Autonomic Nervous System Drugs Practice Questions

Q: Skin blood flow is decreased by ?

Noradrenaline. ***Noradrenaline*** - **Noradrenaline** (norepinephrine) is a potent **vasoconstrictor**, particularly in the skin, which **decreases blood flow** by stimulating alpha-1 adrenergic receptors. - This vasoconstrictive action redirects blood flow to more vital organs during stress or sympathetic activation. *Dopamine* - At low doses, dopamine can cause **renal and mesenteric vasodilation**, while at higher doses it acts similarly to noradrenaline causing **vasoconstriction**. - Its effects on skin blood flow are variable and dose-dependent; it is not primarily known for consistently decreasing skin blood flow like noradrenaline. *Isoprenaline* - **Isoprenaline** (isoproterenol) is a non-selective **beta-adrenergic agonist** that primarily causes **vasodilation** in most vascular beds, thereby **increasing blood flow**. - It would typically **increase skin blood flow** rather than decrease it, due to its strong beta-2 receptor agonism. *Acetylcholine* - **Acetylcholine** is the primary neurotransmitter for **sympathetic innervation of sweat glands** in the skin, but it also causes **vasodilation** when released by parasympathetic nerves. - In the skin, its overall effect on blood flow is typically **vasodilation**, contributing to heat dissipation.

Q: A patient with diabetes and COPD developed postoperative urinary retention. Considering the patient's condition, which of the following drugs can be used for short-term treatment to relieve the symptoms?

Tamsulosin. ***Tamsulosin*** - **Tamsulosin** is a **selective α1A-adrenergic antagonist** that is the most appropriate choice for postoperative urinary retention in this patient with COPD and diabetes. - It relaxes smooth muscle in the **bladder neck and prostatic urethra**, relieving bladder outlet obstruction without affecting respiratory function. - Its **uroselective properties** minimize systemic side effects like hypotension, making it safer in diabetic patients who may have autonomic dysfunction. - **Safe in COPD** as it has no bronchoconstrictive effects and does not affect glucose metabolism. *Bethanechol* - **Bethanechol** is a direct-acting muscarinic agonist that stimulates bladder detrusor muscle contraction. - However, it is **relatively contraindicated in COPD** due to its potential to cause **bronchospasm** and increase bronchial secretions through M3 receptor stimulation in the airways. - The risk of respiratory complications in a COPD patient outweighs its benefits for urinary retention. - Modern practice rarely uses bethanechol for urinary retention due to safety concerns and availability of safer alternatives. *Methacholine* - **Methacholine** is a non-selective muscarinic agonist used primarily for **bronchial provocation testing** to diagnose asthma and airway hyperreactivity. - It causes significant **bronchospasm** and is absolutely contraindicated in COPD patients. - Not used therapeutically for urinary retention due to severe systemic cholinergic side effects. *Terazosin* - **Terazosin** is a non-selective **α1-adrenergic antagonist** used for benign prostatic hyperplasia and hypertension. - While effective for bladder outlet obstruction, it causes more **orthostatic hypotension** than tamsulosin due to its non-selective α1 blockade. - In diabetic patients with potential **autonomic neuropathy**, the risk of postural hypotension makes it less preferable than the more selective tamsulosin.

Q: Which drug, used to lower intraocular pressure (IOP) in a patient with optic disc changes and ciliary congestion, acts by increasing uveoscleral outflow?

Latanoprost. ***Latanoprost*** - Latanoprost is a **prostaglandin analog** that primarily works by increasing the **uveoscleral outflow** of aqueous humor, effectively lowering intraocular pressure. - It is a first-line agent for glaucoma due to its efficacy and once-daily dosing. *Pilocarpine* - Pilocarpine is a **miotic agent** that increases aqueous humor outflow through the **trabecular meshwork** by causing ciliary muscle contraction, not uveoscleral outflow. - Its mechanism involves opening the trabecular spaces to facilitate drainage. *Timolol* - Timolol is a **beta-adrenergic blocker** that reduces intraocular pressure by **decreasing the production of aqueous humor**, not by increasing outflow. - It works by blocking beta-receptors in the ciliary body. *Dorzolamide* - Dorzolamide is a **carbonic anhydrase inhibitor** that lowers intraocular pressure by **reducing the secretion of aqueous humor** by the ciliary body. - It acts on the enzymes responsible for fluid production, not outflow pathways.

Q: A person was given a muscle relaxant that competitively blocks nicotinic receptors. Which of the following drugs is used for reversal of muscle relaxation after surgery?

Neostigmine. ***Neostigmine*** - **Neostigmine** is an **acetylcholinesterase inhibitor** that increases the amount of acetylcholine at the neuromuscular junction, thereby overcoming the competitive block at nicotinic receptors [1], [4]. - This increase in acetylcholine effectively reverses the paralysis caused by **nondepolarizing muscle relaxants**, making it useful for post-surgical recovery [2]. *Carbachol* - **Carbachol** is a **direct-acting cholinergic agonist** that stimulates both muscarinic and nicotinic receptors and is not typically used for reversing competitive neuromuscular blockade. - Its primary use is for glaucoma and to stimulate the bladder or bowels, not to counteract muscle relaxants. *Succinylcholine* - **Succinylcholine** is a **depolarizing muscle relaxant** and would prolong, rather than reverse, muscle blockade if administered after a competitive blocker [3]. - It works by initially causing depolarization and then preventing further muscle contraction, leading to paralysis. *Physostigmine* - **Physostigmine** is an **acetylcholinesterase inhibitor** that crosses the blood-brain barrier, making it more suitable for treating central anticholinergic toxicity rather than peripheral neuromuscular blockade. - While it inhibits acetylcholinesterase, its central effects and potential for seizures limit its use for reversing surgical muscle relaxation.

Q: Which of the following drugs is an alpha 2 agonist?

Apraclonidine. ***Apraclonidine*** - **Apraclonidine** is a synthetic **alpha-2 adrenergic agonist** that reduces aqueous humor production and increases uveoscleral outflow, thereby lowering intraocular pressure. - It is primarily used for the short-term treatment of **open-angle glaucoma** or ocular hypertension. *Timolol* - **Timolol** is a **non-selective beta-adrenergic blocker** that reduces aqueous humor production, leading to a decrease in intraocular pressure. - It does not act on alpha-2 receptors, distinguishing it from apraclonidine. *PG analogues* - **Prostaglandin analogues** (PG analogues) such as latanoprost, bimatoprost, and travoprost are primarily used to treat glaucoma by **increasing uveoscleral outflow** of aqueous humor. - They act on **prostaglandin F2α receptors**, not alpha-2 adrenergic receptors. *Verapamil* - **Verapamil** is a **calcium channel blocker** primarily used to treat hypertension, angina, and arrhythmias. - It acts by blocking calcium channels in vascular smooth muscle and the heart, and does not have significant alpha-2 adrenergic agonist activity.

Q: What is the mechanism of action of neuromuscular blocking agents such as curare?

Antagonizes ACh receptors. ***Antagonizes ACh receptors*** - Curare and related non-depolarizing neuromuscular blocking agents act as **competitive antagonists** at the **nicotinic acetylcholine (ACh) receptors** on the motor end plate of skeletal muscle. - By binding to these receptors without activating them, they prevent ACh from binding and initiating muscle contraction, leading to **flaccid paralysis**. *Inhibits ACh synthesis* - Drugs that inhibit **ACh synthesis**, such as hemicholinium, interfere with the uptake of choline into the presynaptic neuron. - This mechanism would eventually reduce ACh release but is not the direct action of curare-like agents, which block postsynaptic receptors. *Causes persistent depolarization* - This is the mechanism of action of **depolarizing neuromuscular blockers** such as **succinylcholine**, which activate the ACh receptor and cause prolonged depolarization, rendering the muscle unresponsive. - Curare-like drugs are **non-depolarizing** and do not cause persistent depolarization. *Acts as an agonist at ACh receptors* - A drug that acts as an **agonist at ACh receptors** would **activate muscle contraction**, initially causing fasciculations followed by paralysis due to persistent depolarization (as seen with succinylcholine). - Curare, however, **blocks** these receptors, preventing activation.

Q: Which of the following is the only clinically available depolarizing muscle relaxant?

Suxamethonium. ***Suxamethonium*** - **Suxamethonium** (also known as succinylcholine) is currently the **only depolarizing neuromuscular blocker** available for clinical use. - It works by mimicking acetylcholine, binding to and activating nicotinic acetylcholine receptors at the **neuromuscular junction**, causing initial muscle fasciculations followed by relaxation. *Decamethonium* - **Decamethonium** is a depolarizing neuromuscular blocker but is **no longer clinically available** due to its prolonged action and side effects. - It also acts by opening nicotinic acetylcholine receptor channels, leading to depolarization and muscle paralysis. *Mivacurium* - **Mivacurium** is a **nondepolarizing neuromuscular blocker**, meaning it acts as a competitive antagonist at the acetylcholine receptor. - It is known for its **short duration of action** due to rapid hydrolysis by plasma cholinesterases but is not depolarizing. *None of the options* - This option is incorrect because suxamethonium is indeed a clinically available depolarizing muscle relaxant. - The question specifically asks for the *only* clinically available one, which suxamethonium fulfills.

Q: Suxamethonium primarily acts on which type of receptors?

Nicotinic acetylcholine receptors. ***Nicotinic acetylcholine receptors*** - **Suxamethonium** is a depolarizing muscle relaxant that acts as an **agonist at nicotinic acetylcholine receptors** at the neuromuscular junction. - This initial activation leads to muscle fasciculations followed by prolonged depolarization, causing **flaccid paralysis**. *Potassium channels* - While some drugs may affect potassium channels to alter neuronal excitability, suxamethonium's primary mechanism of action is not on these channels. - Blocking potassium channels is characteristic of drugs like **certain antiarrhythmics** or **sulfonylureas**. *Calcium channels* - **Calcium channels** play a role in muscle contraction, but they are not the primary target of suxamethonium. - Drugs like **dihydropyridines** (e.g., nifedipine) target calcium channels for their antihypertensive effects. *Chloride channels* - Chloride channels are involved in maintaining resting membrane potential and inhibitory neurotransmission. - Drugs such as **benzodiazepines** indirectly enhance GABA-mediated chloride influx, which is distinct from suxamethonium's action.

Q: Which of the following substances is commonly known as an arrow poison used by indigenous South American tribes?

Curare. ***Curare*** - **Curare** is the traditional name for South American arrow poisons derived from plants, primarily *Chondrodendron tomentosum* and *Strychnos* species - It acts as a **competitive non-depolarizing neuromuscular blocking agent**, blocking nicotinic receptors at the neuromuscular junction - Causes **skeletal muscle paralysis** by competing with acetylcholine, leading to respiratory failure in prey - **Clinical relevance:** Tubocurarine (d-tubocurarine), derived from curare, was historically used as a muscle relaxant in surgery; modern derivatives include atracurium, vecuronium, and rocuronium *Opium* - **Opium** is derived from *Papaver somniferum* (opium poppy) and contains alkaloids like morphine and codeine - Acts on **opioid receptors** in the CNS to produce analgesia and sedation - Not used as an arrow poison by South American tribes; its effects are analgesic rather than paralytic *Cannabis* - **Cannabis** (*Cannabis sativa*) contains psychoactive compounds like THC (tetrahydrocannabinol) - Acts on **cannabinoid receptors** producing psychoactive and analgesic effects - Not used as an arrow poison; lacks the rapid paralytic action needed for hunting *Cyanide* - **Cyanide** inhibits cytochrome c oxidase, blocking cellular respiration and causing rapid cell death - While highly toxic, it is **not the traditional arrow poison** of South American indigenous tribes - Traditional arrow poisons like curare cause neuromuscular paralysis rather than cellular asphyxiation

Question 1

Skin blood flow is decreased by ?

Accepted Answer

Noradrenaline

Answer

Isoprenaline

Answer

Dopamine

Answer

Acetylcholine

Question 2

A patient with diabetes and COPD developed postoperative urinary retention. Considering the patient's condition, which of the following drugs can be used for short-term treatment to relieve the symptoms?

Accepted Answer

Tamsulosin

Answer

Bethanechol

Answer

Methacholine

Answer

Terazosin

Question 3

Which drug, used to lower intraocular pressure (IOP) in a patient with optic disc changes and ciliary congestion, acts by increasing uveoscleral outflow?

Accepted Answer

Latanoprost

Answer

Pilocarpine

Answer

Timolol

Answer

Dorzolamide

Question 4

A person was given a muscle relaxant that competitively blocks nicotinic receptors. Which of the following drugs is used for reversal of muscle relaxation after surgery?

Accepted Answer

Neostigmine

Answer

Carbachol

Answer

Succinylcholine

Answer

Physostigmine

Question 5

Which of the following drugs is an alpha 2 agonist?

Accepted Answer

Apraclonidine

Answer

Timolol

Answer

PG analogues

Answer

Verapamil

Question 6

What is the mechanism of action of neuromuscular blocking agents such as curare?

Accepted Answer

Antagonizes ACh receptors

Answer

Inhibits ACh synthesis

Answer

Causes persistent depolarization

Answer

Acts as an agonist at ACh receptors

Question 7

Which of the following is the only clinically available depolarizing muscle relaxant?

Accepted Answer

Suxamethonium

Answer

Decamethonium

Answer

Mivacurium

Answer

None of the options

Question 8

What is the mechanism of action of Curare drugs as muscle relaxants?

Accepted Answer

Act competitively on Ach receptors blocking post-synaptically

Answer

Persistently depolarizing at Neuromuscular junction

Answer

Repetitive stimulation of Ach receptors on muscle end plate

Answer

Inhibiting the calcium channel on presynaptic membrane

Question 9

Suxamethonium primarily acts on which type of receptors?

Accepted Answer

Nicotinic acetylcholine receptors

Answer

Potassium channels

Answer

Calcium channels

Answer

Chloride channels

Question 10

Which of the following substances is commonly known as an arrow poison used by indigenous South American tribes?

Accepted Answer

Curare

Answer

Opium

Answer

Cannabis

Answer

Cyanide

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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