Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 1111: The tumor suppressor gene p53 induces cell cycle arrest at which phase?

A. G2-M phase
B. S-G2 phase
C. G1-S phase (Correct Answer)
D. G0 phase

Explanation: **Explanation:** The **p53 protein**, often referred to as the "Guardian of the Genome," is a critical tumor suppressor gene located on chromosome 17p. Its primary function is to maintain genomic stability by monitoring DNA damage. **Why G1-S is correct:** When DNA damage is detected, p53 levels rise and act as a transcription factor for **p21** (a Cyclin-Dependent Kinase Inhibitor). p21 inhibits the **Cyclin D/CDK4** and **Cyclin E/CDK2** complexes. These complexes are responsible for phosphorylating the Retinoblastoma (Rb) protein. By keeping Rb in its hypophosphorylated (active) state, it remains bound to the E2F transcription factor, preventing the cell from transitioning from the **G1 phase to the S phase** [1]. This arrest allows time for DNA repair; if repair fails, p53 induces apoptosis via the BAX/BCL-2 pathway. **Analysis of Incorrect Options:** * **G2-M phase:** While p53 can play a minor role here, the primary regulator of the G2-M checkpoint is the inhibition of the Cdc25 phosphatase and the Cyclin B/CDK1 complex. * **S-G2 phase:** This is not a primary regulatory checkpoint for p53-mediated cell cycle arrest. * **G0 phase:** This is a quiescent, non-dividing state. p53 acts on actively cycling cells to prevent them from replicating damaged DNA, rather than inducing a transition into G0. **High-Yield Clinical Pearls for NEET-PG:** * **Li-Fraumeni Syndrome:** A germline mutation in the *TP53* gene leading to multiple early-onset cancers (SBLA syndrome: Sarcoma, Breast, Leukemia, Adrenal gland). * **Most Common Mutation:** *TP53* is the most frequently mutated gene in human cancers. * **HPV Association:** Human Papillomavirus (HPV) E6 protein degrades p53, while E7 inhibits Rb, leading to cervical cancer.

Question 1112: Who proposed the concept of the paranoid pseudocommunity?

A. Norman Cameron (Correct Answer)
B. K. Schneider
C. Benedict Morel
D. Eugene Bleuler

Explanation: The concept of the **paranoid pseudocommunity** was proposed by **Norman Cameron** in 1943. According to Cameron, this is a psychological construct developed by a paranoid individual who lacks basic trust and misinterprets the actions of others. Due to impaired social communication, the individual weaves together real and imaginary people into a complex, organized "community" that they believe is conspiring against them. This "pseudocommunity" provides a perceived structure to their delusions of persecution, justifying their defensive or aggressive reactions. **Analysis of Incorrect Options:** * **B. K. Schneider:** Known for defining the **First Rank Symptoms (FRS)** of Schizophrenia, which are pivotal in clinical diagnosis but unrelated to the pseudocommunity concept. * **C. Benedict Morel:** A French psychiatrist who coined the term **"Démence précoce"** (early dementia) to describe what we now know as schizophrenia, focusing on its deteriorating course. * **D. Eugene Bleuler:** He replaced Morel’s term with **"Schizophrenia"** and described the **"4 As"** (Association, Affect, Ambivalence, and Autism) as the primary symptoms of the disorder. **Clinical Pearls for NEET-PG:** * **Norman Cameron** also described **"Asyndesis"** (a lack of logical connection between thoughts) and **"Metonyms"** (use of imprecise words), which are features of schizophrenic thought disorders. * The paranoid pseudocommunity is a classic example of how **social isolation** and **faulty social learning** contribute to the systematization of delusions. * Remember: **Schneider = FRS**; **Bleuler = 4 As**; **Morel = Démence précoce**; **Cameron = Pseudocommunity.**

Question 1113: All of the following develop from the endodermal cloaca except:

