Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 1211: Which of the following laryngeal muscles arises from the 4th pharyngeal arch?

A. Cricothyroid (Correct Answer)
B. Transverse arytenoids
C. Posterior cricoarytenoid
D. Lateral arytenoids

Explanation: ### Explanation The development of the larynx is a high-yield topic in neuroanatomy and embryology. The laryngeal muscles are derived from the mesoderm of the **fourth and sixth pharyngeal arches**. **1. Why Cricothyroid is Correct:** The **cricothyroid muscle** is the only laryngeal muscle derived from the **4th pharyngeal arch**. Consequently, it is the only intrinsic muscle of the larynx supplied by the **superior laryngeal nerve** (specifically the external branch), which is the nerve of the 4th arch. **2. Why the Other Options are Incorrect:** * **Posterior cricoarytenoid, Lateral cricoarytenoid, and Transverse/Oblique arytenoids:** All these intrinsic muscles of the larynx are derived from the **6th pharyngeal arch**. * The nerve of the 6th arch is the **recurrent laryngeal nerve** (a branch of the Vagus, CN X) [1], [2]. Therefore, all intrinsic muscles of the larynx—except the cricothyroid—are supplied by the recurrent laryngeal nerve [2]. **3. NEET-PG High-Yield Pearls:** * **The "Tensor" Rule:** The cricothyroid is the primary **tensor** of the vocal cords. Damage to the external laryngeal nerve results in a "weak, husky voice" due to the inability to tense the cords. * **The "Safety" Muscle:** The **posterior cricoarytenoid** is the only **abductor** of the vocal cords (it opens the glottis). Bilateral palsy of the recurrent laryngeal nerve can lead to respiratory distress because the cords cannot abduct. * **Sensory Supply:** Above the vocal cords, sensation is carried by the internal laryngeal nerve (4th arch); below the vocal cords, it is carried by the recurrent laryngeal nerve (6th arch).

Question 1212: Intermediate filaments in glial cells are?

A. Keratin
B. Desmin
C. GFAP (Correct Answer)
D. Bone

Explanation: The enriched explanation with citations is as follows: **Explanation:** **Correct Answer: C. GFAP (Glial Fibrillary Acidic Protein)** Intermediate filaments are key structural components of the cytoskeleton. In the central nervous system, **GFAP** is the specific type III intermediate filament expressed by **astrocytes** (the most abundant glial cells) [1]. It provides mechanical strength to the cells and supports the blood-brain barrier. GFAP is a highly specific marker used in immunohistochemistry to identify astrocytes and tumors derived from them. **Analysis of Incorrect Options:** * **A. Keratin:** These are intermediate filaments found in **epithelial cells** (e.g., skin, hair, nails). They provide structural integrity to the epidermis. * **B. Desmin:** This is a type III intermediate filament found in **muscle cells** (skeletal, cardiac, and smooth muscle). It links myofibrils to the sarcolemma. * **D. Bone:** This is an incorrect classification. Bone is a specialized connective tissue composed of an organic matrix (mostly Type I collagen) and inorganic minerals (hydroxyapatite), not an intermediate filament. **High-Yield Clinical Pearls for NEET-PG:** 1. **Glioblastoma Multiforme (GBM):** This highly malignant brain tumor is characteristically **GFAP positive** on staining [2]. 2. **Vimentin:** Another intermediate filament found in cells of **mesenchymal origin** (fibroblasts, endothelium, macrophages). 3. **Neurofilaments:** These are the specific intermediate filaments found in **neurons**, not glial cells. 4. **Alexander Disease:** A rare genetic disorder caused by mutations in the GFAP gene, leading to the accumulation of **Rosenthal fibers** (eosinophilic inclusions in astrocytes).

Question 1213: A 50-year-old patient presented with attacks of intractable nausea, vomiting, and hiccups that did not subside even after medication. Which of the following statements about the involved structure is FALSE?

A. It is a bilaterally paired structure, located at the caudal limit of the floor of the fourth ventricle.
B. It is a chemoreceptive area that triggers vomiting in response to the presence of emetic substances in the blood.
C. Along with the nucleus tractus solitarius and the dorsal motor nucleus of the vagus, it makes up the so-called dorsal vagal complex.
D. It is a poorly vascularized structure with high permeability for circulating blood signals. (Correct Answer)

