Question:
Choose the correct statements regarding muscle contraction.
A. A motor neuron carries a signal sent by the Central Nervous System (CNS) to the sarcolemma of the muscle fibre.
B. The neural signal generates an action potential which causes the release of $Ca^{++$ into sarcoplasm.
C. Increase in $Ca^{++}$ inactivates the actin for breaking cross bridges.
D. Actin binds to the myosin head to form a cross bridge.
E. Shortening of sarcomere takes place, by pulling actin filaments towards the centre of 'A' band.
Choose the correct answer from the options given below:}
Choose the correct statements regarding muscle contraction.
A. A motor neuron carries a signal sent by the Central Nervous System (CNS) to the sarcolemma of the muscle fibre.
B. The neural signal generates an action potential which causes the release of $Ca^{++$ into sarcoplasm.
C. Increase in $Ca^{++}$ inactivates the actin for breaking cross bridges.
D. Actin binds to the myosin head to form a cross bridge.
E. Shortening of sarcomere takes place, by pulling actin filaments towards the centre of 'A' band.
Choose the correct answer from the options given below:}
A. A motor neuron carries a signal sent by the Central Nervous System (CNS) to the sarcolemma of the muscle fibre.
B. The neural signal generates an action potential which causes the release of $Ca^{++$ into sarcoplasm.
C. Increase in $Ca^{++}$ inactivates the actin for breaking cross bridges.
D. Actin binds to the myosin head to form a cross bridge.
E. Shortening of sarcomere takes place, by pulling actin filaments towards the centre of 'A' band.
Choose the correct answer from the options given below:}
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Logic Tip: Calcium is the universal "Go!" signal for muscle contraction. It exposes binding sites (activates), it never inactivates them. Knowing Statement C is false instantly eliminates options 1 and 4.
Updated On: May 28, 2026
- C and E only
- A, B and E only
- A and B only
- C and D only
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The Correct Option is B
Solution and Explanation
Concept:
The sliding filament theory explains muscle contraction. It states that contraction of a muscle fibre occurs by the sliding of the thin (actin) filaments over the thick (myosin) filaments, driven by cross-bridge formation and ATP hydrolysis.
Step 1:
Muscle contraction is initiated by a neural signal sent by the CNS via a motor neuron. This signal reaches the neuromuscular junction and ultimately depolarizes the sarcolemma. Statement A is correct.
Step 2:
The action potential spreads along the sarcolemma and down the T-tubules, triggering the sarcoplasmic reticulum to release stored calcium ions ($Ca^{++}$) into the sarcoplasm. Statement B is correct.
Step 3:
An increase in $Ca^{++}$ levels leads to calcium binding to troponin on the actin filaments. This binding removes the masking of active sites on actin, activating it for cross-bridge formation, rather than inactivating it or breaking bridges. Statement C is incorrect.
Step 4:
During cross-bridge formation, it is the energized myosin head that actively binds to the exposed active sites on the actin filament, not the other way around. Statement D is incorrect.
Step 5:
Once attached, the myosin heads pivot, pulling the attached actin filaments inwards towards the center of the 'A' band (the M-line). This inward pulling shortens the sarcomere, causing contraction. Statement E is correct.
Step 6:
Since only statements A, B, and E represent accurate physiological events during muscle contraction, Option (2) is the correct choice.
The sliding filament theory explains muscle contraction. It states that contraction of a muscle fibre occurs by the sliding of the thin (actin) filaments over the thick (myosin) filaments, driven by cross-bridge formation and ATP hydrolysis.
Step 1:
Muscle contraction is initiated by a neural signal sent by the CNS via a motor neuron. This signal reaches the neuromuscular junction and ultimately depolarizes the sarcolemma. Statement A is correct.
Step 2:
The action potential spreads along the sarcolemma and down the T-tubules, triggering the sarcoplasmic reticulum to release stored calcium ions ($Ca^{++}$) into the sarcoplasm. Statement B is correct.
Step 3:
An increase in $Ca^{++}$ levels leads to calcium binding to troponin on the actin filaments. This binding removes the masking of active sites on actin, activating it for cross-bridge formation, rather than inactivating it or breaking bridges. Statement C is incorrect.
Step 4:
During cross-bridge formation, it is the energized myosin head that actively binds to the exposed active sites on the actin filament, not the other way around. Statement D is incorrect.
Step 5:
Once attached, the myosin heads pivot, pulling the attached actin filaments inwards towards the center of the 'A' band (the M-line). This inward pulling shortens the sarcomere, causing contraction. Statement E is correct.
Step 6:
Since only statements A, B, and E represent accurate physiological events during muscle contraction, Option (2) is the correct choice.
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पेशी संकुचन के संबंध में सही कथनों का चयन कीजिए।
A. प्रेरक तंत्रिका केंद्रीय तंत्रिका तंत्र (CNS) से प्राप्त संकेत को पेशी तंतु के सार्कोलेमा तक ले जाती है।
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C. Ca\(^{2+}\) की वृद्धि ऐक्टिन को क्रॉस सेतु तोड़ने के लिए निष्क्रिय कर देती है।
D. ऐक्टिन, मायोसिन के शीर्ष से जुड़कर क्रॉस सेतु बनाता है।
E. ऐक्टिन तंतुओं का 'A' बैंड के मध्य की ओर खिंचने से सार्कोमियर छोटा हो जाता है।
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