Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 181: All of the following are true regarding the actions of endothelin-1 except?

A. Bronchodilation (Correct Answer)
B. Vasoconstriction
C. Decreased GFR
D. Has inotrophic effect

Explanation: **Explanation:** Endothelin-1 (ET-1) is one of the most potent endogenous **vasoconstrictors** known [1]. It is produced by vascular endothelial cells and acts primarily through two G-protein coupled receptors: $ET_A$ and $ET_B$ [1]. **Why Option A is the Correct Answer (The Exception):** Endothelin-1 does **not** cause bronchodilation. Instead, it is a potent **bronchoconstrictor**. It stimulates the contraction of airway smooth muscle and is often found in elevated levels in patients with asthma and COPD [2]. Therefore, "Bronchodilation" is the false statement. **Analysis of Incorrect Options:** * **B. Vasoconstriction:** This is the primary action of ET-1. By binding to $ET_A$ receptors on vascular smooth muscle, it causes profound and sustained vasoconstriction, increasing peripheral resistance and blood pressure [1]. * **C. Decreased GFR:** In the kidneys, ET-1 causes constriction of both afferent and efferent arterioles (with a preference for the afferent). This leads to reduced renal blood flow and a subsequent **decrease in Glomerular Filtration Rate (GFR)**. * **D. Inotropic effect:** ET-1 exerts a **positive inotropic effect** on the myocardium (increasing the force of contraction) and can also induce cardiac hypertrophy over time. **NEET-PG High-Yield Pearls:** * **Bosentan:** A non-selective endothelin receptor antagonist ($ET_A$ & $ET_B$) used clinically in the treatment of **Pulmonary Arterial Hypertension (PAH)**. * **Synthesis:** ET-1 is synthesized from "Big Endothelin" by the **Endothelin-Converting Enzyme (ECE)** [1]. * **Stimuli:** Its release is stimulated by thrombin, epinephrine, and low shear stress, while it is inhibited by Nitric Oxide (NO) and Prostacyclin ($PGI_2$).

Question 182: Which of the following conditions could be produced by fracture of the floor of the middle cranial cavity, causing severance of the greater petrosal nerve?

A. Increased lacrimal gland secretion
B. Loss of taste sensation in the epiglottis
C. Dryness in the nose and palate (Correct Answer)
D. Decreased parotid gland secretion

Explanation: The **greater petrosal nerve** is the first branch of the facial nerve (CN VII), arising from the geniculate ganglion. It carries **preganglionic parasympathetic fibers** destined for the **pterygopalatine ganglion**. 1. **Why Option C is Correct:** After synapsing in the pterygopalatine ganglion, postganglionic fibers provide secretomotor supply to the **lacrimal gland** and the **mucous glands of the nasal cavity, paranasal sinuses, and palate**. Severance of this nerve leads to a loss of parasympathetic stimulation, resulting in decreased secretions and subsequent **dryness of the nose and palate**. 2. **Why Other Options are Incorrect:** * **Option A:** Severance would cause **decreased** (not increased) lacrimation (dry eye/xerophthalmia). * **Option B:** Taste from the epiglottis is carried by the **internal laryngeal nerve** (branch of Vagus, CN X). The greater petrosal nerve carries taste only from the soft palate. * **Option D:** The parotid gland receives its parasympathetic supply from the **glossopharyngeal nerve (CN IX)** via the lesser petrosal nerve and the otic ganglion. **High-Yield Clinical Pearls for NEET-PG:** * **Course:** The greater petrosal nerve passes through the **hiatus for the greater petrosal nerve** on the anterior surface of the petrous temporal bone (middle cranial fossa). * **Nerve of Pterygoid Canal (Vidian Nerve):** Formed by the union of the **greater petrosal nerve** (parasympathetic) and the **deep petrosal nerve** (sympathetic from the internal carotid plexus). * **Clinical Sign:** A lesion proximal to the geniculate ganglion (like a temporal bone fracture) presents with the

Question 183: Nephrocalcinosis is seen in which of the following conditions?

A. Hyperparathyroidism (Correct Answer)
B. Diabetes mellitus
C. Amyloidosis of kidney
D. End-stage renal disease

Explanation: **Explanation:** **Nephrocalcinosis** refers to the generalized deposition of calcium salts (calcium phosphate or calcium oxalate) within the renal parenchyma (medulla and cortex). It is a radiological and pathological finding rather than a primary disease. 1. **Why Hyperparathyroidism is correct:** Primary hyperparathyroidism leads to excessive secretion of Parathyroid Hormone (PTH), which increases bone resorption and intestinal calcium absorption. This results in **hypercalcemia** and subsequent **hypercalciuria**. When the concentration of calcium in the renal filtrate exceeds the solubility product, calcium precipitates within the renal tubular cells and interstitium, leading to nephrocalcinosis [1, 2]. It is one of the most common causes of this condition. 2. **Why the other options are incorrect:** * **Diabetes Mellitus:** Primarily causes diabetic nephropathy characterized by glomerular basement membrane thickening and Kimmelstiel-Wilson nodules, not calcium deposition. * **Amyloidosis:** Involves the deposition of extracellular fibrillar proteins (amyloid) in the glomeruli and vessels, leading to nephrotic syndrome, not calcification. * **End-stage Renal Disease (ESRD):** While ESRD can lead to secondary hyperparathyroidism, the kidneys are typically shrunken and scarred. Nephrocalcinosis is a *cause* or a *complication* of specific metabolic derangements rather than a standard feature of ESRD itself [1]. **High-Yield Pearls for NEET-PG:** * **Distinction:** Do not confuse *Nephrocalcinosis* (parenchymal calcification) with *Nephrolithiasis* (calculi in the pelvicalyceal system) [1, 2]. * **Common Causes:** Hyperparathyroidism, Distal Renal Tubular Acidosis (Type 1 RTA), Medullary Sponge Kidney, and Vitamin D intoxication [2]. * **Radiology:** The "Medullary Nephrocalcinosis" pattern is most common, often seen as hyperechoic pyramids on ultrasound. * **Classic Triad of Hyperparathyroidism:** "Stones (renal calculi), Bones (osteitis fibrosa cystica), and Abdominal Groans (peptic ulcers/pancreatitis)" [1].

Question 184: All of the following are morphological features of apoptosis except?

A. Cell shrinkage
B. Chromatin condensation
C. Inflammation (Correct Answer)
D. Apoptotic bodies

Explanation: **Explanation:** Apoptosis is a programmed, energy-dependent process of cell death designed to eliminate unwanted cells without eliciting a host response. The hallmark of apoptosis is that the **cell membrane remains intact**, preventing the leakage of cellular contents into the extracellular space. Consequently, there is **no inflammation** (Option C). In contrast, necrosis involves membrane rupture, leading to the release of lysosomal enzymes and pro-inflammatory signals. **Analysis of Options:** * **Cell Shrinkage (Option A):** This is a key feature. Unlike necrosis (where cells swell), apoptotic cells show dense cytoplasm and tightly packed organelles. * **Chromatin Condensation (Option B):** This is the most characteristic feature of apoptosis. Chromatin aggregates peripherally under the nuclear membrane (pyknosis), followed by nuclear fragmentation (karyorrhexis). * **Apoptotic Bodies (Option C):** The cell breaks into membrane-bound vesicles containing portions of cytoplasm and nucleus. These are rapidly cleared by macrophages via "eat-me" signals (like phosphatidylserine) before they can trigger an inflammatory response. **High-Yield NEET-PG Pearls:** 1. **Caspases:** These are the executioner proteases of apoptosis (Cysteine-Aspartic acid proteases). 2. **DNA Laddering:** On gel electrophoresis, apoptosis shows a "step-ladder" pattern due to internucleosomal cleavage of DNA by endonucleases (at 180-200 bp intervals). Necrosis shows a "smear" pattern. 3. **Bcl-2 Family:** Pro-apoptotic members include **Bax and Bak**; Anti-apoptotic members include **Bcl-2 and Bcl-xL**. 4. **Mitochondrial Pathway:** The release of **Cytochrome c** into the cytosol is the critical step in the intrinsic pathway.

Question 185: Which polyarthritic condition is not common?

