During muscular contraction which of the following events occur?

(a) 'H' zone disappears

(b) 'A' band widens

(c) 'I' band reduces in width

(d) Myosine hydrolyzes ATP, releasing the ADP and Pi.

(e) Z-lines attached to actins are pulled inwards.

Choose the correct answer from the options given below:

The correct answer is (a), (c), (d), (e) only.

(a) “H” zone disappears
During contraction the thin (actin) filaments slide toward the centre of the sarcomere, increasing the overlap with the thick (myosin) filaments. The region that originally contained only thick filaments – the H zone – becomes overlapped by actin, so the H zone is no longer visible.

(c) “I” band reduces in width
The I band is the portion of the sarcomere that contains only thin filaments, extending from the edge of the H zone to the Z‑line. As the thin filaments move inward, the distance between the edges of the H zone and the Z‑lines shortens, causing the I band to become narrower.

(d) Myosin hydrolyzes ATP, releasing the ADP and Pi.
Myosin heads possess ATPase activity. When ATP binds to a myosin head, it is hydrolyzed to ADP + Pi, providing the energy needed for the myosin head to pivot (the power stroke) and pull the actin filament.

(e) Z‑lines attached to actins are pulled inwards.
Because the actin filaments are anchored to the Z‑lines, the sliding of actin toward the centre of the sarcomere draws the Z‑lines closer together. This shortens the entire sarcomere and produces muscle contraction.