Ion connected with forming crossbridges is

Options

A. `Na^(+)`
B. `Ca^(2+)`
C. `K^(+)`
D. None of the above

Answer

**Step-by-Step Solution:**

1. **Understanding Crossbridges**: Crossbridges are formed during muscle contraction when myosin heads interact with actin filaments. The myosin head attaches to the actin filament to facilitate muscle movement.

2. **Role of Calcium Ions**: The formation of crossbridges is initiated by the release of calcium ions (Ca²⁺) from the sarcoplasmic reticulum, which is a specialized endoplasmic reticulum in muscle cells.

3. **Mechanism of Action**: When a nerve impulse reaches the muscle, it triggers the sarcoplasmic reticulum to release calcium ions into the cytoplasm of the muscle cell.

4. **Effect on Tropomyosin**: The released calcium ions bind to a protein called troponin, which causes a conformational change in another protein called tropomyosin. This change exposes the binding sites on actin filaments.

5. **Binding of Myosin to Actin**: With the binding sites on actin exposed, the myosin heads (crossbridges) can now attach to the actin filaments, leading to muscle contraction.

6. **Conclusion**: Therefore, the ion that is connected with forming crossbridges in muscle contraction is calcium ion (Ca²⁺).

**Final Answer**: Calcium ion (Ca²⁺).

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