A. Gout
B. Psoriatic arthritis
C. Ankylosing spondylitis
D. Systemic lupus erythematosus (SLE) (Correct Answer)

Explanation: The classification of arthritis depends on the number of joints involved: **Monoarthritis** (1 joint), **Oligoarthritis** (2-4 joints), and **Polyarthritis** (≥5 joints). **Why SLE is the correct answer:** While Systemic Lupus Erythematosus (SLE) frequently presents with joint pain (arthralgia) and inflammation (arthritis), it is classically characterized as a **migratory, non-erosive polyarthritis**. However, in the context of clinical frequency and standard rheumatological classification, SLE is often considered less "common" as a primary polyarthritic condition compared to the others listed, or it is distinguished by its non-deforming nature (Jaccoud’s arthropathy). In many competitive exams, SLE is highlighted because its joint involvement is often secondary to systemic multi-organ involvement rather than being a primary destructive polyarthritis like Rheumatoid Arthritis. **Analysis of Incorrect Options:** * **Gout:** While typically presenting as acute monoarthritis (Podagra), chronic tophaceous gout frequently progresses to a **polyarthritic** pattern involving multiple small and large joints. * **Psoriatic Arthritis (PsA):** This is a classic cause of inflammatory **polyarthritis**, often involving the DIP joints and presenting with a "symmetric polyarthritis" pattern that mimics Rheumatoid Arthritis [1]. * **Ankylosing Spondylitis (AS):** Although primarily involving the axial skeleton (Sacroiliitis), AS commonly presents with peripheral **polyarthritis** (especially in the lower limbs) in a significant percentage of patients [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Jaccoud’s Arthropathy:** Seen in SLE; it involves reversible joint deformities due to ligamentous laxity rather than bone erosion. * **Symmetric Polyarthritis:** The hallmark of Rheumatoid Arthritis. * **Asymmetric Oligoarthritis:** The most common presentation of Seronegative Spondyloarthropathies (like Psoriatic Arthritis) [1]. * **DIP Joint Involvement:** Characteristic of Psoriatic Arthritis and Osteoarthritis, but notably spared in Rheumatoid Arthritis.

Question 186: The ability to recognize an unseen familiar object placed in the hand depends on the integrity of which neural pathway?

A. Posterior column (Correct Answer)
B. Posterior spinocerebellar tract
C. Spino-olivary tract
D. Spinospinal tract

Explanation: The ability to recognize an object by touch without visual input is known as **stereognosis**. This complex sensory function requires the integration of several fine-touch modalities [1]. ### Why the Posterior Column is Correct The **Posterior Column-Medial Lemniscus (PCML) pathway** is responsible for transmitting "discriminative" sensations [3]. These include: * **Fine touch and pressure:** To perceive the texture and shape [1]. * **Conscious proprioception:** To perceive the position of the fingers around the object [2]. * **Vibration and Two-point discrimination.** Stereognosis is a cortical sensation that depends on the integrity of the PCML to carry these inputs to the primary somatosensory cortex (Brodmann areas 3, 1, 2) and the parietal association cortex (Brodmann areas 5, 7) [2], [3]. A lesion in the posterior columns leads to **astereognosis** [1]. ### Why Other Options are Incorrect * **Posterior spinocerebellar tract:** This pathway carries **unconscious proprioception** from the lower limbs and trunk to the cerebellum to coordinate posture and gait. It does not reach the sensory cortex for conscious perception. * **Spino-olivary tract:** This tract carries information from cutaneous and proprioceptive organs to the cerebellum via the inferior olive, playing a role in motor learning and coordination. * **Spinospinal tract (Fasciculus Proprius):** These are short ascending and descending fibers that stay within the spinal cord to coordinate intersegmental spinal reflexes. ### NEET-PG High-Yield Pearls * **Astereognosis vs. Agraphesthesia:** Astereognosis is the inability to identify objects; **Agraphesthesia** is the inability to recognize letters or numbers traced on the skin. Both indicate PCML or parietal lobe lesions [1]. * **Somatotopy:** In the posterior columns, fibers from the lower body are medial (**Fasciculus Gracilis**), while fibers from the upper body are lateral (**Fasciculus Cuneatus**). * **Decussation:** The PCML pathway decussates in the medulla as **internal arcuate fibers** [3].

Question 187: Which equation is used to measure the resting membrane potential in case of multiple ions?

A. Goldman equation (Correct Answer)
B. Nernst equation
C. Both Goldman and Nernst equations
D. Neither Goldman nor Nernst equation

Explanation: The resting membrane potential (RMP) is a fundamental concept in neurophysiology, representing the electrical potential difference across a cell membrane at rest. [1] ### **Explanation of the Correct Answer** **Option A (Goldman Equation):** The Goldman-Hodgkin-Katz (GHK) equation is the correct choice because it accounts for **multiple ions** (primarily $Na^+$, $K^+$, and $Cl^-$) simultaneously. Unlike simpler models, it considers two critical factors for each ion: 1. The **concentration gradient** across the membrane. [1] 2. The **relative permeability** ($P$) of the membrane to that specific ion. [1] Since the RMP of a neuron (typically -70 mV) is a collective result of all permeant ions, the Goldman equation provides the most accurate physiological measurement. ### **Explanation of Incorrect Options** * **Option B (Nernst Equation):** This equation calculates the **equilibrium potential for a single ion** only. [1] It determines the theoretical voltage at which the electrical and chemical gradients for one specific ion are perfectly balanced (e.g., -94 mV for $K^+$ or +61 mV for $Na^+$). It does not account for the membrane's simultaneous permeability to other ions. * **Options C & D:** These are incorrect as the two equations serve distinct purposes—one for individual ion equilibrium and the other for the total membrane potential. ### **NEET-PG High-Yield Pearls** * **The "K+ Rule":** The RMP is closest to the equilibrium potential of Potassium (-94 mV) because the resting membrane is 20–100 times more permeable to $K^+$ than to $Na^+$. * **The Na+-K+ Pump:** While the Goldman equation calculates the potential based on diffusion, the $Na^+$-$K^+$ ATPase pump is "electrogenic" and directly contributes about -4 mV to the RMP. * **Clinical Correlation:** Hypokalemia makes the RMP more negative (hyperpolarization), making neurons less excitable, which clinically manifests as muscle weakness or paralysis.

Question 188: Which nerve is associated with the 6th branchial arch?

A. Superior laryngeal nerve
B. Internal laryngeal nerve
C. External laryngeal nerve
D. Recurrent laryngeal nerve (Correct Answer)

Explanation: The branchial (pharyngeal) arches are fundamental to head and neck development, with each arch associated with a specific cranial nerve branch. ### **Explanation of the Correct Answer** The **Recurrent Laryngeal Nerve (RLN)** is the nerve of the **6th branchial arch**. During development, the 6th arch gives rise to the intrinsic muscles of the larynx (except the cricothyroid) and the laryngeal cartilages (except the epiglottis). Because the RLN supplies these derivatives, it is embryologically tied to this arch [1, 3]. Its "recurrent" course is due to the descent of the heart and the transformation of the 6th arch arteries (forming the ductus arteriosus on the left and disappearing on the right) [1]. ### **Analysis of Incorrect Options** * **A, B, and C (Superior, Internal, and External Laryngeal Nerves):** These are all branches or components of the **Superior Laryngeal Nerve (SLN)**. The SLN is the nerve of the **4th branchial arch**. It supplies the cricothyroid muscle (via the external branch) and provides sensory innervation above the vocal cords (via the internal branch). ### **High-Yield NEET-PG Pearls** * **Arch-Nerve Correlation Table:** * **1st Arch:** Mandibular nerve ($V_3$) * **2nd Arch:** Facial nerve (VII) * **3rd Arch:** Glossopharyngeal nerve (IX) * **4th Arch:** Superior Laryngeal nerve (branch of X) * **6th Arch:** Recurrent Laryngeal nerve (branch of X) * **Muscles of 6th Arch:** All intrinsic muscles of the larynx **except** the cricothyroid. * **Clinical Correlation:** Injury to the RLN (often during thyroid surgery) leads to hoarseness of voice or respiratory distress if bilateral, as it controls the abductors of the vocal cords (Posterior Cricoarytenoid) [1, 3].

Question 189: Which of the following can cause a soft first heart sound (S1)?

A. Obesity
B. Pleural effusion
C. Mitral regurgitation
D. All the above (Correct Answer)

Explanation: The first heart sound (**S1**) is produced primarily by the closure of the atrioventricular valves (Mitral and Tricuspid) at the onset of ventricular systole [1]. The intensity of S1 depends on the mobility of the leaflets, the rate of pressure rise in the ventricles, and the distance between the heart and the stethoscope [1]. **Explanation of Options:** * **Mitral Regurgitation (C):** This is a classic valvular cause of a soft S1. In chronic MR, the mitral leaflets may fail to coapt properly or are structurally compromised, leading to inadequate "tensing" during closure. Additionally, the PR interval may be prolonged, or the leaflets may already be partially closed at the start of systole, reducing the sound intensity. * **Obesity (A) and Pleural Effusion (B):** These are **extracardiac factors**. S1 is "muffled" or softened because there is increased tissue or fluid (insulation) between the heart and the chest wall, which attenuates the transmission of sound waves to the stethoscope. **Why "All the Above" is Correct:** A soft S1 occurs whenever there is either a structural valvular defect (like MR or severe calcific MS), a physiological delay (long PR interval/First-degree heart block), or an anatomical barrier (obesity, emphysema, or pericardial/pleural effusion) that dampens sound transmission. **High-Yield Clinical Pearls for NEET-PG:** * **Loud S1:** Seen in Mitral Stenosis (pliable leaflets), short PR interval (Tachycardia, WPW syndrome), and hyperdynamic states (Anemia, Thyrotoxicosis). * **Variable S1:** A hallmark of **Atrial Fibrillation** and **Complete Heart Block** (due to varying PR intervals). * **Soft S1 in MI:** A soft S1 in the setting of an acute myocardial infarction may indicate poor ventricular contractility or the development of acute mitral regurgitation.

Question 190: What nerve supplies the skin over the parotid gland?

A. Retroauricular nerve
B. Greater auricular nerve (Correct Answer)
C. Greater occipital nerve
D. Facial nerve

Explanation: The skin over the parotid gland is supplied by the **Greater Auricular Nerve**, which is a branch of the **Cervical Plexus (C2, C3)**. ### Why the Greater Auricular Nerve is Correct: The greater auricular nerve emerges from the posterior border of the sternocleidomastoid muscle (at Erb’s point) and ascends vertically across the muscle toward the parotid gland. It provides sensory innervation to: 1. The skin overlying the **parotid gland**. 2. The skin over the **angle of the mandible**. 3. Both surfaces of the **lower part of the auricle** (pinna). ### Why the Other Options are Incorrect: * **Retroauricular nerve:** This is a motor branch of the Facial nerve (CN VII) that supplies the auricularis posterior muscle and the occipital belly of the occipitofrontalis. It does not provide cutaneous sensation to the parotid region. * **Greater occipital nerve:** This is the medial branch of the posterior ramus of the C2 spinal nerve. It supplies the skin of the **posterior scalp** up to the vertex, far behind the parotid region. * **Facial nerve (CN VII):** While the facial nerve passes *through* the substance of the parotid gland and divides it into superficial and deep lobes, it provides **motor** innervation to the muscles of facial expression. It does **not** provide sensory innervation to the overlying skin. ### NEET-PG High-Yield Pearls: * **Frey’s Syndrome:** Occurs due to aberrant regeneration of the **auriculotemporal nerve** (parasympathetic fibers) joining the **greater auricular nerve** (sympathetic sweat gland fibers) after parotid surgery. This leads to "gustatory sweating" over the parotid skin. * **Nerve Supply of the Parotid Gland:** * **Sensory:** Auriculotemporal nerve (capsule) and Greater auricular nerve (overlying skin). * **Parasympathetic (Secretomotor):** Glossopharyngeal nerve (CN IX) → Lesser petrosal nerve → Otic ganglion → Auriculotemporal nerve. * **Erb’s Point:** The location on the posterior border of the sternocleidomastoid where four cutaneous branches of the cervical plexus emerge (Greater auricular, Lesser occipital, Transverse cervical, and Supraclavicular nerves).

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