Neurophysiology — MCQs
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Which lipoprotein has the highest concentration of endogenous triglycerides?
According to Herrington classification, decerebrate rigidity is characterized by all of the following EXCEPT:
In EEG, delta waves are seen:
The reward or pleasure center is present in which of the following areas?
Damage to the striatum affects which type of memory?
The Node of Ranvier is a gap in the myelin sheath of nerve fibers. Where are these nodes typically found?
Ocular bobbing is a sign associated with lesions in which part of the brainstem?
Which neurotransmitter is depleted in Parkinson's disease?
What is the characteristic EEG rhythm observed in a fully awake and alert state?
Which of the following is NOT a feature of REM sleep?
Neurophysiology Indian Medical PG Practice Questions and MCQs
Question 1: Which lipoprotein has the highest concentration of endogenous triglycerides?
- A. Chylomicrons
- B. VLDL (Very-low-density lipoprotein) (Correct Answer)
- C. LDL (Low-density lipoprotein)
- D. HDL (High-density lipoprotein)
Explanation: **Explanation:** The core of this question lies in distinguishing between **exogenous** and **endogenous** lipid transport. **Why VLDL is correct:** VLDL (Very-low-density lipoprotein) is synthesized in the **liver**. Its primary physiological role is to transport **endogenous triglycerides** (lipids synthesized by the body) from the liver to peripheral tissues. It contains approximately 50-60% triglycerides by weight, making it the lipoprotein with the highest concentration of triglycerides of internal origin. **Why the other options are incorrect:** * **Chylomicrons:** While chylomicrons have the highest *overall* triglyceride content (85-90%), these are **exogenous** (dietary) triglycerides absorbed from the intestines. The question specifically asks for endogenous sources. * **LDL:** Known as the primary carrier of **cholesterol** to peripheral tissues. It is a metabolic byproduct of VLDL (via IDL) and has a low triglyceride concentration. * **HDL:** Known as "good cholesterol," it is involved in **reverse cholesterol transport** (carrying cholesterol from tissues back to the liver). It has the highest protein content and the lowest lipid content. **High-Yield Clinical Pearls for NEET-PG:** * **Apolipoprotein Marker:** B-100 is the characteristic apolipoprotein for VLDL and LDL, while B-48 is unique to Chylomicrons. * **Rate-limiting enzyme:** HMG-CoA reductase is the rate-limiting enzyme for endogenous cholesterol synthesis (target of Statins). * **Lipoprotein Lipase (LPL):** This enzyme, located on capillary endothelium, is responsible for clearing triglycerides from both Chylomicrons and VLDL. * **Friedewald Equation:** LDL = Total Cholesterol – HDL – (Triglycerides/5). Note: This is invalid if TG >400 mg/dL.
Question 2: According to Herrington classification, decerebrate rigidity is characterized by all of the following EXCEPT:
- A. Rigidity occurs in all muscles of the body. (Correct Answer)
- B. Increased rate of discharge of the 'y' efferent neuron.
- C. Increased excitability of the motor neuron pool.
- D. Decerebration produces no phenomenon akin to spinal shock.
Explanation: **Explanation:** Decerebrate rigidity occurs due to a transection of the brainstem between the superior and inferior colliculi (midbrain). This removes the inhibitory influence of higher centers (like the basal ganglia and cortex) on the **Lateral Reticulospinal** and **Vestibulospinal** tracts, leading to an overactive excitatory drive to the extensor muscles. **1. Why Option A is the Correct Answer (The "Except"):** Rigidity in decerebration is **not universal**. It is characterized specifically by **extensor predominance** (antigravity muscles). In humans, this manifests as extension of all four limbs, internal rotation of the shoulders, and plantar flexion. It does not affect all muscles equally; flexor tone is actually inhibited. **2. Analysis of Other Options:** * **Option B:** Decerebrate rigidity is primarily **Gamma ($\gamma$)-driven**. The brainstem excitatory centers increase the discharge of $\gamma$-efferent neurons, which increases muscle spindle sensitivity, leading to a reflex increase in $\alpha$-motor neuron activity. * **Option C:** Due to the loss of cortical inhibition and the facilitation of the Vestibulospinal tract, there is a state of heightened excitability in the **$\alpha$-motor neuron pool**, making the muscles hyper-responsive to stretch. * **Option D:** Unlike spinal cord transection, which leads to "spinal shock" (temporary loss of all reflexes), decerebration results in **immediate hyperactivity** of reflexes and hypertonicity because the vestibulospinal pathways remain intact. **High-Yield Clinical Pearls for NEET-PG:** * **Level of Lesion:** Below the Red Nucleus (Midbrain) but above the Vestibular Nuclei (Pons). * **Decorticate vs. Decerebrate:** Decorticate (lesion above Red Nucleus) presents with **flexion of arms** (due to intact Rubrospinal tract) and extension of legs. Decerebrate (lesion below Red Nucleus) presents with **extension of all four limbs**. * **Mechanism:** It is a form of **spasticity** (velocity-dependent) rather than true lead-pipe rigidity.
Question 3: In EEG, delta waves are seen:
- A. Due to the reticular system
- B. When the thalamus is cut off from the pons
- C. In deep sleep (Correct Answer)
- D. Originating from the thalamocortical area
Explanation: ### Explanation **Correct Answer: C. In deep sleep** **Underlying Medical Concept:** EEG (Electroencephalogram) waves are categorized by their frequency and amplitude, reflecting the synchronized electrical activity of cortical neurons. **Delta waves** are the slowest (0.5–4 Hz) and have the highest amplitude. They are the hallmark of **Stage N3 (Non-REM) sleep**, also known as slow-wave sleep or deep sleep. In a healthy, awake adult, the presence of delta waves is considered abnormal and usually indicates organic brain disease or deep anesthesia. **Analysis of Incorrect Options:** * **Option A:** The **Reticular Activating System (RAS)** is responsible for arousal and wakefulness. High activity in the RAS leads to desynchronized, low-amplitude, high-frequency waves (Beta waves), which are the opposite of Delta waves. * **Option B:** If the thalamus is "cut off" from the lower brainstem (pons), it does not specifically generate delta waves. However, delta waves are known to occur when the **cortex is freed from the influences of the reticular activating system**, often seen in deep coma or major cortical transection, but the primary physiological association remains deep sleep. * **Option D:** While the **thalamus** acts as a pacemaker for many EEG rhythms (like Alpha waves and sleep spindles), Delta waves are primarily generated by the **cortex** itself when it is decoupled from the rhythmic input of the thalamocortical system. **Clinical Pearls for NEET-PG:** * **Alpha Waves (8–13 Hz):** Seen in awake, relaxed individuals with eyes closed (maximal in the occipital cortex). * **Beta Waves (14–30 Hz):** Seen during mental activity, stress, or when eyes are open (Frontal/Parietal). * **Theta Waves (4–7 Hz):** Normal in children; in adults, seen during emotional stress or Stage N1 sleep. * **Delta Waves (0.5–4 Hz):** Normal in infancy and deep sleep; abnormal in awake adults (indicates brain tumors, inflammation, or vascular lesions). * **REM Sleep:** EEG shows a "sawtooth" pattern similar to the awake state (Beta-like waves).
Question 4: The reward or pleasure center is present in which of the following areas?
- A. Ventral tegmental area (Correct Answer)
- B. Ventromedial medulla
- C. Magnus raphe nucleus
- D. Locus coeruleus
Explanation: **Explanation:** The **Ventral Tegmental Area (VTA)** is the primary component of the brain's **reward system** (mesolimbic and mesocortical pathways). It contains a high concentration of dopaminergic neurons that project to the **Nucleus Accumbens**, the amygdala, and the prefrontal cortex. Activation of this circuit by natural rewards (food, sex) or addictive substances leads to the release of dopamine, producing the sensation of pleasure and reinforcing behavior. **Analysis of Incorrect Options:** * **Ventromedial Medulla (VMM):** This area is primarily involved in the **descending modulation of pain**. It contains "on-cells" and "off-cells" that can either facilitate or inhibit pain signals in the spinal cord. * **Magnus Raphe Nucleus:** Located in the brainstem, this nucleus is the principal site of **serotonergic neurons**. It plays a crucial role in the descending pain inhibitory pathway and the regulation of mood and sleep-wake cycles. * **Locus Coeruleus:** This is the primary site for **norepinephrine (noradrenaline)** synthesis in the brain. It is responsible for physiological responses to stress, arousal, and the "fight or flight" response. **High-Yield Facts for NEET-PG:** * **The Reward Pathway:** VTA $\rightarrow$ Nucleus Accumbens (the "pleasure center" proper) $\rightarrow$ Prefrontal Cortex. * **Neurotransmitter:** **Dopamine** is the key neurotransmitter for reward; **Serotonin** for mood; **Norepinephrine** for arousal. * **Punishment Centers:** Primarily located in the **periaqueductal gray (PAG)** and the lateral hypothalamus. * **Addiction:** Most drugs of abuse (e.g., cocaine, amphetamines) act by increasing dopamine levels in the Nucleus Accumbens via the VTA.
