Which mechanism best describes a nerve agent's action on the nervous system?

• A. Blocks acetylcholine release
• B. Inhibits AChE
• C. Stimulates dopamine receptors
• D. Destroys myelin

Answer: (B)

Nerve agents cause a cholinergic crisis by shutting down the enzyme that normally breaks down acetylcholine. They phosphorylate the active site of acetylcholinesterase, so acetylcholine cannot be degraded. This leads to accumulation of acetylcholine at all cholinergic synapses, overstimulating both muscarinic and nicotinic receptors. The result is widespread effects such as excessive secretions, pinpoint pupils, bronchorrhea and bronchospasm, bradycardia, muscle fasciculations, and possible respiratory failure from neuromuscular paralysis.

The other mechanisms don’t fit nerve agents: blocking acetylcholine release would reduce signaling (as with botulinum toxin), stimulating dopamine receptors targets dopaminergic pathways rather than cholinergic ones, and destroying myelin disrupts nerve conduction without causing acetylcholine accumulation.