Final answer:
Muscarinic receptors are G protein-coupled acetylcholine receptors found in the digestive tract and other areas, involved in autonomic nervous system regulation and can be targeted by drugs to modify parasympathetic nervous system activities.
Step-by-step explanation:
Muscarinic receptors are a type of acetylcholine receptor protein that are characterized by their ability to bind to the drug muscarine as well as the neurotransmitter acetylcholine (ACh). They are G protein-coupled receptors that can induce various effects such as depolarization or hyperpolarization, depending on the subtype of the receptor.
There are several types of muscarinic receptors, known as M1-M5. Moreover, muscarinic receptors are associated with the parasympathetic nervous system. Substances such as muscarine can activate these receptors, and muscarinic agonists or antagonists can have therapeutic applications, affecting the parasympathomimetic or anticholinergic drug actions, respectively.