Question 5: Damage to the striatum affects which type of memory?
- A. Procedural memory (Correct Answer)
- B. Short-term memory
- C. Long-term memory
- D. Explicit memory
Explanation: **Explanation:** The **striatum** (comprising the caudate nucleus and putamen) is the primary input component of the **basal ganglia**. It plays a critical role in the formation and execution of **procedural memory**, which is the "how-to" memory for skills, habits, and motor tasks (e.g., riding a bike or playing an instrument). This type of memory is acquired through repetitive practice and does not require conscious awareness. * **Why Procedural Memory is Correct:** The basal ganglia circuit facilitates motor learning by reinforcing successful motor patterns. Damage to the striatum (as seen in Huntington’s disease) leads to significant deficits in learning new motor skills, while facts and events (declarative memory) often remain intact. **Analysis of Incorrect Options:** * **Short-term memory:** Primarily involves the **prefrontal cortex** for working memory and temporary storage. * **Long-term memory:** This is a broad category. While procedural memory is a subtype of long-term memory, the question asks for the *specific* type. Usually, general long-term memory refers to declarative memory. * **Explicit (Declarative) memory:** This involves the conscious recall of facts (semantic) and events (episodic). It is mediated by the **hippocampus** and the **medial temporal lobe**, not the striatum. **High-Yield Clinical Pearls for NEET-PG:** * **Hippocampus:** Essential for **Anterograde memory** (forming new memories). Damage leads to an inability to form new declarative memories. * **Amygdala:** Involved in **Emotional memory** (fear conditioning). * **Cerebellum:** Also involved in procedural memory, specifically for **motor reflex conditioning** and coordination. * **Huntington’s Disease:** Characterized by striatal degeneration, leading to chorea and loss of procedural memory/habit formation.
Question 6: The Node of Ranvier is a gap in the myelin sheath of nerve fibers. Where are these nodes typically found?
- A. Cell body
- B. Dendrites
- C. Axons (Correct Answer)
- D. Terminal buttons
Explanation: **Explanation:** **1. Why the Correct Answer is Right:** The **Node of Ranvier** is a periodic gap in the insulating myelin sheath of a neuron. These nodes are specifically located along the **Axon**. In the Peripheral Nervous System (PNS), myelin is formed by Schwann cells, while in the Central Nervous System (CNS), it is formed by Oligodendrocytes. The primary function of these nodes is to facilitate **Saltatory Conduction**, where the action potential "jumps" from one node to the next. This occurs because voltage-gated sodium channels are highly concentrated at the nodes, allowing for rapid depolarization and significantly increasing the speed of nerve impulse transmission compared to unmyelinated fibers. **2. Why the Incorrect Options are Wrong:** * **Cell Body (Soma):** This is the metabolic center of the neuron containing the nucleus. It lacks a myelin sheath and therefore does not possess Nodes of Ranvier. * **Dendrites:** These are branched projections that receive signals from other neurons. While they can propagate electrical impulses, they are typically unmyelinated. * **Terminal Buttons:** These are the distal ends of the axon that form synapses. By the time the axon reaches the terminal button, the myelin sheath has ended to allow for neurotransmitter release. **3. NEET-PG High-Yield Pearls:** * **Saltatory Conduction:** Conserves energy (ATP) because the Na+/K+ ATPase pump only needs to work at the nodes to restore ionic gradients. * **Demyelinating Diseases:** In **Multiple Sclerosis** (CNS) and **Guillain-Barré Syndrome** (PNS), the loss of myelin disrupts conduction at these nodes, leading to neurological deficits. * **Internode:** The myelinated segment between two nodes. The length of the internode is proportional to the diameter of the fiber; thicker fibers have longer internodes and faster conduction.
Question 7: Ocular bobbing is a sign associated with lesions in which part of the brainstem?
- A. Midbrain
- B. Pons (Correct Answer)
- C. Medulla
- D. Cortex
Explanation: ### Explanation **Ocular bobbing** is a distinctive clinical sign characterized by a **rapid downward jerk** of the eyes followed by a **slow, drifting return** to the primary mid-position. **1. Why Pons is the Correct Answer:** Ocular bobbing is a classic localizing sign for **destructive lesions of the caudal (lower) pons**, most commonly due to a pontine hemorrhage, large infarcts, or tumors. The pathophysiology involves the destruction of the horizontal gaze centers (Paramedian Pontine Reticular Formation - PPRF). When horizontal eye movements are abolished, vertical movements (mediated by the midbrain) are "unmasked" or released, but in a dysfunctional, rhythmic pattern. **2. Why Other Options are Incorrect:** * **Midbrain:** Lesions here typically cause **Parinaud Syndrome** (dorsal midbrain syndrome), characterized by upward gaze palsy, pupillary light-reflex dissociation, and convergence-retraction nystagmus, rather than bobbing. * **Medulla:** Medullary lesions (like Wallenberg syndrome) usually present with nystagmus, ataxia, and sensory deficits, but do not produce the rhythmic vertical "bobbing" motion. * **Cortex:** Cortical lesions (e.g., in the Frontal Eye Fields) cause a horizontal gaze preference (eyes look *towards* the side of the lesion) but do not affect vertical rhythmic movements. **3. High-Yield Clinical Pearls for NEET-PG:** * **Inverse Bobbing (Ocular Dipping):** Slow downward movement followed by a rapid return to mid-position (opposite of bobbing); often seen in **anoxic encephalopathy**. * **Pre-requisite:** For true ocular bobbing to occur, **horizontal eye movements must be absent**. * **Mnemonic:** "Bobbing for Apples in the **Ponds**" (Pons). * **Commonest Cause:** Spontaneous intrapontine hemorrhage.
Question 8: Which neurotransmitter is depleted in Parkinson's disease?
- A. Dopamine (Correct Answer)
- B. Acetylcholine
- C. Glutamate
- D. GABA
Explanation: **Explanation:** **Correct Answer: A. Dopamine** Parkinson’s disease is a progressive neurodegenerative disorder primarily characterized by the loss of **dopaminergic neurons** in the **Substantia Nigra pars compacta (SNpc)** of the midbrain. These neurons project to the striatum (Nigrostriatal pathway). Dopamine normally exerts an inhibitory effect on the indirect pathway and an excitatory effect on the direct pathway of the basal ganglia to facilitate smooth movement. Depletion leads to an imbalance, resulting in the classic triad of bradykinesia, resting tremors, and rigidity. **Why Incorrect Options are Wrong:** * **B. Acetylcholine:** In Parkinson’s, there is a relative **excess** of cholinergic activity due to the loss of dopamine’s inhibitory influence. This imbalance contributes to tremors. (Note: Acetylcholine is depleted in Alzheimer’s disease). * **C. Glutamate:** This is the primary excitatory neurotransmitter. While glutamate excitotoxicity may play a role in neuronal death, it is not the primary neurotransmitter depleted. * **D. GABA:** This is the primary inhibitory neurotransmitter of the basal ganglia output nuclei. While GABAergic signaling is altered in Parkinson’s, it is not the primary site of depletion. **High-Yield Clinical Pearls for NEET-PG:** * **Pathological Hallmark:** Presence of **Lewy bodies** (intracytoplasmic inclusions containing **alpha-synuclein**). * **MPTP:** A neurotoxin that specifically destroys dopaminergic neurons, used to study Parkinsonism in labs. * **Treatment Gold Standard:** Levodopa (a dopamine precursor) combined with Carbidopa (a peripheral DOPA decarboxylase inhibitor). * **Surgical Target:** Subthalamic Nucleus (STN) is the most common site for Deep Brain Stimulation (DBS).
Question 9: What is the characteristic EEG rhythm observed in a fully awake and alert state?
