Autonomic Nervous System Drugs — MCQs
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The schematic diagram is depicting some features of the autonomic and somatic nervous systems. What is the neurotransmitter at site 'F'?
Prolonged muscle paralysis in a healthy individual may be caused by:
Curare poisoning is characterised by:
Which is the most dangerous effect of belladonna in very young children?
Which of the following is NOT a use of anticholinergics?
What is the primary reason dopamine is preferred in the treatment of shock?
Which muscle is injected with botulinum toxin?
Propranolol is useful in all the following conditions EXCEPT:
Which alpha-2 agonist is used in the management of glaucoma?
Nicotinic receptors are seen in all except?
Autonomic Nervous System Drugs Indian Medical PG Practice Questions and MCQs
Question 461: The schematic diagram is depicting some features of the autonomic and somatic nervous systems. What is the neurotransmitter at site 'F'?
- A. Acetylcholine (Correct Answer)
- B. Norepinephrine
- C. Dopamine
- D. Epinephrine
Explanation: ***Acetylcholine*** - **Acetylcholine** is the universal neurotransmitter at **all preganglionic synapses** in both sympathetic and parasympathetic systems, **all parasympathetic postganglionic synapses**, and the **somatic neuromuscular junction**. - Site F likely represents one of these **cholinergic sites** where acetylcholine acts on **nicotinic** or **muscarinic receptors** depending on the location. *Norepinephrine* - **Norepinephrine** is primarily released at **sympathetic postganglionic synapses** targeting organs like the heart, blood vessels, and bronchi. - It acts on **α and β adrenergic receptors** but is not found at preganglionic synapses, parasympathetic postganglionic synapses, or somatic neuromuscular junctions. *Dopamine* - **Dopamine** has limited roles in the peripheral autonomic nervous system, mainly in **renal vasculature** and as a precursor to norepinephrine. - It is not a primary neurotransmitter at standard autonomic synapses and is predominantly found in the **central nervous system**. *Epinephrine* - **Epinephrine** is primarily a **hormone** released from the **adrenal medulla** into the bloodstream rather than a synaptic neurotransmitter. - It is not released at typical autonomic synapses but acts systemically on **α and β adrenergic receptors** throughout the body.
Question 462: Prolonged muscle paralysis in a healthy individual may be caused by:
- A. d-Tubocurarine
- B. Cisatracurium
- C. Pancuronium
- D. Succinylcholine (Correct Answer)
Explanation: **Explanation:** The correct answer is **Succinylcholine**. While Succinylcholine is typically a short-acting depolarizing neuromuscular blocker (duration 5–10 minutes), it can cause **prolonged muscle paralysis** (apnea) in individuals with a **pseudocholinesterase deficiency** (atypical plasma cholinesterase). Since Succinylcholine is metabolized exclusively by this enzyme, a genetic deficiency or functional impairment leads to an inability to degrade the drug, resulting in extended neuromuscular blockade. **Analysis of Options:** * **d-Tubocurarine:** A prototype non-depolarizing blocker. It has a long duration of action (80–120 mins) but does not typically cause "unexpected" prolonged paralysis in healthy individuals unless there is renal failure. * **Cisatracurium:** An isomer of atracurium that undergoes **Hofmann elimination** (spontaneous degradation in plasma). Its metabolism is independent of renal or hepatic function, making its duration highly predictable and unlikely to be abnormally prolonged. * **Pancuronium:** A long-acting non-depolarizing agent. While it has a slow onset and long recovery time, it does not carry the specific risk of "prolonged apnea" associated with enzyme deficiencies seen with Succinylcholine. **NEET-PG High-Yield Pearls:** * **Dibucaine Number:** Used to diagnose pseudocholinesterase deficiency. A **low** dibucaine number (e.g., 20) indicates atypical enzyme (sensitive to Succinylcholine), while a **high** number (e.g., 80) is normal. * **Management:** If prolonged paralysis occurs, the patient must be kept on **mechanical ventilation** until the drug wears off naturally. * **Phase II Block:** Occurs with high doses or continuous infusion of Succinylcholine, where the membrane repolarizes but remains insensitive to Acetylcholine (resembling a non-depolarizing block).
