Neurophysiology Practice Questions

Q: When a stretch reflex occurs, the muscles that antagonize the action of the involved muscle relax. This phenomenon is known as:

Reciprocal innervation. ### Explanation **Correct Answer: B. Reciprocal Innervation** **Why it is correct:** Reciprocal innervation (or reciprocal inhibition) is a fundamental spinal reflex mechanism. When a muscle spindle is stretched, it triggers a reflex contraction of that same muscle (the agonist). Simultaneously, the afferent impulses (Group Ia fibers) branch out in the spinal cord to stimulate **inhibitory interneurons**. These interneurons inhibit the alpha motor neurons of the **antagonist muscles**, causing them to relax. This coordination prevents muscles from working against each other, ensuring smooth and efficient movement. **Why other options are incorrect:** * **A. Inverse stretch reflex:** This is a protective reflex mediated by **Golgi Tendon Organs (GTO)**. When a muscle experiences excessive tension, it causes the muscle itself to relax to prevent injury. * **C. Autogenic inhibition:** This is the mechanism underlying the inverse stretch reflex. It refers to the inhibition of the *same* muscle that is experiencing high tension, mediated by Ib afferents from the GTO. * **D. Lengthening reaction:** This is a clinical manifestation of the inverse stretch reflex, often seen in "clasp-knife" spasticity. When a hypertonic muscle is stretched forcefully, it suddenly gives way and relaxes due to GTO activation. **High-Yield Clinical Pearls for NEET-PG:** * **Afferent Fiber Types:** Stretch reflex (Muscle Spindle) uses **Ia fibers**; Inverse stretch reflex (GTO) uses **Ib fibers**. * **The "Clasp-Knife" Phenomenon:** This is a classic example of the lengthening reaction/inverse stretch reflex seen in Upper Motor Neuron (UMN) lesions. * **Renshaw Cells:** These are inhibitory interneurons in the spinal cord that provide **recurrent inhibition** to the same motor neuron that fired, acting as a "limiter" to prevent over-activity.

Q: Concurrent flexion of both wrists in response to electrical stimulation is characteristic of which area of the nervous system?

Supplementary motor cortex. **Explanation:** The **Supplementary Motor Area (SMA)**, located on the medial surface of the frontal lobe (Brodmann area 6), is primarily involved in the planning and coordination of complex, bilateral movements. Unlike the Primary Motor Cortex (M1), which controls discrete muscles on the contralateral side, electrical stimulation of the SMA typically results in **bilateral, synergistic movements** or postural adjustments, such as the concurrent flexion of both wrists or the raising of both arms. **Analysis of Options:** * **A. Postcentral Gyrus:** This is the Primary Somatosensory Cortex (S1). Stimulation here results in sensory perceptions (tingling, numbness) on the contralateral side of the body, not motor movements. * **B. Vestibulospinal Tract:** This is an extrapyramidal pathway responsible for maintaining equilibrium and muscle tone (primarily extensors) in response to head movements. It does not coordinate complex bilateral wrist flexion. * **C. Dentate Nucleus:** The largest of the deep cerebellar nuclei, it is involved in the planning and timing of movements. While it influences motor output, direct electrical stimulation does not produce the specific bilateral motor patterns characteristic of the SMA. **High-Yield Facts for NEET-PG:** * **SMA vs. Premotor Cortex:** SMA is for **internal cues** (complex sequences from memory), while the Premotor cortex is for **external cues** (sensory-guided movements). * **Jacksonian March:** Associated with the Primary Motor Cortex (M1), not the SMA. * **Alien Hand Syndrome:** Can occur with lesions involving the SMA and corpus callosum. * **Stimulation Threshold:** The SMA has a higher threshold for electrical stimulation compared to the Primary Motor Cortex.

Q: Which of the following acts as a neurotransmitter inhibitor?

GABA. **Explanation:** The correct answer is **GABA (Gamma-Aminobutyric Acid)**. In the central nervous system (CNS), neurotransmitters are classified as either excitatory or inhibitory based on their effect on the postsynaptic membrane potential. 1. **Why GABA is correct:** GABA is the primary **inhibitory neurotransmitter** in the adult brain. When GABA binds to its receptors (GABA-A or GABA-B), it typically causes an influx of chloride ions ($Cl^-$) or an efflux of potassium ions ($K^+$). This leads to **hyperpolarization** of the postsynaptic neuron, making it less likely to fire an action potential. 2. **Why the other options are incorrect:** * **Glutamate:** This is the major **excitatory** neurotransmitter in the CNS. It acts on NMDA and AMPA receptors to cause depolarization. * **Aspartic acid (Aspartate):** Similar to glutamate, aspartate is an **excitatory** neurotransmitter, particularly in the spinal cord and brainstem. * **Lysine:** While an essential amino acid, lysine does not function as a primary neurotransmitter in the CNS. **High-Yield Clinical Pearls for NEET-PG:** * **GABA-A vs. GABA-B:** GABA-A is **ionotropic** (fast-acting, $Cl^-$ channel), while GABA-B is **metabotropic** (slow-acting, G-protein coupled). * **Glycine:** Remember that Glycine is the major inhibitory neurotransmitter in the **spinal cord**, whereas GABA dominates the **brain**. * **Clinical Correlation:** Drugs like Benzodiazepines and Barbiturates work by potentiating the effects of GABA at the GABA-A receptor, leading to sedation and anxiolysis. * **Strychnine:** A potent convulsant that acts by antagonizing Glycine receptors.

Q: In a monkey, following temporal lobectomy, which of the following functions is NOT observed?

Fearfulness. ### Explanation The question describes the classic presentation of **Klüver-Bucy Syndrome**, which results from bilateral destruction of the **amygdala** and surrounding **temporal lobes**. #### Why "Fearfulness" is the Correct Answer: In Klüver-Bucy Syndrome, there is a profound **loss of fear and aggression** (placidity). The amygdala is the primary center for processing emotional responses, particularly fear. Following a temporal lobectomy, the animal no longer perceives threats or reacts to previously frightening stimuli (e.g., snakes or aggressive humans). Therefore, "fearfulness" is **not** observed; instead, the subject becomes abnormally calm. #### Analysis of Incorrect Options: * **A. Sexual Desire (Hypersexuality):** This is a hallmark feature. Subjects show increased libido and inappropriate sexual behavior, often directed toward inanimate objects or other species. * **B. Visual Agnosia (Psychic Blindness):** The subject can see but cannot recognize objects or their significance. This is due to damage to the visual association areas in the temporal cortex. * **C. Oral Tendency (Hyperorality):** There is a compulsive urge to examine all objects by mouth (licking, biting, or chewing) to identify them, compensating for visual agnosia. #### High-Yield Clinical Pearls for NEET-PG: * **Anatomical Site:** Bilateral temporal lobes, specifically the **amygdala**. * **Triad of Symptoms:** Hyperorality, Hypersexuality, and Placidity (loss of fear). * **Human Causes:** Most commonly seen as a sequela of **Herpes Simplex Encephalitis (HSE)**, which has a predilection for the temporal lobes. * **Memory Link:** Temporal lobectomy often involves the hippocampus, leading to **anterograde amnesia**.

Q: In cases of recent memory loss, which brain region is the most probable site of a lesion?

Temporal lobe. **Explanation:** The **Temporal Lobe**, specifically the medial aspect containing the **Hippocampus** and the **Entorhinal cortex**, is the primary site for the consolidation of short-term memory into long-term memory (recent memory). Lesions in this area, particularly bilateral damage, result in profound **anterograde amnesia** (the inability to form new memories), which is the hallmark of recent memory loss. **Analysis of Options:** * **Temporal Lobe (Correct):** The hippocampus (located in the medial temporal lobe) is essential for declarative memory. Damage here prevents the encoding of new information, though remote (long-term) memories often remain intact. * **Thalamus:** While the Mediodorsal nucleus of the thalamus is involved in memory (part of the Papez circuit), lesions here typically present as part of Wernicke-Korsakoff syndrome, characterized by confabulation rather than isolated recent memory loss. * **Frontal Lobe:** This region is primarily responsible for **working memory** (short-term buffering of information) and executive functions. Frontal lesions affect attention and retrieval strategies but do not prevent the formation of permanent memory traces. **High-Yield NEET-PG Pearls:** * **Papez Circuit:** Hippocampus → Fornix → Mammillary bodies → Anterior Thalamic Nucleus → Cingulate Gyrus → Entorhinal Cortex → Hippocampus. * **Klüver-Bucy Syndrome:** Results from bilateral temporal lobe (amygdala) lesions; characterized by hyperorality, hypersexuality, and visual agnosia. * **Alzheimer’s Disease:** The hippocampus is one of the first structures to undergo atrophy, explaining why recent memory loss is the earliest clinical symptom.

Q: Which of the following statements regarding Cerebrospinal Fluid (CSF) is/are true?

CSF has a net weight of approximately 1400g.. **Explanation:** The correct answer is **B**, though it requires a specific physiological context: the **effective weight** of the brain. The actual brain tissue weighs approximately 1400g. However, because the brain is immersed in CSF, it experiences **buoyancy** (Archimedes' principle). This reduces the "net" or effective weight of the brain in situ to about **25–50g**. In many physiological texts, the 1400g figure is used to contrast the actual mass versus the buoyant weight, highlighting the protective "cushioning" function of CSF. **Analysis of Options:** * **A is Incorrect:** The **Dura mater** consists of two layers. While the outer endosteal layer is attached to the skull, the inner meningeal layer is not. More importantly, the **Pia mater** is the layer firmly attached to the brain parenchyma, not the dura. * **C is Incorrect:** The total volume of CSF in an adult is indeed approximately **150 ml** (distributed as 25 ml in ventricles and 125 ml in the subarachnoid space). *Note: If the question allows multiple correct statements, C is also factually true.* * **D is Incorrect:** The daily production rate is approximately **0.35 ml/min**, which totals roughly **500–550 ml/day**. This means the entire CSF volume is replaced about 3.7 times a day. **High-Yield Clinical Pearls for NEET-PG:** * **Composition:** CSF is isotonic with plasma but has **lower pH** (7.33), **lower Glucose** (60% of plasma), and significantly **lower Protein** (15-45 mg/dl). * **Specific Gravity:** 1.005. * **Pressure:** Normal CSF pressure (lateral recumbent) is **70–180 mmH₂O**. * **Absorption:** Occurs primarily through **Arachnoid villi** into the dural venous sinuses. Absorption is a passive process dependent on the pressure gradient.

Q: Which one of the following statements about EEG is true?

Alpha rhythm is most marked at the parieto-occipital area.. ### Explanation **1. Why Option A is Correct:** The **Alpha rhythm (8–13 Hz)** is the characteristic rhythm of an adult who is awake but relaxed with eyes closed. It is most prominent in the **parieto-occipital regions** of the brain. This rhythm represents "idling" of the visual cortex; it disappears immediately upon opening the eyes or focusing on a mental task (a phenomenon known as **Alpha Block** or Desynchronization). **2. Why the Other Options are Incorrect:** * **Option B:** Beta rhythm (13–30 Hz) is associated with mental activity and alertness. It is most prominent in the **frontal and parietal regions**, not the mastoid area. * **Option C:** In REM (Rapid Eye Movement) sleep, the patient is **asleep**, but the EEG shows low-voltage, high-frequency activity that resembles an awake state. This is why REM sleep is termed **"Paradoxical Sleep."** * **Option D:** While EPSPs and IPSPs are the basis of the EEG, they act as dipoles specifically in the **pyramidal cells** of the cerebral cortex. The statement in the option is technically incomplete/vague compared to the definitive localization of the Alpha rhythm. (Note: In some contexts, D is considered partially true, but A is the "most true" and classic textbook fact for NEET-PG). **3. Clinical Pearls & High-Yield Facts:** * **EEG Waves Frequency:** Delta (<4 Hz) < Theta (4–7 Hz) < Alpha (8–13 Hz) < Beta (13–30 Hz). * **Delta Waves:** Normal in deep sleep (Stage 3 NREM) and infancy; abnormal in awake adults (indicates brain injury/coma). * **Theta Waves:** Normal in children and during light sleep; seen in adults during emotional stress. * **EEG Basis:** The EEG does *not* record action potentials. It records the **summation of excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs)** in the dendrites of vertically oriented pyramidal cells.

Question 1

When a stretch reflex occurs, the muscles that antagonize the action of the involved muscle relax. This phenomenon is known as:

Accepted Answer

Reciprocal innervation

Answer

Inverse stretch reflex

Answer

Autogenic inhibition

Answer

Lengthening reaction

Question 2

Facilitation of flexor muscle tone is by which tract?

Accepted Answer

Rubrospinal tract

Answer

Vestibulospinal tract

Answer

Tectospinal tract

Answer

Reticulospinal tract

Question 3

Concurrent flexion of both wrists in response to electrical stimulation is characteristic of which area of the nervous system?

Accepted Answer

Supplementary motor cortex

Answer

Postcentral gyrus

Answer

Vestibulospinal tract

Answer

Dentate nucleus

Question 4

Which of the following acts as a neurotransmitter inhibitor?

Accepted Answer

GABA

Answer

Glutamate

Answer

Aspartic acid

Answer

Lysine

Question 5

In a monkey, following temporal lobectomy, which of the following functions is NOT observed?

Accepted Answer

Fearfulness

Answer

Sexual desire

Answer

Visual agnosia

Answer

Oral tendency

Question 6

In cases of recent memory loss, which brain region is the most probable site of a lesion?

Accepted Answer

Temporal lobe

Answer

Thalamus

Answer

Frontal lobe

Answer

All of the above

Question 7

Which of the following statements regarding Cerebrospinal Fluid (CSF) is/are true?

Accepted Answer

CSF has a net weight of approximately 1400g.

Answer

The dura mater is attached firmly to the skull.

Answer

The total volume of CSF in an adult is about 150 ml.

Answer

The daily production rate of CSF is approximately 550 ml/day.

Question 8

The efferent limb of a myotatic reflex includes which of the following?

Accepted Answer

Anterior horn motor neuron

Answer

Lateral horn visceromotor nucleus

Answer

Muscle spindle

Answer

Preganglionic sympathetic neuron

Question 9

Increased gamma efferent discharge is seen in all except:

Accepted Answer

Rapid shallow breathing

Answer

Jendrassik's maneuver

Answer

Anxiety

Answer

Stimulation of skin

Question 10

Which one of the following statements about EEG is true?

Accepted Answer

Alpha rhythm is most marked at the parieto-occipital area.

Answer

Beta rhythm is most marked at the region below the mastoid.

Answer

In REM sleep, the patient is awake.

Answer

EPSP and IPSP of cortical cells act as dipoles.

Neurophysiology — MCQs

Neurophysiology — MCQs

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