Ibåndet

Ibåndet, or the I-band, is a region of the sarcomere in striated muscle that contains only thin actin filaments and no overlap with thick myosin filaments. It lies on either side of the Z-disc and is the lighter-staining band seen in transverse muscle sections.

The I-band is bounded by the Z-disc on the inner side and by the edge where thick and thin filaments begin to overlap on the outer side; adjacent to it is the A-band. The central portion of the sarcomere within the A-band that lacks thin-filament overlap is called the H-zone. The length of the I-band varies with the degree of muscle contraction.

Actin filaments are the main components of the I-band, along with associated regulatory proteins such as tropomyosin and troponin. Structural proteins like titin extend from the Z-disc toward the M-line and contribute to the elastic properties of the region.

Functionally, the I-band shortens during muscle contraction as the thin and thick filaments slide past each other, while the overall length of the A-band remains relatively constant. This sliding filament action reduces the extent of thin-filament–only regions, shortening the I-band and contributing to sarcomere shortening.

Ibåndet is present in both skeletal and cardiac muscle and contrasts with the neighboring A-band, which contains the full length of the thick filament and the regions of filament overlap.