Muscarinic receptors are a type of acetylcholine receptor found in various tissues throughout the body. They play a crucial role in the parasympathetic nervous system, which is responsible for rest-and-digest functions. These receptors are involved in regulating heart rate, smooth muscle contraction, and glandular secretions. There are five subtypes of muscarinic receptors, labeled M1 to M5, each with distinct functions and locations. For example, M1 receptors are primarily found in the brain and gastric glands, while M2 receptors are located in the heart. Understanding these receptors is important for developing drugs that target specific physiological processes.