
• The H-zone (containing only myosin) narrows or disappears.
• The I-band (containing only actin) narrows.

Determine the constant region

The A-band represents the entire length of the thick myosin filaments. Because the filaments themselves do not change length or shrink during contraction, the width of the A-band remains constant.

Answer:

• a.) I-band distance
• b.) Z-band to Z-band distance
• c.) A-band distance (Correct answer)
• d.) H-zone distance