Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 521: All of the following cross the plasma membrane except?

A. Epinephrine (Correct Answer)
B. Thyroxine
C. Androstenedione
D. Estrogen

Explanation: The core concept behind this question is the **solubility of hormones** and the location of their receptors. To cross the lipid bilayer of the plasma membrane, a molecule must be **lipophilic (lipid-soluble)**. ### **Explanation of the Correct Answer** * **A. Epinephrine:** This is a catecholamine derived from the amino acid tyrosine [1]. Epinephrine is **water-soluble (hydrophilic)** and cannot diffuse through the lipid-rich plasma membrane. Therefore, it binds to **G-protein coupled receptors (GPCRs)** located on the cell surface (extracellular receptors) to trigger a second messenger cascade (cAMP) [1]. ### **Why the Other Options are Incorrect** * **B. Thyroxine (T4):** Although derived from tyrosine like epinephrine, thyroid hormones are unique because they are highly lipophilic. They cross the plasma membrane via specific transporters to bind to **intranuclear receptors**. * **C & D. Androstenedione and Estrogen:** These are **steroid hormones** derived from cholesterol [1]. All steroid hormones (including glucocorticoids, mineralocorticoids, and sex steroids) are lipid-soluble and easily diffuse across the plasma membrane to bind to **cytoplasmic or nuclear receptors** [2]. ### **NEET-PG High-Yield Pearls** 1. **Receptor Locations:** * **Cell Surface:** Catecholamines (Epi/NE), Peptides (Insulin, Glucagon), and PTH [1]. * **Cytoplasmic:** Glucocorticoids, Mineralocorticoids, Progesterone. * **Nuclear:** Thyroid hormones (T3/T4), Estrogen, Vitamin D, Retinoic acid. 2. **Mnemonic for Nuclear Receptors:** "**T**ry **V**itamins **A**nd **RE**st" (**T**hroid, **V**itamin D, **A**ldosterone/Steroids, **RE**tinoic acid). 3. **Exception Note:** While thyroid hormones are lipophilic, they primarily use carrier-mediated transport (like MCT8) rather than simple diffusion to enter cells rapidly.

Question 522: Elastic cartilage is found in which of the following locations?

A. Auditory tube (Correct Answer)
B. Nasal septum
C. Auricular cartilage
D. Costal cartilage

Explanation: **Explanation:** Cartilage is classified into three types based on the composition of its intercellular matrix: Hyaline, Elastic, and Fibrocartilage. **Elastic cartilage** is characterized by a dense network of branching elastic fibers, providing both flexibility and structural integrity. **Why the Auditory Tube is Correct:** The **Auditory (Eustachian) tube** (specifically its cartilaginous part) consists of elastic cartilage. This allows the tube to remain flexible enough to open and close during swallowing or yawning to equalize middle ear pressure. Other classic locations for elastic cartilage include the **Auricle (Pinna)**, **External Auditory Meatus**, and the **Epiglottis** (Mnemonic: The "3 Es" – Eustachian tube, Epiglottis, External ear). **Analysis of Incorrect Options:** * **Nasal Septum (B):** Composed of **Hyaline cartilage**. This is the most common type of cartilage, providing a smooth surface and structural support. * **Auricular Cartilage (C):** While the Auricle *is* elastic cartilage, in the context of standardized NEET-PG questions where multiple options might seem correct, the **Auditory tube** is often the specific focus of histological classification. *Note: If this were a "Multiple Correct" format, both A and C would be right; however, in single-best-answer formats, the Auditory tube is a high-yield anatomical landmark.* * **Costal Cartilage (D):** Composed of **Hyaline cartilage**. These connect the ribs to the sternum and are prone to calcification with age. **High-Yield Clinical Pearls for NEET-PG:** * **Calcification:** Hyaline cartilage commonly calcifies with age, whereas **Elastic cartilage never calcifies**. * **Articular Cartilage:** A subtype of hyaline cartilage found in joints; it lacks a perichondrium. * **Fibrocartilage:** Found in the intervertebral discs, pubic symphysis, and TMJ; it is the strongest type and lacks a perichondrium.

Question 523: What is the total number of ligamentum denticulatum pairs located on both sides of the spinal cord?

