Which of the following statements about the mechanism of muscle contraction are correct? 

(1) Acetylcholine is released when the neural signal reaches the motor end plate.

(2) Muscle contraction is initiated by a signal sent by CNS via sensory neuron.

(3) During muscle contraction, isotropic band gets elongated.

(4) Repeated activation of the muscles can lead to accumulation of lactic acid.

Statements 1 and 4 are correct.

• Acetylcholine is released when the neural signal reaches the motor end plate. Acetylcholine is a neurotransmitter released at the neuromuscular junction (motor end plate) when a nerve impulse (neural signal) reaches it. Acetylcholine binding to receptors on the muscle fibre initiates muscle contraction.
•  Muscle contraction is initiated by a signal sent by CNS via motor neuron. Sensory neurons transmit sensory information from the body to the CNS but do not directly trigger muscle contraction.
• During muscle contraction, the isotropic band (I-band) gets shortened (not elongated). Muscle contraction involves the sliding of actin and myosin filaments, leading to the overlapping of these filaments and a reduction in the length of the I-band.
• Repeated activation of the muscles can lead to the accumulation of lactic acid.