Autonomic Nervous System Drugs Practice Questions

Q: Which of the following is NOT a cholinergic action?

Mydriasis. **Explanation:** Cholinergic actions are mediated by the parasympathetic nervous system (PNS) through the neurotransmitter Acetylcholine (ACh) acting on Muscarinic (M) receptors. To remember these actions, use the mnemonic **DUMBBELLS** (Diarrhea, Urination, Miosis, Bradycardia, Bronchoconstriction, Emesis, Lacrimation, Lethargy, Salivation/Sweating). **Why Mydriasis is the Correct Answer:** **Mydriasis** refers to the dilation of the pupil, which is a **Sympathetic (Adrenergic)** action mediated by $\alpha_1$ receptors on the radial dilator pupillae muscle. In contrast, cholinergic stimulation causes **Miosis** (pupillary constriction) by acting on the $M_3$ receptors of the circular sphincter pupillae muscle. **Analysis of Incorrect Options:** * **Salivation:** Cholinergic stimulation of $M_3$ receptors in the salivary glands increases secretions. * **Sweating:** Although mediated by the sympathetic nervous system anatomically, the postganglionic fibers to eccrine sweat glands are **cholinergic** (releasing ACh onto $M_3$ receptors). Thus, sweating is a cholinergic effect. * **Bradycardia:** ACh acts on $M_2$ receptors in the SA node of the heart to decrease the heart rate (negative chronotropy). **High-Yield Clinical Pearls for NEET-PG:** 1. **Accommodation:** Cholinergic drugs cause contraction of the ciliary muscle ($M_3$), leading to "spasm of accommodation" and a decrease in intraocular pressure (useful in Glaucoma). 2. **Sweat Glands Exception:** Remember that sweat glands are the "exception to the rule"—they are sympathetic in origin but **cholinergic** in transmission. 3. **Atropine:** As a muscarinic antagonist, Atropine will cause the opposite effects: Mydriasis, dry mouth, and tachycardia.

Q: Which beta-blocker drug is contraindicated in asthma patients?

Propranolol. **Explanation:** The correct answer is **C. Propranolol**. **1. Why Propranolol is the correct answer:** Propranolol is a **non-selective beta-blocker**, meaning it blocks both $\beta_1$ receptors (located primarily in the heart) and $\beta_2$ receptors (located in the bronchial smooth muscle). In patients with asthma or COPD, blocking $\beta_2$ receptors leads to bronchoconstriction and can precipitate a life-threatening acute asthmatic attack. Therefore, non-selective beta-blockers are strictly contraindicated in patients with reactive airway diseases. **2. Why the other options are incorrect:** * **Metoprolol and Atenolol (Options A & B):** These are **cardioselective ($\beta_1$) blockers**. At therapeutic doses, they primarily target the heart and have minimal effect on the $\beta_2$ receptors in the lungs. While they should still be used with caution, they are safer than non-selective agents. * **Acebutolol (Option D):** This is also a cardioselective $\beta_1$ blocker with **Intrinsic Sympathomimetic Activity (ISA)**. Like Metoprolol, it is less likely to cause bronchospasm compared to Propranolol. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Cardioselective ($\beta_1$) Blockers:** *"New Beta Blockers Are Exclusive to My Heart"* (Nebivolol, Betaxolol, Bisoprolol, Atenolol, Esmolol, Metoprolol). * **Esmolol:** The shortest-acting beta-blocker (half-life ~9 mins), administered IV for hypertensive emergencies or supraventricular tachycardia. * **Propranolol:** Highly lipid-soluble, crosses the blood-brain barrier (used for prophylaxis of migraine and essential tremors), and inhibits the peripheral conversion of $T_4$ to $T_3$ (used in thyroid storm). * **Absolute Contraindications for Beta-blockers:** Asthma, Bradycardia, 2nd or 3rd-degree Heart Block, and Cardiogenic Shock.

Q: Which of the following receptors does not require the action of adrenaline for the treatment of anaphylactic shock?

