The myofilaments of a muscle :

Options

A. are arranged in compartments known as sarcomeres
B. are composed of proteins known as actin and myosin
C. are the actual contractile elements of the fibre
D. all of the above

Answer

**Step-by-Step Solution:**

1. **Understanding Myofilaments**: Myofilaments are the basic units of muscle contraction. They are primarily composed of two types of proteins: actin and myosin.

2. **Structure of Myofilaments**:
- **Actin**: This is the thin filament. It has a globular shape and is associated with the protein troponin, which plays a crucial role in muscle contraction by masking the binding sites for myosin.
- **Myosin**: This is the thick filament. It is structured to allow interaction with actin during muscle contraction.

3. **Arrangement in Sarcomeres**: Myofilaments are organized into units called sarcomeres. Sarcomeres are the repeating structural units of muscle fibers and are responsible for the striated appearance of skeletal muscle.

4. **Function of Myofilaments**: The interaction between actin and myosin is essential for muscle contraction. When a muscle fiber is stimulated, the myosin heads bind to the actin filaments, leading to a sliding motion that causes contraction. This process requires energy in the form of ATP.

5. **Conclusion**: Therefore, the myofilaments of a muscle are arranged in compartments known as sarcomeres, composed of actin and myosin, which are the actual contractile elements of the muscle fiber.

**Final Answer**: The myofilaments of a muscle are arranged in compartments known as the sarcomere, composed of the proteins actin and myosin, which are the actual contractile elements of the fiber.

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