During muscle contraction, actin and myosin ffrom

Options

A. actomyosin
B. actoplasm
C. plastosine
D. myoplasm.

Answer

**Step-by-Step Solution:**

1. **Understanding Muscle Structure**:
- Skeletal muscles consist of two types of contractile proteins: actin and myosin.
- Actin forms the thin filaments, while myosin forms the thick filaments in muscle fibers.

2. **Role of Actin and Myosin in Contraction**:
- Both actin and myosin are crucial for muscle contraction.
- When these proteins interact, they form a cross-bridge, which is essential for the shortening of the sarcomere, the basic unit of muscle contraction.

3. **Initiation of Muscle Contraction**:
- Muscle contraction begins with a neural signal that stimulates the muscle fiber.
- This stimulation leads to the release of calcium ions, which play a key role in exposing the active sites on the actin filaments.

4. **Binding of Actin and Myosin**:
- In the resting state, the active sites on actin are masked and cannot bind with myosin.
- Upon stimulation, calcium ions bind to troponin (a regulatory protein), causing a conformational change that exposes the active sites on actin.

5. **Formation of Ectomyosin**:
- Once the active sites are exposed, myosin heads can bind to these sites on actin, forming a cross-bridge.
- The complex formed by the binding of actin and myosin is referred to as ectomyosin.

6. **Conclusion**:
- During muscle contraction, actin and myosin form a complex known as ectomyosin, which is essential for the contraction process.

**Final Answer**: During muscle contraction, actin and myosin form a complex known as ectomyosin.

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