Cross bridges of sarcomere in skeletal muscle are made up of

Options

A. Actin
B. Myosin
C. Troponin
D. Tropomyosin.

Answer

To answer the question "Cross bridges of sarcomere in skeletal muscle are made up of," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Sarcomere Structure**:
- The sarcomere is the basic contractile unit of skeletal muscle and consists of thick and thin filaments.

2. **Identifying the Components**:
- The thick filaments are primarily made up of myosin, while the thin filaments are primarily made up of actin. Additionally, regulatory proteins such as troponin and tropomyosin are associated with the thin filaments.

3. **Role of Myosin and Actin**:
- Myosin has a head region that can bind to actin. This binding forms what are known as cross bridges, which are crucial for muscle contraction.

4. **Mechanism of Muscle Contraction**:
- When a muscle is stimulated, calcium ions are released, which bind to troponin. This causes a conformational change that moves tropomyosin away from the active sites on actin, allowing myosin heads to attach to these sites and form cross bridges.

5. **Conclusion**:
- Therefore, the cross bridges in the sarcomere are formed by the interaction between myosin and actin. Thus, the correct answer to the question is that cross bridges of the sarcomere in skeletal muscle are made up of **myosin**.

### Final Answer:
Cross bridges of sarcomere in skeletal muscle are made up of **myosin**.

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