Question

ion are a result of the thin filaments sliding past the thick filaments, resulting in shortening of all the sarcomeres in a myofibril. The striated pattern of skeletal muscle viewed under the microscope is created by the regular arrangement of thin and thick filaments, which results in alternating dark (A) bands and light (I) bands. Which statement below describes the changes in this banding pattern that occur during contraction of a sarcomere?According to the sliding filament theory of muscle contraction, the physical changes that occur in the sarcomere during contraction are a result of the thin filaments sliding past the thick filaments, resulting in shortening of all the sarcomeres in a myofibril. The striated pattern of skeletal muscle viewed under the microscope is created by the regular arrangement of thin and thick filaments, which results in alternating dark (A) bands and light (I) bands. Which statement below describes the changes in this banding pattern that occur during contraction of a sarcomere?A. The I bands and H bands get smaller and the A bands remain the same size.B. The I band gets smaller and the H zone remains the same.C. The I band gets smaller and the A band gets larger.D. The A band and the H band both become smaller.

Answer 1

Answer:

A. The I bands and H bands get smaller and the A bands remain the same size.

Explanation:

The dark-colored central region of the sarcomere that extends the entire length of the thick filaments makes the A band. It also includes the part of the thin filaments that overlap the thick filaments. The lighter region of the sarcomere consisting of the rest of the thin filament but no thick filament makes the I band. The H zone is the narrow region present in the center of each A band and consists only of thick filaments.

During muscle contraction, myosin heads pull the thin filaments towards the M line. This makes the thin filaments to slide inward to allow their ends to overlap and meet at the center of the sarcomere. This makes the I band and H zone narrower. The I band and H zone are disappeared during maximum muscle contraction. Sliding of thin filaments does not change the width of A band which remains unchanged.