A. Rectum
B. Anal canal
C. Sigmoid colon (Correct Answer)
D. Primitive urogenital sinus

Explanation: ### Explanation The **cloaca** is the terminal dilated portion of the hindgut, lined by endoderm. During the 4th to 7th weeks of development, it is divided by the **urorectal septum** into a dorsal primitive rectum and a ventral primitive urogenital sinus [1]. **1. Why Sigmoid Colon is the Correct Answer:** The **sigmoid colon** develops from the **hindgut proper**, not the cloaca. The hindgut gives rise to the distal third of the transverse colon, descending colon, and sigmoid colon [1]. While the cloaca is technically the terminal part of the hindgut, embryologically, the term "cloacal derivatives" is reserved for structures formed after the urorectal septum divides the chamber. **2. Analysis of Incorrect Options:** * **Rectum:** The dorsal part of the divided cloaca forms the primitive rectum and the cranial part of the anal canal [1]. * **Anal Canal:** The upper part (above the pectinate line) develops from the **primitive rectum** (a cloacal derivative) [1], while the lower part develops from the ectodermal proctodeum. * **Primitive Urogenital Sinus:** This is the ventral product of the cloacal division [1]. It further differentiates into the urinary bladder, urethra, and (in males) the prostatic and membranous urethra or (in females) the vestibule of the vagina [2]. ### High-Yield Clinical Pearls for NEET-PG: * **Watershed Area:** The **pectinate line** of the anal canal is a crucial landmark representing the junction between endoderm (cloaca) and ectoderm (proctodeum). * **Blood Supply:** Hindgut structures are supplied by the **Inferior Mesenteric Artery** [3]. * **Urorectal Septum Defects:** Failure of the septum to divide the cloaca properly leads to **rectovesical or rectovaginal fistulas** and **imperforate anus**. * **Allantois Connection:** The apex of the urogenital sinus is continuous with the allantois, which later obliterates to become the **urachus** (median umbilical ligament).

Question 1114: Vertebral arteries of both sides unite to form which of the following arteries?

A. Anterior spinal artery
B. Posterior spinal artery
C. Medullary artery
D. Basilar artery (Correct Answer)

Explanation: ### Explanation The vertebral arteries are the first branches of the subclavian arteries. They ascend through the foramina transversaria of the upper six cervical vertebrae, enter the cranium via the foramen magnum, and run on the ventral surface of the medulla. **Why the Correct Answer is Right:** At the **lower border of the pons** (pontomedullary junction), the two vertebral arteries converge and unite in the midline to form the **Basilar artery**. This artery then travels in the basilar groove of the pons and eventually terminates by dividing into the two posterior cerebral arteries. This system is known as the Vertebro-basilar system, which supplies the brainstem, cerebellum, and posterior part of the cerebrum. **Analysis of Incorrect Options:** * **A. Anterior spinal artery:** This is formed by the union of two small branches, one from each vertebral artery, but it descends along the anterior median fissure of the spinal cord rather than forming the main trunk. * **B. Posterior spinal artery:** These usually arise from the vertebral artery (or the posterior inferior cerebellar artery) and descend on the posterior surface of the spinal cord. They do not unite to form a single large vessel. * **C. Medullary artery:** These are small, segmental branches that supply the medulla oblongata; they do not represent the union of the main vertebral trunks. **High-Yield Facts for NEET-PG:** * **PICA (Posterior Inferior Cerebellar Artery):** The largest branch of the vertebral artery. Occlusion leads to **Wallenberg Syndrome** (Lateral Medullary Syndrome). * **Circle of Willis:** The basilar artery contributes to this circle via its terminal branches (Posterior Cerebral) and the Posterior Communicating arteries. * **Top of the Basilar Syndrome:** Embolic occlusion at the bifurcation of the basilar artery, affecting the midbrain and thickness.

Question 1115: A patient presents with a visual defect characterized by contralateral homonymous hemianopia with macular sparing. What is the most likely cause for this specific visual field defect?

