Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 211: Which of the following tongue muscles is supplied by the cranial root of the accessory nerve?

A. Palatoglossus (Correct Answer)
B. Hyoglossus
C. Styloglossus
D. Genioglossus

Explanation: ### Explanation The innervation of the tongue is a high-yield topic in neuroanatomy. To answer this question, one must distinguish between the **intrinsic** and **extrinsic** muscles of the tongue and their respective nerve supplies. **1. Why Palatoglossus is Correct:** The **Palatoglossus** is unique because it is the only tongue muscle derived from the **fourth pharyngeal arch** rather than the occipital myotomes. Consequently, it is not supplied by the Hypoglossal nerve (CN XII). Instead, it is considered a muscle of the soft palate and is supplied by the **Pharyngeal plexus**. The motor fibers of this plexus are derived from the **cranial root of the Accessory nerve (CN XI)**, which travel via the **Vagus nerve (CN X)**. **2. Why the Other Options are Incorrect:** * **Genioglossus, Hyoglossus, and Styloglossus:** These are the other three extrinsic muscles of the tongue. Along with all the intrinsic muscles (superior/inferior longitudinal, transverse, and vertical), they are derived from **occipital myotomes** and are supplied by the **Hypoglossal nerve (CN XII)**. * *Genioglossus* is the "safety muscle" (protrudes the tongue). * *Hyoglossus* depresses the tongue. * *Styloglossus* retracts the tongue. **3. NEET-PG Clinical Pearls:** * **The Rule of "Glossus":** All muscles ending in "-glossus" are supplied by CN XII, **except** Palatoglossus (CN XI via X). * **The Rule of "Palat":** All muscles with "palat-" in their name are supplied by the Pharyngeal plexus (CN XI via X), **except** Tensor Veli Palatini (supplied by the Mandibular nerve, V3). * **Clinical Sign:** In a Hypoglossal nerve injury, the tongue deviates **towards** the side of the lesion upon protrusion due to the unopposed action of the contralateral Genioglossus.

Question 212: Which of the following represents association fibers?

A. Uncinate
B. Cingulum
C. Longitudinal fasciculus
D. Forceps major (Correct Answer)

Explanation: White matter fibers in the brain are classified into three types: **Association fibers** (connect areas within the same hemisphere), **Commissural fibers** (connect corresponding areas of the two hemispheres), and **Projection fibers** (connect the cortex with lower centers). **Why Forceps Major is the Correct Answer:** The **Forceps major** is a large bundle of **commissural fibers** [2]. It is formed by the fibers of the **splenium** (the posterior part of the corpus callosum) as they curve backward into the occipital lobes [2]. Since the question asks for a fiber type that is *not* an association fiber (or identifies the outlier), Forceps major stands out as it is strictly commissural. **Analysis of Incorrect Options:** * **A. Uncinate Fasciculus:** A short **association fiber** that connects the motor speech area (Broca’s) and orbital cortex of the frontal lobe with the temporal pole. * **B. Cingulum:** A prominent **association fiber** located within the cingulate gyrus, connecting the frontal and parietal lobes with the parahippocampal gyrus and adjacent temporal cortical regions. * **C. Longitudinal Fasciculus:** These are **association fibers**. The *Superior Longitudinal Fasciculus* connects the frontal, parietal, and occipital lobes, while the *Inferior* connects the occipital and temporal lobes. **NEET-PG High-Yield Pearls:** * **Corpus Callosum:** The largest commissural fiber [2]. Parts from anterior to posterior: Rostrum, Genu, Body, Splenium. * **Forceps Minor:** Fibers of the **genu** connecting the two frontal lobes. * **Arcuate Fasciculus:** An association fiber connecting Broca’s and Wernicke’s areas; damage leads to **Conduction Aphasia**. * **Internal Capsule:** The most important example of **projection fibers** [1].

Question 213: What are the most abundant glycoproteins present in the basement membrane?

A. Laminin (Correct Answer)
B. Fibronectin
C. Collagen type 4
D. Heparan sulphate

Explanation: The basement membrane (BM) is a specialized form of extracellular matrix that provides structural support and acts as a biological filter [1]. It is composed of four primary components: Type IV collagen, laminin, entactin (nidogen), and heparan sulfate proteoglycans [2]. **Why Laminin is the correct answer:** Laminins are the **most abundant non-collagenous glycoproteins** in the basement membrane. They are large, heterotrimeric molecules (composed of $\alpha, \beta, \gamma$ chains) that play a crucial role in organizing the BM [2]. Laminin acts as the primary "bridge," binding to cell surface receptors (integrins) and other BM components like Type IV collagen and nidogen, thereby anchoring the epithelium to the underlying connective tissue [2]. **Analysis of Incorrect Options:** * **Fibronectin:** While it is a major adhesive glycoprotein, it is primarily found in the **interstitial extracellular matrix** and plasma, rather than being the dominant component of the basement membrane. * **Collagen Type IV:** This is the most abundant **protein** (structural framework) of the BM, but it is categorized as a fibrous protein rather than a functional glycoprotein in this context [2]. * **Heparan Sulphate:** This is a **proteoglycan** (specifically perlecan), not a glycoprotein [2]. Its primary role is providing a negative charge to the BM, which is essential for selective filtration in the renal glomerulus. **NEET-PG High-Yield Pearls:** * **Goodpasture Syndrome:** Characterized by autoantibodies against the non-collagenous (NC1) domain of **Type IV collagen**. * **Alport Syndrome:** A genetic defect in the synthesis of **Type IV collagen** chains, leading to nephritis and deafness. * **Junctional Epidermolysis Bullosa:** Often associated with mutations in **Laminin-332**, leading to severe skin blistering. * **PAS Stain:** The basement membrane is PAS-positive due to the high carbohydrate content of its glycoproteins.

Question 214: Which of the following structures is NOT lined by urothelium?

A. Ureters
B. Minor calyx
C. Urinary bladder
D. Collecting duct (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Collecting duct**. The urinary system is lined by two distinct types of epithelia based on embryological origin and function. The **urothelium (transitional epithelium)** is a specialized stratified epithelium designed to stretch and provide an impermeable barrier against toxic urine [1]. It lines the entire **conducting portion** of the urinary tract, which originates from the **ureteric bud**. This includes the minor and major calyces, the renal pelvis, the ureters, the urinary bladder, and the proximal part of the urethra [1]. In contrast, the **collecting duct** is the terminal part of the renal tubule system. While it also originates from the ureteric bud, its function is physiological (water and electrolyte reabsorption) rather than merely conductive. Therefore, it is lined by **simple cuboidal to simple columnar epithelium** (containing Principal and Intercalated cells), not urothelium. **Analysis of Incorrect Options:** * **A. Ureters:** Lined by urothelium to allow for peristaltic expansion. * **B. Minor calyx:** This is the first part of the extra-renal collecting system and is lined by urothelium. * **C. Urinary bladder:** Contains the thickest layer of urothelium (up to 6-8 layers when empty) to accommodate significant volume changes [1]. **High-Yield Facts for NEET-PG:** * **Umbrella Cells:** The most superficial layer of the urothelium contains large, often binucleated "umbrella cells" that protect deeper layers from hypertonic urine. * **Embryology:** The urothelium of the bladder (except the trigone) is derived from **endoderm** (vesical part of the urogenital sinus), while the ureters and calyces are derived from **mesoderm** (ureteric bud). * **Pathology:** The most common cancer of the bladder and ureters is **Transitional Cell Carcinoma (TCC)**, now more commonly referred to as Urothelial Carcinoma.

Question 215: Which structure's infarction can give rise to left hypesthesia, left homonymous hemianopia, left facial weakness, tongue deviation to the left side, and plantar extensor on the left side?

A. Left internal capsule
B. Left pulvinar
C. Medial geniculate body
D. Right internal capsule (Correct Answer)

Explanation: ### Explanation The clinical presentation describes a **contralateral dense hemiplegia** involving motor, sensory, and visual pathways. **1. Why Right Internal Capsule is Correct:** The internal capsule (IC) is a compact area where major ascending and descending tracts converge. A lesion in the **Right IC** (specifically the posterior limb and retrolentiform part) results in: * **Left Hypesthesia:** Involvement of the *thalamocortical fibers* (sensory). * **Left Homonymous Hemianopia:** Involvement of *optic radiations* in the retrolentiform part [2]. * **Left Facial Weakness & Tongue Deviation:** Involvement of *corticobulbar tracts* in the genu [2]. Note: The tongue deviates **away** from the side of the cortical lesion (towards the weak side). * **Left Plantar Extensor (Babinski sign):** Involvement of *corticospinal tracts* (upper motor neuron lesion). Because these fibers decussate below the level of the IC, a right-sided lesion produces purely left-sided (contralateral) deficits. A common underlying pathology for such symptoms in hypertensive patients is the development of lacunar infarcts in the internal capsule [1]. **2. Why Other Options are Incorrect:** * **Left Internal Capsule:** This would cause right-sided deficits (Right hemiplegia/hemianopia). * **Left Pulvinar:** This is part of the thalamus involved in visual salience and attention; while it may cause sensory loss, it would not cause dense motor hemiplegia or tongue deviation. * **Medial Geniculate Body (MGB):** This is the thalamic relay station for **hearing** ("M" for Music/Media). A lesion here would cause auditory deficits, not hemiplegia or hemianopia. **3. Clinical Pearls for NEET-PG:** * **IC Blood Supply:** Primarily by **Lenticulostriate arteries** (branches of MCA). The "Artery of Cerebral Hemorrhage" (Charcot’s artery) supplies the IC. * **Rule of 4s:** If the tongue deviates **towards** the side of the lesion, it is a Lower Motor Neuron (LMN) lesion of the Hypoglossal nerve (Cranial Nerve XII). If it deviates **away** from the lesion, it is an Upper Motor Neuron (UMN) lesion (e.g., Internal Capsule). * **Visual Pathway:** Lateral Geniculate Body (LGB) = Light/Vision; Medial Geniculate Body (MGB) = Music/Hearing.

Question 216: Regarding sexual differentiation of the fetus, which of the following statements is correct?

A. Gonadal development begins at the 5th week of intrauterine life. (Correct Answer)
B. The Y chromosome determines the differentiation of ovaries.
C. Female external genitalia development is completed by 10 weeks.
D. Male sexual differentiation occurs earlier than females.

Explanation: ### Explanation **1. Why Option A is Correct:** Gonadal development is initially an "indifferent" stage. The gonadal ridges (thickening of the intermediate mesoderm) first appear during the **5th week** of intrauterine life. Primordial germ cells, which originate in the yolk sac wall, migrate along the dorsal mesentery to reach these ridges by the 6th week. **2. Analysis of Incorrect Options:** * **Option B:** The Y chromosome contains the **SRY gene** (Sex-determining Region on Y), which produces Testis-Determining Factor (TDF). This triggers the differentiation of **testes**, not ovaries. In the absence of the Y chromosome, the default pathway leads to ovarian development. * **Option C:** While external genitalia begin to differentiate around the 9th week, the process is not completed by the 10th week. Distinctive female or male characteristics are usually clearly visible by the **12th to 14th week** [1]. * **Option D:** **Male sexual differentiation occurs earlier than female.** Testicular differentiation begins around the 7th week under the influence of the SRY gene, whereas ovarian differentiation starts later, around the 10th-12th week. **3. High-Yield Clinical Pearls for NEET-PG:** * **SRY Gene:** Located on the short arm of the Y chromosome (Yp11). * **Mullerian Inhibiting Substance (MIS/AMH):** Secreted by **Sertoli cells**; causes regression of Paramesonephric ducts in males [1]. * **Testosterone:** Secreted by **Leydig cells**; stimulates the development of Mesonephric (Wolffian) ducts into the male internal genital tract [1]. * **Dihydrotestosterone (DHT):** Responsible for the development of male **external** genitalia (penis and scrotum) [1]. * **Default Pathway:** In the absence of AMH and Testosterone, Paramesonephric ducts develop into the uterus, fallopian tubes, and upper vagina.

Question 217: What is the approximate percentage increase in height during the first year of life?

A. 40%
B. 50% (Correct Answer)
C. 60%
D. 75%

Explanation: **Explanation:** The growth of an infant during the first year of life follows a predictable and rapid trajectory, which is a high-yield topic in both Anatomy (Developmental) and Pediatrics. **1. Why 50% is correct:** At birth, the average length of a full-term neonate is approximately **50 cm**. During the first year, growth occurs in stages: about 12.5 cm in the first 6 months and another 12.5 cm in the next 6 months. By the end of the first year (12 months), the infant typically reaches a height of **75 cm**. This represents an absolute increase of 25 cm, which is exactly **50%** of the birth length [1]. **2. Analysis of Incorrect Options:** * **A (40%):** This underestimates the rapid growth velocity seen in the first year. * **C (60%) & D (75%):** These figures are too high for the first year. While growth is rapid, a 75% increase (reaching 87.5 cm) usually takes closer to 2 years. **3. High-Yield Clinical Pearls for NEET-PG:** * **Height Doubling:** The birth length doubles (100 cm) at **4 years** of age. * **Height Tripling:** The birth length triples (150 cm) at **13 years** of age. * **Weight Milestones:** Unlike height, weight doubles by 5 months, triples by 1 year, and quadruples by 2 years [1]. * **Formula for Height (2–12 years):** Age (years) × 6 + 77 cm. * **Head Circumference:** At birth, it is ~35 cm; it increases to ~47 cm by 1 year (a 12 cm increase) [1].

Question 218: Location of beta 3 receptors include:

A. Bronchial muscle
B. Vascular muscle
C. Bladder (Correct Answer)
D. Uterus

Explanation: ### Explanation **Correct Answer: C. Bladder** **Underlying Medical Concept:** Beta-3 ($\beta_3$) adrenergic receptors are primarily located in **adipose tissue** and the **detrusor muscle** of the urinary bladder [1]. When stimulated by norepinephrine or selective agonists, $\beta_3$ receptors induce relaxation of the detrusor muscle. This increases the bladder's functional capacity and facilitates urine storage [1]. **Analysis of Options:** * **A. Bronchial muscle:** These are predominantly populated by **$\beta_2$ receptors**. Stimulation leads to bronchodilation (the basis for using Salbutamol in asthma). * **B. Vascular muscle:** Vascular smooth muscle contains **$\alpha_1$ receptors** (vasoconstriction) and **$\beta_2$ receptors** (vasodilation, especially in skeletal muscle vessels). $\beta_3$ receptors do not play a primary role here. * **C. Bladder (Correct):** The detrusor muscle contains $\beta_3$ receptors. Their activation promotes bladder filling [1]. * **D. Uterus:** The myometrium is dominated by **$\beta_2$ receptors**. Stimulation causes uterine relaxation (tocolysis), which is why $\beta_2$ agonists like Ritodrine or Isoxsuprine are used to delay premature labor. **Clinical Pearls for NEET-PG:** 1. **Mirabegron:** A selective $\beta_3$ agonist used clinically for the treatment of **Overactive Bladder (OAB)** and urge incontinence. It works by relaxing the detrusor during the storage phase. 2. **Lipolysis:** $\beta_3$ receptors in adipose tissue mediate thermogenesis and lipolysis (breakdown of fats). 3. **Mnemonic for Beta Receptors:** * $\beta_1$: **1 Heart** (Increases HR/Contractility) * $\beta_2$: **2 Lungs** (Bronchodilation + Uterine/Vascular relaxation) * $\beta_3$: **3 "B"s** (Bladder, Brown fat, Body fat)

Question 219: Skin cancers develop due to sun light exposure induced by which type of ultraviolet rays?

A. UV A rays
B. UV B rays (Correct Answer)
C. UV C rays
D. UV D rays

Explanation: **Explanation:** The development of skin cancer (including Basal Cell Carcinoma, Squamous Cell Carcinoma, and Melanoma) is primarily attributed to **UV B rays (290–320 nm)** [2]. **Why UV B is the Correct Answer:** UV B rays are the most biologically active radiation reaching the Earth's surface. They are directly absorbed by DNA, leading to the formation of **pyrimidine dimers** (specifically thymine dimers). If these mutations occur in tumor suppressor genes like **TP53**, it leads to uncontrolled cell proliferation and carcinogenesis. UV B is often referred to as the "burning ray" because it causes direct DNA damage and sunburns [2]. Factors like C to T transitions are considered hallmarks of UV damage in skin tumors [1]. **Analysis of Incorrect Options:** * **UV A rays (320–400 nm):** These have longer wavelengths and penetrate deeper into the dermis. While they contribute to **photoaging** (wrinkling) by producing reactive oxygen species (ROS) and damaging collagen, they are significantly less potent than UV B in causing direct DNA mutations. * **UV C rays (100–290 nm):** These are the most energetic and lethal; however, they are almost entirely absorbed by the **stratospheric ozone layer** and do not reach the Earth's surface to cause skin cancer. * **UV D rays:** This is not a standard classification of ultraviolet radiation used in medical dermatology. **High-Yield Clinical Pearls for NEET-PG:** * **Xeroderma Pigmentosum:** A genetic condition where the nucleotide excision repair (NER) mechanism is defective, making patients hypersensitive to UV B-induced DNA damage. * **Wavelength Memory:** UV **B** = **B**urning & **B**ad (Cancer); UV **A** = **A**ging. * **Ozone Depletion:** Increases the risk of skin cancer specifically by allowing more UV B to reach the surface.

Question 220: Paraxial mesoderm contributes to the development of which of the following structures?

A. Parietal peritoneum
B. Visceral peritoneum
C. Skeletal muscles (Correct Answer)
D. Peritoneal cavity

Explanation: The **paraxial mesoderm** is a thick column of mesodermal tissue located on either side of the developing neural tube. It undergoes segmentation to form **somites**, which further differentiate into three primary components: the sclerotome (vertebrae and ribs), the dermatome (dermis of the back), and the **myotome**. The myotome is the precursor to the majority of the body's **skeletal muscles**, including those of the trunk and limbs. **Analysis of Options:** * **Option C (Correct):** Skeletal muscles are derived from the myotome of the somites (paraxial mesoderm). This includes the epaxial (back) and hypaxial (body wall and limbs) musculature. * **Option A & B (Incorrect):** The **parietal peritoneum** is derived from the **somatopleuric layer** of the lateral plate mesoderm, while the **visceral peritoneum** is derived from the **splanchnopleuric layer** of the lateral plate mesoderm. * **Option D (Incorrect):** The **peritoneal cavity** develops from the **intraembryonic coelom**, which is the space that forms between the somatopleuric and splanchnopleuric layers of the lateral plate mesoderm. **High-Yield Facts for NEET-PG:** * **Lateral Plate Mesoderm:** Gives rise to the heart, vasculature, and the serous membranes of the body cavities (pleura, pericardium, and peritoneum). * **Intermediate Mesoderm:** Gives rise to the urogenital system (kidneys, gonads, and ducts). * **Clinical Pearl:** Poland Syndrome involves the congenital absence of the Pectoralis major muscle, resulting from a defect in the development of the hypaxial myotome of the paraxial mesoderm.

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