Final answer:
Muscarinic receptors bind to acetylcholine and can cause depolarization or hyperpolarization depending on the subtype. Muscarinic and nicotinic receptors differ in their binding specificities, with nicotine binding to the nicotinic receptor and muscarine binding to the muscarinic receptor.
Step-by-step explanation:
The cholinergic system includes two classes of receptors: the nicotinic receptor and the muscarinic receptor. Both receptor types bind to acetylcholine (ACh) and cause changes in the target cell. The nicotinic receptor is a ligand-gated cation channel, while the muscarinic receptor is a G protein-coupled receptor.
Nicotine will bind to the nicotinic receptor, and muscarine will bind to the muscarinic receptor. However, there is no cross-reactivity between the two receptors. Muscarinic receptors can cause both depolarization or hyperpolarization depending on the subtype.
The molecules that define the muscarinic and nicotinic receptors are exogenous, meaning they are made outside the human body and used as tools for research in the laboratory.