Final answer:
Sympathomimetic drugs mimic the action of the sympathetic involuntary nervous system, while parasympathomimetic drugs mimic the action of the parasympathetic involuntary nervous system.
Step-by-step explanation:
In the autonomic nervous system, sympathetic and parasympathetic divisions have opposite effects on target organs. Drugs that mimic the action of sympathetic involuntary nervous system are called sympathomimetic drugs, which bind to adrenergic receptors and stimulate target organs just like sympathetic activity would. Examples of sympathomimetic drugs include phenylephrine.
On the other hand, drugs that mimic the action of parasympathetic involuntary nervous system are called parasympathomimetic drugs (muscarinic agonists). These drugs act like acetylcholine released by parasympathetic postganglionic fibers. Anticholinergic drugs, on the other hand, block muscarinic receptors and suppress parasympathetic interaction with the organ.