A. 12-14
B. 20-22
C. 30-32
D. 40-42 (Correct Answer)

Explanation: **Explanation:** The **ligamentum denticulatum** (denticulate ligament) is a ribbon-like, serrated extension of the **pia mater** that anchors the spinal cord to the dura mater. It plays a crucial role in stabilizing the spinal cord within the vertebral canal against sudden movements. 1. **Why 40-42 is correct:** There are **21 pairs** of denticulate ligaments (one on each side) extending from the foramen magnum to the level between the T12 and L1 spinal nerves. Since the question asks for the **total number** on both sides, we multiply 21 by 2, resulting in **42** (or a range of 40-42 depending on anatomical variation). 2. **Why other options are wrong:** * **12-14:** This number is too low and does not correlate with spinal segments. * **20-22:** This represents the number of pairs on **one side** only, not the total number. * **30-32:** This roughly corresponds to the number of spinal nerve pairs (31), but denticulate ligaments do not exist at every nerve level (they end at the upper lumbar level). **High-Yield Clinical Pearls for NEET-PG:** * **Origin:** Pia mater (specifically the epipial layer). * **Attachment:** They pierce the arachnoid to attach to the **dura mater** via tooth-like processes. * **Surgical Landmark:** The ligaments are located **between the dorsal and ventral roots** of the spinal nerves. In neurosurgery (like a rhizotomy), they serve as a reliable landmark to distinguish the anterior (motor) roots from the posterior (sensory) roots. * **Extent:** The first process starts at the foramen magnum; the last process is usually between T12 and L1 [1].

Question 524: The globus pallidus and putamen are structures found within which part of the brain?

A. Pons
B. Basal ganglia (Correct Answer)
C. Thalamus
D. Cerebellum

Explanation: **Explanation:** The **Basal Ganglia** (or Basal Nuclei) are a group of subcortical nuclei situated deep within the cerebral hemispheres, primarily involved in the control of voluntary motor movements, procedural learning, and habit formation. Anatomically, the basal ganglia consist of the **striatum** (caudate nucleus and putamen), the **globus pallidus** (internal and external segments), the subthalamic nucleus, and the substantia nigra [1]. Together, the putamen and globus pallidus form a lens-shaped structure known as the **Lentiform Nucleus** [1]. **Analysis of Incorrect Options:** * **Pons:** This is a part of the brainstem located between the midbrain and medulla. It contains cranial nerve nuclei (V, VI, VII, VIII) and respiratory centers, but not the basal nuclei [1]. * **Thalamus:** While the thalamus is a deep gray matter structure and works closely with the basal ganglia as a relay station, it is part of the diencephalon and is functionally distinct. * **Cerebellum:** Located in the posterior cranial fossa, the cerebellum coordinates balance and fine motor control via the "error-correction" mechanism, rather than the initiation of movement associated with the basal ganglia [1], [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Corpus Striatum:** Comprises the Caudate nucleus + Putamen + Globus Pallidus. * **Neostriatum:** Refers specifically to the Caudate + Putamen [1]. * **Blood Supply:** The basal ganglia are primarily supplied by the **Charcot’s artery** (Lenticulostriate branches of the Middle Cerebral Artery), which is a common site for hypertensive hemorrhage. * **Clinical Correlation:** Degeneration of the substantia nigra (part of the basal ganglia circuit) leads to **Parkinson’s disease**, characterized by tremors, rigidity, and bradykinesia [3].

Question 525: CD4 is a marker of which of the following cell types?

A. Monocyte
B. T cell (Correct Answer)
C. B cell
D. None of the above

Explanation: **Explanation:** The correct answer is **B. T cell**. **Understanding the Concept:** CD (Cluster of Differentiation) markers are surface molecules used to identify and differentiate leukocyte subpopulations. **CD4** is a glycoprotein found primarily on the surface of **Helper T cells** (Th cells) [1]. It acts as a co-receptor that assists the T-cell receptor (TCR) in communicating with antigen-presenting cells by binding to **MHC Class II** molecules [1]. **Analysis of Options:** * **T cells (Correct):** T cells are divided into two main subsets: CD4+ (Helper T cells) and CD8+ (Cytotoxic T cells) [1]. While CD3 is the pan-T cell marker, CD4 is the specific marker for the helper subset. * **Monocytes (Incorrect):** While monocytes and macrophages can express low levels of CD4 on their surface (acting as a secondary receptor for HIV entry), they are primarily identified by markers like **CD14** and **CD16**. In the context of standard medical examinations, CD4 is classically associated with T cells. * **B cells (Incorrect):** B cells are characterized by markers such as **CD19, CD20, and CD21**. They do not express CD4 [1]. **NEET-PG High-Yield Pearls:** * **HIV Pathogenesis:** The HIV virus specifically targets **CD4+ cells** (Helper T cells and macrophages) by binding its **gp120** protein to the CD4 receptor. * **MHC Rule of 8:** * CD4 x MHC II = 8 * CD8 x MHC I = 8 * **Pan-Markers:** * All T cells: **CD3** * All B cells: **CD19/20** * NK cells: **CD16/56** * Hematopoietic Stem Cells: **CD34**

Question 526: What is NOT seen in oculomotor palsy?