α2. **Explanation:** In the management of anaphylactic shock, **Adrenaline (Epinephrine)** is the drug of choice because it acts as a physiological antagonist to the mediators of anaphylaxis (like histamine). Its therapeutic efficacy is derived from its action on **$\alpha_1$, $\beta_1$, and $\beta_2$ receptors**, while $\alpha_2$ stimulation plays no significant role in treating the acute crisis. * **Why $\alpha_2$ is the correct answer:** $\alpha_2$ receptors are primarily located presynaptically and function to inhibit the release of norepinephrine (negative feedback). Stimulation of $\alpha_2$ receptors does not contribute to the reversal of shock; in fact, it could theoretically decrease sympathetic outflow, which is counterproductive in a circulatory collapse. **Role of other receptors (Incorrect Options):** * **$\alpha_1$ (Option A):** Stimulation causes **vasoconstriction**, which increases peripheral vascular resistance and blood pressure, effectively reversing the hypotension and reducing mucosal edema (e.g., laryngeal edema). * **$\beta_1$ (Option C):** Stimulation increases **myocardial contractility (inotropy) and heart rate (chronotropy)**, improving cardiac output to combat shock. * **$\beta_2$ (Option D):** This is a life-saving action that causes **bronchodilation** to relieve bronchospasm and **stabilizes mast cells**, preventing further release of inflammatory mediators. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** Adrenaline is the DOC for Anaphylactic Shock. * **Route of Administration:** **Intramuscular (IM)** in the anterolateral thigh (vastus lateralis) is preferred over SC or IV in the initial setting due to faster absorption and safety. * **Concentration:** 1:1000 (1 mg/ml) for IM; 1:10,000 (0.1 mg/ml) for IV. * **Standard Dose:** 0.5 mg IM for adults; 0.01 mg/kg for children.

Q: Which of the following sympathomimetic amines has agonistic action on a1, a2, b1, and b3 adrenoceptors, but not on b2 receptors?

Noradrenaline. **Explanation:** The correct answer is **Noradrenaline (Norepinephrine)**. **1. Why Noradrenaline is Correct:** Noradrenaline is a potent agonist at **$\alpha_1$, $\alpha_2$, and $\beta_1$** receptors. Crucially, it has **negligible or no action on $\beta_2$ receptors**. Recent pharmacological studies also confirm its agonistic activity on **$\beta_3$** receptors (involved in thermogenesis and lipolysis). Because it lacks $\beta_2$ activity (which mediates vasodilation), Noradrenaline causes intense peripheral vasoconstriction, leading to a significant rise in both systolic and diastolic blood pressure. **2. Why the Other Options are Incorrect:** * **Phenylephrine (Option A):** This is a selective **$\alpha_1$ agonist**. It lacks significant action on $\beta$ receptors. * **Isoprenaline (Option B):** This is a non-selective **$\beta$ agonist** ($\beta_1$, $\beta_2$, and $\beta_3$). It has virtually no action on $\alpha$ receptors. * **Adrenaline (Option C):** Adrenaline is a potent agonist at **all** adrenoceptors: $\alpha_1$, $\alpha_2$, $\beta_1$, **and $\beta_2$**. The presence of $\beta_2$ activity distinguishes it from Noradrenaline and allows it to cause bronchodilation and vasodilation in skeletal muscle beds. **3. NEET-PG High-Yield Pearls:** * **Drug of Choice:** Noradrenaline is the first-line vasopressor for **Septic Shock**. * **Reflex Bradycardia:** Unlike Adrenaline, Noradrenaline often causes a "reflex bradycardia" because the intense $\alpha_1$-mediated vasoconstriction triggers the baroreceptor reflex, which overrides its direct $\beta_1$ stimulatory effect on the heart rate. * **Metabolism:** Both Adrenaline and Noradrenaline are metabolized by **COMT** and **MAO**; the end product measured in urine is **Vanillylmandellic acid (VMA)**. * **Rule of Thumb:** If a question mentions "no $\beta_2$ action" among catecholamines, always think of Noradrenaline.

Q: Which of the following agents acts as a mydriatic?

