Final answer:
Mydriasis is the dilation of the pupil that can be induced by substances like norepinephrine or phenylephrine. Pilocarpine is a muscarinic agonist used to reverse mydriasis and treat glaucoma. Atropine and scopolamine also dilate the pupil but can be toxic.
Step-by-step explanation:
Mydriasis refers to the dilation of the pupil, which occurs when the sympathetic nervous system releases norepinephrine that binds to adrenergic receptors in the radial fibers of the iris's smooth muscle. A medication such as phenylephrine can mimic this effect and is used during eye examinations to dilate the pupils. Conversely, pilocarpine is a muscarinic agonist that can reverse mydriasis by constricting the pupil and is often used after eye examinations or to treat glaucoma by reducing intraocular pressure.
Medications like atropine and scopolamine, derived from the Atropa genus, block the muscarinic receptors causing pupil dilation. However, due to the toxicity and side effects of these substances, pilocarpine serves as an antidote for their poisoning. Understanding these pharmacological effects is crucial in fields such as ophthalmology, where they are frequently applied.