Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 791: What structure is present between two successive z-lines?

A. Sarcomere (Correct Answer)
B. M-line
C. Both
D. None

Explanation: **Explanation:** The correct answer is **A. Sarcomere**. **1. Why Sarcomere is correct:** In neuroanatomy and histology, the **sarcomere** is defined as the basic functional and structural unit of a myofibril in skeletal and cardiac muscle [1]. It is the segment of a myofibril that extends from one **Z-line** (or Z-disc) to the next successive Z-line [1]. The Z-line acts as an anchor for thin (actin) filaments. During muscle contraction, the distance between these two Z-lines decreases as the sarcomere shortens [1]. **2. Why other options are incorrect:** * **B. M-line:** The M-line (Mittelscheibe) is the dark line located in the exact **center** of the sarcomere, within the H-zone [1]. It serves as the attachment site for thick (myosin) filaments. It is a component *within* the sarcomere, not the structure spanning the entire distance between Z-lines. * **C & D:** Since the sarcomere is the definitive anatomical unit bounded by Z-lines, these options are incorrect. **High-Yield NEET-PG Pearls:** * **A-band (Anisotropic):** Contains the entire length of thick filaments; its length remains **constant** during contraction [1]. * **I-band (Isotropic):** Contains only thin filaments; it **shortens** during contraction [1]. * **H-zone:** The central part of the A-band containing only thick filaments; it **disappears** during maximal contraction [1]. * **Titn:** The largest protein in the human body, which anchors myosin to the Z-line, acting like a molecular spring. * **Clinical Correlation:** Mutations in proteins forming the Z-line or sarcomere structure (like dystrophin or titin) are often implicated in muscular dystrophies and cardiomyopathies.

Question 792: Which of the following drugs can cause torsades de pointes?

A. Quinidine (Correct Answer)
B. Lignocaine
C. Esmolol
D. Flecainide

Explanation: **Explanation:** **Torsades de Pointes (TdP)** is a specific type of polymorphic ventricular tachycardia associated with a **prolonged QT interval**. The underlying mechanism involves the inhibition of the delayed rectifier potassium current ($I_{Kr}$), which slows repolarization and extends the action potential duration. 1. **Why Quinidine is Correct:** Quinidine is a **Class IA antiarrhythmic**. It works by blocking both sodium channels and, significantly, potassium channels. By blocking potassium efflux during Phase 3 of the cardiac action potential, it prolongs the QT interval. This creates a "pro-arrhythmic" environment where early after-depolarizations (EADs) can trigger TdP. 2. **Why the Other Options are Incorrect:** * **Lignocaine (Class IB):** These drugs preferentially bind to sodium channels in the inactivated state and actually *shorten* the action potential duration and QT interval. They carry the lowest risk of TdP. * **Esmolol (Class II):** As a cardioselective beta-blocker, it decreases the heart rate and conduction velocity but does not prolong the QT interval; in fact, beta-blockers are often used to *prevent* TdP in Long QT Syndrome. * **Flecainide (Class IC):** These are potent sodium channel blockers that significantly slow conduction (prolonging the QRS complex) but have minimal effect on the QT interval. **High-Yield NEET-PG Pearls:** * **Mnemonic for TdP-causing drugs (ABCDE):** **A**ntiarrhythmics (Class IA & III), **B**e-pridil, **C**isapride/Chloroquine, **D**iuretics (due to hypokalemia), **E**rythromycin (Macrolides) and Antipsychotics (e.g., Haloperidol). * **Treatment of Choice:** Intravenous **Magnesium Sulfate** is the first-line treatment for TdP, even if serum magnesium levels are normal. * **Class III Connection:** Sotalol and Ibutilide are other high-yield antiarrhythmics frequently associated with TdP.

Question 793: Raised lactate dehydrogenase (LDH) levels in aqueous humor are seen in which of the following conditions?