Tropicamide. **Explanation:** The correct answer is **D. All of the above**. *Note: While the prompt indicates Tropicamide as the marked correct answer, pharmacologically, all three options belong to the class of **Antimuscarinic (Anticholinergic) agents** which act as both mydriatics (dilating the pupil) and cycloplegics (paralyzing the ciliary muscle).* **1. Why all options are correct:** Mydriatics are drugs that cause dilation of the pupil by blocking the M3 receptors on the sphincter pupillae muscle. * **Tropicamide:** The shortest-acting mydriatic (duration 4–6 hours). It is the drug of choice for diagnostic ophthalmoscopy due to its rapid onset and brief recovery period. * **Homatropine:** An intermediate-acting agent (duration 2–3 days). It is frequently used in the treatment of anterior uveitis to prevent the formation of synechiae. * **Atropine:** The most potent and longest-acting agent (duration 7–10 days). It is the drug of choice for refraction in children under 7 years (due to strong accommodation) and for treating severe uveitis. **2. Clinical Pearls for NEET-PG:** * **Drug of choice for Fundus Examination:** Tropicamide (Fastest action). * **Drug of choice for Refraction in Children:** Atropine (Ointment is preferred over drops to prevent systemic toxicity via the nasolacrimal duct). * **Drug of choice for Refraction in Adults:** Homatropine or Cyclopentolate. * **Side Effects:** All these agents can precipitate **Acute Angle Closure Glaucoma** in predisposed individuals with narrow anterior chamber angles. * **Phenylephrine:** An alternative mydriatic that acts as an alpha-1 agonist; it causes mydriasis *without* cycloplegia [1].

Q: What is the antidote for datura poisoning?

Physostigmine. **Explanation:** Datura poisoning is characterized by **anticholinergic toxicity** (the "central anticholinergic syndrome"), caused by tropane alkaloids like scopolamine and hyoscyamine. These substances cross the blood-brain barrier (BBB), leading to both peripheral symptoms (tachycardia, dry mouth, dilated pupils) and central symptoms (delirium, hallucinations, seizures). **Why Physostigmine is the Correct Answer:** Physostigmine is a **tertiary amine** acetylcholinesterase inhibitor. Unlike other carbamates, its uncharged structure allows it to **cross the blood-brain barrier**. By inhibiting the breakdown of acetylcholine, it increases synaptic concentrations of the neurotransmitter, effectively reversing both the peripheral and, crucially, the **central neurotoxic effects** of Datura. **Analysis of Incorrect Options:** * **Neostigmine & Pyridostigmine:** These are **quaternary ammonium** compounds. They are polar/charged and **cannot cross the blood-brain barrier**. While they might reverse peripheral symptoms, they are ineffective against the life-threatening CNS manifestations of Datura poisoning. * **Atropine:** Atropine is a competitive muscarinic antagonist. Since Datura poisoning is already a state of atropine-like toxicity, administering more atropine would worsen the condition. (Note: Atropine is the antidote for organophosphate poisoning, not Datura). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Datura/Atropine Toxicity:** "Mad as a hatter (delirium), Red as a beet (flushing), Dry as a bone (anhidrosis), Blind as a bat (mydriasis), and Hot as a hare (hyperthermia)." * **Physostigmine Precaution:** It should be administered via slow IV injection. Rapid administration can cause bradycardia or seizures. It is contraindicated in patients with TCA (Tricyclic Antidepressant) overdose due to increased cardiotoxicity. * **DOC:** Physostigmine is also the drug of choice for Belladonna poisoning.

Q: Which of the following is the neuromuscular blocking agent with the shortest onset of action?

Succinylcholine. **Explanation:** The speed of onset of a neuromuscular blocking agent (NMBA) is primarily determined by its **mechanism of action** and **potency**. **Succinylcholine (Option D)** is the correct answer because it is a **depolarizing NMBA**. It acts as an agonist at the nicotinic acetylcholine receptors (nAChR) at the motor endplate, causing rapid and persistent depolarization. Due to its low potency and high concentration of molecules reaching the motor endplate quickly, it has the fastest onset of action (**30–60 seconds**). This makes it the gold standard for **Rapid Sequence Induction (RSI)** to secure the airway quickly. **Analysis of Incorrect Options:** * **Mivacurium (Option A):** A short-acting non-depolarizing agent, but its onset is relatively slow (2–4 minutes). It is metabolized by plasma cholinesterase. * **Vecuronium (Option B):** An intermediate-acting non-depolarizing agent with an onset of 2–3 minutes. It is noted for its cardiovascular stability. * **Rapacuronium (Option C):** A non-depolarizing agent designed to mimic the rapid onset of succinylcholine. While it was faster than other non-depolarizers, it was withdrawn from the market due to the risk of severe bronchospasm. **High-Yield Clinical Pearls for NEET-PG:** * **Fastest Onset:** Succinylcholine (Depolarizer). * **Fastest Non-depolarizer:** Rocuronium (Onset: 60–90 seconds; often used as an alternative to succinylcholine for RSI). * **Metabolism:** Succinylcholine is metabolized by **Pseudocholinesterase** (Butyrylcholinesterase). Deficiency of this enzyme leads to prolonged apnea. * **Key Side Effects of Succinylcholine:** Hyperkalemia (avoid in burn/trauma patients), muscle fasciculations, and triggering of **Malignant Hyperthermia**.

