Final answer:
The cholinergic system includes nicotinic and muscarinic receptors, activated by nicotine and muscarine respectively, with no cross-reactivity between them. Nicotinic receptors are ligand-gated ion channels, while muscarinic receptors are G protein-coupled receptors.
Step-by-step explanation:
The cholinergic system consists of two main receptor types: nicotinic receptors and muscarinic receptors. Nicotinic receptors, which are found at the neuromuscular junction (NMJ) as well as in other synapses, are ligand-gated ion channels that are activated by both acetylcholine (ACh) and nicotine. On the other hand, muscarinic receptors, which are G protein-coupled receptors, are activated by ACh and muscarine, a toxin found in certain mushrooms. However, there is no cross-reactivity between these receptors; nicotine does not activate muscarinic receptors, and muscarine does not activate nicotinic receptors. This specificity is vital for the proper function of the autonomic nervous system, where all ganglionic neurons are activated by ACh binding to nicotinic receptors, resulting in depolarization and subsequent transmission of nerve impulses.