A. Blockage in the optic tract
B. Blockage in the optic nerve
C. Blockage in the optic chiasma
D. Blockage in the posterior cerebral artery supplying the visual cortex (Correct Answer)

Explanation: ### Explanation **1. Why Option D is Correct:** Contralateral homonymous hemianopia with **macular sparing** is the hallmark of a lesion in the **primary visual cortex (Brodmann area 17)**, typically due to an occlusion of the **Posterior Cerebral Artery (PCA)** [1]. The macula is spared because of a **dual blood supply**: while the majority of the visual cortex is supplied by the PCA, the occipital pole (where macular vision is represented) also receives collateral circulation from the **Middle Cerebral Artery (MCA)** [2]. Therefore, if the PCA is blocked, the MCA maintains perfusion to the macular area, preserving central vision [2]. **2. Why Other Options are Incorrect:** * **Option A (Optic Tract):** A lesion here causes **contralateral homonymous hemianopia**, but it is usually **incongruous** and **does not spare the macula**, as the fibers are bundled together before reaching the cortex [1]. * **Option B (Optic Nerve):** Damage to the optic nerve results in **ipsilateral monocular blindness** (total vision loss in one eye) [1]. * **Option C (Optic Chiasma):** Compression of the decussating nasal fibers at the chiasma (e.g., by a pituitary adenoma) results in **bitemporal hemianopia** [1]. **3. Clinical Pearls for NEET-PG:** * **Meyer’s Loop (Temporal lobe):** Lesion causes "Pie in the sky" (Superior quadrantanopia). * **Baum’s Loop (Parietal lobe):** Lesion causes "Pie on the floor" (Inferior quadrantanopia). * **Congruity:** The more posterior the lesion (closer to the cortex), the more symmetric (congruous) the visual field defect between both eyes. * **Macular Sparing:** Always think of **Occipital Cortex** and **PCA-MCA dual supply**.

Question 1116: All of the following are clinical features of myxomas, except?

A. Fever
B. Clubbing
C. Hypertension (Correct Answer)
D. Embolic phenomenon

Explanation: **Explanation:** Atrial myxoma is the most common primary cardiac tumor in adults, typically located in the left atrium (75%). The clinical presentation is characterized by a classic "triad" of symptoms: constitutional, embolic, and obstructive. **Why Hypertension is the Correct Answer:** Hypertension is **not** a feature of atrial myxoma. In fact, myxomas often cause **hypotension** or syncope due to the "ball-valve" effect, where the pedunculated tumor intermittently obstructs the mitral valve orifice, leading to a sudden drop in cardiac output. **Analysis of Incorrect Options:** * **Fever (A):** Myxomas produce cytokines, specifically **Interleukin-6 (IL-6)**. This leads to constitutional symptoms mimicking systemic illness, such as fever, weight loss, and malaise. * **Clubbing (B):** Chronic systemic inflammation and potential pulmonary shunting or recurrent micro-emboli can lead to digital clubbing in these patients. * **Embolic Phenomenon (D):** Myxomas are friable. Fragments of the tumor or overlying thrombi can break off and enter the systemic circulation, leading to strokes, mesenteric ischemia, or peripheral arterial occlusion. **High-Yield Clinical Pearls for NEET-PG:** * **Auscultation:** Characterized by a **"Tumor Plop"** (a low-pitched sound heard during early or mid-diastole as the tumor strikes the ventricular wall). * **Positionality:** Symptoms often change with the patient's body position (e.g., dyspnea when lying on a specific side). * **Diagnosis:** Transthoracic Echocardiography (TTE) is the initial investigation of choice. * **Histology:** Features **Stellate cells** (lepidic cells) in a myxomatous (mucopolysaccharide) stroma. * **Association:** Part of **Carney Complex** (PRKAR1A mutation), which includes myxomas (cardiac/skin), hyperpigmentation (lentigines), and endocrine overactivity.

Question 1117: The left common cardinal vein is reduced to what structure?

