Cholinergic receptors – Muscarinic MCQs With Answer

Cholinergic receptors – Muscarinic MCQs With Answer

Understanding cholinergic muscarinic receptors is essential for B. Pharm students preparing for pharmacology exams and clinical practice. This concise, keyword-rich introduction covers muscarinic receptor subtypes (M1–M5), G-protein coupling (M1/M3/M5: Gq; M2/M4: Gi), physiological roles in heart, smooth muscle, glands, and CNS, and key agonists/antagonists like bethanechol, pilocarpine, atropine, ipratropium and tiotropium. Emphasis is on receptor signaling, therapeutic uses, adverse effects, and structure–activity relationships relevant to drug design. Clear, exam-oriented MCQs below will deepen your conceptual and clinical knowledge. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which muscarinic receptor subtype is primarily responsible for slowing heart rate at the sinoatrial node?

• M1
• M2
• M3
• M4

Correct Answer: M2

Q2. Activation of M3 muscarinic receptors on endothelial cells leads to vasodilation mainly through which mechanism?

• Direct smooth muscle hyperpolarization
• Nitric oxide release from endothelium
• Inhibition of phospholipase C
• Increased cAMP in vascular smooth muscle

Correct Answer: Nitric oxide release from endothelium

Q3. Which G protein is coupled to M1, M3, and M5 muscarinic receptors?

• Gs
• Gi/o
• Gq/11
• G12/13

Correct Answer: Gq/11

Q4. Which pharmacologic agent is a muscarinic agonist commonly used to treat urinary retention by stimulating bladder contractions?

• Bethanechol
Atropine
• Glycopyrrolate
• Tropicamide

Correct Answer: Bethanechol

Q5. Pilocarpine, a muscarinic agonist, is therapeutically used primarily for which condition?

• Bradycardia
• Glaucoma
• Asthma
• Parkinsonism

Correct Answer: Glaucoma

Q6. Which muscarinic receptor subtype predominates in lacrimal and salivary glands to stimulate secretion?

• M2
• M3
• M4
• M5

Correct Answer: M3

Q7. Methacholine is used clinically as a diagnostic agent for bronchial hyperreactivity because it is a:

• Muscarinic antagonist
• Muscarinic agonist
• Nicotinic agonist
• Acetylcholinesterase inhibitor

Correct Answer: Muscarinic agonist

Q8. Which muscarinic antagonist is preferred for preoperative reduction of airway secretions and does not cross the blood–brain barrier appreciably?

• Atropine
• Scopolamine
• Glycopyrrolate
• Pilocarpine

Correct Answer: Glycopyrrolate

Q9. The intracellular signaling cascade following M1 receptor activation primarily involves activation of which enzymes or second messengers?

• Adenylyl cyclase and cAMP
• Guanylyl cyclase and cGMP
• Phospholipase C, IP3 and DAG
• Tyrosine kinase and STATs

Correct Answer: Phospholipase C, IP3 and DAG

Q10. Atropine’s effect on the eye includes which of the following?

• Miosis and increased accommodation
• Mydriasis and cycloplegia
• Increased lacrimation and pupillary constriction
• Reduction of intraocular pressure

Correct Answer: Mydriasis and cycloplegia

Q11. Which muscarinic receptor subtype is most abundant in the central nervous system and associated with cognitive function?

• M1
• M2
• M3
• M5

Correct Answer: M1

Q12. Muscarinic receptor antagonists used in COPD, such as tiotropium, primarily target which receptor to reduce bronchoconstriction?

• M1
• M2
• M3
• M4

Correct Answer: M3

Q13. Which muscarinic receptor subtype couples to Gi proteins to inhibit adenylyl cyclase, thereby reducing cAMP?

• M1 and M3
• M2 and M4
• M3 and M5
• M1 and M5

Correct Answer: M2 and M4

Q14. Which of the following is a quaternary ammonium antimuscarinic that does not readily cross the blood–brain barrier?

• Scopolamine
• Atropine
• Glycopyrrolate
• Pilocarpine

Correct Answer: Glycopyrrolate

Q15. Muscarinic receptor-mediated opening of GIRK (G protein–activated inwardly rectifying K+) channels is most associated with which receptor subtype in the heart?

• M1
• M2
• M3
• M5

Correct Answer: M2

Q16. Which muscarinic agonist is resistant to acetylcholinesterase degradation due to a beta-methyl group and is useful for bladder stimulation?

• Acetylcholine
• Methacholine
• Bethanechol
• Pilocarpine

Correct Answer: Bethanechol

Q17. Which adverse effect is characteristic of excess muscarinic stimulation?

• Tachycardia and dry mouth
• Mydriasis and constipation
• Bradycardia and increased sweating
• Urinary retention and hyperthermia

Correct Answer: Bradycardia and increased sweating

Q18. Which drug is an antimuscarinic used to treat motion sickness and has central nervous system effects such as sedation?