Explanation: ### Explanation **Clinical Correlation:** The patient presents with **Area Postrema Syndrome (APS)**, characterized by intractable nausea, vomiting, and hiccups. This syndrome is a hallmark of **Neuromyelitis Optica Spectrum Disorder (NMOSD)** [1], where inflammatory lesions affect the area postrema. **Why Option D is the Correct (False) Statement:** The area postrema is one of the **circumventricular organs (CVOs)**. While it indeed has high permeability due to the **absence of a blood-brain barrier (BBB)**, it is **highly vascularized**, not poorly vascularized. It contains a dense network of fenestrated capillaries that allow it to "sense" chemical toxins or emetic substances (like dopamine or digitalis) directly from the systemic circulation. **Analysis of Other Options:** * **Option A:** Correct. It is a paired, small subependymal structure located in the **medulla** at the caudal end of the floor of the fourth ventricle, specifically at the **obex**. * **Option B:** Correct. It serves as the **Chemoreceptor Trigger Zone (CTZ)**. It detects blood-borne emetics and sends signals to the central vomiting center in the medulla to initiate the emetic reflex. * **Option C:** Correct. The **Dorsal Vagal Complex (DVC)** consists of the Area Postrema, the Nucleus Tractus Solitarius (NTS), and the Dorsal Motor Nucleus of the Vagus (DMNV). These structures work together to integrate autonomic and emetic functions. **High-Yield NEET-PG Pearls:** * **Location:** Floor of the 4th ventricle, at the **obex**. * **Blood-Brain Barrier:** It is one of the few areas in the brain where the BBB is absent (others include the pineal gland and posterior pituitary). * **Clinical Sign:** Intractable hiccups/vomiting in a young female with vision loss should immediately raise suspicion of **NMOSD (AQP4-antibody positive)** involving the area postrema [1].

Question 1214: Peribulbar injection is given in which space?

A. Subtenon space
B. Muscle space
C. Periorbital space (Correct Answer)
D. Subperiorbital space

Explanation: **Explanation:** The **periorbital space** (also known as the extraconal space) is the anatomical area located outside the cone formed by the rectus muscles but within the bony orbit. In a **peribulbar block**, the local anesthetic is injected into this space, typically via the inferior-temporal quadrant. Unlike retrobulbar blocks, the needle does not penetrate the muscle cone, making it safer as it reduces the risk of optic nerve injury or brainstem anesthesia. **Analysis of Options:** * **A. Subtenon space:** This is the potential space between the Tenon’s capsule and the sclera. A "Sub-Tenon block" involves a blunt cannula and is a distinct technique from peribulbar anesthesia. * **B. Muscle space:** Also known as the **intraconal space**, this is the target for a **retrobulbar block**. Injecting here carries a higher risk of retrobulbar hemorrhage and globe perforation. * **D. Subperiorbital space:** This refers to the potential space between the orbital bones and the periosteum (periorbita). This is not a standard site for anesthetic deposition. **High-Yield Facts for NEET-PG:** * **Peribulbar vs. Retrobulbar:** Peribulbar is preferred today because it is less invasive. It relies on the diffusion of the anesthetic into the muscle cone to achieve akinesia. * **Nerves Blocked:** Both blocks aim to anesthetize CN III, IV, and VI (motor) and the ciliary nerves (sensory). * **Complications:** The most feared complication of orbital blocks is the "Post-block apnea syndrome," caused by accidental injection into the dural sheath of the optic nerve, leading to CNS spread.

Question 1215: Which of the following is an unpaired vessel in the CNS?

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

Explanation: The concept of "paired" vs. "unpaired" vessels in neuroanatomy depends on whether the vessel exists as a single midline structure or as symmetrical left and right counterparts. **Why the Basilar Artery is Correct:** The **Basilar artery** is a unique, **unpaired** midline vessel. It is formed by the union of the two (paired) vertebral arteries at the lower border of the pons. It travels superiorly in the pontine sulcus (basilar groove) before bifurcating into the two posterior cerebral arteries at the upper border of the pons. Because it represents the fusion of two vessels into one central trunk, it is the only unpaired vessel among the options. **Why the Other Options are Incorrect:** * **Anterior Cerebral Artery (ACA):** These are **paired** branches of the internal carotid arteries [1]. While they are connected by the *unpaired* anterior communicating artery, the ACAs themselves exist as distinct left and right vessels. * **Posterior Cerebral Artery (PCA):** These are the **paired** terminal branches of the basilar artery, supplying the occipital lobes. * **Posterior Communicating Artery (PCoA):** These are **paired** vessels that connect the internal carotid system to the vertebrobasilar system on both the left and right sides of the Circle of Willis [1]. **High-Yield Clinical Pearls for NEET-PG:** * **The Circle of Willis:** Remember that the "circle" is formed by the communication of paired vessels (ICA, ACA, PCA, PCoA) via unpaired vessels (Anterior Communicating) and the fusion of the vertebral system (Basilar) [1]. * **Top of the Basilar Syndrome:** Embolic occlusion at the bifurcation of the basilar artery can lead to bilateral visual and oculomotor deficits. * **Pontine Hemorrhage:** Often involves the paramedian branches of the basilar artery, classically presenting with "pinpoint pupils" and "quadriplegia."

