Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 531: Which structure is supplied by the posterior cerebral artery?

A. Pons (Correct Answer)
B. Midbrain
C. Thalamus
D. Striate cortex

Explanation: The **Posterior Cerebral Artery (PCA)** is the terminal branch of the basilar artery. However, this question tests the specific vascular territories of the brainstem and cerebrum. ### **Explanation of the Correct Answer** **A. Pons:** This is the correct answer because the pons is primarily supplied by the **Basilar Artery** via its paramedian, short pontine, and long pontine branches. While the PCA originates at the upper border of the pons, it does not supply the pontine parenchyma. Therefore, in the context of "Which structure is **NOT** supplied by the PCA" (a common framing for this specific question pattern), the Pons stands out as the exception. ### **Analysis of Incorrect Options** * **B. Midbrain:** The PCA provides direct branches (peduncular branches) to the midbrain, specifically supplying the cerebral peduncles and the tegmentum. * **C. Thalamus:** The PCA gives off the **thalamoperforating** and **thalamogeniculate** arteries, which are the primary blood supply to the posterior and lateral portions of the thalamus. * **D. Striate Cortex:** The PCA is the main supply to the visual cortex (Brodmann area 17/Striate cortex) via its **calcarine branch**. ### **NEET-PG High-Yield Pearls** * **Macular Sparing:** Occlusion of the PCA leads to contralateral homonymous hemianopia with macular sparing (because the macula receives collateral supply from the Middle Cerebral Artery). * **Weber’s Syndrome:** Often involves branches of the PCA/Basilar tip supplying the midbrain, resulting in ipsilateral 3rd nerve palsy and contralateral hemiplegia. * **Thalamic Syndrome (Dejerine-Roussy):** Results from PCA territory infarcts involving the VPL/VPM nuclei of the thalamus, causing severe chronic pain. * **Pons Supply:** Remember the "Rule of 4"—the Pons is supplied by the Basilar artery; the Medulla is supplied by the Vertebral and Anterior Spinal arteries.

Question 532: Which of the following structures has lymphatics?

A. Brain
B. Internal ear
C. Nail (Correct Answer)
D. Eye

Explanation: ### Explanation The presence or absence of lymphatic vessels is a high-yield topic in neuroanatomy and general histology. While most vascularized tissues possess lymphatics, certain "privileged" sites are traditionally considered devoid of them [1]. **Why the Correct Answer is Right:** * **Nail (Option C):** Contrary to common misconceptions, the **nail bed and nail matrix** are highly vascularized and contain a rich network of lymphatic vessels. These lymphatics drain into the digital lymph nodes. While the nail plate itself is dead keratin, the underlying living tissue (the nail apparatus) is fully integrated into the lymphatic system. **Why the Incorrect Options are Wrong:** * **Brain (Option A):** The brain parenchyma lacks traditional lymphatic vessels [1]. Instead, it utilizes the **Glymphatic System** (a perivascular waste clearance system mediated by astrocytes) and drains via the newly discovered dural lymphatic vessels. However, in the context of standard anatomical questions, the brain is classified as lacking classic lymphatics. * **Internal Ear (Option B):** The internal ear is contained within the bony labyrinth and lacks lymphatic drainage. It relies on the circulation of endolymph and perilymph. * **Eye (Option D):** The interior of the eyeball (cornea, lens, and vitreous) is devoid of lymphatics [1]. The cornea must remain avascular and "lymph-free" to maintain transparency. (Note: The conjunctiva and eyelids do have lymphatics, but the eye proper does not). **High-Yield Clinical Pearls for NEET-PG:** * **Lymph-free zones:** Brain, Spinal cord, Eye (internal), Internal ear, Hyaline cartilage, Epidermis, and Splenic pulp [1]. * **Placenta:** Also lacks lymphatic vessels. * **Glymphatic System:** Remember this term for recent updates; it involves **Aquaporin-4 (AQP4)** channels on astrocytic end-feet. * **Bone Marrow:** Does not have lymphatic vessels; cells enter circulation directly through sinusoids.

Question 533: Hydrogen peroxide is degraded by which cellular organelle?