A. Great cardiac vein
B. Azygos vein
C. Superior vena cava (SVC)
D. Coronary sinus (Correct Answer)

Explanation: ### Explanation The development of the venous system is a high-yield topic in embryology. The heart tube initially receives blood via the **Sinus Venosus**, which has two horns (right and left). Each horn receives blood from three major veins: the vitelline vein, the umbilical vein, and the **common cardinal vein**. **Why the Correct Answer is Right:** As the venous system undergoes remodeling to shift blood flow to the right side of the heart, the left sinus horn and its associated vessels regress. The **left common cardinal vein** (along with the proximal part of the left horn) undergoes atrophy and is reduced to form the **Coronary Sinus** [1], which serves as the primary venous drainage for the heart muscle into the right atrium. A small portion also persists as the **Oblique vein of the left atrium (Vein of Marshall)**. **Analysis of Incorrect Options:** * **A. Great cardiac vein:** This vein develops independently in the interventricular groove; it is not a derivative of the cardinal system. * **B. Azygos vein:** This is derived from the **right supracardinal vein**. * **C. Superior vena cava (SVC):** The SVC is formed by the fusion of the **right common cardinal vein** and the proximal part of the **right anterior cardinal vein**. **High-Yield Clinical Pearls for NEET-PG:** * **Right Common Cardinal Vein + Right Anterior Cardinal Vein** = Superior Vena Cava. * **Left Common Cardinal Vein** = Coronary Sinus [1] and Oblique vein of the left atrium. * **Left Superior Vena Cava:** Occurs due to the failure of the left anterior cardinal vein to regress. It typically drains into the right atrium via a dilated coronary sinus [1]. * **Azygos Vein:** Derived from the Right Supracardinal vein; the **Hemiazygos** is derived from the Left Supracardinal vein.

Question 1118: Retinoblastoma is associated with which of the following tumors?

A. Osteoclastoma
B. Hepatocellular carcinoma
C. Squamous cell carcinoma
D. Osteosarcoma (Correct Answer)

Explanation: **Explanation:** The association between **Retinoblastoma** and **Osteosarcoma** is a classic high-yield concept in medical genetics and oncology. **1. Why Osteosarcoma is correct:** Retinoblastoma is caused by a mutation in the **RB1 gene** (a tumor suppressor gene) located on **chromosome 13q14** [2]. In the hereditary form (germline mutation), every cell in the patient's body carries one mutated allele. While the first clinical manifestation is usually a retinal tumor in early childhood, these patients have a significantly increased risk of developing secondary malignancies later in life [1]. **Osteosarcoma** is the most common secondary non-ocular cancer associated with hereditary retinoblastoma, occurring most frequently during the adolescent growth spurt [2]. **2. Why the other options are incorrect:** * **A. Osteoclastoma:** Also known as Giant Cell Tumor of the bone, it is typically a benign (though locally aggressive) tumor and is not linked to the RB1 pathway. * **B. Hepatocellular carcinoma:** This is primarily associated with chronic Hepatitis B/C infections, cirrhosis, or aflatoxin exposure, not the RB1 mutation. * **C. Squamous cell carcinoma:** This is generally associated with environmental factors like UV radiation (skin), smoking (lung/esophagus), or HPV (cervix), rather than germline RB1 mutations. **3. Clinical Pearls for NEET-PG:** * **Knudson’s Two-Hit Hypothesis:** Explains that hereditary cases require one somatic "hit" (mutation), while sporadic cases require two. * **Trilateral Retinoblastoma:** Refers to bilateral retinoblastoma associated with a pineoblastoma (pineal gland tumor). * **Most common sign:** Leukocoria (white pupillary reflex). * **Histology:** Look for **Flexner-Wintersteiner rosettes** (pathognomonic). * **Other secondary tumors:** Apart from osteosarcoma, patients are also at risk for soft tissue sarcomas and melanomas.

Question 1119: After which time period does the Ductus Venosus anatomically close?

A. 10 to 96 hours
B. Less than 1 week
C. 2 to 3 weeks (Correct Answer)
D. More than 4 weeks

Explanation: The transition from fetal to neonatal circulation involves the closure of three major shunts: the ductus venosus, foramen ovale, and ductus arteriosus [1]. Understanding the timeline of these closures is a high-yield topic for NEET-PG. ### **Explanation of the Correct Answer** **Option C (2 to 3 weeks)** is the correct anatomical closure time for the **Ductus Venosus**. * **Functional Closure:** Occurs almost immediately (within minutes) after birth due to the cessation of umbilical blood flow and the contraction of the sphincter at the junction of the umbilical vein and ductus venosus. * **Anatomical Closure:** This is a gradual process involving the proliferation of connective tissue and fibrosis [1]. It typically takes **2 to 3 weeks** to complete, after which the ductus venosus becomes the **Ligamentum Venosum**, found in the fissure of the liver [1][2]. ### **Analysis of Incorrect Options** * **Option A & B:** These timeframes (10 hours to 1 week) correspond to the **functional closure** of the Ductus Arteriosus (usually within 10–15 hours) or the initial stages of physiological adaptation. They are too early for the permanent anatomical fibrosis of the ductus venosus. * **Option D:** While some shunts may take longer in pathological states, the standard anatomical timeline for a healthy neonate is established well before 4 weeks. ### **High-Yield NEET-PG Pearls** * **Ductus Venosus Remnant:** Ligamentum Venosum [1]. * **Umbilical Vein Remnant:** Ligamentum Teres (found in the free edge of the falciform ligament) [1]. * **Ductus Arteriosus Remnant:** Ligamentum Arteriosum (Anatomical closure: 2–3 months). * **Foramen Ovale Remnant:** Fossa Ovalis. * **Key Concept:** Functional closure is always faster (mediated by pressure changes/muscular contraction) than anatomical closure (mediated by fibrosis).

Question 1120: Which of the following conditions is characterized by a wide, fixed split S2 sound?

A. Ventricular septal defect (VSD)
B. Mitral stenosis
C. Atrial septal defect (ASD) (Correct Answer)
D. Coarctation of the aorta

Explanation: ### Explanation **Correct Answer: C. Atrial septal defect (ASD)** In **Atrial Septal Defect (ASD)**, there is a continuous left-to-right shunt. This leads to a chronic volume overload of the right ventricle (RV). Because the RV is handling a larger volume of blood, it takes longer to eject it into the pulmonary artery, causing a **delayed closure of the Pulmonary valve (P2)**. The split is **"fixed"** because the communication between the atria equalizes the respiratory variations in intrathoracic pressure. During inspiration, the normal increase in venous return to the right heart is offset by a decrease in the left-to-right shunt. Consequently, the RV stroke volume remains constant throughout the respiratory cycle, maintaining a constant interval between the Aortic (A2) and Pulmonary (P2) components. **Analysis of Incorrect Options:** * **A. Ventricular Septal Defect (VSD):** Typically presents with a **pansystolic murmur**. While it may cause a wide split S2 due to delayed P2, the split is **not fixed**; it still varies with respiration. * **B. Mitral Stenosis:** Characterized by a loud S1 and an **Opening Snap**. It does not typically cause a wide fixed split S2. * **C. Coarctation of the Aorta:** Associated with continuous murmurs or systolic bruits over the back and rib notching. It does not affect the S2 split in this characteristic manner. **NEET-PG High-Yield Pearls:** * **ASD Murmur:** The murmur heard in ASD is actually a **midsystolic flow murmur** over the pulmonary area (due to increased flow across the pulmonary valve), NOT the shunt itself. * **Lutembacher Syndrome:** ASD associated with acquired Mitral Stenosis. * **Paradoxical Splitting:** Seen in conditions that delay Aortic valve closure (e.g., Aortic Stenosis, Left Bundle Branch Block), where P2 occurs before A2.

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