Muscle Contraction Mechanism — NEET Biology
✅ Asked in NEET 2024Select the correct statements regarding mechanism of muscle contraction. A.It is initiated by a signal sent by CNS via sensory neuron. B.Neurotransmitter generates action potential in the sarcolemma. C.Increased Ca++ level leads to the binding of calcium with D.troponin on action filaments. Masking of active site for actin is activated. E.Utilising the energy from ATP hydrolysis to form cross bridge. Choose the most appropriate answer from the options given below [NEET 2024 ]
Select the correct statements regarding mechanism of muscle contraction. A.It is initiated by a signal sent by CNS via sensory neuron. B.Neurotransmitter generates action potential in the sarcolemma. C.Increased Ca++ level leads to the binding of calcium with D.troponin on action filaments. Masking of active site for actin is activated. E.Utilising the energy from ATP hydrolysis to form cross bridge. Choose the most appropriate answer from the options given below [NEET 2024 ]
Name the ion responsible for unmasking of active sites for myosin for cross-bridge activity during muscle contraction. (NEET II 2016)
Answer & NCERT explanation
Correct answer: D — A, B and E only
Statement A is wrong - signal comes via motor neuron, not sensory. Statement B is correct - neurotransmitter (acetylcholine) generates action potential in sarcolemma. Statement C is wrong - calcium binds to troponin, not directly to actin. Statement D is wrong - active sites are unmasked, not masked. Statement E is correct - ATP hydrolysis provides energy for cross-bridge formation.
Read more NCERT concept on the PYQ
Muscle contraction is initiated by a signal sent by the central nervous system (CNS) via a motor neuron. A motor neuron along with the muscle fibres connected to it constitute a motor unit. The junction between a motor neuron and the sarcolemma of the muscle fibre is called the neuromuscular junction or motor end plate. A neural signal reaching this junction releases a neurotransmitter (Acetyl choline) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm. Increase in Ca++ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking 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.
NTA tests how muscle contraction is triggered: a motor neuron releases acetylcholine at the neuromuscular junction, creating an action potential that causes Ca²⁺ release from the sarcoplasm. This calcium binds to troponin on actin filaments, exposing myosin-binding sites and forming cross-bridges using ATP energy. Students commonly confuse which filament (actin vs myosin) binds calcium, or forget that troponin is the regulatory protein on actin. Remember: Ca²⁺ binds troponin (on actin), not myosin. This uncovers active sites, allowing myosin heads to attach and pull actin, causing contraction. This sequential mechanism appears repeatedly because it tests understanding of signal transduction and molecular events combined.
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