A. Galactosemia
B. Glaucoma
C. Hemangioblastoma
D. Retinoblastoma (Correct Answer)

Explanation: **Explanation:** The correct answer is **Retinoblastoma**. **Medical Concept:** Retinoblastoma is the most common primary intraocular malignancy of childhood [1]. The elevation of **Lactate Dehydrogenase (LDH)** in the aqueous humor is a significant biochemical marker for this condition. In a healthy eye, LDH levels in the aqueous humor are lower than those in the serum. However, in Retinoblastoma, the rapid proliferation of malignant cells and subsequent anaerobic glycolysis (Warburg effect) lead to a massive release of LDH into the intraocular fluids. An **Aqueous-to-Serum LDH ratio > 1.0** is highly suggestive of Retinoblastoma. **Analysis of Incorrect Options:** * **Galactosemia:** This metabolic disorder is associated with "oil-drop" cataracts due to the accumulation of dulcitol (galactitol) in the lens, but it does not typically cause an elevation of LDH in the aqueous humor. * **Glaucoma:** While glaucoma involves increased intraocular pressure and potential optic nerve damage, it is not a proliferative malignancy and does not show the characteristic LDH spike seen in retinoblastoma. * **Hemangioblastoma:** These are highly vascular tumors often associated with von Hippel-Lindau (VHL) syndrome. While they occur in the retina, they do not classically present with raised aqueous LDH levels; this marker is specific to the cellular turnover of retinoblastoma. **High-Yield Pearls for NEET-PG:** * **Flexner-Wintersteiner Rosettes:** Pathognomonic histological feature of Retinoblastoma [1]. * **Calcification:** Retinoblastoma is the most common cause of intraocular calcification in a child (visible on CT/Ultrasound) [1]. * **Leukocoria:** The most common presenting sign (white pupillary reflex). * **Genetic Link:** Mutation in the **RB1 gene** on chromosome **13q14** [2].

Question 794: Fibers originating from all of the following cranial nerves are found in the nucleus ambiguus, except:

A. Glossopharyngeal nerve
B. Vagus nerve
C. Accessory nerve
D. Hypoglossal nerve (Correct Answer)

Explanation: The **Nucleus Ambiguus** is a motor nucleus located in the medulla oblongata. It contains the cell bodies of lower motor neurons that provide **Special Visceral Efferent (SVE)** fibers to the muscles of the branchial arches. [1] ### Why Hypoglossal Nerve is the Correct Answer: The **Hypoglossal nerve (CN XII)** is purely a **General Somatic Efferent (GSE)** nerve. Its fibers originate from the **Hypoglossal nucleus**, located near the midline of the medulla, and supply the intrinsic and extrinsic muscles of the tongue. It has no connection to the nucleus ambiguus. [2] ### Explanation of Incorrect Options: The nucleus ambiguus contributes motor fibers to the following cranial nerves: * **Glossopharyngeal Nerve (CN IX):** Provides fibers to the stylopharyngeus muscle (derived from the 3rd branchial arch). * **Vagus Nerve (CN X):** Provides fibers to the muscles of the pharynx, larynx, and soft palate (derived from the 4th and 6th branchial arches). * **Accessory Nerve (CN XI):** The **cranial part** of the accessory nerve originates from the inferior part of the nucleus ambiguus. These fibers eventually join the vagus nerve to supply the laryngeal muscles. ### High-Yield Clinical Pearls for NEET-PG: * **Function:** The nucleus ambiguus is responsible for vital functions like **swallowing and phonation**. * **Lesion:** A lesion of the nucleus ambiguus (e.g., in **Wallenberg Syndrome** or Lateral Medullary Syndrome) results in dysphagia, dysarthria, and loss of the gag reflex. * **Mnemonic:** Remember **"9, 10, 11"** for Nucleus Ambiguus. * **Parasympathetic Role:** It also contains preganglionic parasympathetic neurons that regulate heart rate via the vagus nerve. [2]

Question 795: A child presents with pellagra-like symptoms and amino acids in the urine. There is a family history of two affected siblings and two unaffected siblings, while the parents are normal. What is the diagnosis?

A. Phenylketonuria (PKU)
B. Alkaptonuria
C. Maple syrup urine disease (MSUD)
D. Hartnup disease (Correct Answer)

Explanation: ### Explanation **Correct Option: D. Hartnup disease** **Mechanism:** Hartnup disease is an **autosomal recessive** disorder caused by a mutation in the **SLC6A19 gene**, which encodes a neutral amino acid transporter in the proximal renal tubules and intestinal mucosa. This leads to the malabsorption and excessive urinary loss of neutral amino acids, most notably **Tryptophan**. Tryptophan is a precursor for **Niacin (Vitamin B3)**. A deficiency in Tryptophan results in secondary Niacin deficiency, manifesting as **Pellagra-like symptoms**: Dermatitis (photosensitive rash), Diarrhea, and Dementia/Ataxia. The family history described (affected siblings, normal parents) is classic for an autosomal recessive inheritance pattern. --- ### Why Other Options are Incorrect: * **A. Phenylketonuria (PKU):** Caused by a deficiency of Phenylalanine Hydroxylase. It presents with intellectual disability, "mousy" body odor, and hypopigmentation, but not pellagra-like dermatitis. * **B. Alkaptonuria:** A deficiency of Homogentisate Oxidase. It is characterized by dark urine (on standing), ochronosis (bluish-black pigmentation of connective tissue), and arthritis. * **C. Maple Syrup Urine Disease (MSUD):** A deficiency of the Branched-Chain Alpha-Keto Acid Dehydrogenase complex. It presents in neonates with poor feeding, vomiting, and a characteristic "maple syrup" or burnt sugar odor in the urine. --- ### NEET-PG High-Yield Pearls: * **The "3 Ds" of Pellagra:** Dermatitis, Diarrhea, Dementia (and eventually Death). * **Biochemical Pathway:** Tryptophan → Niacin → NAD+/NADP+. * **Diagnosis:** Confirmed by detecting **neutral aminoaciduria** (specifically Alanine, Serine, Threonine, Valine, Leucine, Isoleucine, Phenylalanine, Tyrosine, and Tryptophan) via paper chromatography. * **Treatment:** High-protein diet and **Nicotinic acid (Niacin) supplementation**.

Question 796: Which tract lies in the dorsal column of the spinal cord?

A. Fasciculus gracilis (Correct Answer)
B. Anterior spinothalamic tract
C. Dorsal spinocerebellar tract
D. Ventral spinocerebellar tract

Explanation: The **Dorsal Column-Medial Lemniscus (DCML) pathway** is located in the posterior (dorsal) funiculus of the spinal cord. It is responsible for carrying sensations of fine touch, conscious proprioception, vibration, and two-point discrimination [1]. 1. **Fasciculus Gracilis (Correct):** This tract occupies the medial portion of the dorsal column. It carries sensory information from the lower limbs and lower trunk (below the T6 spinal level) [1]. At levels above T6, it is joined laterally by the **Fasciculus Cuneatus**, which carries fibers from the upper limbs and chest [1]. 2. **Anterior Spinothalamic Tract (Incorrect):** This tract is located in the **anterior funiculus**. It is responsible for transmitting crude touch and pressure [1]. 3. **Dorsal and Ventral Spinocerebellar Tracts (Incorrect):** These tracts are located in the **lateral funiculus**. They carry unconscious proprioceptive information from the muscles and joints to the cerebellum. **High-Yield Clinical Pearls for NEET-PG:** * **Somatotopy:** In the dorsal columns, fibers are arranged such that those from the sacral levels are most medial, while cervical fibers are most lateral [1]. * **Tabes Dorsalis:** A late manifestation of neurosyphilis that specifically involves the destruction of dorsal column fibers, leading to sensory ataxia and loss of vibration/position sense. * **Subacute Combined Degeneration (SCD):** Vitamin B12 deficiency causes demyelination of both the **Dorsal Columns** and the **Lateral Corticospinal Tracts**. * **First-order neurons:** The cell bodies for the DCML pathway are located in the **Dorsal Root Ganglion (DRG)**, and they synapse for the first time in the medulla (Nucleus Gracilis/Cuneatus) [1].

Question 797: What are the cellular contents of cerebellar cortex?