Question 463: Curare poisoning is characterised by:
- A. Hypertension
- B. Hypotension (Correct Answer)
- C. Does not release histamine
- D. Oral route of administration is the best route
Explanation: **Explanation:** Curare (specifically **d-Tubocurarine**) is a prototype non-depolarizing neuromuscular blocking agent. The primary reason for **Hypotension** in curare poisoning is twofold: 1. **Histamine Release:** d-Tubocurarine is a potent stimulator of mast cells, leading to significant histamine release. Histamine causes peripheral vasodilation and increased capillary permeability, resulting in a drop in blood pressure. 2. **Ganglionic Blockade:** In high doses, curare blocks nicotinic receptors ($N_n$) at the autonomic ganglia, reducing sympathetic tone to the blood vessels and further contributing to hypotension. **Analysis of Incorrect Options:** * **A. Hypertension:** This is incorrect because curare lacks sympathomimetic activity; its ganglionic blocking and histamine-releasing properties lead to a decrease, not an increase, in blood pressure. * **C. Does not release histamine:** This is incorrect. d-Tubocurarine is notorious for histamine release, which can also trigger bronchospasm and excessive secretions, making it risky for asthmatic patients. * **D. Oral route of administration:** This is incorrect. Curare is highly ionized (quaternary ammonium compound) and is **not absorbed from the gastrointestinal tract**. Historically, indigenous hunters used curare-tipped arrows to kill prey; the meat remained safe to eat because the toxin is not absorbed orally. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote:** Neostigmine (AChE inhibitor) is used to reverse the blockade by increasing acetylcholine levels at the NMJ. * **Order of Paralysis:** Small, rapid muscles (eyes, fingers) are affected first; the **diaphragm** is the last to be paralyzed and the first to recover. * **Modern Alternative:** **Vecuronium** and **Rocuronium** are preferred in clinical practice as they do not cause histamine release or ganglionic blockade, ensuring hemodynamic stability.
Question 464: Which is the most dangerous effect of belladonna in very young children?
- A. Dehydration
- B. Hallucinations
- C. Hypertension
- D. Hyperthermia (Correct Answer)
Explanation: **Explanation:** The correct answer is **Hyperthermia**. Belladonna alkaloids (like Atropine) are competitive antagonists at muscarinic receptors. In children, the most critical adverse effect is "Atropine fever." **1. Why Hyperthermia is the correct answer:** Atropine suppresses the activity of eccrine sweat glands by blocking **M3 receptors**. Since sweating is the body's primary mechanism for heat dissipation, its inhibition leads to a rapid rise in body temperature. Children are particularly vulnerable because their thermoregulatory centers are immature and they have a higher surface-area-to-body-mass ratio. In severe cases, this can lead to fatal hyperpyrexia. **2. Why the other options are incorrect:** * **Dehydration:** While belladonna causes "dryness" (dry mouth, dry skin), it does not cause systemic fluid loss or dehydration. The danger is the inability to cool down, not a lack of total body water. * **Hallucinations:** Central Nervous System (CNS) effects like delirium and hallucinations occur (the "Mad as a hatter" sign), but these are generally manageable and less life-threatening than extreme hyperpyrexia. * **Hypertension:** Atropine typically causes tachycardia, but it does not have a significant or dangerous effect on blood pressure in children compared to the risk of hyperthermia. **Clinical Pearls for NEET-PG:** * **Mnemonic for Atropine Poisoning:** "Hot as a hare (Hyperthermia), Red as a beet (Flushing), Dry as a bone (Anhidrosis), Blind as a bat (Mydriasis), Mad as a hatter (Delirium)." * **Antidote:** The drug of choice for belladonna poisoning is **Physostigmine** (a tertiary amine carbamate that crosses the Blood-Brain Barrier). * **Contraindication:** Atropine is contraindicated in patients with narrow-angle glaucoma and prostatic hypertrophy.
