Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 161: Which of the following is NOT seen in Kluver-Bucy syndrome?

A. Seizures (Correct Answer)
B. Hypersexuality
C. Metamorphopsia
D. Visual agnosia

Explanation: ### Explanation **Kluver-Bucy Syndrome (KBS)** is a clinical behavioral syndrome resulting from **bilateral lesions of the anterior temporal lobes**, specifically involving the **amygdala**. #### Why "Seizures" is the Correct Answer While temporal lobe epilepsy can *cause* the brain damage that leads to KBS, **seizures are not a clinical feature of the syndrome itself**. KBS is defined by a specific constellation of behavioral and cognitive changes. In fact, if KBS occurs following surgery (like a bilateral temporal lobectomy), the procedure is often performed specifically to *treat* intractable seizures, not to cause them. #### Analysis of Incorrect Options (Features of KBS) * **Visual Agnosia (Option D):** Often called "psychic blindness," patients can see but cannot recognize or understand the meaning of objects. * **Metamorphopsia (Option C):** This refers to visual distortions (objects appearing smaller, larger, or misshapen). In the context of KBS, it is part of the broader visual processing deficit where patients fail to process the "what" of an object. * **Hypersexuality (Option B):** Patients exhibit a loss of sexual inhibition, often manifesting as inappropriate suggestions or attempts to mate with inanimate objects. #### High-Yield Clinical Pearls for NEET-PG To remember the features of KBS, use the mnemonic **"6 H's"**: 1. **Hyperphagia:** Excessive eating or pica (placing non-food items in the mouth). 2. **Hyperorality:** A compulsion to examine all objects by mouth. 3. **Hypersexuality:** Increased libido and loss of social sexual inhibitions. 4. **Hypermetamorphosis:** An irresistible impulse to notice and react to every visual stimulus. 5. **Hypo-emotionality (Placidity):** Flattened affect; loss of fear and anger (the "tame" animal). 6. **Hyper-agnosia (Visual Agnosia):** Inability to recognize objects visually. **Key Anatomical Site:** Bilateral Amygdala. **Common Causes:** Herpes Simplex Encephalitis (most common), trauma, or Pick’s disease.

Question 162: Posture is maintained by which reflex mechanism?

A. Crossed extensor reflex
B. Stretch reflex (Correct Answer)
C. Golgi tendon reflex
D. None of the above

Explanation: **Explanation:** The maintenance of posture and muscle tone is primarily mediated by the **Stretch Reflex (Myotatic Reflex)**. When gravity causes a slight displacement of a joint, the associated muscles are stretched. This activates **Muscle Spindles** (the sensory receptors), which send impulses via Type Ia afferent fibers to the spinal cord. These fibers synapse directly with alpha motor neurons, causing the stretched muscle to contract, thereby resisting the displacement and maintaining an upright posture. This is a monosynaptic reflex and is the only reflex that is continuously active to counteract gravity. **Analysis of Incorrect Options:** * **A. Crossed Extensor Reflex:** This is a polysynaptic withdrawal reflex. When one limb encounters a painful stimulus and withdraws (flexion), the opposite limb extends to support the body weight. While it helps in balance during sudden movements, it is not the primary mechanism for steady-state posture. * **C. Golgi Tendon Reflex (Inverse Stretch Reflex):** This is a protective disynaptic reflex mediated by Golgi Tendon Organs (GTOs). It causes muscle **relaxation** in response to excessive tension to prevent tendon avulsion. It acts as a "safety valve" rather than a postural mechanism. **High-Yield NEET-PG Pearls:** * **Muscle Spindle:** Detects change in muscle **length** (Static and Dynamic). * **Golgi Tendon Organ:** Detects change in muscle **tension**. * **Gamma Motor Neurons:** Regulate the sensitivity of the muscle spindle; they are crucial for maintaining the "stretch reflex" during voluntary contraction (Alpha-Gamma Co-activation). * **Supraspinal Control:** The Pontine Reticulospinal and Lateral Vestibulospinal tracts are the primary excitatory pathways to the gamma motor neurons that maintain postural tone.

Question 163: What is the receptor for Brain-Derived Neurotrophic Factor (BDNF)?

