Question

Which of the statements about muscle contraction is correct?A) During muscle contraction the sarcomere becomes shorter.B) During muscle contraction the I band becomes shorter.C) During muscle contraction the H zone becomes shorter.D) During muscle contraction the distance between the Z disk and the M disk becomes shorter.E) All of the answers above are correct.2.During muscle contractionA) myosin pulls actin filaments toward the M disk.B) myosin pushes actin filaments toward the Z disk.C) actin pulls myosin toward the Z disk.D) actin pushes myosin toward the M disk.E) All of the answers above are correct.

Answer 1

Answer:

1. E) During muscle contraction all of the answers above are correct.

2. A) Myosin pulls actin filaments toward the M disk.

Explanation:

The mechanism of muscle contraction is also known as the sliding filament theory. It explains the activities which occur during contraction of muscles.

Muscles are made up of functional units called sarcomeres and these sarcomeres made up of myofibrils which are long and thin strands of protein. Myofibrils contain thin filaments called actin and thick filaments called myosin. Interactions between the thin and thick filaments results in contraction.

The I band contains thin filaments. The H band is the area of no thin filaments. The M line is the midline of the thick filaments. The Z line is the boundary between adjacent sarcomeres and the A band is the area of thick filaments.

Contraction occurs when muscle fibres are activated by neurons through the release of calcium ion. On stimulation, the H and I band get smaller, the zone of overlap gets larger and the Z lines move closer together and the A band remains constant. This the thin filaments slide towards the center resulting in the shortening of the sarcomeres and the muscle fibres as a whole.