A. Golgi apparatus
B. Peroxisomes (Correct Answer)
C. Mitochondria
D. All of the above

Explanation: **Explanation:** The correct answer is **Peroxisomes**. **1. Why Peroxisomes are correct:** Peroxisomes (also known as microbodies) are membrane-bound organelles specialized for oxidative reactions [1]. They contain high concentrations of **catalase** and **peroxidases**. These enzymes are responsible for the degradation of hydrogen peroxide ($H_2O_2$), a toxic byproduct of cellular metabolism, into water and oxygen ($2H_2O_2 \rightarrow 2H_2O + O_2$) [1]. This process protects the cell from oxidative damage. **2. Why other options are incorrect:** * **Golgi apparatus:** Its primary function is the post-translational modification, sorting, and packaging of proteins and lipids. It does not possess the enzymatic machinery to degrade $H_2O_2$. * **Mitochondria:** While mitochondria are the primary site of ATP production and actually *generate* reactive oxygen species (ROS) as a byproduct of the electron transport chain, the specific organelle defined by its $H_2O_2$ detoxification role is the peroxisome. **3. High-Yield Clinical Pearls for NEET-PG:** * **Functions:** Peroxisomes are also involved in **Beta-oxidation of Very Long Chain Fatty Acids (VLCFA)**, bile acid synthesis, and plasmalogen synthesis (important for myelin). * **Zellweger Syndrome:** A high-yield clinical correlation where a genetic defect in protein import into peroxisomes leads to "empty" peroxisomes. Patients present with hypotonia, seizures, hepatomegaly, and early death. * **Adrenoleukodystrophy:** A disorder of peroxisomal beta-oxidation leading to the accumulation of VLCFAs in the adrenal glands and white matter of the brain. * **Marker Enzyme:** Catalase is the classic marker enzyme for peroxisomes.

Question 534: Through which of the following spaces does Cerebrospinal Fluid (CSF) not pass?

A. Ventricles
B. Venous sinuses
C. Epidural spaces (Correct Answer)
D. Subarachnoid space

Explanation: ### Explanation **1. Why Epidural Space is the Correct Answer:** The **epidural space** is a potential space (in the cranium) or a real space (in the spinal canal) located between the dura mater and the overlying bone. It contains fat, connective tissue, and the internal vertebral venous plexus [1]. Crucially, it is **separated from the CSF circulation** by the thick, fibrous dura mater. CSF is confined within the ventricular system and the subarachnoid space; it never enters the epidural space under normal physiological conditions. **2. Analysis of Incorrect Options:** * **Ventricles (A):** CSF is produced by the **choroid plexus** within the lateral, third, and fourth ventricles [2]. This is the starting point of the CSF flow. * **Subarachnoid Space (D):** CSF exits the fourth ventricle via the Foramina of Luschka and Magendie to enter this space (located between the arachnoid and pia mater) [1], [2]. This is where CSF cushions the brain and spinal cord. * **Venous Sinuses (B):** This is the site of **CSF absorption**. CSF passes from the subarachnoid space into the dural venous sinuses (primarily the Superior Sagittal Sinus) through **arachnoid granulations/villi** [1], [2]. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Flow Sequence:** Choroid Plexus → Ventricles → Subarachnoid Space → Arachnoid Villi → Dural Venous Sinuses [2]. * **Epidural vs. Subdural Hematoma:** An **Epidural hemorrhage** (usually Middle Meningeal Artery) occurs outside the dura, while a **Subdural hemorrhage** (bridging veins) occurs between the dura and arachnoid. Neither involves the CSF-filled subarachnoid space. * **Lumbar Puncture:** The needle must pierce the dura and arachnoid mater to reach the subarachnoid space (usually at L3-L4 or L4-L5) to sample CSF. * **Total CSF Volume:** Approximately 150 ml, with a production rate of ~0.3–0.5 ml/min (500 ml/day).

Question 535: The temporal lobe contains which of the following areas?

A. Broca's area
B. Prefrontal area
C. Primary visual area
D. Primary auditory area (Correct Answer)

Explanation: **Explanation:** The **temporal lobe** is primarily responsible for processing sensory input, particularly auditory information, and is crucial for memory and language comprehension [1, 2]. **1. Why the Correct Answer is Right:** * **Primary Auditory Area (Brodmann areas 41 and 42):** This area is located on the superior surface of the superior temporal gyrus, specifically within the **Heschl’s gyri**. It receives auditory information directly from the medial geniculate body of the thalamus. Damage to this area results in difficulty interpreting sound frequency and pitch. **2. Why the Other Options are Incorrect:** * **Broca’s Area (Brodmann areas 44 and 45):** Located in the **inferior frontal gyrus** of the dominant hemisphere. It is responsible for motor speech production. * **Prefrontal Area:** Located in the anterior part of the **frontal lobe**. It governs executive functions, personality, and complex decision-making. * **Primary Visual Area (Brodmann area 17):** Located in the **occipital lobe**, specifically in the walls of the calcarine sulcus. It is responsible for processing visual stimuli. **High-Yield Clinical Pearls for NEET-PG:** * **Wernicke’s Area (Brodmann area 22):** Also located in the posterior part of the superior temporal gyrus. Lesions here lead to **sensory aphasia** (fluent but meaningless speech) [2]. * **Meyer’s Loop:** Part of the visual pathway that passes through the temporal lobe. A lesion here causes **superior homonymous quadrantanopia** ("pie in the sky" defect). * **Klüver-Bucy Syndrome:** Results from bilateral temporal lobe (amygdala) destruction, characterized by hypersexuality, hyperphagia, and visual agnosia [1].

