What receptor sites does atropine block in order to increase heart rate?

Atropine primarily blocks muscarinic receptors, which are a type of acetylcholine receptor found in various tissues, including the heart. By antagonizing these receptors, atropine inhibits the effects of the parasympathetic nervous system, which typically slows down the heart rate through the action of acetylcholine. With the blockade of muscarinic receptors, there is less parasympathetic influence on the heart, allowing the heart rate to increase.

This mechanism is particularly significant in clinical settings, such as during bradycardia (abnormally slow heart rate), where atropine is used to counteract the slowing effect of the vagus nerve on heart function, thus raising the heart rate to a more normal range. Understanding the specific target of atropine as muscarinic receptors is crucial for comprehending its pharmacological effects on cardiac function.