Neurophysiology Practice Questions

Q: Which function is primarily associated with the spinocerebellum?

Smoothening and coordination of movements. **Explanation:** The cerebellum is functionally divided into three parts: the Vestibulocerebellum, the Spinocerebellum, and the Neocerebellum (Cerebrocerebellum). **Why Option B is Correct:** The **Spinocerebellum** (comprising the vermis and intermediate zones) primarily receives sensory input from the spinal cord (proprioception) and motor commands from the cortex. Its main function is **"Comparator" action**: it compares the intended movement with the actual performance and provides real-time corrective feedback. This ensures the **smoothening and coordination of movements**, preventing tremors and ensuring accuracy (synergy). **Analysis of Incorrect Options:** * **Option A (Maintenance of postural balance):** This is the primary function of the **Vestibulocerebellum** (Flocculonodular lobe), which maintains equilibrium and controls eye movements via connections with the vestibular apparatus. * **Option C (Planning and programming of movements):** This is the hallmark of the **Neocerebellum/Cerebrocerebellum** (Lateral hemispheres). It works with the premotor and sensory cortex to plan complex motor sequences before they are executed. * **Option D (Initiation of skilled voluntary movements):** Initiation is primarily a function of the **Basal Ganglia** and the **Motor Cortex**. The cerebellum coordinates movement once initiated but does not start it. **High-Yield Clinical Pearls for NEET-PG:** * **Lesion of Spinocerebellum:** Results in **Ataxia** (uncoordinated gait) and **Action/Intention Tremors**. * **Lesion of Vestibulocerebellum:** Results in **Trunkal Ataxia** and Nystagmus. * **Lesion of Neocerebellum:** Results in **Dysmetria** (past-pointing) and **Dysdiadochokinesia** (inability to perform rapid alternating movements). * **Memory Aid:** **S**pinocerebellum = **S**moothing/Execution; **C**erebrocerebellum = **C**onception/Planning.

Q: The Monro-Kellie doctrine is related to the doctrine of non-compressible contents within which part of the body?

Head. ### Explanation **The Monro-Kellie Doctrine (Hypothesis)** The correct answer is **Head (A)**. The Monro-Kellie doctrine states that the cranial vault is a rigid, non-expandable container with a fixed total volume. This volume is composed of three nearly incompressible components: 1. **Brain parenchyma** (~80%) 2. **Cerebrospinal fluid (CSF)** (~10%) 3. **Blood** (~10%) According to this principle, because the total volume is constant, an increase in any one of these components (or the addition of a pathological mass like a tumor or hematoma) must be compensated by an equal decrease in the volume of another. If compensation fails, **Intracranial Pressure (ICP)** rises sharply. **Why the other options are incorrect:** * **B. Abdomen & C. Chest:** Unlike the skull, the abdominal and thoracic cavities have flexible walls (diaphragm, intercostal muscles, and skin) that can expand to accommodate volume changes. * **D. Leg:** The limbs are not enclosed in a rigid bony vault; while they can experience compartment syndrome, they do not follow the specific volumetric constraints of the Monro-Kellie doctrine. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Compensatory Mechanisms:** When ICP rises, the body first displaces **CSF** into the spinal subarachnoid space and shunts **venous blood** out of the skull. * **Cushing’s Triad:** A late sign of increased ICP resulting from the Monro-Kellie doctrine failure, characterized by **Hypertension, Bradycardia, and Irregular Respiration.** * **Clinical Application:** This doctrine explains why even small intracranial hemorrhages can lead to rapid neurological deterioration and brain herniation.

Q: What is the root value of the plantar reflex?

Afferent S1, Efferent L5, S1. **Explanation:** The **Plantar Reflex** is a superficial (polysynaptic) reflex elicited by stroking the lateral aspect of the sole of the foot. Understanding its reflex arc is crucial for localizing spinal cord lesions. 1. **Why Option B is Correct:** * **Afferent (Sensory) Limb:** The stimulus is carried from the skin of the S1 dermatome (lateral sole) via the **Tibial nerve** to the **S1 spinal segment**. * **Efferent (Motor) Limb:** The motor response involves the contraction of the flexor muscles of the toes. These muscles are primarily innervated by the **Tibial nerve (S1)** and the **Peroneal nerve (L5)**. Specifically, the Great Toe flexion involves L5, while the other toes involve S1. Thus, the complete reflex arc is **Afferent S1, Efferent L5, S1**. 2. **Why Other Options are Incorrect:** * **Options A & C:** These include **L3** in the efferent limb. L3 is primarily involved in the **Knee Jerk (Patellar reflex)** and supplies the quadriceps; it has no role in toe flexion. * **Options C & D:** These suggest **S2** as the primary afferent. While S2 provides some sensation to the foot, the classic dermatomal trigger point for the plantar reflex on the lateral sole is specifically **S1**. **NEET-PG High-Yield Pearls:** * **Babinski Sign:** An abnormal plantar reflex (extensor response) indicating an **Upper Motor Neuron (UMN) lesion**. It is physiological (normal) in infants up to 1–2 years due to incomplete myelination of the corticospinal tracts. * **Receptor:** Nociceptors in the skin (not muscle spindles). * **Reflex Center:** S1 segment of the spinal cord. * **Quick Recall for Deep Tendon Reflexes:** * Ankle (Achilles): S1, S2 * Knee (Patellar): L2, L3, L4 * Biceps: C5, C6 * Triceps: C7, C8

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.

Question 1

Which function is primarily associated with the spinocerebellum?

Accepted Answer

Smoothening and coordination of movements

Answer

Maintenance of postural balance

Answer

Planning and programming of movements

Answer

Initiation of skilled voluntary movements

Question 2

The Monro-Kellie doctrine is related to the doctrine of non-compressible contents within which part of the body?

Accepted Answer

Head

Answer

Abdomen

Answer

Chest

Answer

Leg

Question 3

What is the root value of the plantar reflex?

Accepted Answer

Afferent S1, Efferent L5, S1

Answer

Afferent S1, Efferent L3, S1

Answer

Afferent S2, Efferent L3, S1

Answer

Afferent S2, Efferent L5, S1

Question 4

Gamma motor neurons are mainly influenced by which of the following tracts?

Accepted Answer

Rubrospinal tract

Answer

Vestibulospinal tract

Answer

Anterior corticospinal tract

Answer

Tectospinal tract

Question 5

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 6

Facilitation of flexor muscle tone is by which tract?

Accepted Answer

Rubrospinal tract

Answer

Vestibulospinal tract

Answer

Tectospinal tract

Answer

Reticulospinal tract

Question 7

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 8

Which of the following acts as a neurotransmitter inhibitor?

Accepted Answer

GABA

Answer

Glutamate

Answer

Aspartic acid

Answer

Lysine

Question 9

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 10

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

Neurophysiology — MCQs

Neurophysiology — MCQs

On this page

Practice by Chapter

Want unlimited practice?