Question 536: By what age does a newborn's weight typically double?

A. 6 months (Correct Answer)
B. 1 year
C. 2 years
D. 4 years

Explanation: ### Explanation The growth and development of a child follow a predictable pattern, which is a high-yield topic for NEET-PG. Weight is one of the most sensitive indicators of a child's nutritional status and general health. **1. Why 6 Months is Correct:** A healthy, full-term newborn typically loses about 5–10% of their birth weight in the first week of life [1] but regains it by the 10th day [2]. Following this, weight gain occurs rapidly. On average, a child **doubles their birth weight by 5 to 6 months** of age [1]. For example, if a baby is born at 3 kg, they are expected to weigh approximately 6 kg by 6 months. **2. Analysis of Incorrect Options:** * **B. 1 year:** By 12 months (1 year), a child typically **triples** their birth weight [1]. * **C. 2 years:** By 24 months (2 years), a child typically **quadruples** their birth weight. * **D. 4 years:** This is not a standard milestone for weight multiplication; however, by age 4, a child’s **height** usually doubles from their birth length. **3. Clinical Pearls & High-Yield Facts:** * **Weight Multiples:** * 3x birth weight: 1 year [1] * 4x birth weight: 2 years * 5x birth weight: 3 years * 7x birth weight: 7 years * 10x birth weight: 10 years * **Daily Weight Gain:** In the first 3 months, an infant gains about **25–30 grams/day** [3]. * **Height Milestones:** Average birth length is 50 cm. It increases to 75 cm at 1 year and doubles (100 cm) at 4 years. * **Head Circumference:** At birth, it is ~35 cm; it reaches ~45 cm at 1 year and ~50 cm by 2 years.

Question 537: Which of the following is seen in both apoptosis and necrosis?

A. May be physiological
B. May be pathological (Correct Answer)
C. Inflammation
D. Intact cell membrane

Explanation: ### Explanation The fundamental distinction between **apoptosis** (programmed cell death) and **necrosis** (accidental cell death) lies in their mechanisms and triggers. **1. Why "May be pathological" is correct:** Both processes can occur as a result of disease or injury [1]. * **Necrosis** is *always* pathological, resulting from irreversible exogenous injury (e.g., ischemia, toxins, or trauma). * **Apoptosis** is often physiological (e.g., embryogenesis, endometrial breakdown), but it can also be **pathological**. Pathological apoptosis occurs when cells are damaged beyond repair without causing a massive inflammatory response, such as in DNA damage (radiation/chemotherapy), accumulation of misfolded proteins (neurodegenerative diseases), or certain viral infections (e.g., viral hepatitis forming Councilman bodies) [1]. **2. Why other options are incorrect:** * **A. May be physiological:** This applies **only to apoptosis**. Necrosis is never a normal biological process; it is always a consequence of a harmful stimulus. * **C. Inflammation:** This is a hallmark of **necrosis** [1]. In necrosis, the cell membrane ruptures, releasing intracellular contents that trigger an inflammatory response. Apoptosis does not elicit inflammation because the cell contents are neatly packaged into apoptotic bodies. * **D. Intact cell membrane:** This is a feature of **apoptosis**. In necrosis, the loss of membrane integrity is a defining early event, leading to enzymatic leakage. ### NEET-PG High-Yield Pearls * **Councilman Bodies:** Eosinophilic apoptotic globules seen in the liver during Viral Hepatitis. * **Caspases:** The executioner enzymes of apoptosis (Cysteine proteases). * **Mitochondria:** The "central powerhouse" for the intrinsic pathway of apoptosis (releasing Cytochrome c). * **Pyknosis $\rightarrow$ Karyorrhexis $\rightarrow$ Karyolysis:** The classic sequence of nuclear changes seen in necrosis.

Question 538: Which of the following is a peroxisomal free radical scavenger?

A. Superoxide dismutase
B. Glutathione peroxidase
C. Catalase
D. All the above (Correct Answer)

Explanation: The correct answer is **D. All the above.** Peroxisomes are membrane-bound organelles involved in lipid metabolism and the detoxification of reactive oxygen species (ROS). During the oxidation of fatty acids, peroxisomes produce **hydrogen peroxide ($H_2O_2$)**, a potent free radical. To prevent cellular damage, peroxisomes house a specific battery of antioxidant enzymes (scavengers) to neutralize these radicals. 1. **Catalase:** This is the marker enzyme for peroxisomes. It directly decomposes $H_2O_2$ into water and oxygen, preventing oxidative stress. 2. **Superoxide Dismutase (SOD):** Peroxisomes contain the copper-zinc form (CuZn-SOD), which converts superoxide radicals ($O_2^-$) into $H_2O_2$, which is then handled by catalase. 3. **Glutathione Peroxidase (GPx):** While primarily cytosolic and mitochondrial, specific isoforms of GPx are present in peroxisomes to reduce lipid hydroperoxides and $H_2O_2$ using glutathione as a reducing agent. **Why "All the above" is correct:** While Catalase is the most famous peroxisomal enzyme, modern cell biology confirms that SOD and GPx are also localized within the peroxisomal matrix to provide a comprehensive defense system against oxidative burst. **High-Yield Clinical Pearls for NEET-PG:** * **Zellweger Syndrome:** A "ghost organelle" syndrome caused by a mutation in *PEX* genes, leading to empty peroxisomes. It presents with hypotonia, seizures, and hepatomegaly. * **X-linked Adrenoleukodystrophy (X-ALD):** Defective breakdown of Very Long Chain Fatty Acids (VLCFA) due to a peroxisomal membrane transporter defect (ABCD1). * **Marker Enzyme:** Always remember **Catalase** as the definitive biochemical marker for identifying peroxisomes in histology/biochemistry questions.

Question 539: Which organelle plays a pivotal role in apoptosis?

A. Cytoplasm
B. Golgi complex
C. Mitochondria (Correct Answer)
D. Nucleus

Explanation: **Explanation:** **Mitochondria** are considered the central executioners of the **intrinsic (mitochondrial) pathway** of apoptosis. The pivotal event in this process is the increase in mitochondrial membrane permeability, regulated by the Bcl-2 family of proteins. Pro-apoptotic proteins (Bax and Bak) create pores in the outer mitochondrial membrane, leading to the leakage of **Cytochrome c** into the cytoplasm. Once released, Cytochrome c binds with Apaf-1 to form the **apoptosome**, which activates Caspase-9, initiating the proteolytic cascade that leads to cell death. **Analysis of Incorrect Options:** * **Cytoplasm (A):** While the execution phase of apoptosis occurs in the cytoplasm (via caspases), the "pivotal" regulatory control and initiation of the intrinsic pathway reside within the mitochondria. * **Golgi Complex (B):** The Golgi is primarily involved in post-translational modification, sorting, and packaging of proteins. It does not play a primary role in the initiation of programmed cell death. * **Nucleus (D):** Although nuclear changes (chromatin condensation and DNA fragmentation) are hallmarks of apoptosis, they are downstream effects of the caspase cascade rather than the initiating factor. **High-Yield NEET-PG Pearls:** * **Anti-apoptotic proteins:** Bcl-2, Bcl-xL (they stabilize the mitochondrial membrane). * **Pro-apoptotic proteins:** Bax, Bak, Bim, Bid, Bad. * **Apoptosome components:** Cytochrome c + Apaf-1 + Procaspase-9 + ATP. * **Mitochondrial Marker:** Succinate Dehydrogenase (also part of the TCA cycle and Electron Transport Chain).

Question 540: The height of a child is double the birth weight at what age?

A. 1 year
B. 2 years
C. 4 years (Correct Answer)
D. 9 months

Explanation: The growth and development of a child follow predictable patterns, which are high-yield topics for NEET-PG. The question pertains to the doubling of **birth height (length)**. At birth, the average length of a full-term neonate is approximately **50 cm**. [1] 1. **Why 4 years is correct:** A child’s height typically doubles their birth length at the age of **4 years** (reaching approximately 100 cm). The growth rate is fastest in the first year and then gradually slows down: 25 cm is added in the 1st year, 12 cm in the 2nd year, and about 6–9 cm per year thereafter until puberty. 2. **Analysis of Incorrect Options:** * **1 year:** At one year, the height increases by 50% (reaching ~75 cm), it does not double. However, the **birth weight** triples at 1 year. [1] * **2 years:** At two years, the child is roughly half of their eventual adult height, not double their birth height. * **9 months:** This is an irrelevant milestone for height doubling; however, by 5–6 months, the **birth weight** typically doubles. [1] **Clinical Pearls for NEET-PG:** * **Weight Milestones:** Doubles at 5 months, Triples at 1 year, Quadruples at 2 years. [1] * **Height Milestones:** Increases by 50% at 1 year, **Doubles at 4 years**, Triples at 13 years. * **Head Circumference:** Average at birth is 35 cm; it reaches 45 cm at 1 year and 50 cm at 2 years. * **Formula for Height (2–12 years):** (Age in years × 6) + 77 cm.

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