Which region is the light area with thin filaments only?

Which region is the light area with thin filaments only?

• A. A band
• B. I band
• C. H zone
• D. Z disc

Answer: (B)

The light area with thin filaments only is the I band. It sits between the A bands of adjacent sarcomeres and contains actin filaments that extend from the Z discs. Because this region lacks overlap with thick filaments, it appears lighter under a microscope. The A band encompasses the full length of the thick filament and overlapping thin filaments, while the H zone (within the A band) is the part with only thick filaments during relaxation. When the muscle contracts, the actin filaments slide inward, narrowing the I band, whereas the A band stays the same length.

The light area with thin filaments only is the I band. It sits between the A bands of adjacent sarcomeres and contains actin filaments that extend from the Z discs. Because this region lacks overlap with thick filaments, it appears lighter under a microscope. The A band encompasses the full length of the thick filament and overlapping thin filaments, while the H zone (within the A band) is the part with only thick filaments during relaxation. When the muscle contracts, the actin filaments slide inward, narrowing the I band, whereas the A band stays the same length.