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Question #45782
The Question
Myasthenia gravis is an autoimmune disorder affecting the neuromuscular junction. Suppose a novel autoimmune myopathy generates autoantibodies that specifically destroy the Z-lines within the myofibrils of skeletal muscles. Which of the following statements correctly describes the physiological state of the muscle fiber during an attempted voluntary contraction in this novel myopathy?
Options
- A.
The sarcolemma remains polarized because autoantibodies block the binding of acetylcholine at the motor end-plate.
- B.
Calcium ions fail to release from the sarcoplasmic reticulum, completely halting the unmasking of myosin-binding sites.
- C.
Cross-bridge cycling occurs and ATP is consumed, but the muscle fiber fails to generate effective macroscopic tension.
- D.
Myosin heads remain permanently bound to actin, creating a state of rigor due to the rapid depletion of sarcoplasmic ATP.
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
Myosin|Actin|Autoimmunity_Principles|MALT
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often confuse the electrical/signaling failure of muscle contraction (like in Myasthenia Gravis) with mechanical/structural failure.
The trap is assuming that if a muscle cannot contract, it must be due to a lack of ATP, Calcium, or Action Potentials.
By targeting the Z-line, the question tests the understanding that the Z-line is the mechanical anchor essential for tension transmission, and its absence decouples ATP-dependent cross-bridge cycling from actual muscle shortening.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Locomotion and Movement - Class 11 |
| Concept | Myofilament Protein Composition |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |