Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 591: Which of the following arteries is likely to be involved in a 3rd cranial nerve lesion?

A. Anterior communicating artery
B. Posterior communicating artery (Correct Answer)
C. Posterior cerebral artery
D. Anterior cerebral artery

Explanation: ### Explanation The **Oculomotor nerve (CN III)** has a highly specific anatomical relationship with the vessels of the Circle of Willis. As it emerges from the midbrain in the interpeduncular fossa, it passes forward between the **Posterior Cerebral Artery (PCA)** and the **Superior Cerebellar Artery (SCA)**. It then runs lateral to and parallel with the **Posterior Communicating Artery (PCoA)**. **Why Option B is Correct:** Aneurysms at the junction of the **Posterior Communicating Artery** and the Internal Carotid Artery are the most common cause of surgical 3rd nerve palsy [2]. Because the pupilloconstrictor fibers are located superficially (peripherally) in the nerve, they are the first to be compressed by an expanding aneurysm [1]. This leads to a **"surgical third"**—presenting with a dilated, non-reactive pupil alongside ptosis and "down and out" eye deviation. **Analysis of Incorrect Options:** * **A & D (Anterior Communicating/Anterior Cerebral):** These arteries are located in the anterior part of the Circle of Willis, near the optic chiasm. They are more likely to cause visual field defects (bitemporal hemianopia) rather than oculomotor nerve compression. * **C (Posterior Cerebral Artery):** While the nerve passes *below* the PCA, aneurysms here are statistically less common causes of isolated 3rd nerve palsy compared to PCoA aneurysms [2]. **NEET-PG High-Yield Pearls:** * **Rule of Pupil:** If the pupil is involved (dilated), suspect **compression** (e.g., PCoA aneurysm). If the pupil is spared, suspect **ischemia** (e.g., Diabetes Mellitus), as ischemia affects the deep microvasculature but spares the superficial parasympathetic fibers [1]. * **Anatomical Sandwich:** CN III is "sandwiched" between the PCA (above) and SCA (below). * **Weber Syndrome:** Midbrain infarction involving the CN III fascicles and the cerebral peduncle (contralateral hemiplegia).

Question 592: Memory impairment occurs in embolism of the posterior cerebral artery due to damage to which of the following structures?

A. Hippocampal gyrus (Correct Answer)
B. Superior temporal gyrus
C. Prefrontal gyrus
D. Angular gyrus

Explanation: The **Posterior Cerebral Artery (PCA)** is the terminal branch of the basilar artery. It supplies the occipital lobe, the inferior surface of the temporal lobe, and deep structures including the thalamus and the medial temporal lobe. [1] **Why the Hippocampal Gyrus is correct:** The **Hippocampal gyrus (Parahippocampal gyrus)** and the underlying hippocampus are located in the medial temporal lobe. These structures are primarily supplied by the **temporal branches of the PCA**. The hippocampus is the critical center for the formation of new memories (anterograde memory) and the consolidation of short-term memory into long-term memory. [1] Therefore, an embolism or infarct in the PCA leads to ischemia of the hippocampal formation, resulting in significant memory impairment. **Analysis of Incorrect Options:** * **Superior Temporal Gyrus:** Supplied by the **Middle Cerebral Artery (MCA)**. It contains Wernicke’s area (posterior part); damage here leads to sensory aphasia, not primary memory loss. * **Prefrontal Gyrus:** Located in the frontal lobe and supplied by the **Anterior Cerebral Artery (ACA)** and **MCA**. It is involved in executive function, personality, and motor planning. [1] * **Angular Gyrus:** Located in the parietal lobe and supplied by the **MCA**. Damage here (usually in the dominant hemisphere) leads to Gerstmann Syndrome (acalculia, agraphia, finger agnosia, and right-left disorientation). **High-Yield Clinical Pearls for NEET-PG:** * **Visual Deficits:** The most common finding in PCA stroke is **contralateral homonymous hemianopia with macular sparing** (due to dual supply to the macula by the MCA). * **Thalamic Syndrome:** PCA involvement of the posterolateral thalamus can cause contralateral hemisensory loss followed by severe burning pain (Dejerine-Roussy syndrome). * **Memory:** Bilateral PCA infarction can lead to profound permanent amnesia. [1]

Question 593: What is the principal cause of death in renal transplant patients?

A. Uremia
B. Malignancy
C. Rejection
D. Infection (Correct Answer)

Explanation: The principal cause of death in renal transplant patients is **Infection (Option D)**. This is primarily due to the lifelong requirement for **potent immunosuppressive therapy** (such as corticosteroids, calcineurin inhibitors, and antimetabolites) to prevent graft rejection [1]. These drugs suppress the patient’s cell-mediated and humoral immunity, making them highly susceptible to opportunistic pathogens (CMV, BK virus, Pneumocystis jirovecii) and common bacterial infections. While cardiovascular disease is often cited as the leading cause of long-term mortality, in the context of transplant-specific complications and early post-operative periods, infection remains the most significant threat. **Analysis of Incorrect Options:** * **A. Uremia:** This was the leading cause of death before the advent of dialysis and successful transplantation. Modern renal replacement therapy and successful grafting have made uremia a rare cause of death in these patients. * **B. Malignancy:** Immunosuppression does increase the risk of certain cancers (e.g., Kaposi sarcoma, Lymphoma/PTLD, and Squamous Cell Carcinoma), but it is generally a late-stage complication and less frequent than fatal infections. * **C. Rejection:** While rejection is the most common cause of **graft loss**, it is rarely the cause of **patient death**, as patients can return to dialysis if the graft fails [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Most common viral infection:** Cytomegalovirus (CMV) – typically occurs 1–6 months post-transplant. * **Most common malignancy:** Skin cancer (Squamous Cell Carcinoma). * **PTLD (Post-Transplant Lymphoproliferative Disorder):** Strongly associated with Epstein-Barr Virus (EBV) infection. * **BK Virus:** Associated with nephropathy and graft failure.

Question 594: Which of the following is true about Tanner stage 3?

A. Penis increases in length (Correct Answer)
B. Penis increases in width
C. Scanty hair at the base of the penis
D. Darkening of the scrotum

Explanation: The **Tanner Staging (Sexual Maturity Rating)** is a high-yield topic in NEET-PG, used to objectively track the progression of secondary sexual characteristics during puberty. ### Explanation of the Correct Option **Option A (Penis increases in length)** is the hallmark of **Tanner Stage 3** in males [1]. During this stage, the penis begins to enlarge, specifically increasing in **length** more than width [1]. Additionally, the testes and scrotum continue to enlarge (volume 10–15 ml), and the pubic hair becomes darker, coarser, and curlier, spreading over the junction of the pubis. ### Explanation of Incorrect Options * **Option B (Penis increases in width):** This occurs primarily in **Tanner Stage 4** [1]. While the penis continues to grow in length, the significant increase in breadth (width) and the development of the glans penis are characteristic of Stage 4 [1]. * **Option C (Scanty hair at the base of the penis):** This describes **Tanner Stage 2**. This stage marks the "pubertal onset," characterized by sparse, long, slightly pigmented, downy hair primarily at the base of the penis. * **Option D (Darkening of the scrotum):** This is a feature of **Tanner Stage 4**. In this stage, the scrotal skin darkens (hyperpigmentation) and the development of the glans penis becomes more prominent. ### NEET-PG High-Yield Pearls * **First sign of puberty in males:** Testicular enlargement (Volume ≥ 4ml or Length > 2.5 cm), occurring in **Stage 2** [1]. * **First sign of puberty in females:** Thelarche (Breast budding), occurring in **Stage 2** [1]. * **Tanner Stage 5:** Represents adult genitalia in size and shape; pubic hair extends to the medial surface of the thighs [1]. * **Growth Spurt:** In boys, the peak height velocity typically occurs during **Tanner Stage 4**.

Question 595: Dense regular collagen is found in all of the following tissues EXCEPT:

A. Ligament
B. Periosteum (Correct Answer)
C. Aponeurosis
D. Tendon

Explanation: The classification of connective tissue depends on the arrangement and density of collagen fibers. **Dense regular connective tissue** consists of collagen fibers arranged in parallel bundles, providing maximum tensile strength in a single direction. **Why Periosteum is the Correct Answer:** The **periosteum** is composed of **dense irregular connective tissue**. Its collagen fibers are arranged in a haphazard, multidirectional network. This structural arrangement allows the bone to withstand mechanical stresses and tension applied from multiple different directions, rather than just one. It consists of an outer fibrous layer (dense irregular) and an inner osteogenic layer. **Analysis of Incorrect Options:** * **Tendons:** These connect muscle to bone. They consist of dense regular collagen fibers packed parallel to each other to resist the unidirectional pull of muscle contraction. * **Ligaments:** These connect bone to bone. Like tendons, they are composed of dense regular connective tissue to provide stability and resist strain along the axis of the fiber. * **Aponeuroses:** These are broad, sheet-like tendons. Despite their flat shape, the collagen fibers within them are organized in a highly regular, parallel fashion, classifying them as dense regular tissue. **High-Yield NEET-PG Pearls:** * **Dense Regular:** Tendons, Ligaments, Aponeuroses, and Corneal stroma. * **Dense Irregular:** Periosteum, Perichondrium, Dermis of skin, and Organ capsules (e.g., Glisson’s capsule of the liver). * **Type I Collagen** is the predominant collagen type found in all the structures mentioned in this question [1], [2]. * **Sharpey’s Fibers:** These are specific collagen fibers from the periosteum that penetrate into the bone tissue to anchor it firmly.

Question 596: Why is the regeneration of nerve fibres possible in the peripheral nervous system but more limited in the central nervous system?

A. Presence of neurilemmal sheath in peripheral nerves (Correct Answer)
B. Presence of neurilemmal sheath in the central nervous system
C. Absence of myelin sheath in the central nervous system
D. Disturbed vascular supply in the central nervous system

Explanation: The regenerative capacity of nerve fibers depends primarily on the presence of the **neurilemma (Sheath of Schwann)** [1]. **1. Why Option A is Correct:** In the Peripheral Nervous System (PNS), axons are myelinated by **Schwann cells** [1], [4]. The outermost layer of the Schwann cell cytoplasm forms the **neurilemmal sheath**. When a peripheral nerve is injured, this sheath remains intact as a hollow tube (forming the *Bands of Büngner*). It produces neurotrophic factors and provides a physical scaffold that guides the sprouting axon toward its target organ, facilitating successful regeneration [1]. **2. Why the Other Options are Incorrect:** * **Option B:** The CNS lacks a neurilemmal sheath. Myelination in the CNS is performed by **oligodendrocytes**, which do not form a continuous basement membrane or neurilemma [3]. * **Option C:** The CNS is heavily myelinated; however, CNS myelin contains inhibitory proteins (like **Nogo-A**) that actively prevent axonal regrowth. * **Option D:** While vascularity is vital for tissue health, the primary limiting factor for nerve regeneration is the cellular environment (glial scarring and lack of neurilemma), not blood supply. **High-Yield NEET-PG Pearls:** * **Wallerian Degeneration:** The process of antegrade degeneration of the distal segment of an axon following injury [1]. * **Glial Scarring:** In the CNS, **astrocytes** proliferate at the injury site, forming a physical and chemical barrier that prevents regeneration [2]. * **Key Difference:** One Schwann cell myelinates only **one** internode of a single axon, whereas one oligodendrocyte can myelinate up to **50** different axons [3], [4].

Question 597: Which of the following is a predisposing factor for venous thrombosis?

A. Antithrombin III deficiency
B. Protein S deficiency
C. Protein C deficiency
D. All of the above (Correct Answer)

Explanation: Venous thrombosis is primarily driven by **Virchow’s Triad**: endothelial injury, stasis of blood flow, and **hypercoagulability** [3, 4]. The options provided represent hereditary causes of hypercoagulability (thrombophilia), where a deficiency in natural anticoagulants tips the balance toward clot formation [1]. 1. **Antithrombin III (ATIII) Deficiency:** ATIII is a potent natural anticoagulant that inactivates thrombin (Factor IIa) and Factor Xa [1]. Its deficiency significantly increases the risk of venous thromboembolism (VTE) and is clinically notable because it causes **heparin resistance**, as heparin requires ATIII to function [2]. 2. **Protein C Deficiency:** Protein C, when activated, degrades Factors Va and VIIIa. A deficiency leads to unchecked thrombin generation [1]. A high-yield clinical association is **Warfarin-induced skin necrosis**, occurring when therapy starts without a heparin bridge. 3. **Protein S Deficiency:** Protein S acts as a necessary cofactor for Protein C [1]. Therefore, its deficiency results in a similar inability to inactivate Factors Va and VIIIa, predisposing the patient to deep vein thrombosis (DVT) and pulmonary embolism. Since all three proteins are essential components of the body’s natural anticoagulation system, a deficiency in any of them leads to a prothrombotic state [1]. **High-Yield NEET-PG Pearls:** * **Most common inherited cause of hypercoagulability:** Factor V Leiden (resistance to Protein C) [1]. * **Most common inherited cause of venous thrombosis overall:** Factor V Leiden [1]. * **Prothrombin G20210A mutation:** Leads to increased prothrombin levels [1]. * **Hyperhomocysteinemia:** Another important risk factor for both arterial and venous thrombosis.

Question 598: All of the following are true about the notochord, EXCEPT:

A. Derived from mesoderm between the prochordal plate and primitive pit
B. Causes induction of the overlying ectoderm to form the nervous system
C. Becomes the annulus fibrosus of the adult intervertebral disc (Correct Answer)
D. Remnants may persist and give rise to a chordoma

Explanation: The notochord is a primitive, solid, flexible rod that serves as the basis for the axial skeleton. Understanding its fate and function is high-yield for NEET-PG. **Explanation of the Correct Answer (C):** The notochord does **not** become the annulus fibrosus. Instead, it forms the **nucleus pulposus** (the gelatinous inner core) of the intervertebral disc. The annulus fibrosus (the outer fibrous ring) is derived from the surrounding **sclerotome** (mesoderm). **Analysis of Incorrect Options:** * **Option A:** This is a correct anatomical description. The notochordal process develops from the primitive pit and extends cranially until it reaches the prochordal plate (the future oropharyngeal membrane). * **Option B:** This describes **Primary Induction**. The notochord secretes signaling molecules (like Sonic Hedgehog) that induce the overlying surface ectoderm to thicken and form the neural plate, the precursor to the CNS. * **Option D:** While most of the notochord disappears as vertebrae form, remnants can persist. These remnants may undergo malignant transformation into a **chordoma**, a rare tumor typically found at the base of the skull (clivus) or the sacrococcygeal region. **High-Yield Clinical Pearls for NEET-PG:** * **Fate of Notochord:** Nucleus pulposus (adult) and Apical ligament of dens. * **Inducer:** It is the primary inducer of the neural tube and the body of the vertebrae. * **Remnants:** If found in the cranial cavity, they are called *Ecchordosis physaliphora* (benign) or *Chordoma* (malignant). * **Molecular Marker:** Brachyury is a specific transcription factor used to diagnose chordomas.

Question 599: Which of the following is used in the treatment of achalasia cardia?

A. Botox (Correct Answer)
B. Antibiotic
C. Digoxin
D. All of the above

Explanation: **Explanation:** **Achalasia Cardia** is a primary esophageal motility disorder characterized by the failure of the Lower Esophageal Sphincter (LES) to relax and the absence of peristalsis in the lower esophagus [1]. This is primarily due to the degeneration of inhibitory neurons (containing Nitric Oxide and VIP) in the **Myenteric (Auerbach’s) plexus** [1]. **Why Botox is Correct:** Botulinum toxin (Botox) is a potent inhibitor of acetylcholine release from presynaptic nerve terminals at the neuromuscular junction. In achalasia, there is an imbalance where excitatory cholinergic stimuli cause the LES to remain hypertensive. Injecting Botox endoscopically into the LES blocks these excitatory signals, leading to muscle relaxation and symptomatic relief [1]. **Why Other Options are Incorrect:** * **Antibiotics:** Achalasia is a neurodegenerative/motility disorder, not an infectious process. While Chagas disease (caused by *Trypanosoma cruzi*) can cause secondary achalasia, standard antibiotics are not a treatment for the motility defect itself [1]. * **Digoxin:** This is a cardiac glycoside used in heart failure and atrial fibrillation to increase contractility and slow AV conduction. It has no role in esophageal smooth muscle relaxation. **Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Esophageal Manometry (shows "incomplete LES relaxation" and "aperistalsis") [1]. * **Radiology:** Barium swallow shows the classic **"Bird’s Beak" appearance** [1]. * **Definitive Treatment:** Heller’s Myotomy (often with Dor/Toupet fundoplication) or POEM (Peroral Endoscopic Myotomy) [1]. * **Pharmacotherapy:** Nitrates and Calcium Channel Blockers (Nifedipine) can also be used as temporary measures to relax the LES [1].

Question 600: A baby can follow an object till 180 degrees and can hold their neck, and can sit without support. What is the approximate age of the baby?

A. 1 month
B. 3 months
C. 5 months
D. 6 months (Correct Answer)

Explanation: This question tests the integration of **Gross Motor** and **Visual Development** milestones, which are high-yield topics in both Anatomy (Neuroanatomy) and Pediatrics for NEET-PG. ### **Explanation of the Correct Answer** The baby in the scenario exhibits three key milestones: 1. **Sitting without support:** This is the hallmark milestone of **6 months**. (Sitting *with* support occurs at 5 months). 2. **Following an object to 180°:** While binocular vision and following to the midline start earlier, smooth tracking across a full 180-degree arc is typically consolidated by 6 months. 3. **Neck holding:** This is achieved by 3 months, so it is expected to be present at 6 months. Since "sitting without support" is the most advanced milestone mentioned, the approximate age must be **6 months**. ### **Analysis of Incorrect Options** * **A. 1 month:** At this age, a baby can only lift their chin momentarily and can barely follow objects to the midline. * **B. 3 months:** The baby achieves **neck holding** and can follow objects up to 180°, but they **cannot sit** without significant support. * **C. 5 months:** The baby can sit **with support** (tripod position) and can roll from supine to prone, but independent sitting is not yet established. ### **NEET-PG High-Yield Pearls** * **Social Smile:** 2 months (Earliest social milestone). * **Mirror Recognition:** 9 months. * **Pincer Grasp (Immature):** 9 months; **Mature:** 12 months. * **Creeping/Crawling:** 9 months. * **Rule of Thumb for Sitting:** 5 months (with support), 6 months (without support), 8 months (steady sitting). * **Red Flag:** If a child cannot sit without support by **9 months**, it is considered a developmental delay.

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