NEET 2024 Re Exam Biology Solved Paper

The correct answer is option (1) as muscle contraction is initiated by a signal sent by the CNS via a motor neuron. A neural signal reaching the neuromuscular junction releases a neurotransmitter (acetylcholine) which generates an action potentialin the sarcolemma. This spreads through the muscle fibre and causes the release of Ca2+ into the sarcoplasm. Increase in Ca2+ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove themasking of active sites for myosin. Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge.