Basic and Clinical Sciences (BCSE) Practice Exam

What is a characteristic of hypocalcaemia regarding muscle function?

1. Decreased neuromuscular excitability

2. Increased cardiac contractility

3. Muscle spasms

4. Tetany

The correct answer is: Tetany

Hypocalcaemia, or low levels of calcium in the blood, significantly affects muscle function due to the vital role calcium plays in neuromuscular transmission and muscle contraction. One of the hallmark characteristics of hypocalcaemia is tetany, which is a condition marked by intermittent muscle spasms, cramps, or increased muscle tone. This phenomenon occurs because calcium is critical for the normal functioning of the nerves and muscles; when calcium levels drop, the threshold for nerve excitability decreases, leading to spontaneous muscle contractions. Tetany in hypocalcaemia is often related to heightened excitability of the motor neurons due to the lowered plasma calcium levels, which can disturb the balance of ions necessary to maintain proper membrane potential and function. This increased excitability causes involuntary contractions and prolonged muscle tension rather than relaxation, resulting in muscle spasms that are characteristic of tetany. Other conditions related to calcium levels may affect muscle function, but the presence of tetany clearly indicates a direct correlation with the low calcium state in hypocalcaemia. Understanding the mechanism behind tetany helps clarify why it is a prominent sign associated with this condition.