Question 1216: The ureter is lined by which type of epithelium?

A. Stratified squamous
B. Cuboidal
C. Ciliated columnar
D. Transitional (Correct Answer)

Explanation: **Explanation:** The ureter is lined by **Transitional Epithelium** (also known as **Urothelium**). This is a specialized type of stratified epithelium found exclusively in the urinary tract, extending from the renal pelvis to the proximal part of the urethra [1]. **Why Transitional Epithelium is correct:** The primary function of the ureter is to transport urine from the kidneys to the bladder. Transitional epithelium is uniquely adapted for this because it is **distensible**. When the ureter is empty, the surface cells (Umbrella cells) appear large and rounded; when the ureter is distended by urine, these cells flatten out, allowing the tissue to stretch without losing its protective barrier function against toxic urine components [1]. **Why other options are incorrect:** * **Stratified squamous:** Found in areas subject to mechanical friction (e.g., esophagus, skin). It lacks the distensibility required for the urinary tract. * **Cuboidal:** Typically found in glandular ducts or kidney tubules (e.g., PCT/DCT) where secretion or absorption occurs, rather than high-pressure transport. * **Ciliated columnar:** Found in the respiratory tract or fallopian tubes to move mucus or ova; it does not provide the barrier or stretch needed in the ureter. **High-Yield NEET-PG Pearls:** * **Umbrella Cells:** The superficial layer of the urothelium contains large, binucleated "umbrella cells" that possess **uroplakins**, which make the barrier impermeable to water and ions. * **Extent of Urothelium:** It lines the renal pelvis, ureters, urinary bladder, and the prostatic/membranous parts of the male urethra [1]. * **Clinical Correlation:** Transitional Cell Carcinoma (TCC) is the most common primary malignancy of the ureter and bladder.

Question 1217: The posterior cerebral artery supplies all of the following except?

A. Pons (Correct Answer)
B. Thalamus
C. Midbrain
D. Lentiform nucleus

Explanation: The **Posterior Cerebral Artery (PCA)** is the terminal branch of the basilar artery. It primarily supplies the posterior aspects of the brain, including the occipital lobe, inferior temporal lobe, and deep structures of the diencephalon and midbrain. **Why Pons is the correct answer:** The **Pons** is supplied by the **Basilar Artery** via its paramedian, short circumflex, and long circumflex (including the Superior Cerebellar Artery and Anterior Inferior Cerebellar Artery) branches. The PCA originates at the superior border of the pons but does not contribute to its blood supply. **Analysis of Incorrect Options:** * **Thalamus:** The PCA gives off the **thalamoperforating** and **thalamogeniculate** arteries, which are the primary blood supply to the thalamus. * **Midbrain:** As the PCA winds around the midbrain, it provides direct branches to the **tectum** and **cerebral peduncles**. * **Lentiform Nucleus:** While the Middle Cerebral Artery (MCA) is the main supply via lenticulostriate arteries, the **posterior part** of the lentiform nucleus receives supply from the PCA (specifically the medial branch of the posterior choroidal artery). **NEET-PG High-Yield Pearls:** 1. **Visual Field Deficits:** Occlusion of the PCA typically results in **contralateral homonymous hemianopia with macular sparing** (due to collateral supply to the occipital pole from the MCA). 2. **Weber’s Syndrome:** A midbrain stroke involving the PCA branches can lead to ipsilateral CN III palsy and contralateral hemiplegia. 3. **Thalamic Syndrome (Dejerine-Roussy):** PCA territory infarcts involving the thalamus can cause severe chronic pain and sensory loss.

Question 1218: All of the following are glycogen storage disorders except?

A. Pompe disease
B. Hers disease
C. Anderson disease
D. All of the above (Correct Answer)

Explanation: **Explanation:** This question tests your knowledge of **Glycogen Storage Disorders (GSDs)**, which are a group of inherited metabolic disorders caused by enzyme deficiencies affecting glycogen synthesis or breakdown. **1. Why "All of the above" is correct:** All three options listed are classic examples of Glycogen Storage Disorders. Each represents a deficiency in a specific enzyme required for glycogen metabolism: * **Pompe Disease (GSD Type II):** Caused by a deficiency of **Acid α-1,4-glucosidase** (Acid Maltase). It is unique because it is also a lysosomal storage disorder, leading to glycogen accumulation in the heart and skeletal muscles. * **Anderson Disease (GSD Type IV):** Caused by a deficiency of the **Branching enzyme**. This leads to the formation of abnormal glycogen with long outer chains (amylopectin-like), which triggers an immune response leading to liver cirrhosis. * **Hers Disease (GSD Type VI):** Caused by a deficiency of **Liver Phosphorylase**. This results in the inability to break down glycogen in the liver, leading to hepatomegaly and mild hypoglycemia. **2. Clinical Pearls for NEET-PG:** * **Von Gierke Disease (Type I):** Most common GSD; deficiency of Glucose-6-Phosphatase. Presents with severe hypoglycemia, lactic acidosis, and hyperuricemia. * **Cori Disease (Type III):** Deficiency of Debranching enzyme; presents with milder hypoglycemia than Type I. * **McArdle Disease (Type V):** Deficiency of Muscle Phosphorylase; presents with exercise-induced cramps and myoglobinuria. * **Mnemonic for Types I-VI:** "**V**on **P**ompe **C**orrects **A**nderson's **M**uscular **H**ers" (Von Gierke, Pompe, Cori, Anderson, McArdle, Hers). **Conclusion:** Since Pompe, Anderson, and Hers are all recognized types of GSDs, the correct answer is "All of the above."

Question 1219: What is true about the fourth ventricle?

A. The rhomboid fossa forms its floor. (Correct Answer)
B. The choroid plexus lies at its floor.
C. It forms a connection between the two cerebral hemispheres.
D. It lies inferior to the inferior cerebellar peduncle.

Explanation: ### Explanation **1. Why Option A is Correct:** The fourth ventricle is a tent-shaped cavity located between the brainstem (anteriorly) and the cerebellum (posteriorly). Its **floor** is formed by the posterior surfaces of the pons and the upper part of the medulla oblongata. This floor is diamond-shaped and is anatomically referred to as the **rhomboid fossa**. It contains vital structures such as the facial colliculus, hypoglossal triangle, and vagal triangle. **2. Why the Other Options are Incorrect:** * **Option B:** The **choroid plexus** of the fourth ventricle is located in its **roof** (specifically the lower part of the roof formed by the inferior medullary velum), not the floor. * **Option C:** The fourth ventricle connects the cerebral aqueduct (of Sylvius) superiorly to the central canal of the spinal cord inferiorly. The connection between the two cerebral hemispheres is facilitated by the **corpus callosum**, while the **third ventricle** lies between the two thalami. * **Option D:** The fourth ventricle lies **medial** to the cerebellar peduncles. The inferior cerebellar peduncles actually form the lower part of the lateral boundaries of the rhomboid fossa. **3. High-Yield Clinical Pearls for NEET-PG:** * **Foramina:** CSF exits the fourth ventricle into the subarachnoid space via three openings: the median **Foramen of Magendie** and two lateral **Foramina of Luschka** [1] (*Mnemonic: **M**agendie is **M**idline; **L**uschka is **L**ateral*). Fluid also accumulates proximal to the block and distends the ventricles when these foramina are obstructed [1]. * **Facial Colliculus:** Found in the floor (pons part), it is formed by the fibers of the facial nerve hooking around the abducens nucleus. * **Area Postrema:** Located in the inferolateral part of the floor (near the obex), it lacks a blood-brain barrier and serves as the **chemoreceptor trigger zone (CTZ)** for vomiting.

Question 1220: At what age does a child typically achieve head control?

A. 2 months
B. 3 months (Correct Answer)
C. 4 months
D. 5 months

Explanation: **Explanation:** The development of motor skills in infants follows a **cephalocaudal (head-to-toe)** and **proximodistal** pattern. Head control is the first major gross motor milestone achieved as the neck extensors and flexors gain sufficient strength and coordination. * **Why 3 Months is Correct:** By the age of 3 months, an infant can typically hold their head up steadily (at a 45° to 90° angle) while in a prone position and maintains head stability when held upright. The "head lag" seen when pulling a newborn to a sitting position significantly diminishes and disappears by this age. * **Analysis of Incorrect Options:** * **2 Months:** While an infant begins to lift their head briefly while prone, they lack the muscular endurance to maintain it steadily; significant head lag is still present. * **4 Months:** By this stage, head control is fully established. A child at 4 months can lift their chest off the bed using their forearms (the "swimming" position). * **5 Months:** This is the age where a child begins to roll from supine to prone. Delaying head control to 5 months would be considered a developmental lag. **High-Yield NEET-PG Pearls:** 1. **Primitive Reflexes:** Head control coincides with the disappearance of the **Asymmetric Tonic Neck Reflex (ATNR)**; if ATNR persists, it can interfere with midline head control. 2. **The "Pull-to-Sit" Test:** This is the clinical gold standard for assessing head lag. Persistent head lag beyond 4–6 months is a red flag for cerebral palsy or hypotonia. 3. **Sequence of Milestones:** Head control (3m) → Sitting with support (6m) → Sitting without support (8m) → Standing with support (9m) → Walking (12m).

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