Receptor pharmacology and dental drug interactions · Neuroanatomy
Autonomic Nervous System MCQ
Sympathetic vs parasympathetic anatomy, neurotransmitters, receptor subtypes (α/β, muscarinic), and dental-relevant drug interactions including epinephrine + β-blockers. 25 board-style MCQs plus 12 INBDE patient cases.
25 practice MCQsQuick-reference tableMnemonics + clinical pearlsFull distractor explanations
High-yield review
Concept summary and clinical relevance.
Quick-reference structure first, then detailed coverage. Mnemonics in amber, clinical pearls in blue.
The autonomic nervous system is high-yield for the INBDE because it directly governs how dental drugs and emergencies behave: epinephrine in local anesthetic, atropine for dry-field surgery, vasovagal syncope in the chair, β-blocker interactions, and xerostomia from anticholinergics. Get the neurotransmitter pairs and receptor subtypes locked in, and the clinical scenarios fall out of them.
Sympathetic vs parasympathetic: anatomy
| Sympathetic (fight or flight) | Parasympathetic (rest & digest) | |
|---|---|---|
| Origin | Thoracolumbar (T1–L2) | Craniosacral (CN III, VII, IX, X + S2–S4) |
| Preganglionic fiber | Short, myelinated | Long, myelinated |
| Preganglionic NT | ACh → nicotinic | ACh → nicotinic |
| Postganglionic fiber | Long | Short |
| Postganglionic NT | Norepinephrine (sweat glands = ACh) | ACh → muscarinic |
Receptor subtypes: what each does
| Receptor | Location / target | Effect |
|---|---|---|
| α1 | Vascular smooth muscle | Vasoconstriction (basis of epinephrine vasoconstriction) |
| α2 | Presynaptic neurons | Inhibits NE release (negative feedback) |
| β1 | Heart (“1 heart”) | ↑ Heart rate, ↑ contractility |
| β2 | Lungs, vascular smooth muscle (“2 lungs”) | Bronchodilation; vasodilation in skeletal muscle |
| M2 | Heart | ↓ Heart rate (parasympathetic vagal) |
| M3 | Glands, smooth muscle, eye | Salivation, GI motility, pupil constriction (miosis) |
| Nicotinic (NN) | All autonomic ganglia (SNS & PNS) | Fast excitatory transmission |
Sympathetic vs parasympathetic: effects you must know
| Organ | Sympathetic | Parasympathetic |
|---|---|---|
| Heart | ↑ HR, ↑ contractility (β1) | ↓ HR (M2) |
| Bronchi | Bronchodilation (β2) | Bronchoconstriction |
| Pupil | Mydriasis (α1) | Miosis (M3) |
| Salivary glands | Thick, viscous saliva | Watery, copious saliva |
| GI motility | Decreased | Increased |
| Vasculature | Vasoconstriction (α1) | Minimal direct effect |
Clinical pearl, Why epinephrine in local anesthetic, and the β-blocker trap
Epinephrine acts on α1 receptors at the injection site to vasoconstrict, prolonging anesthesia and reducing bleeding. In a patient on a non-selective β-blocker (e.g., propranolol), β2-mediated vasodilation is blocked: leaving α1 vasoconstriction unopposed. This can produce a hypertensive crisis and reflex bradycardia. Limit epinephrine dose in these patients and aspirate carefully.
Clinical pearl, Vasovagal syncope in the dental chair
The most common dental emergency is vasovagal syncope: a parasympathetic surge causing bradycardia, hypotension, and loss of consciousness, often triggered by anxiety or pain. Position the patient supine with legs elevated; recovery is usually rapid. Don't confuse with cardiac syncope or true seizure.
Clinical pearl, Anticholinergic side effects matter for caries risk
Many medications dental patients take (tricyclics, antihistamines, antimuscarinics for overactive bladder) block muscarinic receptors → xerostomia. Reduced salivary flow accelerates caries and periodontal disease. Recognizing this medication list during health-history review changes the prevention conversation.
Mnemonic, Receptor cardio-pulmonary mapping
“Beta-1, 1 heart. Beta-2, 2 lungs.” β1 receptors dominate the heart; β2 receptors dominate the lungs (and skeletal muscle vasculature).
Mnemonic, Saliva consistency
“PNS pools, SNS sticks.” Parasympathetic activation produces watery saliva that pools in the mouth; sympathetic activation produces thick, sticky saliva (the “anxious dry mouth” a nervous patient describes).
