During contraction of muscles `:-`

Options

A. Actin Filament slide over actin
B. Myosin filament slide over actin
C. Actin filament slide over myosin
D. Myosin filament slide over actin

Answer

### Step-by-Step Solution:

1. **Understanding Muscle Contraction**: Muscle contraction is a complex process that involves the interaction between two types of protein filaments: actin (thin filaments) and myosin (thick filaments).

2. **Sliding Filament Theory**: According to the sliding filament theory, muscle contraction occurs when the actin filaments slide over the myosin filaments. This sliding action causes the muscle fibers to shorten, leading to contraction.

3. **Filament Structure**: Actin filaments have a diameter of approximately 7 nanometers, while myosin filaments are about 15 nanometers in diameter. This size difference is crucial for their interaction during contraction.

4. **Mechanism of Contraction**: When a muscle is stimulated to contract, the myosin heads attach to binding sites on the actin filaments. The myosin heads then pull the actin filaments towards the center of the sarcomere, which is the functional unit of muscle contraction.

5. **Conclusion**: Based on the sliding filament theory, during muscle contraction, it is the actin filaments that slide over the myosin filaments. Therefore, the correct answer to the question is: **Actin filament slide over myosin**.