Which mineral deficiency or endocrine disruption causes 'tetany', characterized by sustained, painful spasms of skeletal muscles?

Answer and explanation

Correct answer: C. Hypocalcemia (low extracellular calcium concentration), often caused by hypoparathyroidism

  1. Step 1: Extracellular calcium () normally stabilizes voltage-gated sodium channels by binding to the outer cell membrane.
  2. Step 2: When plasma calcium drops below normal (hypocalcemia, often due to deficiency of Parathyroid Hormone), the threshold for sodium channel activation decreases sharply.
  3. Step 3: This makes motor neurons and muscle membranes hyper-excitable, firing spontaneous bursts of action potentials that lead to uncontrollable, painful sustained muscle twitches and spasms known as tetany.
Answer
Hypocalcemia (low extracellular calcium concentration), often caused by hypoparathyroidism
Why not the others: 'Hyperkalemia...' causes cardiac conduction disturbances and flaccid muscle weakness rather than classic tetany; 'Hypercalcemia...' decreases neuronal excitability causing muscle weakness, lethargy, and kidney stones; 'Hypermagnesemia...' causes deep tendon reflex depression and respiratory arrest.

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