A. Lateral and upward gaze (Correct Answer)
B. Ptosis
C. Loss of light reflex
D. Dilatation of pupil

Explanation: To understand oculomotor (CN III) nerve palsy, one must recall that this nerve supplies the majority of extraocular muscles (Superior, Inferior, and Medial Recti; Inferior Oblique), the Levator Palpebrae Superioris (LPS), and carries parasympathetic fibers to the sphincter pupillae. [2] **Explanation of the Correct Answer:** In a complete 3rd nerve palsy, the eye typically assumes a **"down and out"** position. This occurs because the only remaining functional extraocular muscles are the **Lateral Rectus** (CN VI - abduction) and the **Superior Oblique** (CN IV - depression and intorsion) [2]. Therefore, a patient with oculomotor palsy **cannot** perform an upward gaze or a medial gaze. The option "Lateral and upward gaze" is incorrect because while the eye is deviated laterally, it is deviated **downward**, not upward. [3] **Analysis of Incorrect Options:** * **Ptosis:** Occurs due to paralysis of the **Levator Palpebrae Superioris**. This is a hallmark sign. * **Dilatation of pupil (Mydriasis):** Occurs because the parasympathetic fibers (which cause constriction) are damaged, leaving the sympathetic innervation to the dilator pupillae unopposed. [1] * **Loss of light reflex:** Since the efferent limb of the light reflex is carried by CN III, damage results in a non-reactive, dilated pupil. [1] **NEET-PG High-Yield Pearls:** 1. **Medical vs. Surgical Third Nerve Palsy:** In "Medical" palsy (e.g., Diabetes), the pupil is often **spared** because parasympathetic fibers are peripheral and receive collateral blood supply. In "Surgical" palsy (e.g., PCom artery aneurysm), the **pupil is involved** due to external compression. 2. **Rule of Thumb:** If the pupil is dilated and fixed, suspect an aneurysm or uncal herniation. 3. **The "Down and Out" eye:** Remember the formula **LR6(SO4)3**—Lateral Rectus (VI), Superior Oblique (IV), and all others (III).

Question 527: Which ganglion is associated with the accommodation of the eye for near vision?

A. Geniculate
B. Ciliary (Correct Answer)
C. Otic
D. Sphenopalatine

Explanation: **Explanation:** The **Ciliary ganglion** is the correct answer because it serves as the peripheral parasympathetic relay station for the visual reflexes [1]. **1. Why Ciliary Ganglion is Correct:** The parasympathetic pathway for accommodation begins in the **Edinger-Westphal nucleus** (midbrain). Pre-ganglionic fibers travel via the **Oculomotor nerve (CN III)** to synapse in the **Ciliary ganglion** [1]. Post-ganglionic fibers (Short ciliary nerves) then innervate the **Ciliary muscle** and the **Sphincter pupillae**. Contraction of the ciliary muscle relaxes the suspensory ligaments (zonules), allowing the lens to become more convex, which increases its refractive power for near vision. **2. Why Other Options are Incorrect:** * **Geniculate Ganglion:** A sensory ganglion of the Facial nerve (CN VII) located in the facial canal; it is involved in taste (anterior 2/3 of tongue) and does not have a motor role in accommodation. * **Otic Ganglion:** Associated with the Glossopharyngeal nerve (CN IX); it relays secretomotor fibers to the **parotid gland**. * **Sphenopalatine (Pterygopalatine) Ganglion:** Associated with the Facial nerve (CN VII); it supplies the **lacrimal gland** and nasal/palatine mucosal glands. **3. NEET-PG High-Yield Pearls:** * **The Accommodation Reflex Triad:** 1. Pupillary constriction (miosis), 2. Convergence of eyeballs, 3. Increased lens curvature (accommodation). * **Argyll Robertson Pupil:** A classic clinical condition where the pupil "accommodates but does not react" to light, often seen in neurosyphilis (lesion in the pretectal nucleus) [2]. * **Sympathetic supply:** Unlike the parasympathetic supply, the sympathetic fibers (from the Superior Cervical Ganglion) cause pupillary dilation (mydriasis) and do not participate in accommodation.

Question 528: All of the following are true regarding the trochlear nerve EXCEPT:

A. It innervates the contralateral superior oblique muscle.
B. It causes depression of the eyeball when in the adducted position.
C. It lies outside the ring of Zinn.
D. In case of a lesion, the patient typically tilts their head ipsilaterally. (Correct Answer)

