A sarcomere is :

Options

A. the area between two intercalated discs
B. the nonfunctional unit of skeletal muscle
C. the wavy lines on the cell, as seen in a microscope
D. the contractile unit between two Z disc

Answer

**Step-by-Step Solution:**

1. **Definition of Sarcomere**: A sarcomere is defined as the basic functional unit of striated muscle tissue, particularly found in skeletal and cardiac muscles.

2. **Structure of Sarcomere**: Each sarcomere is bounded by two Z-lines (or Z-discs). These Z-lines serve as the anchoring points for the thin filaments.

3. **Components of Sarcomere**: The sarcomere contains two types of myofilaments:
- **Thick Filaments**: Primarily composed of the protein myosin.
- **Thin Filaments**: Made up of the protein actin.

4. **Arrangement of Filaments**: The thick and thin filaments are arranged in a specific pattern within the sarcomere, leading to the characteristic striations observed in skeletal muscle under a microscope. The alternating arrangement of these filaments creates dark and light bands.

5. **Function of Sarcomere**: The sarcomere is responsible for muscle contraction. When a muscle contracts, the thick and thin filaments slide past each other, shortening the overall length of the sarcomere.

6. **Conclusion**: Therefore, the sarcomere can be described as the contractile unit of muscle fibers, situated between two Z-discs.

**Final Answer**: A sarcomere is the contractile unit of muscle fibers located between two Z-discs.

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