Question:

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

Updated On: Nov 13, 2025

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

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The Correct Option is B

Solution and Explanation

To determine the correct events that occur during muscular contraction, let's analyze each option with relevant concepts from muscle physiology:

‘H’ zone disappears: During muscle contraction, the myofilaments slide past one another, causing the sarcomere to shorten. As the sarcomere shortens, the 'H' zone, which is the part of the A band where there is no actin, disappears. This statement is correct.
‘A’ band widens: The 'A' band, which is the length of the thick filaments (myosin), does not change its length during contraction. Thus, the A band does not widen. This statement is incorrect.
‘I’ band reduces in width: The 'I' band is the region containing only thin filaments (actin). As the sarcomere contracts and the myofilaments slide past each other, the 'I' band shortens. This statement is correct.
Myosine hydrolyzes ATP, releasing the ADP and Pi: During muscle contraction, myosin heads hydrolyze ATP to produce energy, releasing ADP and inorganic phosphate (Pi). This is essential for the power stroke, which allows myosin heads to move along actin filaments. This statement is correct.
Z-lines attached to actins are pulled inwards: During contraction, the Z-lines move closer together as the actin filaments slide towards the center of the sarcomere. This effectively shortens the sarcomere, contributing to muscle contraction. This statement is correct.

Based on the analysis, the correct combination of events is:

(a) ‘H’ zone disappears
(c) ‘I’ band reduces in width
(d) Myosine hydrolyzes ATP, releasing the ADP and Pi
(e) Z-lines attached to actins are pulled inwards

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

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Concepts Used:

The Musculoskeletal System

The musculoskeletal system comprises bones, cartilage, ligaments, tendons, and connective tissues. The skeleton contributes a framework for the muscles and other soft tissues. Together, they hold up our body’s weight, maintain our posture and help us move.

The parts of the musculoskeletal system are:

Bones: Bones of all shapes and sizes support our body, protect organs and tissues, store calcium and fat, and make blood cells. A bone’s hard outside shell encircling a spongy center. Bones provide structure and form for our bodies. They work with muscles, ligaments, tendons, and other connective tissues to help you move.
Cartilage: Cartilage cushions bones inside our joints, along our spine, and in our ribcage. Firm, rubbery cartilage secures bones from rubbing against each other. We also have cartilage in our nose, ears, pelvis, and lungs.
Joints: Bones come together to build joints. Some of the joints have a large range of motion like the ball-and-socket shoulder joint. Other joints such as the knee allow bones to move back and forth but not rotate.
Muscles: Each muscle is made of thousands of extending fibers. our muscles allow us to move, sit upright and stay still. Some muscles help us to run, dance and lift. We use others to write our name, fasten a button, talk and swallow.
Ligaments: Made of tough collagen fibers, ligaments attach bones and help stabilize joints.
Tendons: Tendons associate muscles with bones. Made of fibrous tissue and collagen, tendons are resilient but not very stretchy.