During the sliding filament contraction, which region of the sarcomere shortens?

During the sliding filament contraction, which region of the sarcomere shortens?

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

Answer: (A)

During contraction, the filaments slide past one another, shortening the sarcomere overall. The length of the thick filaments (the A band) stays the same, because they don’t shorten. As actin slides inward, the region that contains only thin filaments—the I band—becomes narrower since overlap with myosin increases. The central H zone (thick filaments with no overlap) also disappears as overlap grows. The Z lines move closer together, but the specific region that actually shortens in length is the I band.

During contraction, the filaments slide past one another, shortening the sarcomere overall. The length of the thick filaments (the A band) stays the same, because they don’t shorten. As actin slides inward, the region that contains only thin filaments—the I band—becomes narrower since overlap with myosin increases. The central H zone (thick filaments with no overlap) also disappears as overlap grows. The Z lines move closer together, but the specific region that actually shortens in length is the I band.