What is the main action of atropine in treating bradycardia?

Atropine is an anticholinergic medication primarily used to treat bradycardia by blocking the action of the parasympathetic nervous system. In a healthy individual, the vagus nerve, which is part of the parasympathetic nervous system, releases acetylcholine that slows down the heart rate. By administering atropine, the drug competitively inhibits the muscarinic receptors that respond to acetylcholine. This inhibition leads to an increase in heart rate as the sympathetic influence on the heart becomes more prominent relative to the parasympathetic activity. Therefore, the main action of atropine in treating bradycardia is its ability to block parasympathetic signals, allowing the heart rate to increase and thus counteracting the effects of bradycardia.