Question 465: Which of the following is NOT a use of anticholinergics?
- A. Peptic ulcer disease
- B. Motion sickness
- C. Tachycardia (Correct Answer)
- D. Spasmodic pain
Explanation: **Explanation:** Anticholinergics (Muscarinic antagonists) act by blocking the action of acetylcholine at M-receptors. One of the hallmark effects of these drugs on the heart is the blockade of M2 receptors in the SA node, which leads to an **increase in heart rate (Tachycardia)**. Therefore, anticholinergics are used to treat *bradycardia* (e.g., Atropine in ACLS), but they are contraindicated in patients with pre-existing tachycardia as they would exacerbate the condition. **Why the other options are uses of Anticholinergics:** * **Peptic Ulcer Disease (PUD):** Drugs like **Pirenzepine** (selective M1 blocker) were historically used to reduce gastric acid secretion, though they are now largely replaced by PPIs. * **Motion Sickness:** **Hyoscine (Scopolamine)** is the drug of choice. It acts on the vestibular apparatus and the vomiting center in the brain to prevent nausea and vomiting associated with motion. * **Spasmodic Pain:** Anticholinergics like **Dicyclomine** and **Hyoscine butylbromide** act as antispasmodics by relaxing the smooth muscles of the GI and biliary tracts, providing relief from colic. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of choice for Mushroom poisoning (Inocybe type):** Atropine. * **Ipratropium/Tiotropium:** M3 blockers used via inhalation for COPD and Asthma (Bronchodilators). * **Oxybutynin/Darifenacin:** Used for overactive bladder (Urinary incontinence). * **Contraindications:** Anticholinergics should be avoided in **Glaucoma** (causes mydriasis/increased IOP) and **Benign Prostatic Hyperplasia (BPH)** (causes urinary retention).
Question 466: What is the primary reason dopamine is preferred in the treatment of shock?
- A. Renal vasodilatory effect (Correct Answer)
- B. Increased cardiac output
- C. Peripheral vasoconstriction
- D. Prolonged action
Explanation: **Explanation:** The primary reason dopamine is preferred in the management of shock (particularly cardiogenic or septic shock) is its unique, dose-dependent effect on renal hemodynamics. **1. Why Option A is Correct:** At low doses (**0.5–2 µg/kg/min**), dopamine acts primarily on **D1 receptors** located in the renal, mesenteric, and coronary vascular beds. Activation of these receptors causes vasodilation, increasing renal blood flow and glomerular filtration rate (GFR). This helps maintain urine output and prevents acute tubular necrosis (renal failure), a common complication of shock. **2. Why Other Options are Incorrect:** * **Option B:** While dopamine does increase cardiac output via **β1 receptors** (at medium doses: 2–10 µg/kg/min), other inotropes like Dobutamine are more potent and selective for this purpose. The "preference" for dopamine specifically highlights its renal-sparing property. * **Option C:** Peripheral vasoconstriction occurs at high doses (>10 µg/kg/min) via **α1 receptors**. This is generally undesirable in many shock states as it increases afterload and can further decrease organ perfusion. * **Option D:** Dopamine has a very short half-life (approx. 2 minutes) and must be administered via continuous IV infusion. It does not have a prolonged action. **High-Yield Clinical Pearls for NEET-PG:** * **Dose-Dependent Action:** Remember the mnemonic **"DBA"** (Dopaminergic → Beta → Alpha) as the dose increases. * **Fenoldopam:** A selective D1 agonist used for hypertensive emergencies; it also maintains renal perfusion. * **Drug of Choice:** While dopamine was traditionally favored, current guidelines (like Surviving Sepsis) often prefer **Norepinephrine** as the first-line vasopressor for septic shock, but dopamine remains a high-yield answer for its renal vasodilatory profile in exams.
