Dantrolene treats malignant hyperthermia by which mechanism?

• A. Blocks acetylcholine receptors at the neuromuscular junction
• B. Inhibits calcium release from the sarcoplasmic reticulum
• C. Enhances calcium uptake into mitochondria
• D. Inhibits glycolysis in muscle cells

Answer: (B)

The important idea is that malignant hyperthermia causes a dangerous surge of calcium release inside skeletal muscle cells, driving unrelenting muscle contraction and rapid metabolism. Dantrolene directly counters this by blocking the calcium release channel on the sarcoplasmic reticulum (the ryanodine receptor). With the channel inhibited, less calcium enters the cytoplasm, so the muscle fibers don’t stay maximally contracted and the excessive metabolic activity, heat production, and acidosis begin to subside. This targeted action on the calcium source is why dantrolene is effective.

Other mechanisms don’t fit the problem: blocking acetylcholine receptors at the neuromuscular junction would dampen signaling to the muscle rather than stop the internal calcium surge; enhancing calcium uptake into mitochondria or inhibiting glycolysis doesn’t specifically address the calcium-driven hypermetabolic state seen in malignant hyperthermia.