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Question #47427

Difficulty: 8/10 | 🟢 Free

The Question

During synaptic transmission at the neuromuscular junction, the arrival of an action potential stimulates the influx of $Ca^{2+}$ ions, which triggers synaptic vesicles to fuse with the pre-synaptic membrane. Botulinum toxin is known to cause severe flaccid paralysis. Electrophysiological tests on a poisoned synapse reveal normal action potential propagation and normal $Ca^{2+}$ influx, yet no acetylcholine is released. Which of the following best explains the precise mechanism of this toxin?

Options

A.
It blocks voltage-gated $Ca^{2+}$ channels, preventing the formation of the calcium-protein complex required for vesicle movement.
B.
It acts as an endopeptidase that cleaves the SNARE protein complex, physically preventing the docking and exocytosis of synaptic vesicles.
C.
It competitively binds to nicotinic acetylcholine receptors on the motor end plate, preventing post-synaptic depolarization.
D.
It inhibits the enzyme acetylcholinesterase in the synaptic cleft, leading to rapid depletion of pre-synaptic neurotransmitter stores.

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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

Synaptobrevin|Syntaxin|SNAP-25|Neurotransmitter_Release

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Students often assume that calcium influx alone is sufficient for neurotransmitter release, overlooking the essential structural protein machinery (SNARE complex) required for membrane fusion.

The trap also tests the ability to differentiate between pre-synaptic release inhibitors (Botulinum), post-synaptic blockers (Curare), and synaptic cleft enzyme inhibitors (Organophosphates).

Quick Facts About This Question

Question Information

Subject	Biology
Chapter	Neural Control and Coordination - Class 11
Concept	Synaptic Vesicle Exocytosis Trigger
Difficulty	8
Cognitive Load	5
Target Solve Time	120 sec
Access	Free