Contraction of a muscle is caused by

Answer

**Step-by-Step Solution:**

1. **Understanding Muscle Structure:**
- Muscles are made up of fibers that contain two main types of proteins: myosin and actin.
- Myosin filaments are thicker and longer, while actin filaments are thinner and shorter.

2. **Role of Myosin and Actin:**
- During muscle contraction, myosin and actin interact with each other.
- Myosin heads attach to binding sites on the actin filaments, forming connections known as cross bridges.

3. **Formation of Ectomyosin Complex:**
- The interaction between myosin and actin, through the formation of cross bridges, results in the creation of a complex called the ectomyosin complex.
- This complex is essential for muscle contraction.

4. **Conclusion:**
- Therefore, the contraction of a muscle is primarily caused by the formation of the ectomyosin complex during the interaction of myosin and actin filaments.

**Final Answer:**
Contraction of a muscle is caused by the ectomyosin complex.

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