Final answer:
Nicotinic receptors and muscarinic receptors are two classes of receptors in the cholinergic system. They bind to acetylcholine (ACh) and cause changes in the target cell. Nicotinic receptors are ligand-gated cation channels, while muscarinic receptors are G protein-coupled receptors.
Step-by-step explanation:
The cholinergic system includes two classes of receptor: the nicotinic receptor and the muscarinic receptor. Both receptor types bind to ACh and cause changes in the target cell. The nicotinic receptor is a ligand-gated cation channel and the muscarinic receptor is a G protein-coupled receptor. The receptors are named for, and differentiated by, other molecules that bind to them. Whereas nicotine will bind to the nicotinic receptor, and muscarine will bind to the muscarinic receptor, there is no cross-reactivity between the receptors. This is similar to locks and keys. The molecules that define these receptors are not crucial; they are simply tools for researchers to use in the laboratory.