Read the following statements and select the correct option :
I. In the skeletal muscles fibre, large number of myofilaments are arranged in the sarcoplasm.
II. The central part of an anisotropic band where the only thick , filament is present and thin filament is absent is called 'A' band.
III. In the resting state , a tropomyosin protein masks the active b binding sites for myosin on the active filaments .
IV. The junction between a motor neuron and the sarcolemma of the muscle fibres is called motor-end plate.

Options

A. I , II and IV are true
B. II, III and IV are true
C. I and IV are true
D. only IV true

Answer

To solve the question, we will evaluate each statement one by one to determine their correctness.

### Step-by-Step Solution:

1. **Statement I**: "In the skeletal muscles fibre, large number of myofilaments are arranged in the sarcoplasm."
- **Evaluation**: This statement is correct. Skeletal muscle fibers contain numerous myofilaments (actin and myosin) arranged in a parallel manner within the sarcoplasm, forming structures called myofibrils.

2. **Statement II**: "The central part of an anisotropic band where the only thick filament is present and thin filament is absent is called 'A' band."
- **Evaluation**: This statement is incorrect. The central part of the A-band where only thick filaments (myosin) are present is referred to as the H-zone, not the A-band. The A-band includes both thick and overlapping thin filaments.

3. **Statement III**: "In the resting state, a tropomyosin protein masks the active binding sites for myosin on the active filaments."
- **Evaluation**: This statement is misleading. While tropomyosin does play a role in masking the binding sites on actin filaments, it is actually the troponin complex that regulates this process. Thus, this statement is incorrect.

4. **Statement IV**: "The junction between a motor neuron and the sarcolemma of the muscle fibres is called motor-end plate."
- **Evaluation**: This statement is correct. The motor end plate is indeed the specialized region where the motor neuron communicates with the muscle fiber, facilitating muscle contraction.

### Conclusion:
Based on the evaluations:
- Correct statements: I and IV
- Incorrect statements: II and III

The correct option is **Option 3**, which includes statements I and IV as true.