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Question #46921
The Question
A patient undergoes a total thyroidectomy, during which the parathyroid glands are accidentally removed. Within 48 hours, the patient develops severe, rapid muscle spasms (tetany). Which of the following best explains the primary physiological mechanism behind this condition?
Options
- A.
Decreased extracellular Ca2+ increases the permeability of neuronal membranes to Na+, lowering the threshold for spontaneous action potentials.
- B.
Depletion of sarcoplasmic Ca2+ prevents the binding of troponin to tropomyosin, leaving myosin-binding sites permanently exposed.
- C.
Reduced Ca2+ influx at the axon terminal prevents the exocytosis of acetylcholine, leading to spontaneous muscle fiber depolarization.
- D.
Absence of parathyroid hormone directly triggers the continuous release of Ca2+ from the sarcoplasmic reticulum into the sarcoplasm.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Comparative_Analysis
Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.
Concepts Behind This Question
Calcium Homeostasis|Tetany Logic|Neuromuscular Junction Signal
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students frequently confuse the roles of extracellular vs. intracellular calcium.
A common misconception is that 'low calcium' should logically lead to 'weak muscle contraction' because Ca2+ is needed to bind troponin.
However, the trap lies in the fact that extracellular hypocalcemia primarily affects the nervous system first, making motor neurons hyperexcitable (causing tetany) long before the muscle's internal sarcoplasmic reticulum stores of Ca2+ are depleted.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | The Living World - Class 11 |
| Concept | Botanical and Zoological Codes |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |