Central Nervous System Pharmacology Practice Questions

Q: Which of the following muscle relaxants is a depolarizing agent?

Succinylcholine. ***Succinylcholine*** - **Succinylcholine** is the only **depolarizing neuromuscular blocker** in common clinical use, acting as an acetylcholine receptor agonist. - It works by initially causing muscle fasciculations (depolarization) followed by **sustained muscle paralysis** (desensitization phase). *Rocuronium* - **Rocuronium** is a **nondepolarizing neuromuscular blocker**. - It acts as a **competitive antagonist** at the nicotinic acetylcholine receptors at the neuromuscular junction, preventing acetylcholine from binding. *Vecuronium* - **Vecuronium** is also a **nondepolarizing neuromuscular blocker**. - It competes with acetylcholine for binding sites on the **nicotinic receptors** at the motor end plate without activating them. *Atracurium* - **Atracurium** is another **nondepolarizing neuromuscular blocker**. - Its mechanism involves **competitive antagonism** of acetylcholine at the neuromuscular junction, leading to muscle relaxation.

Q: Ketamine acts on which of the following?

NMDA receptor. ***NMDA receptor*** - **Ketamine** primarily acts as an **N-methyl-D-aspartate (NMDA) receptor antagonist**, blocking the effects of **glutamate**. - This action leads to its **dissociative anesthetic** effects, including analgesia, amnesia, and a cataleptic state. *Glycine receptor* - The **glycine receptor** is an inhibitory ionotropic receptor, primarily found in the **spinal cord** and brainstem. - Its activation leads to **hyperpolarization** and a decrease in neuronal excitability, a mechanism distinct from ketamine's action. *GABAa receptor* - The **GABAa receptor** is the primary inhibitory neurotransmitter receptor in the brain, and drugs like **benzodiazepines** and **barbiturates** act on it to produce sedation. - While ketamine has some indirect GABAergic effects at high doses, its primary mechanism of action is not through direct binding to GABAa receptors. *Ach receptor* - The **acetylcholine (Ach) receptor** is involved in various functions, including muscle contraction (nicotinic receptors) and parasympathetic responses (muscarinic receptors). - Drugs like **atropine** and **neostigmine** target these receptors, which are not the primary site of action for **ketamine**.

Q: A patient with epilepsy is given a drug that enhances GABA activity to prevent seizure activity. Which drug is appropriate?

Valproic acid. ***Valproic acid*** - **Valproic acid** primarily enhances **GABAergic activity** by inhibiting GABA transaminase, increasing GABA synthesis, and reducing GABA reuptake, which collectively help to stabilize neuronal activity and prevent seizures. - It is a **broad-spectrum anticonvulsant** effective against various seizure types, including generalized tonic-clonic, absence, and myoclonic seizures. *Phenytoin* - **Phenytoin** works by **blocking voltage-gated sodium channels**, thereby stabilizing neuronal membranes and preventing repetitive firing of action potentials. - It is effective for **focal (partial) seizures** and generalized tonic-clonic seizures, but its primary mechanism is not direct GABA potentiation. *Gabapentin* - **Gabapentin** modulates the **voltage-gated calcium channels** (specifically the α₂δ subunit), reducing the release of excitatory neurotransmitters. - While it has broad-spectrum effects that can reduce seizure activity, its direct mechanism of action is not primarily through enhancing GABA activity. *Lamotrigine* - **Lamotrigine** stabilizes neuronal membranes by **blocking voltage-gated sodium channels** and, to a lesser extent, inhibiting voltage-gated calcium channels. - It also reduces the release of excitatory neurotransmitters like glutamate, but it does not directly enhance GABAergic transmission.

Q: What are the possible CNS effects of local anesthetic agents?

All of the options. ***All of the options*** - **All three listed effects are genuine CNS manifestations** of local anesthetic systemic toxicity (LAST). - Local anesthetics produce a **biphasic CNS effect**: initial excitatory symptoms (perioral numbness, seizures) followed by depressive symptoms at higher concentrations. - Since the question asks for "**possible** CNS effects" (not the most severe or primary effect), all listed options are medically accurate answers. **CNS Effects of Local Anesthetics:** **Early/Excitatory Phase:** - *Perioral numbness* - Often the first CNS sign, indicating rising plasma levels; numbness and tingling around the mouth and tongue - *Convulsions/Seizures* - Result from blockade of inhibitory neurons, causing uninhibited excitatory activity; a serious manifestation requiring immediate treatment **Late/Depressive Phase:** - *Depression* - Occurs at very high toxic concentrations; includes CNS depression, loss of consciousness, respiratory depression, and potentially coma - This follows the excitatory phase as local anesthetics depress all neuronal activity at extremely high doses *Convulsions alone* - While convulsions are a serious and characteristic CNS effect, they represent only one possible manifestation, not all possible effects. *Perioral numbness alone* - This is an early warning sign of LAST but not the only CNS effect possible. *Depression alone* - This is a late-stage effect but not the only CNS manifestation possible.

Q: Which of the following drugs is useful in the prophylaxis of migraine?

Propranolol. ***Propranolol*** - **Propranolol** is a **beta-blocker** commonly used for **migraine prophylaxis** by reducing the frequency and severity of attacks. - It works by modulating **serotonergic pathways** and reducing the body's **fight-or-flight response**, which can be a trigger for migraines. *Sumatriptan* - **Sumatriptan** is a **serotonin (5-HT1B/1D) receptor agonist** used for the **acute treatment** of migraine attacks, not for prophylaxis. - It works by causing **vasoconstriction** of cranial blood vessels and inhibiting the release of **pro-inflammatory neuropeptides**. *Domperidone* - **Domperidone** is a **dopamine antagonist** used as an **antiemetic** to relieve nausea and vomiting, which can be associated with migraine attacks. - It does not have a role in the **prophylactic treatment** of migraine itself. *Ergotamine* - **Ergotamine** is an **ergot alkaloid** used for the **acute treatment** of moderate to severe migraines. - Due to its potential for **vasoconstriction** and **drug-induced headache** (medication overuse headache), it is not recommended for routine prophylaxis.

Q: Oculogyric crisis is known to be produced by all of the following drugs except:

Atropine. ***Atropine*** - **Atropine** is an **anticholinergic drug** that primarily causes mydriasis (pupil dilation) and cycloplegia (paralysis of ciliary muscle), but it is not known to cause oculogyric crisis. - Oculogyric crisis is a form of **acute dystonia**, which is typically associated with dopamine antagonists. *Prochlorperazine* - **Prochlorperazine** is a **dopamine receptor antagonist** and a typical antipsychotic, commonly used as an antiemetic. - It is known to produce **extrapyramidal symptoms**, including **acute dystonias** like oculogyric crisis, due to its dopamine-blocking effects. *Perphenazine* - **Perphenazine** is a **first-generation (typical) antipsychotic** with potent dopamine-blocking activity. - Similar to other typical antipsychotics, it can cause **extrapyramidal side effects**, including **oculogyric crisis**. *Trifluoperazine* - **Trifluoperazine** is a **high-potency typical antipsychotic** that strongly blocks dopamine D2 receptors. - Its strong dopamine antagonism makes it highly prone to causing **extrapyramidal symptoms**, such as **acute dystonias** like oculogyric crisis.

Q: Modafinil is a drug used in which of the following conditions?

Shift work disorder. ***Shift work disorder*** - **Modafinil** is a **wake-promoting agent** approved by the FDA for improving wakefulness in patients with excessive sleepiness associated with **shift work sleep disorder**. - It helps individuals maintain alertness during atypical work hours, overcoming disruption to their natural circadian rhythm. - **Note:** Modafinil's **primary indication is narcolepsy**, but among the given options, shift work disorder is the correct answer. *Chronic fatigue syndrome* - While fatigue is a primary symptom of **chronic fatigue syndrome**, modafinil is generally **not recommended** as a standard treatment. - Its efficacy in this condition is limited and inconsistent, and management focuses on symptom control and lifestyle adjustments. *Chronic pain syndrome* - **Modafinil has no direct analgesic properties** and is not indicated for **chronic pain syndrome**. - Treatment for chronic pain involves addressing underlying causes with appropriate analgesics or interventional therapies. *Insomnia* - **Modafinil is a wakefulness-promoting agent** and would be **contraindicated in insomnia**, as it would worsen the inability to sleep. - Insomnia is treated with sleep hygiene, cognitive behavioral therapy, or sedative-hypnotics.

Q: Which of the following is used for the patient on antiparkinsonian medication levodopa + carbidopa, but patient showing marked on-off effect?

Selegiline. ***Selegiline*** - **Selegiline** is a **MAO-B inhibitor** that slows the breakdown of dopamine in the brain, thus extending the therapeutic effect of **levodopa** and reducing motor fluctuations including "on-off" phenomena. - It works by inhibiting the enzyme monoamine oxidase type B, which metabolizes dopamine, thereby preserving both endogenous and levodopa-derived dopamine for more sustained dopaminergic stimulation. - **MAO-B inhibitors** are established adjuncts to levodopa therapy for managing motor complications and reducing "off" time. *Bromocriptine* - **Bromocriptine** is a **dopamine agonist** that directly stimulates dopamine receptors (particularly D2 receptors) and has a longer half-life than levodopa, providing more continuous dopaminergic stimulation [1]. - While dopamine agonists are also effective for motor fluctuations, **Selegiline** is often preferred as an initial adjunct due to its better tolerability profile and lower risk of inducing dyskinesias. - Bromocriptine can cause more side effects including **dyskinesias**, **hallucinations**, and **nausea**, particularly in elderly patients [1]. *Amantadine* - **Amantadine** is an **NMDA receptor antagonist** primarily used to treat **levodopa-induced dyskinesia** rather than motor fluctuations. - While it has mild antiparkinsonian effects, it is not the preferred agent for managing "on-off" phenomena specifically. - Its mechanism does not directly prolong levodopa's effect or prevent dopamine breakdown. *Rimonabant* - **Rimonabant** is a **cannabinoid receptor 1 (CB1) antagonist** that was previously marketed for obesity and smoking cessation but was **withdrawn from the market** due to serious psychiatric adverse effects including depression and suicidality. - It has **no role** in the management of **Parkinson's disease** or its motor complications.

Q: All of the following are CNS stimulants except?

Benzodiazepines. ***Correct Answer: Benzodiazepines*** - **Benzodiazepines** are the correct answer because they are central nervous system (CNS) **depressants**, NOT stimulants. - They enhance the effect of the neurotransmitter **GABA** at the GABA-A receptor, leading to decreased neuronal excitability. - They cause sedation, anxiolysis, muscle relaxation, and anticonvulsant effects. *Incorrect: Amphetamines* - **Amphetamines** are potent CNS **stimulants** that increase the release of dopamine and norepinephrine, leading to increased alertness, energy, and focus. - They are commonly prescribed for conditions like attention-deficit/hyperactivity disorder (ADHD) and narcolepsy, but also have high potential for abuse. *Incorrect: Cocaine* - **Cocaine** is a powerful CNS **stimulant** that blocks the reuptake of dopamine, norepinephrine, and serotonin in the brain, resulting in a rapid onset of euphoria, increased energy, and heightened sensory perception. - Its effects are short-lived, leading to a strong craving for more, and it has significant cardiovascular and neurological risks. *Incorrect: Methylphenidate* - **Methylphenidate** is a CNS **stimulant** structurally similar to amphetamines, primarily used in the treatment of ADHD and narcolepsy. - It works by blocking the reuptake of dopamine and norepinephrine, increasing the concentration of these neurotransmitters in the synaptic cleft, and improving attention and focus.

Question 1

Which of the following muscle relaxants is a depolarizing agent?

Accepted Answer

Succinylcholine

Answer

Rocuronium

Answer

Vecuronium

Answer

Atracurium

Question 2

Ketamine acts on which of the following?

Accepted Answer

NMDA receptor

Answer

Glycine receptor

Answer

GABAa receptor

Answer

Ach receptor

Question 3

A patient with epilepsy is given a drug that enhances GABA activity to prevent seizure activity. Which drug is appropriate?

Accepted Answer

Valproic acid

Answer

Phenytoin

Answer

Gabapentin

Answer

Lamotrigine

Question 4

A patient presents with a rapid onset of muscle weakness after starting a new medication. Which physiological mechanism should be primarily investigated?

Accepted Answer

Acetylcholine receptor blocking

Answer

Sodium channel blocking

Answer

Potassium channel activation

Answer

Calcium channel enhancement

Question 5

What are the possible CNS effects of local anesthetic agents?

Accepted Answer

All of the options

Answer

Convulsions

Answer

Perioral numbness

Answer

Depression

Question 6

Which of the following drugs is useful in the prophylaxis of migraine?

Accepted Answer

Propranolol

Answer

Sumatriptan

Answer

Domperidone

Answer

Ergotamine

Question 7

Oculogyric crisis is known to be produced by all of the following drugs except:

Accepted Answer

Atropine

Answer

Perphenazine

Answer

Prochlorperazine

Answer

Trifluoperazine

Question 8

Modafinil is a drug used in which of the following conditions?

Accepted Answer

Shift work disorder

Answer

Chronic fatigue syndrome

Answer

Chronic pain syndrome

Answer

Insomnia

Question 9

Which of the following is used for the patient on antiparkinsonian medication levodopa + carbidopa, but patient showing marked on-off effect?

Accepted Answer

Selegiline

Answer

Bromocriptine

Answer

Amantadine

Answer

Rimonabant

Question 10

All of the following are CNS stimulants except?

Accepted Answer

Benzodiazepines

Answer

Cocaine

Answer

Methylphenidate

Answer

Amphetamines

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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