Q: Which of the following drugs does not act on the neuromuscular junction?

Dantrolene. ### Explanation The **Neuromuscular Junction (NMJ)** is the synapse between a motor neuron and a skeletal muscle fiber. Drugs acting here typically interfere with the nicotinic acetylcholine receptors ($N_m$) or the release of acetylcholine. **Why Dantrolene is the correct answer:** Dantrolene is a **direct-acting skeletal muscle relaxant**. Unlike the other options, it does not act at the NMJ (the synapse). Instead, it acts **intracellularly** by binding to the **Ryanodine Receptor (RyR1)** on the sarcoplasmic reticulum. This inhibits the release of calcium ions into the cytosol, thereby preventing excitation-contraction coupling. **Analysis of Incorrect Options:** * **Succinylcholine (Option A):** A **depolarizing neuromuscular blocker**. It acts as an agonist at the $N_m$ receptors at the NMJ, causing persistent depolarization and subsequent paralysis. * **Vecuronium (Option C):** An intermediate-acting **non-depolarizing neuromuscular blocker**. It acts as a competitive antagonist at the $N_m$ receptors at the NMJ. * **Mivacurium (Option D):** A short-acting **non-depolarizing neuromuscular blocker** that also acts as a competitive antagonist at the $N_m$ receptors. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Dantrolene is the life-saving treatment for **Malignant Hyperthermia** (triggered by volatile anesthetics or succinylcholine) and **Neuroleptic Malignant Syndrome (NMS)**. * **Metabolism:** Mivacurium is unique among non-depolarizing blockers because it is metabolized by **plasma cholinesterase** (pseudocholinesterase), similar to succinylcholine. * **Hofmann Elimination:** Remember **Atracurium and Cisatracurium** for their organ-independent elimination, making them safe in liver and kidney failure.

Question 1

Which of the following is NOT a cholinergic action?

Accepted Answer

Mydriasis

Answer

Salivation

Answer

Sweating

Answer

Bradycardia

Question 2

Within 5 minutes after a bee sting, a 15-year-old girl suddenly has difficulty breathing, with marked inspiratory stridor from laryngeal edema. She experiences marked urticaria and notes swelling of the hand that was stung. Which of the following is the best pharmacologic agent to treat her signs and symptoms?

Accepted Answer

Epinephrine

Answer

Cyclosporine

Answer

Glucocorticoids

Answer

Methotrexate

Question 3

Which beta-blocker drug is contraindicated in asthma patients?

Accepted Answer

Propranolol

Answer

Metoprolol

Answer

Atenolol

Answer

Acebutolol

Question 4

Which of the following receptors does not require the action of adrenaline for the treatment of anaphylactic shock?

Accepted Answer

α2

Answer

α1

Answer

β1

Answer

β2

Question 5

Which of the following sympathomimetic amines has agonistic action on a1, a2, b1, and b3 adrenoceptors, but not on b2 receptors?

Accepted Answer

Noradrenaline

Answer

Phenylephrine

Answer

Isoprenaline

Answer

Adrenaline

Question 6

Which of the following agents acts as a mydriatic?

Accepted Answer

Tropicamide

Answer

Atropine

Answer

Homatropine

Answer

All of the above

Question 7

What is the antidote for datura poisoning?

Accepted Answer

Physostigmine

Answer

Neostigmine

Answer

Pyridostigmine

Answer

Atropine

Question 8

Which of the following is the neuromuscular blocking agent with the shortest onset of action?

Accepted Answer

Succinylcholine

Answer

Mivacurium

Answer

Vecuronium

Answer

Rapacuronium

Question 9

Which of the following drugs does not act on the neuromuscular junction?

Accepted Answer

Dantrolene

Answer

Succinylcholine

Answer

Vecuronium

Answer

Mivacurium

Question 10

A gardener was accidentally poisoned by a weed killer that inhibits acetylcholinesterase. Which of the following alterations in neurochemical transmission at brain cholinergic synapses is the most likely result of this poisoning?

Accepted Answer

A pileup of acetylcholine outside the cholinergic neuron in the synaptic cleft

Answer

Blockade of cholinergic receptors

Answer

A pileup of choline outside the cholinergic neuron in the synaptic cleft

Answer

Up-regulation of postsynaptic cholinergic receptors

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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