- A. Alpha rhythm
- B. Beta rhythm (Correct Answer)
- C. Theta rhythm
- D. Delta rhythm
Explanation: **Explanation:** The Electroencephalogram (EEG) reflects the summation of excitatory and inhibitory postsynaptic potentials in the cerebral cortex. The correct answer is **Beta rhythm** because it is the hallmark of an active, alert, and focused mind. **1. Why Beta rhythm is correct:** Beta waves have the highest frequency (**13–30 Hz**) and the lowest amplitude. They are observed when a person is **fully awake, alert, and mentally active** (e.g., solving a math problem) or during REM sleep. This state is known as "desynchronization" because the cortical neurons are firing rapidly and independently to process information. **2. Analysis of Incorrect Options:** * **Alpha rhythm (8–13 Hz):** Characteristic of an adult who is **awake but relaxed with eyes closed**. It is best seen in the parieto-occipital region and disappears (alpha block) upon opening the eyes or mental concentration. * **Theta rhythm (4–7 Hz):** Normal in children and during **Stage N1 sleep** in adults. If seen in an awake adult, it may indicate emotional stress or degenerative brain states. * **Delta rhythm (<4 Hz):** The slowest waves with the highest amplitude. They are characteristic of **deep sleep (Stage N3/SWS)** and are strictly pathological in an awake adult. **Clinical Pearls for NEET-PG:** * **Mnemonic for Frequency (High to Low):** **B**at **A**te **T**he **D**og (**B**eta > **A**lpha > **T**heta > **D**elta). * **REM Sleep Paradox:** Although it is deep sleep, the EEG shows **Beta waves**, similar to an awake state (hence "paradoxical sleep"). * **Epilepsy:** The classic EEG finding in Absence Seizures (Petit Mal) is a **3 Hz spike-and-wave pattern**. * **Brain Death:** Confirmed by a "flat" or isoelectric EEG.
Question 10: Which of the following is NOT a feature of REM sleep?
- A. Bruxism (Correct Answer)
- B. Irregular breathing
- C. Muscle tone in the body is depressed
- D. Associated with active dreaming
Explanation: **Explanation:** The correct answer is **A. Bruxism**. **1. Why Bruxism is the correct answer:** Bruxism (teeth grinding) is a **parasomnia** that typically occurs during **Stage N2 (Non-REM)** sleep, not REM sleep. During REM sleep, the body undergoes profound somatic muscle atonia (paralysis) mediated by the pontine reticular formation and glycine-mediated inhibition of spinal motor neurons. This physiological paralysis prevents the physical acting out of dreams, making repetitive motor activities like bruxism highly unlikely during this phase. **2. Analysis of Incorrect Options:** * **B. Irregular breathing:** REM sleep is characterized by autonomic instability. This leads to fluctuations in heart rate, blood pressure, and notably, an irregular respiratory rate and pattern. * **C. Muscle tone is depressed:** As mentioned, **REM atonia** is a hallmark feature. The only muscles spared are the extraocular muscles (leading to Rapid Eye Movements) and the diaphragm. * **D. Associated with active dreaming:** REM is often called "Paradoxical Sleep" because the EEG shows high-frequency, low-voltage activity (similar to wakefulness) associated with vivid, narrative, and emotional dreaming. **3. High-Yield Clinical Pearls for NEET-PG:** * **REM Sleep Markers:** PGO spikes (Ponto-Geniculo-Occipital), Beta/Gamma waves on EEG, and penile/clitoral tumescence. * **REM Sleep Behavior Disorder (RBD):** A condition where REM atonia is lost, causing patients to "act out" dreams; it is a strong predictor of future alpha-synucleinopathies (e.g., Parkinson’s disease). * **Sleep Walking/Night Terrors:** These occur during **Stage N3 (Deep NREM)**, not REM. * **Drugs and REM:** Alcohol and Benzodiazepines **decrease** REM sleep duration.
Practice by Chapter
Neurons and Glial Cells
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Synaptic Transmission
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Sensory Processing
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Motor Control Systems
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Autonomic Nervous System
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Hypothalamus and Limbic System
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Cerebral Cortex Functions
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Electroencephalography
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Neuroplasticity
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Sleep and Wakefulness
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