The Z disc is at the center of which band?

The Z disc is at the center of which band?

• A. A band
• B. I band
• C. Z disc
• D. M line

Answer: (B)

The Z disc marks the boundary between sarcomeres and anchors thin actin filaments. The region that contains only these thin filaments, not overlapping thick filaments, is the I band. In the relaxed state, the Z disc sits in the center of that light, thin-filament region, so the Z disc is at the center of the I band. The A band, by contrast, corresponds to the length of the thick filaments (and includes overlap with thin filaments), with the M line at its mid-point. Thus, the Z disc relates to the I band, not the A band or the M line.

The Z disc marks the boundary between sarcomeres and anchors thin actin filaments. The region that contains only these thin filaments, not overlapping thick filaments, is the I band. In the relaxed state, the Z disc sits in the center of that light, thin-filament region, so the Z disc is at the center of the I band. The A band, by contrast, corresponds to the length of the thick filaments (and includes overlap with thin filaments), with the M line at its mid-point. Thus, the Z disc relates to the I band, not the A band or the M line.