A. TrkB
B. Trk-B (Correct Answer)
C. Trk-C
D. None of the above

Explanation: **Explanation:** **Brain-Derived Neurotrophic Factor (BDNF)** is a key member of the neurotrophin family, essential for the survival, growth, and plasticity of neurons in the central and peripheral nervous systems. 1. **Why Option B is Correct:** Neurotrophins exert their effects by binding to specific high-affinity transmembrane tyrosine kinase receptors known as **Trk (Tropomyosin receptor kinase) receptors**. BDNF specifically binds to and activates **TrkB**. Upon binding, TrkB undergoes dimerization and autophosphorylation, triggering intracellular signaling pathways (like MAPK and PI3K) that promote neuronal survival and long-term potentiation (LTP). 2. **Why Other Options are Incorrect:** * **TrkA:** This is the primary receptor for **Nerve Growth Factor (NGF)**. * **TrkC:** This is the primary receptor for **Neurotrophin-3 (NT-3)**. * *Note:* All neurotrophins (NGF, BDNF, NT-3, and NT-4/5) can also bind to a low-affinity receptor called **p75NTR**, which belongs to the tumor necrosis factor receptor family and often mediates apoptosis. 3. **High-Yield Clinical Pearls for NEET-PG:** * **BDNF & Memory:** BDNF is crucial for **Long-Term Potentiation (LTP)** in the hippocampus, making it vital for memory formation. * **Depression Link:** The "Neurotrophic Hypothesis of Depression" suggests that decreased levels of BDNF contribute to hippocampal atrophy in clinical depression; many antidepressants work by increasing BDNF expression. * **Val66Met Polymorphism:** A common genetic variation in the BDNF gene is associated with altered memory function and susceptibility to neuropsychiatric disorders. * **Exercise:** Physical activity is one of the most potent physiological stimulators of BDNF production in the brain.

Question 164: The EEG curves are called:

A. Delta curves
B. Berger's Rhythm (Correct Answer)
C. Alpha waves
D. REM Rhythm

Explanation: ***Berger's Rhythm*** - Named after **Hans Berger**, the German psychiatrist who invented the **electroencephalogram (EEG)** in 1929 and first recorded human brain electrical activity. - **Berger's Rhythm** is the original term used to describe the **rhythmic electrical patterns** recorded from the brain, encompassing all EEG waveforms. *Delta curves* - **Delta waves** are a specific type of EEG wave with **low frequency (0.5-4 Hz)** and **high amplitude**, predominantly seen during **deep sleep**. - They represent only one component of EEG patterns, not the general term for all EEG curves. *Alpha waves* - **Alpha waves** are **8-12 Hz frequency** waves that appear when a person is **awake but relaxed** with eyes closed. - They are a **subtype** of Berger's Rhythm, not the overall term for EEG curves themselves. *REM Rhythm* - **REM (Rapid Eye Movement)** refers to a **sleep stage** characterized by vivid dreams and rapid eye movements. - During REM sleep, EEG shows **mixed frequency patterns** similar to wakefulness, but this is not a general term for EEG curves.

Question 165: Slow wave sleep predominates in the first one-third of the night's sleep. Which phase of sleep is characterized by this?

A. NREM stages 3 and 4 (Correct Answer)
B. NREM stages 1 and 2
C. NREM stage 1
D. REM sleep

Explanation: **Explanation:** Sleep is divided into two main types: **NREM (Non-Rapid Eye Movement)** and **REM (Rapid Eye Movement)**. NREM sleep is further subdivided into stages 1 through 4 (in traditional classification). **Why NREM Stages 3 and 4 are correct:** Slow Wave Sleep (SWS), also known as **Deep Sleep**, specifically refers to NREM stages 3 and 4. It is characterized by high-amplitude, low-frequency **Delta waves** (0.5–4 Hz) on EEG. SWS is most prominent during the **first one-third of the night**, as the body prioritizes physical restoration and growth hormone secretion early in the sleep cycle. As the night progresses, SWS duration decreases while REM sleep duration increases. **Analysis of Incorrect Options:** * **NREM Stages 1 and 2:** These are "Light Sleep" phases. Stage 1 is a transition from wakefulness (Theta waves), and Stage 2 is characterized by **Sleep Spindles** and **K-complexes**. They occur throughout the night but do not constitute "Slow Wave Sleep." * **REM Sleep:** Also called "Paradoxical Sleep," it is characterized by high brain activity (Beta-like waves) and muscle atonia. REM sleep predominates in the **last one-third** of the night. **High-Yield Clinical Pearls for NEET-PG:** * **EEG Waves:** Remember the mnemonic **BATS Drink Blood** (Beta, Alpha, Theta, Spindles/K-complex, Delta, Beta) for the sequence of EEG waves from wakefulness to deep sleep and REM. * **Parasomnias:** Sleepwalking (Somnambulism), Sleep Terrors, and Bedwetting (Enuresis) typically occur during **Stage 4 NREM** (SWS). * **Growth Hormone:** Peak secretion occurs during NREM stages 3 and 4. * **Bruxism (Teeth grinding):** Occurs predominantly in Stage 2 NREM.

Question 166: Motor aphasia refers to a defect in what?

A. Peripheral speech apparatus
B. Verbal expression (Correct Answer)
C. Auditory comprehension
D. Verbal comprehension

Explanation: **Explanation:** **Motor aphasia**, also known as **Broca’s aphasia** or non-fluent aphasia, results from a lesion in **Broca’s area (Brodmann areas 44 and 45)** located in the posterior part of the inferior frontal gyrus of the dominant hemisphere. 1. **Why "Verbal expression" is correct:** Broca’s area is responsible for the motor programming of speech. Patients with motor aphasia understand language (intact comprehension) but struggle to produce speech. Their speech is characterized as "telegraphic"—slow, labored, and lacking grammatical structure—representing a primary defect in **verbal expression**. 2. **Why other options are incorrect:** * **Peripheral speech apparatus (A):** Defects here result in **Dysarthria**, not aphasia. Aphasia is a higher-order cortical processing disorder, whereas dysarthria is a mechanical problem involving muscles, nerves (CN VII, IX, X, XII), or the larynx. * **Auditory/Verbal comprehension (C & D):** These are hallmarks of **Sensory aphasia (Wernicke’s aphasia)**, caused by lesions in the posterior superior temporal gyrus (Brodmann area 22). In Wernicke’s, expression is fluent but meaningless ("word salad"). **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Broca’s = Frontal lobe (Motor); Wernicke’s = Temporal lobe (Sensory). * **Arcuate Fasciculus:** Connects Broca’s and Wernicke’s areas. A lesion here causes **Conduction Aphasia** (impaired repetition). * **Global Aphasia:** Loss of both expression and comprehension (large perisylvian lesions). * **Key differentiator:** In Broca’s aphasia, the patient is usually frustrated and aware of their deficit, whereas in Wernicke’s, they are often unaware (anosognosia).

Question 167: Which of the following is true about Galvanic Skin Response?

A. It is an indicator of thermal sweating.
B. It is an indicator of emotional sweating.
C. A fall in GSR is associated with yogic practice.
D. All of the above. (Correct Answer)

Explanation: **Explanation:** **Galvanic Skin Response (GSR)**, also known as Electrodermal Activity (EDA), refers to changes in the electrical conductance of the skin. This phenomenon is primarily driven by the activity of **eccrine sweat glands**, which are uniquely innervated by **sympathetic cholinergic fibers**. 1. **Indicator of Thermal and Emotional Sweating:** While eccrine glands are found all over the body for thermoregulation (thermal sweating), they are highly concentrated on the palms and soles, where they react intensely to psychological stimuli (emotional sweating). GSR measures the moisture level on the skin; as sweat increases, skin resistance decreases and conductance increases. Therefore, it serves as a sensitive marker for both thermal and emotional sympathetic arousal. 2. **Yogic Practice and GSR:** During relaxation, meditation, or yogic practices, there is a shift from sympathetic to parasympathetic dominance (the "relaxation response"). This leads to decreased sweat gland activity, increased skin resistance, and a subsequent **fall in GSR**. 3. **Conclusion:** Since GSR reflects sympathetic activity triggered by heat, emotions, and the reversal of these states during relaxation, all the provided statements are correct. **High-Yield Clinical Pearls for NEET-PG:** * **Neurotransmitter Exception:** Remember that sweat glands are an exception to the rule—they are part of the sympathetic nervous system but use **Acetylcholine (ACh)** as their postganglionic neurotransmitter. * **Polygraphy:** GSR is a core component of "Lie Detector" tests because autonomic emotional responses are difficult to suppress consciously. * **Center:** The primary control center for emotional sweating is the **limbic system**, whereas thermal sweating is regulated by the **hypothalamus**.

Question 168: Which sleep stage is characterized by the presence of sleep spindles on an electroencephalogram (EEG)?

A. Stage 1
B. Stage 2 (Correct Answer)
C. Stage 3
D. Stage 4

Explanation: **Explanation:** Sleep is broadly divided into Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) sleep. NREM sleep is further subdivided into three stages (N1, N2, and N3) based on EEG patterns. **Correct Answer: B. Stage 2** Stage 2 (N2) is the "light sleep" phase and is characterized by two hallmark EEG findings: **Sleep Spindles** and **K-complexes**. * **Sleep Spindles:** Bursts of oscillatory brain activity (12–14 Hz) resulting from interactions between thalamic reticular neurons and thalamocortical cells. They are thought to play a role in memory consolidation and protecting sleep from external stimuli. * **K-complexes:** High-amplitude, long-duration biphasic waves. **Incorrect Options:** * **Stage 1 (N1):** The transition from wakefulness to sleep. The EEG shows low-voltage, mixed-frequency activity with a predominance of **Theta waves** (4–7 Hz). Alpha waves disappear. * **Stage 3 & 4 (N3):** These are now grouped together as "Slow Wave Sleep" (SWS) or deep sleep. The EEG is dominated by high-voltage, low-frequency **Delta waves** (0.5–2 Hz). **High-Yield NEET-PG Pearls:** 1. **Bruxism** (teeth grinding) occurs most commonly in Stage 2. 2. **Night Terrors, Somnambulism (Sleepwalking), and Enuresis** (bedwetting) typically occur during Stage 3 (Deep Sleep). 3. **REM Sleep** is characterized by "sawtooth waves," muscle atonia, and dreaming. It is also called "paradoxical sleep" because the EEG resembles an awake state (Beta waves). 4. **PGO Spikes** (Pontine-Geniculate-Occipital) are the earliest signs of REM sleep.

