Final answer:
Cholinergic agents mimic acetylcholine, a key neurotransmitter in the cholinergic system that binds to nicotinic and muscarinic receptors, important in muscle activation and autonomic nervous system functions.
Step-by-step explanation:
Cholinergic agents imitate the neurotransmitter called acetylcholine (ACh), which is a chemical messenger released by nerve cells to send signals to other cells. The cholinergic system includes not only acetylcholine itself but also the receptors it binds to and the enzyme acetylcholinesterase which breaks it down. There are two main types of acetylcholine receptors: nicotinic receptors and muscarinic receptors. Nicotinic receptors are found at the neuromuscular junction (NMJ), where acetylcholine is responsible for muscle excitement. Drugs that can act on these receptors and either mimic or block the effect of acetylcholine are crucial in medicine but must be used with care due to potential severe effects ranging from paralysis to convulsions.