• Glycopyrrolate
• Scopolamine
• Tropicamide
• Bethanechol

Correct Answer: Scopolamine

Q19. The muscarinic receptor subtype implicated in modulation of dopaminergic pathways and potentially involved in schizophrenia is:

• M1
• M2
• M4
• M5

Correct Answer: M4

Q20. Which ocular muscarinic agonist causes contraction of the ciliary muscle to open the trabecular meshwork and facilitate aqueous outflow?

• Atropine
• Pilocarpine
• Tropicamide
• Edrophonium

Correct Answer: Pilocarpine

Q21. Which muscarinic antagonist is commonly used to produce short-acting mydriasis for retinal examination?

• Atropine (long-acting)
• Tropicamide (short-acting)
• Scopolamine (patch for motion sickness)
• Glycopyrrolate (preanesthetic)

Correct Answer: Tropicamide (short-acting)

Q22. In organophosphate poisoning, muscarinic effects such as bronchorrhea and bronchospasm are treated with which drug?

• Neostigmine
• Atropine
• Physostigmine
• Pilocarpine

Correct Answer: Atropine

Q23. Which property differentiates tertiary amine muscarinic antagonists from quaternary ammonium antagonists?

• Tertiary amines do not bind muscarinic receptors
• Tertiary amines cross the blood–brain barrier more readily
• Quaternary ammoniums have higher CNS penetration
• Quaternary ammoniums are more lipid soluble

Correct Answer: Tertiary amines cross the blood–brain barrier more readily

Q24. Which muscarinic receptor subtype in the gastrointestinal tract primarily mediates increased motility and secretions?

• M2
• M3
• M4
• M5

Correct Answer: M3

Q25. Which of the following is an indirect-acting cholinergic agent used to increase ACh availability by inhibiting acetylcholinesterase and is used in glaucoma?

• Neostigmine
• Physostigmine
• Edrophonium
• Physostigmine or echothiophate (organophosphate)

Correct Answer: Physostigmine or echothiophate (organophosphate)

Q26. Which muscarinic receptor subtype is mainly implicated in regulation of sweat glands (sympathetic cholinergic innervation)?

• M1
• M2
• M3
• M4

Correct Answer: M3

Q27. Tachyphylaxis or rapid desensitization of muscarinic receptors is most likely due to which cellular process?

• Increased G-protein expression
• Receptor phosphorylation and internalization
• Enhanced receptor synthesis
• Upregulation of adenylate cyclase

Correct Answer: Receptor phosphorylation and internalization

Q28. Which clinical test uses a muscarinic agonist to provoke bronchoconstriction and diagnose asthma?

• Spirometry after methacholine challenge
• Edrophonium test
• Tensilon test
• Atropine challenge test

Correct Answer: Spirometry after methacholine challenge

Q29. Which muscarinic antagonist is used chronically by inhalation in COPD and has slow dissociation from M3 receptors, conferring long duration?

• Ipratropium
• Tiotropium
• Atropine
• Scopolamine

Correct Answer: Tiotropium

Q30. Blockade of M2 receptors in the heart by an antagonist will most likely cause which immediate effect?

• Bradycardia
• Increased AV nodal conduction and tachycardia
• Vasodilation via nitric oxide
• Increased cardiac K+ conductance

Correct Answer: Increased AV nodal conduction and tachycardia

Q31. Which muscarinic receptor subtype contributes to dopamine release modulation in midbrain and is a target in addiction research?

• M1
• M2
• M4
• M5

Correct Answer: M5

Q32. Which statement about pilocarpine is correct?

• It is a quaternary amine that does not cross the BBB
• It is used topically for glaucoma and can cause sweating
• It is an acetylcholinesterase inhibitor
• It selectively antagonizes M2 receptors

Correct Answer: It is used topically for glaucoma and can cause sweating

Q33. Which of the following muscarinic antagonists is most likely to cause central anticholinergic syndrome (confusion, agitation) at high doses?

• Glycopyrrolate
• Quaternary ammonium atropine analogues
• Scopolamine or atropine (tertiary amines)
• Ipratropium (inhaled)

Correct Answer: Scopolamine or atropine (tertiary amines)

Q34. A drug that nonselectively blocks muscarinic receptors would be expected to cause which combination of effects?

• Miosis, increased secretions, bronchospasm
• Mydriasis, dry mouth, urinary retention
• Bradycardia, increased lacrimation, diarrhea
• Increased GI motility, sweating, salivation

Correct Answer: Mydriasis, dry mouth, urinary retention

Q35. Which muscarinic receptor subtype is most directly involved in contraction of the urinary bladder detrusor muscle?

• M1
• M2 and M3 with M3 mediating contraction
• M4
• M5

Correct Answer: M2 and M3 with M3 mediating contraction

Q36. Edrophonium is used diagnostically in myasthenia gravis; its mechanism involves which action relevant to cholinergic transmission?

