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NEET 2026, Biology Q71: Muscle

NEET2026Biology
Q.

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 :

  1. A

    C and D only

  2. B

    A and B only

  3. C

    C and E only

  4. D

    A, B, D and E only

Solution

A neural signal from a motor neuron generates an action potential on the sarcolemma, triggering release of Ca into the sarcoplasm. The Ca binds to troponin on actin filaments, exposing active sites for myosin to bind and form cross bridges. The sarcomere shortens as actin filaments are pulled toward the centre of the ‘A’ band.

Statement C is wrong because Ca does not inactivate actin; it removes the masking of active sites and facilitates cross-bridge formation. The correct statements are A, B, D and E.

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