Sympathetic nervous system
- Origin: thoracolumbar cord (T1–L2).
- Preganglionic fibers are short and myelinated; release ACh onto nicotinic receptors at sympathetic chain ganglia.
- Postganglionic fibers are long; release norepinephrine onto α and β adrenergic receptors. Sweat glands are the exception (ACh onto muscarinic receptors).
- Adrenal medulla is a modified ganglion: preganglionic fibers release ACh, the chromaffin cells release epinephrine into the blood.
Parasympathetic nervous system
- Origin: craniosacral (CN III, VII, IX, X + S2–S4 spinal segments).
- Cranial outflow: CN VII → submandibular and sublingual glands; CN IX → parotid; CN X → thoracic and abdominal viscera.
- Preganglionic fibers are long and synapse close to the target organ; postganglionic fibers are short; both use ACh (nicotinic at the ganglion, muscarinic at the effector).
Dental-relevant drug interactions
- Local anesthetic + epinephrine: α1 vasoconstriction prolongs anesthesia and reduces bleeding.
- Atropine / scopolamine: muscarinic blockade → reduced salivation (helpful for dry-field surgery, but causes xerostomia long-term).
- Non-selective β-blockers + epinephrine: unopposed α1 → hypertensive crisis risk.
- α1-blockers (e.g., for BPH): orthostatic hypotension when patient stands from chair.
- β2 agonists (e.g., albuterol): allow asthmatic patients to use their inhaler before procedures.
Core Recall Check
25 board-style MCQs.
Active recall is the highest-yield study method. Pick an answer, check it, and read why every distractor is wrong.
0 of 25 answered · 0 correct
Keys: A-E or 1-5, Enter to check
- Question 1EasyWhich division of the nervous system is responsible for “fight or flight” responses?
- Question 2EasySympathetic fibers originate from which spinal cord region?
- Question 3EasyMost sympathetic postganglionic neurons release which neurotransmitter?
- Question 4ModerateParasympathetic fibers arise from which cranial nerves?
- Question 5EasyWhich neurotransmitter is released at all autonomic ganglia (sympathetic and parasympathetic)?
- Question 6EasySympathetic stimulation of the pupil produces:
- Question 7EasyParasympathetic activation of the salivary glands produces:
- Question 8ModerateWhich adrenergic receptor mediates vasoconstriction?
- Question 9ModerateWhich receptor subtype increases heart rate and contractility when activated?
- Question 10EasyWhich receptor subtype produces bronchodilation when stimulated?
- Question 11EasyParasympathetic activation of the eye produces:
- Question 12EasyThe sacral parasympathetic outflow arises from which spinal segments?
- Question 13ModerateWhich effector is sympathetic but uses acetylcholine on muscarinic receptors?
- Question 14ModerateThe adrenal medulla is best described as a:
- Question 15HardActivation of presynaptic α2 receptors has what effect?
- Question 16ModerateVagal (parasympathetic) slowing of the heart is mediated by which receptor?
- Question 17ModerateSalivary gland secretion and pupillary constriction are both mediated by which muscarinic receptor subtype?
- Question 18ModerateWhich receptor type transmits the signal across both sympathetic and parasympathetic ganglia?
- Question 19HardA patient takes the nonselective β-blocker propranolol. Why must epinephrine in local anesthetic be used cautiously?
- Question 20ModerateAn anxious patient faints in the dental chair with bradycardia and hypotension. The best immediate position is:
- Question 21ModerateA patient on a tricyclic antidepressant and an antihistamine reports a persistently dry mouth and has new cervical caries. The mechanism is:
- Question 22ModerateAtropine reduces salivation by acting as a(n):
- Question 23ModerateA patient on tamsulosin (an α1-blocker for BPH) is most at risk for which event when getting up from the dental chair?
- Question 24ModerateParasympathetic secretomotor fibers to the parotid gland travel with which cranial nerve?
- Question 25ModerateSympathetic preganglionic neuron cell bodies are located in which region of the spinal cord?
Clinical Reasoning Cases
INBDE patient cases.
12 ADA INBDE-format patient cases on autonomic ns. Each case is a shared patient box plus linked questions with full distractor explanations.
INBDE Patient Cases
Autonomic NS INBDE Patient Cases →
12 patient cases · 60 linked questions
Open cases →
Author
Dr. Isaac Sun, DDS
Founder, KYT Dental Services. These MCQs are reviewed by a practicing clinician and offered as an educational reference for dental students.
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