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Question #47384
The Question
A novel neurotoxin specifically inhibits temporal summation at the neuromuscular junctions of skeletal muscles. If a healthy individual with a structurally intact axial skeleton is exposed to this toxin, they rapidly develop respiratory failure. Which of the following statements most accurately describes the physiological mechanism behind this collapse?
Options
- A.
The toxin prevents the initial release of calcium ions from the sarcoplasmic reticulum, completely blocking the formation of cross-bridges in the respiratory muscles.
- B.
The motor units of the diaphragm and external intercostals fail to achieve the sustained contractions required to increase the volume of the thoracic chamber.
- C.
The toxin degrades the cartilaginous articulations of the 80-bone axial skeleton, drastically reducing the functional compliance of the respiratory cage.
- D.
The inhibition of summation causes hyper-excitability of the phrenic nerve, leading to an irreversible tetanic spasm of the respiratory muscles.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Summation Kinetics|Sarcomere Functional Boundaries|Axial Skeleton Count
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Distinguishing between structural integrity and functional neuromuscular capacity.
The trap lies in misunderstanding 'summation kinetics'.
Students often confuse the inability to sustain a contraction (failure of summation) with the inability to initiate a contraction at all (calcium block) or assume that respiratory failure must involve a structural breakdown of the rib cage or a tetanic spasm (like tetanus toxin).
This question tests the deep NCERT concept that normal physiological movements require sustained, summated motor unit recruitment.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Locomotion and Movement - Class 11 |
| Concept | Axial Skeleton Count |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |