Which of the following statements about the mechanism of muscle contraction are correct ?
(i) Acetylcholine is released when the neural signal reaches the motor end plate.
(ii)Muscle contraction is initiated by a signal sent by CNS via sensory neuron.
(iii) During muscle contraction, isotropic band gets elongated
(iv) Repeated activation of the muscles can lead to lactic acid accumulation.

Options

A. (i) and (iv)
B. (i) and (iii)
C. (ii) and (iii)
D. (i), (ii) and (iii)

Explanation

To determine which statements about the mechanism of muscle contraction are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement (i): Acetylcholine is released when the neural signal reaches the motor end plate.**
- This statement is **correct**. When a neural signal reaches the neuromuscular junction (motor end plate), it triggers the release of the neurotransmitter acetylcholine from vesicles. This neurotransmitter binds to receptors on the muscle fiber, initiating muscle contraction.

2. **Statement (ii): Muscle contraction is initiated by a signal sent by CNS via sensory neuron.**
- This statement is **incorrect**. Muscle contraction is initiated by signals sent from the Central Nervous System (CNS) via motor neurons, not sensory neurons. Sensory neurons are responsible for sending information from sensory receptors to the CNS.

3. **Statement (iii): During muscle contraction, isotropic band gets elongated.**
- This statement is **incorrect**. The isotropic (I) bands do not get elongated during muscle contraction. Instead, during contraction, the thick (myosin) and thin (actin) filaments slide over each other, causing the sarcomere to shorten, which results in the I bands becoming narrower, not elongated.

4. **Statement (iv): Repeated activation of the muscles can lead to lactic acid accumulation.**
- This statement is **correct**. During intense or prolonged muscle activity, when oxygen supply is insufficient, muscles switch to anaerobic respiration, leading to the production of lactic acid as a by-product. This accumulation can cause muscle fatigue.

### Conclusion:
Based on the analysis:
- **Correct Statements**: (i) and (iv)
- **Incorrect Statements**: (ii) and (iii)

Thus, the correct answer is that statements (i) and (iv) are correct.