Which ions are involved in muscle contraction ?

Options

A. `Ca^(++),Mg^(++)`
B. `Ca^(++),Na^(+)`
C. `Na^(+),K^(+)`
D. `Mg^(++),K^(+)`

Answer

**Step-by-Step Solution:**

1. **Understanding Muscle Contraction**: Muscle contraction involves the interaction between two types of protein filaments: actin (thin filaments) and myosin (thick filaments). For contraction to occur, the active sites on actin must be exposed.

2. **Role of Calcium Ions**: Calcium ions (Ca²⁺) play a crucial role in muscle contraction. When a muscle is stimulated, calcium ions are released from the sarcoplasmic reticulum into the muscle cell. This increase in calcium concentration leads to the binding of calcium to troponin, a protein that is part of the actin filament.

3. **Troponin and Tropomyosin Interaction**: The binding of calcium to troponin causes a conformational change that moves tropomyosin away from the active sites on actin. This exposure allows myosin heads to bind to actin, initiating the contraction process.

4. **Role of Magnesium Ions**: Magnesium ions (Mg²⁺) also play a significant role in muscle function. While calcium is involved in the contraction phase, magnesium acts as a natural blocker of calcium. It helps regulate the muscle's relaxation phase by preventing excessive contraction and allowing the muscle to return to its resting state.

5. **Conclusion**: Both calcium and magnesium ions are essential for proper muscle contraction and relaxation. Calcium facilitates contraction, while magnesium helps regulate and promote relaxation.

**Final Answer**: The ions involved in muscle contraction are calcium (Ca²⁺) and magnesium (Mg²⁺).

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