Question

During muscular contraction which of the following events occur?

• A. (a), (b), (c), (d) only
• B. (a), (c), (d), (e) only
• C. (b), (c), (d), (e) only
• D. (b), (d), (e), (a) only

Answer 1

The correct option is B

(a), (c), (d), (e) only

The correct option is B.

An explanation for the correct option is:

1. The sliding filament theory explains the process of muscle contraction during which the thin filaments slide over the thick filaments, which shortens the myofibril.
2. Each muscle fibre has an alternate light and dark band, which contains a special contractile protein, called actin and myosin respectively.
3. Myosin is a protein that converts ATP into ADP and Pi . This helps in muscular contraction.
4. Actin is a thin contractile protein present in the light band and is known as the I-band, whereas myosin is a thick contractile protein present in the dark band and is known as the A-band.
5. There is an elastic fibre called z line that bisects each I-band. The thin filament is firmly anchored to the z line.
6. The central part of the thick filament that is not overlapped by the thin filament is known as the H-zone.
7. During muscle contraction, the myosin heads or cross bridges come in close contact with the thin filaments.
8. As a result, the thin filaments are pulled towards the middle of the sarcomere.
9. The Z line attached to the actin filaments is also pulled leading to the shortening of the sarcomere.
10. Hence, the length of the band A remains constant as its original length and the I-band shortens and the H-zone disappears.

Final answer: During muscular contraction (a) ‘H’ zone disappears, (c) ‘I’ band reduces in width, (d) Myosin hydrolyzes ATP, releasing the ADP and Pi and (e) Z-lines attached to actins are pulled inwards. thus, option B is correct.