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Question #45802
The Question
A researcher applies a bioactive neurotoxin, which acts as a potent competitive inhibitor of nicotinic acetylcholine receptors, to a skeletal muscle preparation. Which of the following best describes the immediate state of the sarcomere's contractile machinery following motor neuron stimulation?
Options
- A.
Myosin heads remain in a high-energy state with ADP and inorganic phosphate bound, while actin active sites remain masked.
- B.
Myosin heads remain tightly bound to actin, forming a permanent state of rigor due to the absence of calcium ions.
- C.
Myosin heads remain in a low-energy state with unhydrolyzed ATP, as calcium is required to activate myosin ATPase.
- D.
The troponin-tropomyosin complex shifts to expose active sites, but the lack of sarcolemma depolarization prevents the power stroke.
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
Actomyosin_Complex|Curare-like_Toxins|Synaptic_Transmission
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students frequently confuse the specific roles of ATP and Ca2+ in the cross-bridge cycle.
A common misconception is that ATP hydrolysis occurs only after myosin binds to actin, or that Ca2+ is required to activate myosin ATPase.
The NCERT clearly illustrates that ATP hydrolysis 'cocks' the myosin head into a high-energy state prior to cross-bridge formation, where it waits for Ca2+ to unmask the actin binding sites.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Locomotion and Movement - Class 11 |
| Concept | Cross-bridge Cycling Energy |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |