Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs Indian Medical PG Practice Questions and MCQs

Question 31: Telenzepine acts on which receptors?

A. M2
B. M1 (Correct Answer)
C. M3
D. Nm

Explanation: **Explanation:** **Telenzepine** is a selective **M1 muscarinic receptor antagonist**. It is a more potent analogue of Pirenzepine. 1. **Why M1 is correct:** M1 receptors are primarily located in the gastric parietal cells and autonomic ganglia. By selectively blocking M1 receptors, Telenzepine reduces gastric acid secretion. Historically, it was developed for the treatment of peptic ulcer disease, though it has largely been replaced by Proton Pump Inhibitors (PPIs). 2. **Why other options are incorrect:** * **M2:** These receptors are primarily found in the **heart** (SA and AV nodes). Blockade here (by drugs like Atropine) leads to tachycardia. A selective M2 blocker is **Methoctramine**. * **M3:** These are located in **smooth muscles** (bronchi, bladder, GI tract) and **exocrine glands**. Blockade leads to side effects like dry mouth and constipation. Selective M3 blockers include **Darifenacin** and **Solifenacin** (used for overactive bladder). * **Nm:** These are **nicotinic receptors** at the neuromuscular junction. Blockade here results in skeletal muscle relaxation (e.g., d-Tubocurarine, Vecuronium). **High-Yield Clinical Pearls for NEET-PG:** * **Pirenzepine and Telenzepine** are the classic examples of selective M1 blockers. * **Mnemonic for Muscarinic Receptors:** **M1** (Glands/Gastric), **M2** (Heart), **M3** (Smooth Muscle/Secretions). * **Ipratropium/Tiotropium:** Non-selective muscarinic blockers used in COPD/Asthma to prevent bronchoconstriction. * **Oxybutynin:** A non-selective tertiary amine used for urinary urge incontinence, though M3 selective agents are now preferred to reduce side effects.

Question 32: Pilocarpine:

A. Lowers the intraocular pressure in glaucoma (Correct Answer)
B. Cleaved by acetylcholinesterase
C. Inhibits sweat and lacrimation
D. Causes tachycardia

Explanation: **Explanation:** **Pilocarpine** is a naturally occurring alkaloid that acts as a **direct-acting parasympathomimetic (muscarinic agonist)**. **1. Why Option A is Correct:** Pilocarpine is primarily used in ophthalmology to treat glaucoma. It acts on the **M3 receptors** of the **sphincter pupillae** (causing miosis) and the **ciliary muscle** (causing contraction). Contraction of the ciliary muscle pulls on the scleral spur, opening the trabecular meshwork. This increases the drainage of aqueous humor, thereby **lowering intraocular pressure (IOP)**. It is particularly used as a first-line emergency treatment for acute angle-closure glaucoma. **2. Why Other Options are Incorrect:** * **Option B:** Unlike acetylcholine, Pilocarpine is an alkaloid and is **not a substrate for acetylcholinesterase (AChE)**. This gives it a significantly longer duration of action compared to endogenous acetylcholine. * **Option C:** As a muscarinic agonist, Pilocarpine **stimulates** exocrine glands. It is a potent sialogogue (increases saliva) and diaphoretic (increases sweat). It is clinically used to treat xerostomia (dry mouth) in Sjögren’s syndrome. * **Option D:** Parasympathomimetics typically cause **bradycardia** (via M2 receptors in the heart). While reflex tachycardia can occasionally occur due to systemic vasodilation, the primary direct effect is a decrease in heart rate. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Pilocarpine is the drug of choice for **acute angle-closure glaucoma**. * **Ciliary Muscle Contraction:** This causes "accommodation spasm," which can lead to transient brow ache and myopia. * **Adie’s Tonic Pupil:** Diagnosis is confirmed using **dilute pilocarpine (0.125%)**, which causes constriction in the affected eye due to cholinergic supersensitivity.

Question 33: Besides stimulation of M3 receptors located on endothelial cells, what is the main mechanism of vasodilatory actions of acetylcholine?

A. Decrease in endothelin by acetylcholine released from cholinergic nerves in blood vessels
B. Inhibition of norepinephrine release from adrenergic nerve endings (Correct Answer)
C. Stimulation of vascular smooth muscle cells
D. Effects on autoregulation particularly in coronary vascular beds.

Explanation: ### Explanation The vasodilatory effect of Acetylcholine (ACh) is mediated through two distinct mechanisms: 1. **Direct (Endothelial-dependent):** ACh stimulates **M3 receptors** on vascular endothelial cells, leading to the release of **Nitric Oxide (NO)** (formerly known as Endothelium-Derived Relaxing Factor or EDRF). NO diffuses to adjacent smooth muscle, increasing cGMP and causing relaxation. 2. **Indirect (Neural-dependent):** This is the "main" alternative mechanism. ACh acts on **presynaptic M2 receptors** located on sympathetic (adrenergic) nerve terminals. Stimulation of these inhibitory muscarinic receptors **decreases the release of Norepinephrine (NE)**. Since NE normally maintains vascular tone via $\alpha_1$ receptors, its inhibition leads to vasodilation. #### Analysis of Incorrect Options: * **Option A:** While endothelin is a potent vasoconstrictor, the primary rapid regulation of vascular tone by ACh does not involve the modulation of endothelin levels. * **Option C:** Direct stimulation of muscarinic receptors on **vascular smooth muscle cells** (if endothelium is damaged) actually causes **vasoconstriction**, not dilation. * **Option D:** Autoregulation refers to the intrinsic ability of organs to maintain blood flow despite pressure changes; while ACh affects coronary flow, it is not the primary mechanism of its systemic vasodilatory action. #### NEET-PG High-Yield Pearls: * **The "Furchgott" Observation:** If the endothelium is removed/damaged, IV Acetylcholine causes **vasoconstriction** because it acts directly on M3 receptors on the smooth muscle without the mediating effect of NO. * **M2 Receptors:** Remember that M2 receptors are generally inhibitory (Gi-coupled) and are found in the heart (SA/AV node) and on presynaptic nerve terminals. * **Vascular Innervation:** Most blood vessels lack direct cholinergic innervation; therefore, circulating ACh acts on "non-innervated" muscarinic receptors.

Question 34: Which of the following statements about Histamine is true?

A. Is found in Mast cells
B. Increases gastric acid secretion
C. Related to arousal and blood pressure
D. All of the above (Correct Answer)

Explanation: **Explanation:** Histamine is a biogenic amine that acts as a critical mediator in various physiological and pathological processes. The correct answer is **D (All of the above)** because histamine performs diverse functions across different organ systems via specific receptors ($H_1$ to $H_4$). * **Option A (Mast cells):** Histamine is primarily synthesized and stored in the granules of **mast cells** (in connective tissue) and **basophils** (in blood). It is released during Type I hypersensitivity reactions (IgE-mediated). * **Option B (Gastric acid):** Histamine is released by **Enterochromaffin-like (ECL) cells** in the stomach. It acts on **$H_2$ receptors** located on gastric parietal cells, stimulating the proton pump to increase gastric acid secretion. This is the physiological basis for using $H_2$ blockers (e.g., Ranitidine) in peptic ulcer disease. * **Option C (Arousal and BP):** In the CNS, histamine acts as a neurotransmitter via **$H_1$ receptors** to maintain wakefulness and alertness (arousal). This explains why first-generation antihistamines cause sedation. Peripherally, histamine causes significant **vasodilation** (via NO release) and increased capillary permeability, leading to a fall in blood pressure. **High-Yield NEET-PG Pearls:** 1. **Triple Response of Lewis:** Following intradermal histamine injection, three signs appear: Red spot (local vasodilation), Flare (axonal reflex), and Wheal (edema due to permeability). 2. **Receptors:** $H_1$ (Gq) – Allergy/Arousal; $H_2$ (Gs) – Gastric acid; $H_3$ (Gi) – Presynaptic autoreceptors in CNS. 3. **Drug of Choice:** Adrenaline (Epinephrine) is the **physiological antagonist** of histamine and is the DOC for anaphylactic shock.

Question 35: Sweating as a result of excretion is mediated through which of the following pathways?

A. Adrenal hormone
B. Sympathetic adrenergic
C. Parasympathetic cholinergic
D. Sympathetic cholinergic (Correct Answer)

Explanation: **Explanation:** The correct answer is **Sympathetic cholinergic**. **1. Why it is correct:** In the Autonomic Nervous System (ANS), most sympathetic postganglionic neurons release norepinephrine (adrenergic). However, there is a notable exception: the **eccrine sweat glands**. While these glands are anatomically part of the **sympathetic nervous system** (originating from the thoracolumbar outflow), their postganglionic neurons release **Acetylcholine (ACh)**, which acts on **Muscarinic (M3) receptors**. This is why sweating is described as "sympathetic cholinergic" mediation. **2. Why other options are incorrect:** * **Adrenal hormone:** While the adrenal medulla is part of the sympathetic system, it primarily releases epinephrine/norepinephrine into the blood. It does not directly mediate the localized nerve-to-gland signaling required for thermoregulatory sweating. * **Sympathetic adrenergic:** Most sympathetic functions (like vasoconstriction or pupillary dilation) use norepinephrine. However, using an adrenergic blocker (like a Beta-blocker) does not stop thermoregulatory sweating, proving it is not an adrenergic process. * **Parasympathetic cholinergic:** Although the neurotransmitter (ACh) is the same, the anatomical nerves supplying sweat glands do not originate from the craniosacral (parasympathetic) outflow. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Exception Rule:** Remember the "Two Exceptions" to the sympathetic-adrenergic rule: **Sweat glands** and **Skeletal muscle vasodilation** (though the latter is of minor clinical significance in humans). * **Atropine Effect:** Since sweating is mediated by Muscarinic receptors, **Atropine** (an anticholinergic) inhibits sweating, leading to "Atropine fever," especially in children. * **Apocrine vs. Eccrine:** Only **Eccrine** glands (thermoregulation) are cholinergic. **Apocrine** glands (axilla/groin, stress-induced) are actually **adrenergic**. * **Gustatory Sweating:** Occurs after nerve injury (e.g., Frey’s Syndrome), where parasympathetic fibers meant for salivary glands mistakenly regrow to sweat glands.

Question 36: Ergometrine is commonly used for?

A. Postpartum Hemorrhage (Correct Answer)
B. To shorten the second stage of labor
C. Dysmenorrhea
D. Toxemia of pregnancy

Explanation: **Explanation:** **Ergometrine** is an ergot alkaloid that acts as a potent **oxytocic** agent. Its primary mechanism involves the stimulation of alpha-adrenergic, serotonergic, and dopaminergic receptors, leading to powerful, sustained (tetanic) contractions of the uterine smooth muscle. 1. **Why Option A is Correct:** In **Postpartum Hemorrhage (PPH)**, the goal is to induce strong uterine contractions to compress the bleeding intramyometrial blood vessels (the "living ligatures"). Ergometrine is highly effective for this purpose, particularly in the third stage of labor or immediately postpartum, to prevent or treat uterine atony. 2. **Why the Other Options are Incorrect:** * **Option B:** Ergometrine is **contraindicated** before the delivery of the baby (first and second stages) because its tetanic contractions can cause fetal hypoxia, uterine rupture, or cervical entrapment. * **Option C:** It is not used for dysmenorrhea; standard treatment involves NSAIDs or hormonal contraceptives. * **Option D:** Ergometrine is strictly **contraindicated in Toxemia of pregnancy (Preeclampsia/Eclampsia)** because it causes significant vasoconstriction and can lead to a dangerous rise in blood pressure (hypertensive crisis). **High-Yield NEET-PG Pearls:** * **Route:** Usually given IM. IV administration is avoided as it can cause sudden, severe hypertension. * **Contraindications:** Hypertension, Preeclampsia, Peripheral Vascular Disease (Raynaud's), and Sepsis. * **Storage:** It is light-sensitive and heat-sensitive; it must be stored in a cool, dark place (refrigerated). * **Methylergometrine:** A semi-synthetic derivative often preferred over ergometrine due to its slightly faster onset and fewer side effects.

Question 37: All of the following drugs are non-selective Beta blockers EXCEPT?

A. Propranolol
B. Timolol
C. Sotalol
D. Carvedilol (Correct Answer)

Explanation: **Explanation:** The classification of Beta-blockers is a high-yield topic for NEET-PG. Beta-blockers are categorized into three generations based on their receptor selectivity and additional properties. **1. Why Carvedilol is the correct answer:** While Propranolol, Timolol, and Sotalol are **Pure Non-selective Beta-blockers** (blocking both $\beta_1$ and $\beta_2$ receptors), **Carvedilol** belongs to the **Third Generation** of beta-blockers. It is unique because it provides **Non-selective Beta-blockade ($\beta_1 + \beta_2$) PLUS Alpha-1 ($\alpha_1$) blockade**. This dual action leads to peripheral vasodilation, making it a "vasodilatory beta-blocker" rather than just a simple non-selective one. **2. Analysis of Incorrect Options:** * **A. Propranolol:** The prototype 1st generation non-selective beta-blocker. It has no $\alpha$-blocking activity and is highly lipid-soluble (crosses BBB). * **B. Timolol:** A 1st generation non-selective blocker primarily used topically in glaucoma to reduce aqueous humor production. * **C. Sotalol:** A 1st generation non-selective blocker that also possesses **Class III anti-arrhythmic** properties (potassium channel blockade). **3. Clinical Pearls for NEET-PG:** * **Cardioselective ($\beta_1$) Blockers (Mnemonic: New Beta Blockers Are Exclusive):** **N**ebivolol, **B**isoprolol, **B**etaxolol, **A**tenolol, **A**cebutolol, **E**smolol, **M**etoprolol. * **Mixed $\alpha + \beta$ Blockers:** Carvedilol and Labetalol. * **Labetalol** is the drug of choice for hypertension in pregnancy. * **Esmolol** has the shortest half-life (~9 mins) and is given IV for hypertensive emergencies or supraventricular tachycardia. * **Nebivolol** is the most $\beta_1$ selective blocker and also increases Nitric Oxide (NO) release.

Question 38: Lid retraction is a side effect of which anti-glaucoma drug?

A. Latanoprost
B. Brimonidine (Correct Answer)
C. Brinzolamide
D. Pilocarpine

Explanation: **Explanation:** **Brimonidine** is a highly selective **alpha-2 (α2) adrenergic agonist** used to treat glaucoma by decreasing aqueous humor production and increasing uveoscleral outflow. The side effect of **lid retraction** occurs because Brimonidine has a slight cross-reactivity with **alpha-1 (α1) receptors**. Stimulation of α1 receptors on the **superior tarsal muscle (Müller’s muscle)** causes it to contract, leading to an upward displacement of the upper eyelid (lid retraction) and a widened palpebral fissure. **Analysis of Incorrect Options:** * **Latanoprost (Prostalgandin Analog):** Known for causing **Prostalgandin-associated Periorbitopathy (PAP)**, which includes deepening of the eyelid sulcus, eyelash darkening/growth, and iris hyperpigmentation, but not lid retraction. * **Brinzolamide (Carbonic Anhydrase Inhibitor):** Primarily causes local irritation, bitter taste (dysgeusia), and transient blurred vision. It does not affect the sympathetic innervation of the eyelid. * **Pilocarpine (Cholinergic Agonist):** A miotic agent that typically causes **miosis** (pupillary constriction) and **brow ache** due to ciliary muscle contraction. It may cause mild ptosis (drooping) rather than retraction. **NEET-PG High-Yield Pearls:** * **Brimonidine** is contraindicated in infants and children (<2 years) as it can cross the blood-brain barrier and cause **CNS depression and apnea**. * It is frequently associated with **allergic conjunctivitis** (follicular conjunctivitis). * **Apraclonidine**, another alpha-agonist, is also known to cause lid retraction and is sometimes used clinically to temporarily treat ptosis in Horner’s syndrome.

Question 39: Which of the following drugs is commonly used for narcoanalysis?

A. Atropine sulfate
B. Scopolamine hydrochloride (Correct Answer)
C. Phenobarbitone
D. Morphine

Explanation: **Explanation:** **Scopolamine hydrochloride** (Hyoscine) is the correct answer because it is a potent central nervous system (CNS) depressant with significant **amnestic properties**. In the context of narcoanalysis (often colloquially termed "truth serum"), scopolamine induces a state of "twilight sleep." It inhibits the higher cortical functions required for complex mental processes like lying, making the subject more suggestible and likely to reveal suppressed information. Chemically, it is a tertiary amine belladonna alkaloid that crosses the blood-brain barrier more effectively than atropine. **Analysis of Incorrect Options:** * **Atropine sulfate:** While also a belladonna alkaloid, atropine has minimal CNS effects at standard doses compared to scopolamine. It is primarily used to treat bradycardia or as a pre-anesthetic to reduce secretions. * **Phenobarbitone:** This is a long-acting barbiturate used mainly as an anticonvulsant. While ultra-short-acting barbiturates (like **Thiopental sodium**) are used in narcoanalysis, phenobarbitone is too slow-acting and sedative for this specific purpose. * **Morphine:** An opioid analgesic used for pain management and pulmonary edema. It induces euphoria and sedation but does not facilitate the disinhibited, suggestible state required for narcoanalysis. **High-Yield NEET-PG Pearls:** * **Drug of Choice for Motion Sickness:** Scopolamine (administered via transdermal patch behind the pinna). * **Narcoanalysis Agents:** Besides Scopolamine, **Sodium Thiopental** and **Sodium Amytal** are the most frequently cited "truth serums." * **Mnemonic:** Scopolamine = **S**ecretion reduction, **S**edation, and **S**hort-term memory loss (Amnesia). * **Contraindication:** Avoid in patients with Angle-closure Glaucoma and Benign Prostatic Hyperplasia (BPH).

Question 40: Adrenalin increases all of the following blood pressures significantly except?

A. Systolic
B. Diastolic (Correct Answer)
C. Mean BP
D. Pulse pressure

Explanation: **Explanation:** The effect of Adrenaline (Epinephrine) on blood pressure is determined by its non-selective action on **$\alpha_1, \beta_1,$ and $\beta_2$ receptors**. 1. **Systolic BP (SBP):** Adrenaline significantly increases SBP primarily through its **$\beta_1$ agonist** action, which increases myocardial contractility (inotropy) and heart rate (chronotropy). 2. **Pulse Pressure:** Since SBP increases significantly while DBP remains relatively stable (or decreases slightly), the difference between the two—the pulse pressure—increases significantly. 3. **Mean BP:** Mean BP is a weighted average of SBP and DBP. Because the rise in SBP is substantial, the Mean BP generally shows a net increase. 4. **Diastolic BP (DBP):** This is the correct answer because the effect on DBP is **variable and dose-dependent**. At standard therapeutic doses, Adrenaline stimulates both $\alpha_1$ (vasoconstriction) and $\beta_2$ (vasodilation) receptors. The potent $\beta_2$ effect in skeletal muscle beds often offsets the $\alpha_1$ effect, leading to a DBP that may slightly rise, stay the same, or even fall. Therefore, it does not increase "significantly" compared to the other parameters. **High-Yield NEET-PG Pearls:** * **Dale’s Vasomotor Reversal:** If an $\alpha$-blocker (e.g., Phentolamine) is given before Adrenaline, the $\alpha_1$ effect is abolished, leaving the $\beta_2$ effect unopposed. This causes a paradoxical **fall** in BP. * **Drug of Choice:** Adrenaline is the DOC for **Anaphylactic Shock** (1:1000 IM) because it provides bronchodilation ($\beta_2$), increases BP ($\alpha_1, \beta_1$), and inhibits mast cell degranulation. * **Pure $\alpha$ agonist (Phenylephrine):** Increases both SBP and DBP, often leading to reflex bradycardia.

Practice by Chapter

Cholinergic Agonists

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Cholinergic Antagonists

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Adrenergic Agonists

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Adrenergic Antagonists

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Ganglionic Agents

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Neuromuscular Blocking Agents

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Autonomic Drugs in Ophthalmology

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Autonomic Drugs in Cardiovascular Disease

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Autonomic Drugs in Respiratory Disease

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Autonomic Drugs in Urological Disorders

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