Which mechanism best describes atropine's pharmacologic effect?

• A. Stimulation of muscarinic receptors
• B. Activation of beta-adrenergic receptors
• C. Blockade of muscarinic receptors
• D. Blockade of nicotinic receptors

Answer: (C)

Atropine works by blocking muscarinic acetylcholine receptors in the parasympathetic nervous system. By occupying these receptors, it prevents acetylcholine from producing parasympathetic effects, which shifts the body toward sympathetic-like responses. This results in increased heart rate, reduced secretions (such as saliva and airway secretions), bronchodilation, and pupil dilation. Clinically, this makes atropine useful for treating bradycardia from vagal overactivity and for counteracting muscarinic effects in certain poisonings. It does not activate muscarinic receptors, block nicotinic receptors, or block beta-adrenergic receptors, which is why those mechanisms are not how atropine works.