Explanation: The **Trochlear Nerve (CN IV)** is unique among cranial nerves due to its dorsal exit from the brainstem and its decussation before exiting. ### **Explanation of the Correct Answer (D)** In a trochlear nerve lesion, the affected eye cannot intort and is slightly extorted and elevated (hypertropia). To compensate for the resulting vertical and torsional diplopia [2], the patient **tilts their head to the contralateral (opposite) side**. This maneuver uses the vestibular system to intort the "good" eye, aligning the images. Tilting the head to the ipsilateral side would worsen the diplopia (Bielschowsky’s sign). ### **Analysis of Other Options** * **A. Innervates the contralateral muscle:** This is **true**. The trochlear nuclei are located in the midbrain; the fibers decussate in the superior medullary velum before emerging. Thus, the right nucleus supplies the left superior oblique (SO) muscle. * **B. Depression in adduction:** This is **true**. The primary action of the SO is intorsion. However, when the eye is adducted (turned inward), the muscle's insertion makes it the primary **depressor** of the eyeball [1]. * **C. Outside the ring of Zinn:** This is **true**. The trochlear nerve, along with the frontal and lacrimal nerves (branches of V1) and the superior ophthalmic vein, enters the orbit through the superior orbital fissure **outside** the common tendinous ring (Ring of Zinn). ### **NEET-PG High-Yield Pearls** * **Smallest & Longest:** CN IV is the smallest cranial nerve but has the longest intracranial (subarachnoid) course, making it highly susceptible to trauma. * **Dorsal Exit:** It is the only cranial nerve to emerge from the posterior aspect of the brainstem. * **Clinical Sign:** Patients often present with difficulty walking downstairs because the SO is required for depression during adduction.

Question 529: The 3rd ventricle develops from which embryonic structure?

A. Diencephalon (Correct Answer)
B. Telencephalon
C. Mesencephalon
D. Prosencephalon

Explanation: ### Explanation The ventricular system of the brain develops from the central cavity of the neural tube. As the primary brain vesicles differentiate into secondary vesicles, their internal cavities evolve into specific ventricles. **Why Diencephalon is Correct:** The **Diencephalon** is the caudal part of the forebrain (prosencephalon). Its internal cavity narrows to form the **3rd ventricle**. The walls of the diencephalon eventually develop into the thalamus, hypothalamus, and epithalamus, all of which border this slit-like midline cavity. **Analysis of Incorrect Options:** * **B. Telencephalon:** This rostral part of the forebrain gives rise to the cerebral hemispheres. Its internal cavities expand to form the **Lateral ventricles**. * **C. Mesencephalon:** This vesicle forms the midbrain. Its cavity does not expand into a ventricle but remains a narrow canal known as the **Cerebral Aqueduct (of Sylvius)**, connecting the 3rd and 4th ventricles. * **D. Prosencephalon:** While the 3rd ventricle does originate from the prosencephalon (forebrain), this is a primary vesicle. In NEET-PG, when both a primary and its specific secondary vesicle (Diencephalon) are listed, the **more specific secondary vesicle** is the preferred answer. **High-Yield Clinical Pearls for NEET-PG:** * **Foramina of Monro:** These interventricular foramina connect the lateral ventricles to the 3rd ventricle. * **4th Ventricle:** Develops from the cavities of the **Metencephalon** and **Myelencephalon** (Rhombencephalon). * **Hydrocephalus:** Obstruction at the narrow Cerebral Aqueduct (Mesencephalon) is a common cause of non-communicating hydrocephalus, leading to dilation of both lateral and 3rd ventricles. * **Lamina Terminalis:** Represents the cephalic end of the neural tube and forms the anterior wall of the 3rd ventricle.

Question 530: Which phase of the cell cycle has a fixed duration?

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

Explanation: **Explanation:** In the eukaryotic cell cycle, the **G2 phase (Gap 2)** is characterized by a relatively **fixed and constant duration** (typically 3–4 hours in most human cells). During this phase, the cell performs final metabolic preparations, protein synthesis (e.g., tubulin for spindles), and DNA error checking before entering mitosis [1]. Because these biochemical "check-off" lists are standardized, the time taken is remarkably consistent across different cell types. **Analysis of Options:** * **G1 phase (Option C):** This is the **most variable phase** of the cell cycle. Its duration determines the overall length of the cell cycle. In rapidly dividing cells, G1 is short; in non-dividing cells, it can extend indefinitely (G0 phase). * **S phase (Option A):** While relatively stable, the duration of DNA synthesis can vary depending on the total DNA content and the number of replication origins activated [2]. * **M phase (Option B):** Though it is the shortest phase (approx. 1 hour), its duration can fluctuate based on the complexity of chromosomal alignment and the activation of the spindle assembly checkpoint. **High-Yield NEET-PG Pearls:** * **Sequence:** G1 → S → G2 → M. * **Longest Phase:** G1 (highly variable). * **Shortest Phase:** M phase. * **DNA Content:** It is diploid (2n) in G1 and becomes tetraploid (4n) at the end of the S phase, remaining 4n throughout G2 until cytokinesis is complete [2]. * **Radiosensitivity:** Cells are most sensitive to radiation in the **M and G2 phases** and most resistant during the late S phase.

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

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