OSMT (Ontario Society of Medical Technologists) Practice Exam

What is the role of calcium ions in muscle contraction?

1. Trigger release of acetylcholine

2. Activate ATP production

3. Bind to troponin for muscle contraction

4. Initiate nerve impulses for muscle movement

The correct answer is: Bind to troponin for muscle contraction

Calcium ions play a critical role in muscle contraction by binding to the protein troponin, which is located on the thin filaments of muscle fibers. When a muscle receives a signal to contract, calcium ions are released from the sarcoplasmic reticulum into the muscle cell's cytoplasm. These calcium ions then bind to troponin, causing a conformational change in the troponin-tropomyosin complex. This change shifts tropomyosin away from the binding sites on actin filaments, allowing myosin heads to bind to actin and initiate contraction through the sliding filament mechanism. This mechanism is fundamental in muscle physiology, as the presence of calcium ions directly influences the interaction between actin and myosin, which are essential for muscle contraction. The other options describe processes that are not directly related to the primary action of calcium ions in muscle contraction. For instance, while acetylcholine is indeed crucial for initiating muscle contraction, it does so by transmitting a nerve impulse rather than being affected by calcium ions directly.