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Question #46859
The Question
A researcher applies a neurotoxin to a skeletal muscle preparation that competitively blocks the nicotinic acetylcholine receptors at the motor end plate. Upon electrical stimulation of the motor neuron, despite the presence of abundant intracellular ATP, the muscle fails to contract. Which of the following best describes the structural state of the sarcomere and the underlying molecular mechanism in this condition?
Options
- A.
The H-zone is completely obliterated because the myosin heads are locked onto the actin filaments in a rigor state.
- B.
The distance between two consecutive Z-lines remains maximal because the troponin-tropomyosin complex continues to mask the myosin-binding sites on actin.
- C.
The I-band shortens significantly because calcium ions fail to be pumped back into the sarcoplasmic reticulum.
- D.
The A-band retains its length, but cross-bridge cycling occurs futilely without generating tension due to the uncoupling of ATP hydrolysis.
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
Skeletal Muscle Striation Pattern|Neurotransmitter Receptor Specificity|Acetylcholine|Actin-Myosin
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Distinguishing the specific roles of ATP and Calcium in the Sliding Filament Theory.
Students often confuse flaccid paralysis (failure of excitation/Ca2+ release) with rigor mortis (ATP depletion).
The trap lies in mentioning 'abundant ATP', which might lead students to incorrectly assume cross-bridge cycling (Option D) or rigor (Option A) occurs, missing that Calcium is the absolute prerequisite 'on-switch' for exposing actin's active sites.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Structural Organisation in Animals - Class 11 |
| Concept | Skeletal Muscle Striation Pattern |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |