Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 1141: The greater petrosal nerve carries fibers of which nerve?

A. Trochlear nerve
B. Facial nerve (Correct Answer)
C. Vagus nerve
D. Oculomotor nerve

Explanation: The **Greater Petrosal Nerve (GPN)** is the first branch of the **Facial Nerve (CN VII)**, arising at the level of the geniculate ganglion within the facial canal of the temporal bone. ### Why the Facial Nerve is Correct: The GPN carries **preganglionic parasympathetic (secretomotor) fibers** originating from the **superior salivatory nucleus** in the pons. These fibers travel via the Nervus Intermedius (of Wrisberg) before branching off at the geniculate ganglion. The GPN eventually joins the deep petrosal nerve to form the **nerve of the pterygoid canal (Vidian nerve)**, synapsing in the pterygopalatine ganglion. Postganglionic fibers then provide secretomotor supply to the **lacrimal gland** and the mucous glands of the nose and palate. ### Why the Other Options are Incorrect: * **Trochlear Nerve (CN IV):** A purely motor nerve that supplies only the Superior Oblique muscle of the eye. It has no parasympathetic or petrosal branches. * **Vagus Nerve (CN X):** While it carries extensive parasympathetic fibers, these are destined for the thoracic and abdominal viscera. Its branches in the head/neck (like the auricular branch) do not form the GPN. * **Oculomotor Nerve (CN III):** Carries parasympathetic fibers from the Edinger-Westphal nucleus, but these synapse in the **ciliary ganglion** to supply the sphincter pupillae and ciliary muscles, not the lacrimal gland. ### High-Yield Clinical Pearls for NEET-PG: * **Schirmer’s Test:** Used to evaluate GPN function; a lesion proximal to the geniculate ganglion results in a dry eye (loss of lacrimation). * **Vidian Nerve Composition:** Greater Petrosal (Parasympathetic) + Deep Petrosal (Sympathetic). * **Lesser Petrosal Nerve:** Often confused with GPN; it is a branch of the **Glossopharyngeal nerve (CN IX)** and carries secretomotor fibers to the **parotid gland** via the otic ganglion.

Question 1142: In relation to the subclavian artery, which of the following vessels does NOT contribute to collateral circulation around the outer border of the first rib to the upper limb?

A. Subscapular artery
B. Superior thoracic artery (Correct Answer)
C. Thyrocervical trunk
D. Suprascapular artery

Explanation: **Explanation:** The question tests your knowledge of the **scapular anastomosis**, a vital collateral pathway that maintains blood flow to the upper limb if the subclavian or axillary artery is obstructed between the first rib and the subscapularis muscle [1]. **Why Superior Thoracic Artery is the Correct Answer:** The **superior thoracic artery** is the first branch of the axillary artery. It supplies the upper parts of the pectoralis major and minor muscles and the thoracic wall. Crucially, it does **not** participate in the scapular anastomosis. Therefore, it does not contribute to the collateral circulation bypassing the outer border of the first rib. **Analysis of Incorrect Options:** * **Suprascapular Artery (Option D):** A branch of the **thyrocervical trunk** (subclavian artery). it passes over the transverse scapular ligament to reach the posterior surface of the scapula. * **Thyrocervical Trunk (Option C):** This is the parent vessel for both the suprascapular and the deep branch of the transverse cervical artery (dorsal scapular artery), both of which are primary contributors to the anastomosis from the subclavian side. * **Subscapular Artery (Option A):** A branch of the third part of the axillary artery. Its branch, the **circumflex scapular artery**, enters the infraspinous fossa to anastomose with the suprascapular and dorsal scapular arteries. **NEET-PG High-Yield Pearls:** 1. **The "Bridge":** The scapular anastomosis connects the **1st part of the subclavian artery** with the **3rd part of the axillary artery**. 2. **Key Vessels:** Suprascapular (Subclavian) + Dorsal Scapular (Subclavian) ↔ Circumflex Scapular (Axillary). 3. **Clinical Significance:** If the axillary artery is ligated proximal to the subscapular artery, blood flow to the distal limb is preserved via "reversal of flow" through the circumflex scapular artery [1].

Question 1143: Which of the following drugs does not cross the blood-brain barrier?

A. Pralidoxime (Correct Answer)
B. Obidoxime
C. Diacetyl-monooxime
D. Physostigmine

Explanation: **Explanation:** The **Blood-Brain Barrier (BBB)** is a highly selective semipermeable border that prevents the passage of large, polar, or ionized molecules into the central nervous system (CNS). The ability of a drug to cross this barrier depends primarily on its lipid solubility and electrical charge. **1. Why Pralidoxime is the Correct Answer:** Pralidoxime (2-PAM) is a **quaternary ammonium compound**. Due to its permanent positive charge, it is highly polar and lipid-insoluble. Consequently, it **cannot cross the BBB** and is only effective in regenerating acetylcholinesterase at the peripheral neuromuscular junctions [1]. This is why it treats muscle paralysis in organophosphate poisoning but does not address CNS symptoms like respiratory depression or seizures [1]. **2. Analysis of Incorrect Options:** * **Obidoxime:** Like Pralidoxime, it is a quaternary oxime. While its CNS penetration is clinically negligible, in the context of standard NEET-PG questions, Pralidoxime is the classic prototype for a drug that does not cross the BBB. * **Diacetyl-monooxime:** Unlike Pralidoxime, this is a **non-quaternary oxime**. It is lipid-soluble and **can cross the BBB**, allowing it to regenerate acetylcholinesterase within the CNS. * **Physostigmine:** This is a **tertiary amine** anticholinesterase. Being uncharged and lipid-soluble, it **crosses the BBB** easily. It is the drug of choice for treating atropine (central) toxicity. (Note: Neostigmine and Pyridostigmine are quaternary amines and do *not* cross). **Clinical Pearls for NEET-PG:** * **Mnemonic:** "Tertiary crosses, Quaternary stays." (Physostigmine = Tertiary = CNS; Neostigmine/Pralidoxime = Quaternary = Peripheral). * In Organophosphate poisoning, **Atropine** crosses the BBB to treat central muscarinic symptoms, but **Pralidoxime** only treats peripheral nicotinic symptoms [1]. * **Dopamine** does not cross the BBB (hence we use **Levodopa** for Parkinson’s).

Question 1144: A cut/lesion above the pyramidal tract decussation results in what?

A. Paralysis of the opposite half of the body (Correct Answer)
B. Contralateral loss of proprioception
C. Ipsilateral loss of pain and temperature
D. Contralateral loss of vibration and joint position

Explanation: The **pyramidal tract (Corticospinal tract)** is the primary motor pathway responsible for voluntary movements. It originates in the motor cortex, descends through the internal capsule and brainstem, and undergoes **decussation (crossing over)** at the lower medulla [1]. **1. Why Option A is Correct:** Since the fibers cross to the opposite side at the decussation of the pyramids, any lesion **above** this level (e.g., in the motor cortex, internal capsule, or midbrain) involves fibers that have not yet crossed. Consequently, the motor deficit manifests as **contralateral hemiplegia** (paralysis of the opposite half of the body) [1]. **2. Why the Other Options are Incorrect:** * **Options B & D:** These refer to the **Dorsal Column-Medial Lemniscal (DCML)** pathway. While a lesion above the sensory decussation (medial lemniscus) would cause contralateral loss of proprioception and vibration, the question specifically asks about the *pyramidal tract*, which is a motor pathway. * **Option C:** Pain and temperature are carried by the **Lateral Spinothalamic Tract**. These fibers decussate at the level of the spinal cord (within 1-2 segments of entry). A lesion above the medulla would result in *contralateral* (not ipsilateral) loss of these sensations. **Clinical Pearls for NEET-PG:** * **Lesion Above Decussation:** Contralateral UMN (Upper Motor Neuron) signs [1]. * **Lesion Below Decussation (Spinal Cord):** Ipsilateral UMN signs. * **Weber’s Syndrome:** A classic high-yield example of a lesion above the decussation (midbrain) resulting in contralateral hemiplegia and ipsilateral CN III palsy. * **Pyramidal Decussation Level:** Occurs at the junction of the medulla and the spinal cord (foramen magnum level) [1].

Question 1145: Crouzon syndrome is characterized by which of the following findings?

A. Maxillary hypoplasia (Correct Answer)
B. Syndactyly
C. Macrocephaly
D. Microcephaly

Explanation: **Explanation:** **Crouzon syndrome** (Craniofacial Dysostosis) is an autosomal dominant disorder caused by a mutation in the **FGFR2 gene**. It is characterized by **craniosynostosis**, which is the premature fusion of cranial sutures (most commonly the coronal and sagittal sutures) [1]. **Why Maxillary Hypoplasia is Correct:** The premature fusion of sutures affects the growth of the midface. In Crouzon syndrome, the midface fails to grow forward normally, leading to **maxillary hypoplasia**. This results in a characteristic "sunken" midface appearance, relative mandibular prognathism (the lower jaw appears to stick out), and shallow orbits leading to **proptosis** (bulging eyes). **Analysis of Incorrect Options:** * **B. Syndactyly:** This is the key clinical differentiator. While Crouzon syndrome presents with craniofacial features similar to **Apert syndrome**, it is distinguished by the **absence of hand and foot abnormalities** (no syndactyly). * **C. & D. Macrocephaly/Microcephaly:** The skull shape in Crouzon syndrome is typically **brachycephalic** (short and wide) or "cloverleaf" in severe cases, rather than a simple increase or decrease in overall brain volume. **High-Yield Clinical Pearls for NEET-PG:** * **Triad of Crouzon:** Craniosynostosis, Midface hypoplasia, and Exophthalmos/Proptosis. * **Genetics:** FGFR2 mutation on Chromosome 10q. * **Differential Diagnosis:** Always differentiate from **Apert Syndrome**, which presents with similar facial features PLUS "mitten-hand" syndacytly and mental retardation (Crouzon patients usually have normal intelligence). * **Radiology:** Look for the **"Beaten Metal" appearance** on a skull X-ray, indicating increased intracranial pressure.

Question 1146: Obsession is a disorder of which of the following?

A. Content
B. Perception
C. Stream
D. Possession (Correct Answer)

Explanation: In psychiatric semiology, **Obsessions** are defined as recurrent, persistent thoughts, impulses, or images that are experienced as intrusive and inappropriate. The hallmark of an obsession is that the individual recognizes these thoughts as **products of their own mind** (not inserted by outside forces) but feels they have lost control over them. **1. Why "Possession" is Correct:** The term "Possession" in this context refers to the **sense of ownership** of one's thoughts. In an obsession, the patient experiences a "disorder of the possession of thought" because, while they know the thought is theirs (internal origin), they cannot exclude it from their consciousness despite attempts to ignore or suppress it. This creates a subjective sense of loss of control over their mental space. **2. Analysis of Incorrect Options:** * **A. Content:** Disorders of content involve *what* the person is thinking, primarily **Delusions** (fixed false beliefs). While obsessions have specific themes, they are classified fundamentally by the patient's relationship to the thought (possession/control) rather than just the theme itself. * **B. Perception:** Disorders of perception involve sensory experiences without external stimuli, such as **Hallucinations** or **Illusions**. * **C. Stream:** Disorders of stream (or flow) refer to the speed and continuity of thought, such as **Flight of ideas**, **Retardation**, or **Circumstantiality**. **Clinical Pearls for NEET-PG:** * **Ego-dystonic:** Obsessions are typically ego-dystonic (repugnant or inconsistent with the person’s self-image), whereas delusions are often ego-syntonic. * **Insight:** Insight is preserved in Obsessive-Compulsive Disorder (OCD), distinguishing it from psychotic disorders. * **Thought Insertion:** If a patient feels thoughts are being put into their head by an external agency, it is a disorder of possession called "Thought Insertion" (a Schneiderian First Rank Symptom of Schizophrenia).

Question 1147: All of the following help in the detoxification of drugs except?

A. NADPH cytochrome P450 reductase
B. Cytochrome P450
C. Cytochrome oxidase (Correct Answer)
D. Monooxygenase

Explanation: **Explanation:** The detoxification of drugs and xenobiotics primarily occurs in the liver through the **Microsomal Mixed-Function Oxidase System** (located in the smooth endoplasmic reticulum). **Why Cytochrome Oxidase is the correct answer:** Cytochrome oxidase (also known as **Cytochrome c oxidase** or Complex IV) is a key enzyme in the **Electron Transport Chain (ETC)** located in the inner mitochondrial membrane. Its primary role is cellular respiration—transferring electrons to oxygen to form water and generate ATP. It is **not** involved in the metabolic degradation or detoxification of drugs. **Analysis of Incorrect Options (Involved in Detoxification):** * **Cytochrome P450 (B) & NADPH cytochrome P450 reductase (A):** These are the core components of the Phase I detoxification system. The reductase transfers electrons from NADPH to Cytochrome P450, which then binds to the drug and oxygen to perform oxidative reactions [1]. * **Monooxygenase (D):** This is a functional name for the Cytochrome P450 system. These enzymes incorporate one atom of molecular oxygen into the substrate (the drug) and reduce the other atom to water, making the drug more polar and easier to excrete. **High-Yield Clinical Pearls for NEET-PG:** * **Phase I Reactions:** Include Oxidation (most common), Reduction, and Hydrolysis. These reactions usually make a drug more hydrophilic but can sometimes produce toxic intermediates (e.g., NAPQI from Paracetamol). * **Phase II Reactions:** Involve Conjugation (e.g., Glucuronidation, Sulfation). **Glucuronidation** is the most common Phase II reaction. * **Inducers vs. Inhibitors:** Phenytoin and Rifampicin are potent CYP450 **inducers**, while Ketoconazole and Cimetidine are potent **inhibitors**. * **Inhibition of Cytochrome Oxidase:** Cyanide and Carbon Monoxide (CO) toxicity occurs by binding to and inhibiting Cytochrome oxidase (Complex IV), halting ATP production.

Question 1148: Unilateral injury to the hypoglossal nerve leads to all of the following except?

A. Hemiatrophy of the involved side of the tongue
B. Deviation of the tongue towards the same side
C. Loss of taste sensation in the opposite half of the tongue (Correct Answer)
D. Fasciculations of the tongue

Explanation: ### Explanation The **Hypoglossal nerve (CN XII)** is a purely motor nerve responsible for supplying all intrinsic and extrinsic muscles of the tongue, with the sole exception of the Palatoglossus (supplied by the Vagus nerve via the pharyngeal plexus). **Why Option C is the Correct Answer:** The Hypoglossal nerve has **no sensory component**. Taste sensation from the tongue is mediated by the **Chorda tympani** (branch of CN VII) for the anterior 2/3 and the **Glossopharyngeal nerve** (CN IX) for the posterior 1/3. Therefore, an injury to CN XII will result in motor deficits but will never cause a loss of taste sensation. **Analysis of Incorrect Options:** * **Option A (Hemiatrophy):** Since CN XII provides trophic motor support to the tongue muscles, a Lower Motor Neuron (LMN) lesion leads to muscle wasting and shrinkage (atrophy) on the affected side. * **Option B (Deviation):** The **Genioglossus** muscle is the "safety muscle" of the tongue that protrudes it. In a unilateral lesion, the action of the healthy contralateral Genioglossus is unopposed, pushing the tongue **towards the side of the lesion**. * **Option D (Fasciculations):** These are spontaneous, involuntary muscle twitches visible under the lingual mucosa, characteristic of an LMN lesion of the hypoglossal nucleus or nerve. **High-Yield Clinical Pearls for NEET-PG:** * **LMN vs. UMN:** In a **Lower Motor Neuron** lesion (nerve/nucleus), the tongue deviates **towards** the side of the lesion. In an **Upper Motor Neuron** lesion (cortex/corticobulbar tract), the tongue deviates **away** from the side of the lesion (to the contralateral side). * **The "Safety Muscle":** Genioglossus is the only muscle that prevents the tongue from falling back and obstructing the oropharynx. * **Nucleus Location:** The hypoglossal nucleus is located in the medulla, underlying the **hypoglossal trigone** in the floor of the fourth ventricle.

Question 1149: What are the myelin-forming cells in the peripheral nervous system (PNS)?

A. Oligodendrocytes
B. Schwann cells (Correct Answer)
C. Both
D. None

Explanation: **Explanation:** The formation of the myelin sheath is a critical process for increasing the velocity of nerve impulse conduction (saltatory conduction). The specific cell responsible for this process depends entirely on the anatomical location of the nerve fiber [1]. **Why Schwann Cells are Correct:** In the **Peripheral Nervous System (PNS)**, which includes cranial and spinal nerves, **Schwann cells** are the sole producers of myelin. A unique characteristic of Schwann cells is that **one cell myelinates only one segment (internode) of a single axon** [1]. They also play a vital role in nerve regeneration following injury by forming the "Bands of Büngner" to guide axonal regrowth [2]. **Why Other Options are Incorrect:** * **Oligodendrocytes:** These are the myelinating cells of the **Central Nervous System (CNS)**—the brain and spinal cord [1]. Unlike Schwann cells, one oligodendrocyte can extend its processes to myelinate segments of **multiple axons** (up to 50) [1]. * **Both/None:** These are incorrect because the blood-brain barrier and the transition zone (Obersteiner-Redlich zone) strictly demarcate the territories of these two cell types. **High-Yield Clinical Pearls for NEET-PG:** 1. **Demyelinating Diseases:** **Multiple Sclerosis** affects the CNS (Oligodendrocytes), whereas **Guillain-Barré Syndrome (GBS)** affects the PNS (Schwann cells) [1]. 2. **Origin:** Schwann cells are derived from the **Neural Crest**, while Oligodendrocytes are derived from the **Neural Tube (Neuroectoderm)**. 3. **Acoustic Neuroma:** This is a tumor of Schwann cells (Schwannoma) typically affecting the vestibular nerve (CN VIII). 4. **Unmyelinated Fibers:** In the PNS, even unmyelinated fibers are enveloped by the cytoplasm of Schwann cells (Remak bundles), though no spiral myelin sheath is formed [1].

Question 1150: Intracellular calcification begins in which of the following organelles?

A. Mitochondria (Correct Answer)
B. Golgi body
C. Lysosomes
D. Endoplasmic reticulum

Explanation: Explanation: The correct answer is **A. Mitochondria**. **Why Mitochondria?** Intracellular calcification, particularly pathologic calcification (dystrophic or metastatic), typically begins in the **mitochondria**. Mitochondria are the primary sites for calcium sequestration within the cell. Under conditions of cell injury or metabolic stress, there is an influx of calcium into the cytosol. The mitochondria attempt to buffer this by actively pumping calcium into their matrix. When the concentration exceeds the solubility limit, calcium precipitates with phosphates to form crystalline **hydroxyapatite**, appearing as electron-dense deposits on microscopy. This is often the first morphological sign of irreversible cell injury. **Analysis of Incorrect Options:** * **B. Golgi body:** While involved in protein modification and trafficking, the Golgi apparatus does not play a primary role in calcium storage or the initiation of calcification. * **C. Lysosomes:** Lysosomes are involved in enzymatic degradation. While they may contain debris in later stages of cell death, they are not the initial site of mineral deposition. * **D. Endoplasmic reticulum (ER):** The smooth ER is a major reservoir for *soluble* calcium ions used in signaling; however, the actual formation of solid mineral crystals (calcification) preferentially initiates in the mitochondria due to the high phosphate environment and metabolic changes during injury. **NEET-PG High-Yield Pearls:** * **Dystrophic Calcification:** Occurs in dead/dying tissues with **normal** serum calcium levels (e.g., Atherosclerosis, Monckeberg’s arteriosclerosis, Psammoma bodies). * **Metastatic Calcification:** Occurs in normal tissues due to **hypercalcemia** (e.g., Hyperparathyroidism, Vitamin D toxicity). * **Morphology:** On H&E stain, calcium appears as basophilic (blue-purple), granular, or clumpy deposits. * **Extracellular Calcification:** Begins in **membrane-bound vesicles** (matrix vesicles) derived from degenerating cells.

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