A. Cortical cells (Correct Answer)
B. Glomus cells
C. Principle cells
D. Intercalated cells

Explanation: The cerebellar cortex is a highly organized structure consisting of three distinct layers: the **Molecular layer**, **Purkinje cell layer**, and **Granular layer** [1]. ### **Explanation of Options** * **A. Cortical cells (Correct):** This is a collective term for the specific neurons residing within the cerebellar layers [1]. These include **Purkinje cells** (the only output cells), **Granule cells** (the most numerous), and interneurons such as **Stellate cells**, **Basket cells**, and **Golgi cells** [1]. Together, these constitute the functional cellular architecture of the cerebellar cortex. * **B. Glomus cells:** These are specialized chemoreceptors found in the **Carotid body** and **Aortic body**. They detect changes in blood pH, $pCO_2$, and $pO_2$; they are not found in the central nervous system. * **C. Principle cells:** While "Principal cells" is a generic term for the primary output neurons of an organ (e.g., in the collecting duct of the kidney or the mitral cells of the olfactory bulb), it is not the standard nomenclature for cerebellar histology. * **D. Intercalated cells:** These are primarily found in the **distal convoluted tubule and collecting ducts** of the kidney (involved in acid-base balance) or within the **salivary gland ducts**. ### **High-Yield NEET-PG Pearls** 1. **Layers (Outer to Inner):** Molecular $\rightarrow$ Purkinje $\rightarrow$ Granular. 2. **Inhibitory vs. Excitatory:** All cells in the cerebellar cortex are **inhibitory (GABAergic)** EXCEPT for the **Granule cells**, which are excitatory (Glutamatergic) [1]. 3. **Afferent Fibers:** * **Climbing fibers:** Arise from the Inferior Olivary Nucleus; synapse directly on Purkinje cells [1]. * **Mossy fibers:** Arise from all other sources; synapse on Granule cells (forming the "Cerebellar Glomerulus") [1]. 4. **Clinical Correlation:** Damage to these cells results in **ipsilateral** cerebellar signs (Ataxia, Hypotonia, Dysmetria, and Intention tremor).

Question 798: A patient is brought to the emergency department following a road traffic accident. MRI shows injury to the corpus striatum. This patient is MOST likely to suffer from which of the following movement disorders?

A. Chorea (Correct Answer)
B. Parkinsonism
C. Hemiballismus
D. Athetosis

Explanation: The **corpus striatum** (composed of the caudate nucleus and the putamen) is a key component of the basal ganglia circuitry. It serves as the primary input station, receiving excitatory signals from the cortex and projecting inhibitory signals to the globus pallidus [2]. **Why Chorea is the Correct Answer:** Injury to the corpus striatum, particularly the **caudate nucleus**, leads to the loss of GABAergic inhibitory neurons [3]. This results in the disinhibition of the thalamus, causing involuntary, jerky, "dance-like" movements known as **Chorea**. This is classically seen in Huntington’s disease, where atrophy of the caudate nucleus is the hallmark [1]. **Analysis of Incorrect Options:** * **Parkinsonism:** This is primarily caused by the degeneration of dopaminergic neurons in the **Substantia Nigra pars compacta (SNpc)**, leading to a deficiency of dopamine in the striatum [3]. * **Hemiballismus:** This characterized by violent, flinging movements of the limbs and is specifically associated with a lesion in the **Subthalamic Nucleus (STN)**. * **Athetosis:** This involves slow, writhing, "snake-like" movements, typically resulting from lesions in the **Globus Pallidus**. **High-Yield Clinical Pearls for NEET-PG:** * **Corpus Striatum** = Caudate Nucleus + Lentiform Nucleus (Putamen + Globus Pallidus). * **Neostriatum (Striatum)** = Caudate + Putamen. * **Lentiform Nucleus** = Putamen + Globus Pallidus. * **Wilson’s Disease:** Characterized by cavitation and degeneration of the **Putamen**. * **Huntington’s Disease:** Characterized by **Caudate** atrophy and **Chorea** [3].

Question 799: In lateral medullary syndrome (Wallenberg), where is the lesion located?

A. Trigeminal motor nucleus
B. Spinal tract of the trigeminal nerve (Correct Answer)
C. Medial lemniscus
D. Pyramidal tract

Explanation: **Explanation:** **Lateral Medullary Syndrome (Wallenberg Syndrome)** occurs due to an infarct in the territory of the **Posterior Inferior Cerebellar Artery (PICA)** or the vertebral artery. It involves the dorsolateral portion of the medulla. 1. **Why Option B is correct:** The **Spinal tract and nucleus of the Trigeminal nerve** are located in the lateral medulla. Damage to these structures results in the classic clinical finding of **ipsilateral loss of pain and temperature sensation over the face**. This is a hallmark of the syndrome, alongside contralateral loss of pain/temperature in the body (due to lateral spinothalamic tract involvement). 2. **Why incorrect options are wrong:** * **A. Trigeminal motor nucleus:** This nucleus is located in the **Pons**, not the medulla. Its involvement would affect the muscles of mastication. * **C. Medial lemniscus:** This structure is located **medially** in the medulla. Its involvement occurs in **Medial Medullary Syndrome (Dejerine Syndrome)**, leading to loss of vibration and proprioception. * **D. Pyramidal tract:** Also located **medially** (forming the pyramids), its involvement in Medial Medullary Syndrome causes contralateral hemiplegia. Lateral medullary syndrome characteristically **spares** motor function. **High-Yield Clinical Pearls for NEET-PG:** * **Nucleus Ambiguus involvement:** Leads to dysphagia, dysarthria, and loss of gag reflex (CN IX, X). * **Vestibular Nuclei involvement:** Causes vertigo, nystagmus, and nausea. * **Sympathetic tract involvement:** Leads to **ipsilateral Horner’s syndrome** (miosis, ptosis, anhidrosis). * **Inferior Cerebellar Peduncle:** Causes ipsilateral ataxia. * **Rule of 4s:** Remember that "Lateral" syndromes (Wallenberg) involve cranial nerve nuclei that do not divide evenly into 12 (V, VII, IX, X, XI), whereas "Medial" syndromes involve those that do (III, IV, VI, XII).

Question 800: Lines of Zahn are found in which of the following?

A. Thrombus (Correct Answer)
B. Infarct tissue
C. Postmortem clot
D. All of the above

Explanation: **Explanation:** **Lines of Zahn** are a characteristic morphological feature of a **thrombus** that forms in flowing blood (arterial or cardiac) [1]. They appear macroscopically as alternating pale and dark laminations. 1. **Why Option A is Correct:** The pale layers represent aggregates of **platelets and fibrin**, while the darker layers consist of **trapped red blood cells**. Their presence is a definitive sign that the clot formed in a **living person** under the influence of blood flow (hemodynamics), which causes the rhythmic layering of blood components [1]. 2. **Why Other Options are Incorrect:** * **Option B (Infarct tissue):** An infarct is an area of ischemic necrosis resulting from the occlusion of blood supply. While a thrombus often *causes* an infarct, the lines of Zahn are a feature of the intravascular clot itself, not the necrotic tissue [1]. * **Option C (Postmortem clot):** These form after death when blood is stagnant. Because there is no active circulation, the blood components settle by gravity rather than layering by flow. Postmortem clots are typically described as "chicken fat" (upper plasma layer) and "currant jelly" (lower RBC layer) and **lack** lines of Zahn. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Lines of Zahn are most prominent in arterial thrombi and cardiac (mural) thrombi where flow is rapid [1]. They are less distinct in venous thrombi (Phlebothrombosis). * **Diagnostic Significance:** They are the primary histological tool used to distinguish a **pre-mortem thrombus** from a **post-mortem clot**. * **Virchow’s Triad:** Remember the three factors leading to thrombus formation: Endothelial injury, Stasis/Turbulence, and Hypercoagulability.

Practice by Chapter

Organization of the Nervous System

Practice Questions

Spinal Cord Anatomy

Practice Questions

Brainstem Anatomy

Practice Questions

Cerebellum

Practice Questions

Diencephalon

Practice Questions

Cerebral Cortex

Practice Questions

Basal Ganglia

Practice Questions

Limbic System

Practice Questions

Cranial Nerves

Practice Questions

Autonomic Nervous System

Practice Questions

Neural Pathways and Tracts

Practice Questions

Neurovascular Anatomy

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free