Question 467: Which muscle is injected with botulinum toxin?
- A. Masseter
- B. Buccinator
- C. Lateral Pterygoid (Correct Answer)
- D. Temporalis
Explanation: ***Lateral Pterygoid*** - The **lateral pterygoid muscle** is commonly injected with botulinum toxin for **TMJ disorders** and **jaw muscle dysfunction**. - It controls **jaw opening** and **lateral movement**, making it a key target for treating **temporomandibular joint pain** and muscle spasms. *Masseter* - While masseter can be injected with botulinum toxin, it's primarily for **bruxism** (teeth grinding) and **masseteric hypertrophy**. - The masseter is responsible for **jaw closing** and **chewing**, not the primary indication mentioned in this context. *Buccinator* - The **buccinator muscle** is involved in **cheek compression** and **blowing actions**, not jaw movement. - Botulinum toxin injection here would be for **facial asymmetry** or **drooling**, not typical TMJ-related issues. *Temporalis* - The **temporalis muscle** assists in **jaw closing** and **chewing** but is less commonly targeted with botulinum toxin. - Injection sites are more technically challenging due to its **broad, fan-shaped** anatomy across the temporal region.
Question 468: Propranolol is useful in all the following conditions EXCEPT:
- A. Atrial flutter
- B. Parkinsonian tremor (Correct Answer)
- C. Thyrotoxicosis
- D. Hypertrophic cardiomyopathy
Explanation: **Explanation:** Propranolol is a non-selective beta-blocker ($B_1$ and $B_2$) with high lipid solubility. The correct answer is **Parkinsonian tremor** because its pathophysiology and treatment differ significantly from other types of tremors. **1. Why Parkinsonian Tremor is the Correct Answer:** Parkinsonian tremor is a **resting tremor** caused by a dopamine deficiency in the nigrostriatal pathway. The mainstay of treatment involves increasing dopamine (Levodopa) or using central anticholinergics (Benztropine). Propranolol is ineffective here. In contrast, Propranolol is the **drug of choice for Essential Tremor** (action tremor), which is mediated by peripheral $B_2$ receptors. **2. Analysis of Incorrect Options:** * **Atrial Flutter:** Propranolol is a Class II antiarrhythmic. It decreases the heart rate by slowing AV node conduction, making it useful for rate control in supraventricular tachycardias. * **Thyrotoxicosis:** Propranolol is used to manage symptomatic sympathetic overactivity (palpitations, tremors). Crucially, it also **inhibits the peripheral conversion of $T_4$ to the more active $T_3$**, making it the preferred beta-blocker in thyroid storm. * **Hypertrophic Cardiomyopathy (HCM/HOCM):** It is a first-line agent. By decreasing the heart rate and contractility (negative inotropy), it increases diastolic filling time and reduces the left ventricular outflow tract (LVOT) gradient. **Clinical Pearls for NEET-PG:** * **Membrane Stabilizing Activity (MSA):** Propranolol possesses local anesthetic-like effects (Quinidine-like), making it dangerous in overdose. * **Lipid Solubility:** High lipid solubility allows it to cross the BBB, causing side effects like vivid dreams or depression, but also making it effective for **Migraine Prophylaxis**. * **Contraindications:** Always avoid in Bronchial Asthma (due to $B_2$ blockade) and Prinzmetal Angina.
Question 469: Which alpha-2 agonist is used in the management of glaucoma?