• Direct muscarinic receptor agonism
• Reversible inhibition of acetylcholinesterase
• Irreversible inhibition of AChE (organophosphate-like)
• Blockade of presynaptic choline uptake

Correct Answer: Reversible inhibition of acetylcholinesterase

Q37. Which feature distinguishes muscarinic receptor agonists like bethanechol from acetylcholine in therapeutic use?

• Greater susceptibility to AChE breakdown
• Longer duration of action and selectivity for muscarinic receptors
• Higher affinity for nicotinic receptors
• Exclusive CNS activity

Correct Answer: Longer duration of action and selectivity for muscarinic receptors

Q38. Which sign is part of muscarinic excess in organophosphate poisoning and results from bronchial gland stimulation?

• Dry skin
• Bronchorrhea (excessive bronchial secretions)
• Tachycardia
• Hyperthermia due to reduced sweating

Correct Answer: Bronchorrhea (excessive bronchial secretions)

Q39. The muscarinic receptor antagonist used as an antidote for central anticholinergic toxicity due to a tertiary amine overdose is:

• Neostigmine
• Glycopyrrolate
• Physostigmine
• Pilocarpine

Correct Answer: Physostigmine

Q40. Which structural feature of a muscarinic agonist increases resistance to acetylcholinesterase hydrolysis?

• Presence of an ester susceptible to AChE
• Beta-methyl substitution on the ammonium-bearing carbon
• Lack of an ammonium group
• Large bulky aromatic ring far from the charged center

Correct Answer: Beta-methyl substitution on the ammonium-bearing carbon

Q41. Which muscarinic receptor subtype plays a role in gastric acid secretion by parietal cells?

• M1
• M2
• M3
• M4

Correct Answer: M1

Q42. A patient given a high dose of a muscarinic antagonist develops dry mouth, blurred vision, tachycardia, and urinary retention. Which drug class was most likely administered?

• Beta blockers
• Muscarinic antagonists (anticholinergics)
• Cholinesterase inhibitors
• Alpha-2 agonists

Correct Answer: Muscarinic antagonists (anticholinergics)

Q43. Which statement about muscarinic receptor selectivity is true?

• Most clinically used muscarinic antagonists are highly subtype-selective (M1–M5)
• Most classical muscarinic drugs are nonselective among receptor subtypes
• M2-selective agonists are common in clinical practice
• M5-selective antagonists are widely used for COPD

Correct Answer: Most classical muscarinic drugs are nonselective among receptor subtypes

Q44. Which therapeutic use of muscarinic antagonists exploits blockade of M3 receptors in the bladder to reduce detrusor overactivity?

• Treatment of acute urinary retention
• Management of overactive bladder (urge incontinence)
• Treatment of glaucoma
• Spirometry for asthma diagnosis

Correct Answer: Management of overactive bladder (urge incontinence)

Q45. Which of the following best explains why quaternary ammonium antimuscarinics like ipratropium have fewer CNS side effects?

• They are more lipid soluble and rapidly cross the BBB
• Their positive charge limits penetration of the blood–brain barrier
• They are extremely potent at central muscarinic receptors only
• They are rapidly metabolized into inactive CNS-penetrant metabolites

Correct Answer: Their positive charge limits penetration of the blood–brain barrier

Q46. Which pathological condition is best treated by topical pilocarpine to increase outflow of aqueous humor?

• Acute closed-angle glaucoma (emergency management in some settings)
• Chronic dry eye
• Uveitis requiring pupil dilation
• Diabetic retinopathy

Correct Answer: Acute closed-angle glaucoma (emergency management in some settings)

Q47. Which muscarinic receptor subtype is predominantly expressed on presynaptic terminals and modulates neurotransmitter release via Gi signaling?

• M3
• M2
• M5
• M1

Correct Answer: M2

Q48. Which clinical action is chiefly mediated by muscarinic receptor activation in the eye leading to accommodation for near vision?

• Relaxation of ciliary muscle
• Contraction of ciliary muscle and lens rounding
• Dilation of pupil by radial muscle contraction
• Inhibition of aqueous humor production

Correct Answer: Contraction of ciliary muscle and lens rounding

Q49. Which medication would be contraindicated or used cautiously in a patient with narrow-angle glaucoma due to antimuscarinic-induced mydriasis?

• Topical pilocarpine
• Atropine or systemic antimuscarinics
• Timolol (beta-blocker)
• Echothiophate (AChE inhibitor)

Correct Answer: Atropine or systemic antimuscarinics

Q50. Which pharmacological approach increases parasympathetic muscarinic signaling by preventing acetylcholine breakdown at synapses?

• Muscarinic antagonists
• Beta-adrenergic agonists
• Acetylcholinesterase inhibitors
• Alpha-1 blockers

Correct Answer: Acetylcholinesterase inhibitors

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

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