Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 451: Plasma is considered a Newtonian fluid because:

A. Viscosity is directly proportional to shear stress.
B. Viscosity is equal to shear rate.
C. Viscosity is inversely related to shear stress.
D. Viscosity is independent of shear stress. (Correct Answer)

Explanation: ### Explanation **Core Concept: Newtonian vs. Non-Newtonian Fluids** A **Newtonian fluid** is defined as a fluid whose viscosity remains constant regardless of the forces applied to it. In mathematical terms, the shear stress is linearly proportional to the shear rate, meaning the ratio between them (**viscosity**) is a constant value. **Plasma** is considered a Newtonian fluid because it is essentially a solution of water, electrolytes, and proteins. Unlike whole blood, it does not contain suspended cellular elements (like RBCs) that can aggregate or deform. Therefore, its **viscosity is independent of shear stress** (Option D). **Analysis of Incorrect Options:** * **Option A & C:** In Newtonian fluids, viscosity is a constant property of the fluid itself (at a given temperature). It does not increase or decrease based on the flow velocity or pressure (shear stress). * **Option B:** Viscosity is the *ratio* of shear stress to shear rate ($\eta = \tau / \gamma$), not equal to the shear rate itself. **High-Yield NEET-PG Pearls:** 1. **Whole Blood is Non-Newtonian:** Unlike plasma, whole blood is **pseudoplastic (shear-thinning)**. At low shear rates (slow flow), RBCs form "Rouleaux" stacks, increasing viscosity. At high shear rates (fast flow), RBCs disperse and deform, decreasing viscosity. 2. **Fahraeus-Lindqvist Effect:** This refers to the decrease in apparent viscosity of blood as it flows through very small capillaries (radii < 1.5 mm) due to the "cell-free marginal layer." 3. **Key Determinants:** The primary determinant of **plasma** viscosity is the concentration of plasma proteins (especially **Fibrinogen**). The primary determinant of **whole blood** viscosity is the **Hematocrit**.

Question 452: Stress-induced analgesia occurs due to the release of which of the following?

A. Cannabinoids (Correct Answer)
B. Cortisol
C. Serotonin
D. Substance P

Explanation: **Explanation:** **Stress-Induced Analgesia (SIA)** is a physiological phenomenon where exposure to stressful or life-threatening stimuli leads to a reduction in pain sensitivity. This serves as an evolutionary survival mechanism, allowing an organism to prioritize escape or defense over pain response. **Why Cannabinoids are correct:** While the endogenous opioid system (endorphins/enkephalins) was traditionally linked to SIA, recent research highlights the critical role of the **Endocannabinoid system**. Stress triggers the release of endocannabinoids (like Anandamide and 2-AG) in the **Periaqueductal Gray (PAG)** and the **Rostral Ventromedial Medulla (RVM)**. These act on CB1 receptors to suppress GABAergic inhibitory neurons, thereby activating the descending inhibitory pain pathway to provide non-opioid mediated analgesia. **Why other options are incorrect:** * **B. Cortisol:** While cortisol is the primary "stress hormone" released via the HPA axis, its role is metabolic and anti-inflammatory; it does not directly mediate acute stress-induced analgesia. * **C. Serotonin:** Serotonin is involved in the descending pain modulatory pathway (released from the Nucleus Raphe Magnus), but it is a downstream neurotransmitter rather than the primary trigger released *due* to acute stress to initiate SIA. * **D. Substance P:** This is a pro-nociceptive neurotransmitter released by primary afferent fibers (A-delta and C fibers) in the spinal cord to **transmit** pain, not reduce it. **High-Yield Facts for NEET-PG:** * **Gate Control Theory:** Proposed by Melzack and Wall; occurs in the Substantia Gelatinosa of Rolando (Lamina II). * **Primary Neurotransmitter of Pain:** Glutamate (fast) and Substance P (slow). * **Descending Inhibitory Pathway:** Key areas include the PAG (Midbrain) → Nucleus Raphe Magnus (Pons/Medulla) → Dorsal Horn of Spinal Cord. * **SIA Types:** Can be **Opioid-mediated** (blocked by Naloxone) or **Non-opioid mediated** (involving Endocannabinoids).

Question 453: Which of the following structures is involved in equilibrium, gait, and learning-induced changes in the vestibulo-ocular reflex?

A. Vestibulocerebellum (Correct Answer)
B. Spinocerebellum
C. Cerebrocerebellum
D. All of the above

Explanation: ### Explanation **1. Why Vestibulocerebellum is Correct:** The **Vestibulocerebellum** (comprising the flocculonodular lobe and parts of the vermis) is the oldest part of the cerebellum. It receives primary sensory input from the vestibular apparatus and the lateral geniculate bodies. * **Equilibrium and Gait:** It regulates axial musculature and proximal limb muscles to maintain balance and posture. * **Vestibulo-Ocular Reflex (VOR):** It coordinates head and eye movements. Crucially, it is the site of **motor learning** for the VOR; it adjusts the gain of the reflex to ensure that the eyes move exactly opposite to the head, maintaining a stable image on the retina. **2. Why Other Options are Incorrect:** * **Spinocerebellum (Paleocerebellum):** This consists of the vermis and intermediate zones. It primarily receives proprioceptive input from the spinal cord and regulates **muscle tone** and the execution of ongoing movements (coordination). * **Cerebrocerebellum (Neocerebellum):** This consists of the lateral cerebellar hemispheres. It communicates with the cerebral cortex to assist in the **planning, programming, and timing** of complex, skilled voluntary movements. **3. High-Yield Clinical Pearls for NEET-PG:** * **Lesion of Vestibulocerebellum:** Results in **Truncal Ataxia**, swaying while standing, and a wide-based "drunken" gait. Nystagmus is also a common feature. * **The "Comparator" Function:** The cerebellum as a whole acts as a comparator, correcting the "error" between intended movement (from the cortex) and actual movement (from proprioceptors). * **Purkinje Cells:** These are the only output cells of the cerebellar cortex and are always **inhibitory** (GABAergic). * **Climbing Fibers:** Originating from the **Inferior Olive**, these fibers are essential for the induction of long-term depression (LTD) involved in motor learning (like VOR adaptation).

Question 454: Which cells are most susceptible to hypoxia?

A. Neuron (Correct Answer)
B. Myocytes
C. Hepatocytes
D. Epithelium

Explanation: **Explanation:** The correct answer is **A. Neuron**. **Why Neurons are Most Susceptible:** Neurons have the highest metabolic rate of any cell in the body and possess virtually no capacity for anaerobic metabolism. They rely almost exclusively on a continuous supply of oxygen and glucose to maintain the ATP-dependent sodium-potassium pumps ($Na^+/K^+$ ATPase). When hypoxia occurs, ATP levels plummet rapidly, leading to pump failure, cellular swelling (cytotoxic edema), and irreversible damage. Irreversible brain damage typically begins after only **3–5 minutes** of total anoxia. Within the brain, the most sensitive areas are the **Pyramidal cells of the Hippocampus (CA1)** and the **Purkinje cells of the Cerebellum**. **Why Other Options are Incorrect:** * **B. Myocytes:** While cardiac muscle is sensitive to hypoxia, it can survive for approximately 20–30 minutes before irreversible necrosis occurs. Skeletal muscle is even more resistant, capable of surviving several hours of ischemia. * **C. Hepatocytes:** The liver has a dual blood supply (portal vein and hepatic artery) and cells contain significant glycogen stores, making them more resilient to hypoxic insult than neurons. * **D. Epithelium:** Epithelial cells (like those in the skin or GI tract) have lower metabolic demands and can tolerate hypoxia for significantly longer periods compared to neural tissue. **NEET-PG High-Yield Pearls:** * **Order of Susceptibility:** Neurons > Cardiac Myocytes > Hepatocytes > Skeletal Muscle > Connective Tissue. * **Vulnerable Brain Regions:** Hippocampus (Sommer’s sector) > Purkinje cells > Neocortex (Layers III, V, VI) > Striatum. * **Haldane Effect vs. Bohr Effect:** Often tested alongside neuro-respiratory physiology; remember that the Bohr effect describes how $CO_2/H^+$ affects $O_2$ affinity, whereas the Haldane effect describes how $O_2$ affects $CO_2$ affinity.

Question 455: Which of the following growth factors maintains neurons by reducing apoptosis, thereby preventing memory cells from undergoing apoptosis?

A. Platelet-derived growth factor
B. Nerve growth factor (Correct Answer)
C. Insulin-like growth factor
D. Fibroblast growth factor

Explanation: **Explanation:** **1. Why Nerve Growth Factor (NGF) is Correct:** Nerve Growth Factor (NGF) is the prototypical neurotrophin essential for the survival, development, and maintenance of specific neurons. Its primary mechanism involves binding to high-affinity **TrkA receptors**, which triggers signaling pathways that **inhibit pro-apoptotic proteins** (like Bad and Bax) and promote anti-apoptotic factors (like Bcl-2). By suppressing the "cell suicide" program (apoptosis), NGF ensures the persistence of cholinergic neurons in the basal forebrain—areas critical for learning and memory. **2. Why the Other Options are Incorrect:** * **Platelet-derived growth factor (PDGF):** Primarily involved in wound healing, angiogenesis, and the proliferation of connective tissue and glial cells (astrocytes/oligodendrocytes), rather than the direct anti-apoptotic maintenance of memory neurons. * **Insulin-like growth factor (IGF):** While it has neuroprotective properties, its primary role is systemic growth, glucose metabolism, and general cell proliferation. It is not the specific factor defined by the classical "neurotrophic hypothesis" for neuronal survival. * **Fibroblast growth factor (FGF):** Involved in neural stem cell proliferation and repair (neurogenesis), but it does not play the primary role in preventing apoptosis in established memory circuits compared to neurotrophins. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Retrograde Transport:** NGF is taken up by nerve terminals and transported **retrogradely** to the cell body to exert its effects. * **Alzheimer’s Connection:** A deficiency in NGF or its transport is linked to the atrophy of cholinergic neurons, a hallmark of Alzheimer’s disease. * **Other Neurotrophins:** Remember the family: **BDNF** (Brain-derived neurotrophic factor), **NT-3**, and **NT-4/5**. BDNF is particularly high-yield for its role in long-term potentiation (LTP) and synaptic plasticity. * **Receptors:** Neurotrophins bind to **Trk receptors** (tyrosine kinase) for survival and **p75NTR** (low affinity) which can actually promote apoptosis if not balanced.

Question 456: Posterolateral lesions of the ventral spinal cord lead to which of the following?

A. Pyramidal signs
B. Loss of joint sense
C. Loss of pressure and touch (Correct Answer)
D. Loss of pain and temperature

Explanation: ### Explanation The spinal cord is organized into specific tracts that carry sensory and motor information. To answer this question, one must understand the anatomical localization of the **Anterior Spinothalamic Tract (ASTT)**. **1. Why "Loss of pressure and touch" is correct:** The **Anterior Spinothalamic Tract** is located in the **ventral (anterior) column** of the spinal cord, specifically in the **posterolateral** aspect of the ventral horn/column area. This tract is responsible for carrying **crude touch and pressure** sensations. Therefore, a lesion in the posterolateral part of the ventral spinal cord directly interrupts these fibers, leading to a loss of these specific modalities. **2. Analysis of Incorrect Options:** * **Pyramidal signs (Option A):** These occur due to lesions of the Lateral Corticospinal Tract, which is located in the **lateral column**, not the ventral column. * **Loss of joint sense (Option B):** Proprioception, vibration, and fine touch (joint sense) are carried by the **Dorsal Columns** (Fasciculus Gracilis and Cuneatus), located in the posterior part of the cord. * **Loss of pain and temperature (Option D):** These sensations are carried by the **Lateral Spinothalamic Tract (LSTT)**. While also a spinothalamic tract, it is located in the **lateral column**, lateral to the ventral horn. **3. NEET-PG High-Yield Pearls:** * **Spinothalamic Tract Rule:** The *Lateral* tract is for *Pain/Temp*, and the *Anterior* tract is for *Crude Touch/Pressure*. * **Somatotopic Arrangement:** In the spinothalamic tracts, fibers from the sacral and lumbar segments are most **lateral**, while cervical fibers are most **medial**. * **Clinical Correlation:** In **Syringomyelia**, the crossing fibers of the spinothalamic tract are compressed first, leading to a "dissociated sensory loss" (loss of pain/temp but preservation of touch/proprioception). * **Brown-Séquard Syndrome:** Remember that spinothalamic fibers cross 1-2 segments above their entry point; thus, a lesion causes **contralateral** loss of pain/touch/pressure.

Question 457: Which of the following is an inhibitory neurotransmitter in the central nervous system?

A. Glycine (Correct Answer)
B. Glutamine
C. Aspartate
D. Nitric Oxide

Explanation: **Explanation:** Neurotransmitters are chemical messengers that either excite or inhibit post-synaptic neurons. In the Central Nervous System (CNS), the balance between excitation and inhibition is crucial for normal neurological function. **Why Glycine is Correct:** **Glycine** is the primary **inhibitory neurotransmitter** in the **spinal cord** and brainstem. It acts by binding to ionotropic receptors that open **chloride (Cl⁻) channels**. The influx of negatively charged chloride ions causes hyperpolarization of the post-synaptic membrane, resulting in an Inhibitory Post-Synaptic Potential (IPSP), which makes the neuron less likely to fire. **Analysis of Incorrect Options:** * **Glutamine:** This is a non-essential amino acid that serves as a precursor for glutamate. It is not a neurotransmitter itself but is part of the "glutamate-glutamine cycle" between neurons and astrocytes. * **Aspartate:** This is an **excitatory** neurotransmitter found primarily in the visual cortex. Like glutamate, it increases neuronal excitability. * **Nitric Oxide (NO):** This is a gaseous signaling molecule. While it acts as a neuromodulator, it is generally considered to have excitatory effects (e.g., in Long-Term Potentiation) and does not function as a classic inhibitory neurotransmitter. **High-Yield Clinical Pearls for NEET-PG:** * **GABA** is the primary inhibitory neurotransmitter in the **Brain**, while **Glycine** is the primary one in the **Spinal Cord**. * **Strychnine Poisoning:** Strychnine is a potent antagonist of glycine receptors. By blocking inhibition, it leads to unchecked muscular contractions and convulsions (opisthotonus). * **Tetanus Toxin:** Prevents the release of glycine and GABA from Renshaw cells in the spinal cord, leading to spastic paralysis and "lockjaw." * **Glutamate** is the most common excitatory neurotransmitter in the entire CNS.

Question 458: What is the typical presentation of a Wernicke's aphasia lesion?

A. Fluent speech with meaningful content
B. Fluent speech with meaningless content (Correct Answer)
C. Non-fluent speech with meaningful content
D. Non-fluent speech with meaningless content

Explanation: **Explanation:** Wernicke’s aphasia, also known as **Sensory or Receptive Aphasia**, results from a lesion in the posterior part of the superior temporal gyrus (Brodmann area 22) of the dominant hemisphere. **1. Why Option B is Correct:** In Wernicke’s aphasia, the motor ability to produce speech remains intact, but the **comprehension of language** is lost. Patients exhibit "fluent" speech—meaning the rate, rhythm, and articulation are normal—but the content is "meaningless." This is often described as **"word salad"** or jargon aphasia, where the patient uses neologisms (made-up words) and paraphasias (word substitutions) without realizing their speech lacks sense. **2. Why Other Options are Incorrect:** * **Option A:** Fluent speech with meaningful content describes normal, healthy communication. * **Option C:** Non-fluent speech with meaningful content is the hallmark of **Broca’s Aphasia** (Motor Aphasia). These patients struggle to produce words (telegraphic speech) but understand what is being said to them. * **Option D:** Non-fluent speech with meaningless content is characteristic of **Global Aphasia**, where both Broca’s and Wernicke’s areas (and the arcuate fasciculus) are damaged. **Clinical Pearls for NEET-PG:** * **Anatomical Site:** Posterior Superior Temporal Gyrus (supplied by the inferior division of the Middle Cerebral Artery). * **Key Feature:** Patients are typically **unaware** of their deficit (anosognosia), unlike Broca’s patients who are often frustrated. * **Conduction Aphasia:** If the **Arcuate Fasciculus** (the connection between Broca’s and Wernicke’s) is damaged, the patient has fluent speech and good comprehension but **impaired repetition**. * **Memory Trick:** **W**ernicke’s = **W**ord Salad; **B**roca’s = **B**roken speech.

Question 459: Which receptor is acted upon by a slow EPSP in the postganglionic neuron of a sympathetic ganglion?

A. Nicotinic
B. Muscarinic (Correct Answer)
C. Dopaminergic
D. GnRH

Explanation: In autonomic ganglia, synaptic transmission is more complex than a single excitatory event. It involves a sequence of potential changes in the postganglionic neuron: **1. Why Muscarinic is Correct:** While the primary, fast transmission in sympathetic ganglia is mediated by Nicotinic (Nn) receptors, the **Slow EPSP (Excitatory Postsynaptic Potential)** is mediated by **Muscarinic (M1) receptors**. * **Mechanism:** Acetylcholine (ACh) binds to M1 receptors, leading to the **closure of K+ channels** (specifically the M-channel). This decrease in K+ conductance prevents the exit of positive ions, causing a slow, prolonged depolarization that lasts several seconds. This serves to modulate the excitability of the postganglionic neuron. **2. Why Other Options are Incorrect:** * **Nicotinic (A):** These receptors mediate the **Fast EPSP**. They are ligand-gated ion channels that allow rapid influx of Na+, leading to immediate depolarization. * **Dopaminergic (C):** Dopamine, released by Small Intense Fluorescent (SIF) cells within the ganglion, mediates the **Slow IPSP** (Inhibitory Postsynaptic Potential) by increasing K+ conductance. * **GnRH (D):** Peptides like GnRH or Substance P are responsible for the **Late Slow EPSP**, which can last for minutes. **High-Yield NEET-PG Pearls:** * **Sequence of Potentials:** Fast EPSP (Nicotinic) $\rightarrow$ Slow IPSP (Dopamine) $\rightarrow$ Slow EPSP (Muscarinic M1) $\rightarrow$ Late Slow EPSP (Peptides like GnRH). * **The "M-Current":** The specific potassium current inhibited during a slow EPSP is the M-current; its inhibition makes the neuron more likely to fire in response to subsequent stimuli. * **Primary Neurotransmitter:** ACh is the neurotransmitter for *all* preganglionic autonomic fibers (both sympathetic and parasympathetic).

Question 460: What is the major determinant for the rate of cerebral blood flow?

A. Intracranial pressure (Correct Answer)
B. Aortic blood pressure
C. Arterial PaCO2
D. Neurogenic regulation

Explanation: **Explanation:** The rate of cerebral blood flow (CBF) is primarily determined by the **Cerebral Perfusion Pressure (CPP)**. According to the physiological formula: **CBF = CPP / Cerebral Vascular Resistance (CVR)** Where **CPP = Mean Arterial Pressure (MAP) – Intracranial Pressure (ICP).** In a clinical context, especially concerning the "rate" and regulation of flow within the rigid confines of the skull (Monro-Kellie doctrine), **Intracranial Pressure (Option A)** is the major determinant. Any increase in ICP directly opposes the perfusion pressure, significantly reducing CBF unless compensated for by a massive rise in systemic blood pressure. **Analysis of Other Options:** * **B. Aortic Blood Pressure:** While MAP is part of the CPP formula, the brain possesses a robust **autoregulation** mechanism that keeps CBF constant despite fluctuations in systemic pressure (between 60–140 mmHg). Thus, it is not the primary determinant under normal conditions. * **C. Arterial PaCO2:** This is the most potent *chemical* regulator of CBF. Hypercapnia causes vasodilation and increases flow, while hypocapnia causes vasoconstriction. However, it is considered a regulator of vascular resistance rather than the primary driving determinant of the flow rate itself. * **D. Neurogenic Regulation:** The sympathetic and parasympathetic nervous systems have a minimal role in the day-to-day regulation of CBF compared to metabolic and pressure factors. **High-Yield Clinical Pearls for NEET-PG:** 1. **Cushing’s Triad:** A clinical sign of increased ICP characterized by hypertension, bradycardia, and irregular respiration. 2. **PaCO2 Sensitivity:** CBF changes by approximately **2–3% for every 1 mmHg change in PaCO2**. 3. **Monro-Kellie Doctrine:** The sum of volumes of brain, CSF, and intracerebral blood is constant; an increase in one must be offset by a decrease in another, or ICP will rise.

Practice by Chapter

Neurons and Glial Cells

Practice Questions

Synaptic Transmission

Practice Questions

Sensory Processing

Practice Questions

Motor Control Systems

Practice Questions

Autonomic Nervous System

Practice Questions

Hypothalamus and Limbic System

Practice Questions

Cerebral Cortex Functions

Practice Questions

Electroencephalography

Practice Questions

Neuroplasticity

Practice Questions

Sleep and Wakefulness

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free