Choose the correct statements regarding muscle contraction.

A. Amotorneuroncarries 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:

Statement A says that a motor neuron carries a signal sent by the Central Nervous System (CNS) to the sarcolemma of the muscle fibre. This is the correct description of the efferent pathway: the CNS sends an impulse down the motor neuron, which terminates on the muscle membrane (sarcolemma) and releases acetylcholine.

Statement B states that the neural signal generates an action potential which causes the release of Ca⁺⁺ into the sarcoplasm. The action potential that travels along the sarcolemma and transverse (T‑tubules) indeed triggers the opening of voltage‑sensitive dihydropyridine receptors, leading to calcium release from the sarcoplasmic reticulum into the sarcoplasm.

Statement C claims that an increase in Ca⁺⁺ inactivates the actin for breaking cross‑bridges. In reality, Ca⁺⁺ binds to troponin, which moves tropomyosin away from the myosin‑binding sites on actin, thereby activating actin for cross‑bridge formation, not inactivating it. Hence C is false.

Statement D says that actin binds to the myosin head to form a cross‑bridge. The correct sequence is that the myosin head binds to the exposed binding sites on actin; however, the wording “actin binds to the myosin head” reverses the direction of the interaction and is misleading. Moreover, the cross‑bridge is formed by the myosin head attaching to actin, not the other way around, so D is considered incorrect in this context.

Statement E describes that shortening of the sarcomere occurs by pulling actin filaments towards the centre of the ‘A’ band. During contraction the myosin heads pull the actin filaments toward the M‑line, which shortens the I‑band and the overall sarcomere length while the A‑band remains unchanged. This description matches the accepted mechanism, so E is true.

Putting the correct statements together, the only set that matches the truth is A, B and E only.