Sliding filament theory can be best explained as

Options

A. Actin and Myosin filaments shorten and slide pass each other
B. Actin and Myosin filaments do not shorten but rather slide pass each other
C. When myofilaments slide pass each other, myosin filaments shorten while Actin filaments do not shorten
D. When myofilaments slide pass each other actin filament do not shorten

Answer

### Step-by-Step Solution:

1. **Understanding the Sliding Filament Theory**: The sliding filament theory explains how muscle contraction occurs at the molecular level. It was proposed by A. F. Huxley and H. E. Huxley in 1954.

2. **Components Involved**: The two main proteins involved in muscle contraction are actin (thin filaments) and myosin (thick filaments).

3. **Mechanism of Contraction**: According to the sliding filament theory:
- Myosin heads bind to actin filaments.
- Upon binding, the myosin heads change shape (alter their configuration), which results in a power stroke.
- This power stroke pulls the actin filaments toward the center of the sarcomere, the basic unit of muscle contraction.

4. **Length of Filaments**: A key point of the sliding filament theory is that during contraction:
- The lengths of the actin and myosin filaments do not change.
- Instead, they slide past each other, allowing the muscle to contract without shortening the individual filaments.

5. **Evaluating the Options**:
- **Option 1**: "Actin and myosin filaments shorten." - This is incorrect because the filaments do not shorten.
- **Option 2**: "Actin and myosin filaments do not shorten but rather slide past each other." - This is correct as it accurately describes the sliding filament mechanism.
- **Option 3**: "When myofilaments slide past each other, myofilaments shorten." - This is incorrect as both filaments maintain their length during contraction.
- **Option 4**: "When myofilaments slide past each other, actin filaments do not shorten." - This is partially correct but does not encompass the behavior of myosin.

6. **Conclusion**: The best explanation of the sliding filament theory is that "actin and myosin filaments do not shorten but rather slide past each other."