Question 169: All results from Sympathetic nervous stimulation, except:

A. Vasodilation of cutaneous blood vessel (Correct Answer)
B. Bronchodilatation
C. Dilator pupillae contraction
D. Renin secretion

Explanation: **Explanation:** The sympathetic nervous system (SNS) is the body’s "fight or flight" mechanism, designed to redirect blood flow and resources to vital organs (heart, brain, and skeletal muscles) during stress. **1. Why Option A is Correct:** Sympathetic stimulation causes **vasoconstriction** of cutaneous (skin) blood vessels, not vasodilation. This is mediated by **$\alpha_1$-adrenergic receptors**. By constricting these vessels, the body shunts blood away from the periphery toward essential organs and prevents excessive heat loss. This is why a person in shock or under intense stress often appears "pale and cold." **2. Analysis of Incorrect Options:** * **B. Bronchodilatation:** Sympathetic activation releases norepinephrine/epinephrine which acts on **$\beta_2$ receptors** in the bronchioles. This causes relaxation of smooth muscle to increase airflow for better oxygenation. * **C. Dilator pupillae contraction:** The SNS stimulates the radial muscles of the iris via **$\alpha_1$ receptors**, leading to **mydriasis** (pupillary dilation) to improve peripheral vision in emergency situations. * **D. Renin secretion:** Sympathetic nerves innervating the juxtaglomerular apparatus of the kidney stimulate **$\beta_1$ receptors**, triggering renin release. This activates the RAAS pathway to maintain blood pressure. **Clinical Pearls for NEET-PG:** * **Exception to the rule:** While most sympathetic postganglionic neurons release norepinephrine, those supplying **sweat glands** are **cholinergic** (release Acetylcholine). * **Dual effect on vessels:** SNS causes vasoconstriction in skin/viscera ($\alpha_1$) but can cause vasodilation in skeletal muscle vessels ($\beta_2$) to enhance exercise performance. * **Mnemonic:** "S" for Sympathetic = "S" for Stress (Dilation of pupils, Dilation of bronchi, Constriction of skin vessels).

Question 170: Agnosia is caused by a lesion in which part of the brain?

A. Parietal lobe (Correct Answer)
B. Occipital lobe
C. Frontal lobe
D. None of the above

Explanation: **Explanation:** **Agnosia** is the inability to recognize or identify objects, persons, or sounds despite intact sensory functions (vision, hearing, and touch). This occurs because the brain cannot process or interpret the sensory information it receives. **Why the Parietal Lobe is correct:** The **Parietal Lobe**, specifically the **posterior parietal association cortex**, is responsible for integrating sensory information from various modalities. A lesion in the non-dominant (usually right) parietal lobe leads to **Astereognosis** (inability to identify an object by touch) and **Anosognosia** (lack of awareness of one's own disability). It is also the site for spatial processing; damage here often results in **Neglect Syndrome**. **Why the other options are incorrect:** * **Occipital Lobe:** While lesions here can cause *Visual Agnosia* (inability to recognize objects by sight), the parietal lobe is the primary site for the complex integration required for general agnosia. Occipital lesions more typically present with cortical blindness or visual field defects (e.g., hemianopia). * **Frontal Lobe:** Lesions here primarily result in motor deficits, personality changes, expressive aphasia (Broca’s), and impaired executive function, rather than recognition deficits. **High-Yield Clinical Pearls for NEET-PG:** * **Gerstmann Syndrome:** Caused by a lesion in the **dominant (left) angular gyrus** of the parietal lobe. It presents with a tetrad: 1. Agraphia, 2. Acalculia, 3. Finger agnosia, 4. Left-right disorientation. * **Prosopagnosia:** The inability to recognize familiar faces; it is specifically associated with lesions in the **fusiform gyrus** (at the junction of the temporal and occipital lobes). * **Apraxia vs. Agnosia:** Apraxia is the inability to carry out *motor* tasks despite intact motor function; Agnosia is a failure of *recognition* despite intact sensory function. Both are hallmark parietal lobe signs.

Practice by Chapter

Neurons and Glial Cells

Practice Questions

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

Practice Questions

Cerebral Cortex Functions

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Electroencephalography

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Neuroplasticity

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Sleep and Wakefulness

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