Question

Which of the statements about the mechanism of muscle contraction are correct?
(I) Acetycholine is released when the neural signal reaches the motor end plate.
(II) Muscle contraction is initiated by a signal sent by CNS via a sensory neuron.
(III) During muscle contraction, isotropic band gets elongated.
(IV) Repeated activation of the muscles can lead to lactic acid accumulation.

• A. I and IV
• B. I and III
• C. II and III
• D. I, II and III
• E. I and II

Answer 1

Answer: (A)

I and IV

Muscles are made up of two protein filaments a thick filament composed of the protein myosin and a thin filament composed of the protein actin. Contraction of muscles occurs when these filaments slide over one another in a series of repetitive events. Biochemical changes that take place during muscle contraction are that the motor nerve impulse reaches the neuromuscular junction, and the vesicles present in the motor end plate secrete a neurotransmitter chemical called acetylcholine (ACh). Further, the striations or isotropic bands formed when the series of basic units called sarcomeres are stacked throughout the muscle tissue change in length thereby elongating the muscle cells. So, the correct answer is option A.