The cross bridging process in muscle contraction requires potassium.
True
False
The correct answer and explanation is :
False
The cross-bridging process in muscle contraction primarily requires calcium (Ca²⁺) and adenosine triphosphate (ATP), not potassium (K⁺).
Explanation:
Muscle contraction occurs through the sliding filament theory, where actin and myosin filaments interact via cross-bridges. This process follows these key steps:
- Resting State: In a relaxed muscle, tropomyosin blocks the myosin-binding sites on actin, preventing cross-bridge formation.
- Calcium Release: When a nerve impulse reaches the muscle, the sarcoplasmic reticulum releases calcium ions (Ca²⁺) into the sarcoplasm.
- Binding of Calcium to Troponin: Calcium binds to the protein troponin, causing a conformational change that moves tropomyosin away from the myosin-binding sites on actin.
- Cross-Bridge Formation: Myosin heads, which are energized by ATP hydrolysis, attach to the exposed binding sites on actin, forming cross-bridges.
- Power Stroke: Myosin heads pivot, pulling the actin filaments toward the center of the sarcomere, leading to muscle contraction.
- ATP Binding and Cross-Bridge Detachment: A new ATP molecule binds to the myosin head, causing it to detach from actin. ATP is then hydrolyzed to reset the myosin head for the next cycle.
- Calcium Reuptake: When the nerve impulse stops, Ca²⁺ is pumped back into the sarcoplasmic reticulum, allowing tropomyosin to re-block actin’s binding sites, leading to muscle relaxation.
Role of Potassium (K⁺):
Potassium is essential for maintaining the resting membrane potential and repolarizing the muscle cell after contraction, but it does not directly participate in the cross-bridging process.
Thus, the correct answer is False—potassium is not required for cross-bridge formation.