Question

Read the following statements about muscle contraction in humans:

i. Chemical energy is converted into mechanical energy during muscle contraction

ii. Acetylcholineeasterase is an enzyme that catalyzes the production of acetylcholine

iii. In a contracted muscle, volume remains the same.

iv. A contracted muscle becomes shorter and thicker.

• A. Only iv) is correct.
• B. Only i) and iv) are correct.
• C. Only ii), iii) and iv) are correct.
• D. Only i), iii) and iv) are correct.

Answer 1

The correct option is D

Only i), iii) and iv) are correct.

The electric impulse is carried into the muscle fiber, where it causes muscle contraction. This represents energy transduction: the electric energy on the surface of the muscle fiber is converted into mechanical energy. Acetylcholinesterase, also known as AChE or acetylhydrolase, is the primary cholinesterase in the body. It is an enzyme that catalyzes the breakdown of acetylcholine
When a muscle is stimulated, a short latent period follows, during which it is taking up the stimulus. It then contracts, where it becomes short and thick, and finally, it relaxes and elongates.

During muscle contraction, the laterally projecting heads (cross bridges) of the thick myosin myofilaments come in contact with the thin actin myofilaments and rotate on them. This pulls the thin myofilaments towards the middle of the sarcomere past the thick myofilaments. The Z lines come closer together and the sarcomere becomes shorter. The length of the A band remains constant. Myofilaments stay the same length. The free end of actin myofilaments moves closer to the center of the sarcomere, bringing Z lines closer together. I bands shorten and H zone narrows. A similar action in all the sarcomeres results in shortening of the entire myofibril, and thereby of the whole fiber and the whole muscle. A contracted muscle becomes shorter and thicker and its volume remains the same.