- A. Guanacare
- B. Guanabenz
- C. Brimonidine (Correct Answer)
- D. Tizanidine
Explanation: **Explanation:** **Brimonidine** is the correct answer because it is a highly selective **alpha-2 adrenergic agonist** specifically designed for ophthalmic use. In the management of glaucoma, it works through a dual mechanism: 1. **Decreasing aqueous humor production** by causing vasoconstriction of the ciliary body blood vessels. 2. **Increasing uveoscleral outflow**, which further helps in lowering intraocular pressure (IOP). Unlike earlier non-selective drugs, Brimonidine is more lipophilic and has better ocular penetration with fewer systemic side effects. **Analysis of Incorrect Options:** * **Guanfacine & Guanabenz (Options A & B):** These are centrally acting alpha-2 agonists used primarily as **antihypertensive agents**. They cross the blood-brain barrier to decrease sympathetic outflow from the vasomotor center. * **Tizanidine (Option D):** This is a centrally acting alpha-2 agonist used as a **skeletal muscle relaxant**. It acts on the spinal cord to inhibit presynaptic motor neurons, reducing spasticity in conditions like multiple sclerosis. **High-Yield Clinical Pearls for NEET-PG:** * **Apraclonidine** is another alpha-2 agonist used in glaucoma, primarily to prevent post-laser IOP spikes, but it is less selective than Brimonidine. * **Side Effect:** A unique side effect of Brimonidine is **follicular conjunctivitis** (allergic reaction). * **Contraindication:** It is strictly contraindicated in **infants and young children** (under 2 years) as it can cross the blood-brain barrier and cause CNS depression, apnea, and bradycardia.
Question 470: Nicotinic receptors are seen in all except?
- A. Neuromuscular junction
- B. Autonomic ganglia of autonomic nervous system
- C. Bronchial smooth muscle (Correct Answer)
- D. Brain
Explanation: The cholinergic system utilizes two main types of receptors: **Nicotinic (N)** and **Muscarinic (M)** [2]. Nicotinic receptors are ligand-gated ion channels (ionotropic), whereas muscarinic receptors are G-protein coupled receptors (metabotropic) [4]. **Why Bronchial Smooth Muscle is the Correct Answer:** Bronchial smooth muscle contains **Muscarinic M3 receptors**, not nicotinic receptors. Activation of M3 receptors by acetylcholine (ACh) leads to bronchoconstriction and increased secretions. This is why anticholinergic drugs like Ipratropium bromide are used to induce bronchodilation in asthma and COPD. **Analysis of Incorrect Options:** * **Neuromuscular Junction (NMJ):** These contain **$N_M$ receptors** [1]. Stimulation leads to the opening of Na+/K+ channels, causing depolarization of the endplate and skeletal muscle contraction. * **Autonomic Ganglia:** Both sympathetic and parasympathetic ganglia contain **$N_N$ receptors** [1]. They mediate fast excitatory postsynaptic potentials (EPSP) to propagate the nerve impulse [3]. * **Brain:** The Central Nervous System (CNS) contains **$N_N$ receptors** (specifically subtypes like $\alpha4\beta2$ and $\alpha7$) [1]. These play significant roles in cognitive functions, memory, and the rewarding effects of nicotine. **High-Yield Clinical Pearls for NEET-PG:** 1. **Nicotinic Antagonists:** $N_M$ receptors are blocked by skeletal muscle relaxants (e.g., **d-Tubocurarine**), while $N_N$ receptors are blocked by ganglion blockers (e.g., **Hexamethonium**) [3]. 2. **Adrenal Medulla:** It is considered a modified sympathetic ganglion and expresses **$N_N$ receptors**, which trigger catecholamine release. 3. **Mnemonic:** Remember **"N"** for **N**icotinic = **N**erve (ganglia) and **N**euro-muscular junction. All other parasympathetic effector organs (Heart, Glands, Smooth muscle) primarily have **M**uscarinic receptors.
Practice by Chapter
Cholinergic Agonists
Practice Questions
Cholinergic Antagonists
Practice Questions
Adrenergic Agonists
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Adrenergic Antagonists
Practice Questions
Ganglionic Agents
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Neuromuscular Blocking Agents
Practice Questions
Autonomic Drugs in Ophthalmology
Practice Questions
Autonomic Drugs in Cardiovascular Disease
Practice Questions
Autonomic Drugs in Respiratory Disease
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Autonomic Drugs in Urological Disorders
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