A marathon runner started experiencing muscle cramps towards the end of the race. This is thought to be due to electrolyte loss.

Which of the following is most critical for muscle contraction?

Question

A marathon runner started experiencing muscle cramps towards the end of the race.  This is thought to be due to electrolyte loss.

Which of the following is most critical for muscle contraction?

BlackTom AI · Accepted Answer

Consider the question: a marathon runner experiences cramps likely due to electrolyte loss, and we are asked what is most critical for muscle contraction.
Option 1: Chloride. While chloride is an electrolyte involved in maintaining electrical neutrality and fluid balance, it is not the primary trigger or regulator of the molecular events that drive muscle contraction. Deficiencies can affect overall excitability, but it is not the key charged ion controlling contraction strength.
Option 2: Iron. Iron is essential for oxygen transport in hemoglobin and for many enzymes, but it does not directly initiate or regulate the contraction mechanism inside muscle fibers. Its deficiency impacts endurance indirectly, not the core contraction trigger.
Option 3: Vitamin D. Vitamin D plays a role in bone health and mineral metabolism, and severe deficiency can affect muscle function indirectly, yet it is not the direct mediator of the contraction cycle within muscle cells. It does not acutely control the interaction of contractile proteins.
Option 4: Calcium. Calcium is central to the contraction process. In skeletal muscle, an action potential triggers calcium release from the sarcoplasmic reticulum. The rise in intracellular calcium binds to troponin C, causing a conformational change that moves tropomyosin away from actin’s myosin-binding sites, allowing cross-bridge cycling and contraction. Additionally, calcium contributes to excitation–contraction coupling and is tightly linked to electrolyte balance.
Option 5: Cholesterol. Cholesterol is a structural component of membranes and a precursor for steroid hormones, but it has no direct, immediate role in triggering the molecular steps of muscle contraction. It does not regulate the interaction between actin and myosin in response to calcium signaling.
In summary, while several electrolytes and nutrients influence overall muscle function and performance, the specific ion that acts as the pivotal trigger for the contraction machinery is calcium, making it the most critical factor among the options provided.

BMI5102 BMI5102 Final Assessment Section - MCQs & SAQs

A marathon runner started experiencing muscle cramps towards the end of the race. This is thought to be due to electrolyte loss. Which of the following is most critical for muscle contraction?

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