How do organophosphates exert their effect?

Organophosphates exert their effect primarily by stimulating the cholinergic nervous system. They inhibit an enzyme called acetylcholinesterase, which is responsible for breaking down acetylcholine in the synaptic cleft. When this enzyme is inhibited, acetylcholine accumulates, leading to prolonged stimulation of both muscarinic and nicotinic receptors in the body. This results in signs and symptoms associated with cholinergic toxicity, such as salivation, lacrimation, urination, diarrhea, gastrointestinal distress, and muscle twitching or respiratory failure.

The other choices do not accurately describe the mechanism of action of organophosphates. They do not destroy acetylcholine; instead, they increase its levels. They do not block the parasympathetic nervous system as that would reduce cholinergic activity rather than augment it. Similarly, they do not agonize the sympathetic nervous system; the primary effect of organophosphates is on the cholinergic pathways, leading to increased activity rather than sympathomimetic effects.