Hypocalcemia predisposes to laryngospasm by decreasing which electrical property of nerve membranes?

Hypocalcemia predisposes to laryngospasm by decreasing which electrical property of nerve membranes?

• A. Increasing threshold potential
• B. Decreasing threshold potential
• C. Increasing nerve conduction velocity
• D. Decreasing membrane excitability

Answer: (B)

Hypocalcemia raises nerve membrane excitability by lowering the threshold for depolarization. Calcium ions help stabilize the membrane and screen surface charges; when calcium is low, the membrane becomes more easily permeable to sodium, so a smaller stimulus is needed to reach the threshold and trigger an action potential. In the laryngeal muscles, this increased excitability makes laryngospasm more likely, especially during airway manipulation. That’s why decreasing the threshold potential is the best answer. If the threshold were increased, nerve firing would be harder, not easier; increasing conduction velocity or decreasing membrane excitability would not explain the increased tendency for spasm seen with hypocalcemia.

Hypocalcemia raises nerve membrane excitability by lowering the threshold for depolarization. Calcium ions help stabilize the membrane and screen surface charges; when calcium is low, the membrane becomes more easily permeable to sodium, so a smaller stimulus is needed to reach the threshold and trigger an action potential. In the laryngeal muscles, this increased excitability makes laryngospasm more likely, especially during airway manipulation.

That’s why decreasing the threshold potential is the best answer. If the threshold were increased, nerve firing would be harder, not easier; increasing conduction velocity or decreasing membrane excitability would not explain the increased tendency for spasm seen with hypocalcemia.