Sarcoplasmic reticulum of muscle fibres is the store house of

Options

A. Calcium
B. Sodium
C. Chloride
D. Potassium.

Answer

**Step-by-Step Solution:**

1. **Understanding Sarcoplasmic Reticulum**: The sarcoplasmic reticulum (SR) is a specialized type of endoplasmic reticulum found in muscle fibers. It plays a crucial role in muscle contraction.

2. **Function of Sarcoplasmic Reticulum**: The primary function of the sarcoplasmic reticulum is to store and release calcium ions (Ca²⁺). These ions are essential for muscle contraction.

3. **Role of Calcium Ions**: When a muscle fiber is stimulated by a neurotransmitter called acetylcholine, it triggers the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm (the cytoplasm of muscle cells).

4. **Initiation of Muscle Contraction**: The influx of calcium ions into the sarcoplasm initiates the contraction process of the muscle fibers by interacting with the contractile proteins (actin and myosin).

5. **Evaluating the Options**:
- **A. Calcium**: Correct, as the sarcoplasmic reticulum stores calcium ions.
- **B. Sodium**: Incorrect, as sodium is not stored in the sarcoplasmic reticulum.
- **C. Chloride**: Incorrect, as chloride ions are not stored in the sarcoplasmic reticulum.
- **D. Potassium**: Incorrect, as potassium is also not stored in the sarcoplasmic reticulum.

6. **Conclusion**: The correct answer is **A. Calcium**, as the sarcoplasmic reticulum of muscle fibers is indeed the storehouse of calcium ions.

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