Steps of Muscle Contraction — NEET Biology
📚 Practice ConceptDescribe the important steps in muscle contraction.
Which of the following statements correctly describe the roles of various components during skeletal muscle contraction and relaxation? S1: The binding of Ca²⁺ to troponin leads to the removal of the masking of active sites for myosin on the actin filaments. S2: ATP hydrolysis provides the energy required for the myosin head to bind to actin and form a cross-bridge, as well as for the subsequent pulling of the actin filament. S3: A fresh molecule of ATP is essential for the detachment of the myosin head from the actin filament, thereby breaking the cross-bridge. S4: Muscle relaxation occurs when Ca²⁺ ions are actively pumped out of the sarcoplasm and back into the extracellular fluid, resulting in the masking of actin sites. S5: White muscle fibres are characterised by a high myoglobin content and abundant mitochondria, making them primarily dependent on aerobic respiration.
View solution & NCERT explanation
Correct answer: A — S1, S2 and S3 are correct
Let's evaluate each statement regarding muscle contraction and relaxation based on NCERT: S1: 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. This statement is correct. S2: Utilizing the energy from ATP hydrolysis, the myosin head binds to the exposed active sites on actin to form a cross-bridge and pulls the attached actin filaments. This statement is correct. S3: A new ATP binds and the cross-bridge is broken. This statement is correct. S4: Muscle relaxation occurs when Ca++ ions are pumped back to the *sarcoplasmic cisternae* (sarcoplasmic reticulum), not into the extracellular fluid, resulting in the masking of actin filaments. Therefore, this statement is incorrect. S5: Muscles with high myoglobin content and plenty of mitochondria, utilizing large amounts of oxygen for ATP production, are called Red fibres. White fibres possess very less myoglobin and fewer mitochondria, depending on anaerobic processes. This statement describes Red fibres, making it incorrect for White muscle fibres. Only S1, S2, and S3 are correct.
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Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
176/180MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.