From the Research
I'll provide 5 UWorld-style questions about the sympathetic and parasympathetic nervous systems with answers.
Question 1: A 50-year-old man presents with orthostatic hypotension due to autonomic failure. Which medication would be most appropriate for management?
The most appropriate medication for management would be midodrine, an alpha-adrenoceptor agonist. Midodrine has been shown to increase standing blood pressure and decrease orthostatic symptoms in patients with orthostatic hypotension due to autonomic failure 1. Other medications such as octreotide, indomethacin, or ergotamine may also be effective, but midodrine is a well-established treatment option.
Question 2: A 30-year-old woman experiences urinary retention after receiving atropine during surgery. Which neurotransmitter's effects are being blocked by this medication?
The neurotransmitter acetylcholine's effects are being blocked by atropine. Atropine is a competitive antagonist at muscarinic acetylcholine receptors, which are found throughout the parasympathetic nervous system. The parasympathetic nervous system normally promotes bladder contraction and internal urethral sphincter relaxation via muscarinic receptors. By blocking these receptors, atropine inhibits bladder emptying, resulting in urinary retention.
Question 3: A 60-year-old man with hypertension develops erectile dysfunction after starting propranolol. Which component of the erectile response is most likely affected by this medication?
The vasodilatory component of the erectile response is most likely affected by propranolol. Erection involves parasympathetic-mediated vasodilation of penile arteries, which increases blood flow to erectile tissue. While primarily a beta-blocker, propranolol can interfere with vasodilation through several mechanisms: it blocks beta-2 receptors that normally promote vasodilation, it may have alpha-1 agonist effects at high doses promoting vasoconstriction, and it reduces cardiac output which decreases overall perfusion pressure.
Question 4: A 25-year-old woman experiences severe hypotension during anaphylaxis. Which receptor agonist would be most appropriate for immediate management?
An alpha-1 adrenergic receptor agonist, specifically epinephrine, would be most appropriate for immediate management. During anaphylaxis, massive vasodilation occurs due to inflammatory mediator release, leading to distributive shock. Epinephrine acts on alpha-1 receptors to cause vasoconstriction, increasing peripheral vascular resistance and blood pressure. It simultaneously stimulates beta-1 receptors to increase heart rate and contractility, and beta-2 receptors to cause bronchodilation, addressing multiple aspects of anaphylaxis.
Question 5: A 70-year-old man with Parkinson's disease experiences dry mouth, constipation, and urinary retention after starting a new medication. Which neurotransmitter system is likely affected by this drug?
The cholinergic (parasympathetic) neurotransmitter system is likely affected by this drug. The patient is experiencing classic anticholinergic side effects, suggesting he was prescribed an anticholinergic medication such as trihexyphenidyl or benztropine. These drugs block muscarinic acetylcholine receptors to reduce tremor and rigidity in Parkinson's disease by restoring the balance between dopaminergic and cholinergic systems in the basal ganglia. However, they also block parasympathetic functions throughout the body, resulting in decreased salivation (dry mouth), reduced gastrointestinal motility (constipation), and inhibition of bladder contraction (urinary retention) 2.