Neuroanatomy Practice Questions

Q: What effect does UV radiation have on cells?

Stimulates formation of pyrimidine dimers. **Explanation:** The primary mechanism of cellular damage caused by **Ultraviolet (UV) radiation** (specifically UV-B) is the induction of DNA lesions. When DNA absorbs UV photons, it triggers a photochemical reaction between adjacent pyrimidine bases (Cytosine or Thymine) on the same strand. 1. **Why Option B is correct:** UV radiation provides the energy required to form covalent bonds between adjacent pyrimidines, most commonly resulting in **Thymine-Thymine (T-T) dimers** (cyclobutane pyrimidine dimers). These dimers create a "kink" in the DNA strand, which interferes with base pairing, inhibits transcription, and halts DNA replication. 2. **Why Options A and C are incorrect:** UV radiation **promotes** rather than prevents the formation of these dimers. Furthermore, the reaction specifically targets **pyrimidines**; purine dimers (Adenine-Guanine) are not a characteristic feature of UV-induced damage. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Repair Mechanism:** In healthy humans, these dimers are repaired via **Nucleotide Excision Repair (NER)**, which involves endonucleases that "cut and patch" the damaged segment. * **Clinical Correlation:** A genetic defect in the NER pathway leads to **Xeroderma Pigmentosum**. Patients present with extreme photosensitivity and a 2000-fold increased risk of skin cancers (Basal Cell Carcinoma, Squamous Cell Carcinoma, and Melanoma). * **Mutational Signature:** UV damage typically results in **C → T transitions**, a hallmark "signature mutation" found in skin malignancies. (Note: None of the provided references were found to be relevant to the mechanisms of UV radiation and DNA damage.)

Q: At what age is the pincer grasp typically attained?

10 months. The development of the **pincer grasp** is a critical milestone in fine motor development, reflecting the maturation of the corticospinal tracts and neuromuscular coordination. It involves the ability to pick up small objects (like a pea or pellet) using the thumb and index finger. * **Why 10 months is correct:** While the process begins earlier, the **mature pincer grasp** (using the tips of the thumb and index finger) is typically attained by **10 months**. Some sources describe an "immature" pincer grasp (using the pads of the fingers) appearing around 9 months, but for NEET-PG purposes, 10 months is the standard benchmark for the functional pincer grasp. **Analysis of Incorrect Options:** * **4 months:** At this age, the infant uses a **primitive palmar grasp** (reflexive grasping) and is just beginning to reach for objects with both hands. * **12 months:** By one year, the child has already mastered the pincer grasp and is moving toward more complex tasks like releasing objects into a container or trying to use a spoon. * **18 months:** This is the age for more advanced fine motor skills, such as building a tower of 3–4 cubes or scribbling spontaneously. **High-Yield Clinical Pearls for NEET-PG:** * **Palmar Grasp:** Disappears by 2–3 months; replaced by voluntary reach at 4 months. * **Transfers objects hand-to-hand:** 6 months. * **Immature Pincer Grasp:** 9 months (uses finger pads). * **Mature Pincer Grasp:** 10 months (uses finger tips). * **Hand dominance:** Usually develops after 18–24 months; early handedness (before 1 year) may indicate a contralateral motor deficit.

Q: Which of the following is a cerebellar nucleus?

Dentate. **Explanation:** The cerebellum contains four pairs of deep nuclei embedded within its white matter. These nuclei represent the primary output centers of the cerebellum [1]. The correct answer is **Dentate**, which is the largest and most lateral of these nuclei. **Deep Cerebellar Nuclei (from Lateral to Medial):** A useful mnemonic to remember them is **"Don’t Eat Greasy Food"**: 1. **D**entate (Largest, involved in planning and initiation of movement) 2. **E**mboliform 3. **G**lobose 4. **F**astigial (Most medial, involved in balance) [1] **Analysis of Incorrect Options:** * **A. Caudate:** Part of the **Basal Ganglia** [2]. It forms the lateral wall of the lateral ventricle and is involved in cognitive functions and motor control. * **B. Subthalamic:** Located in the **Diencephalon**. It is part of the indirect pathway of the basal ganglia [2]; its lesion leads to Hemiballismus. * **C. Globus pallidus:** A component of the **Basal Ganglia** (specifically the Lentiform nucleus along with the Putamen) [2]. It is responsible for regulating voluntary movement. **High-Yield Clinical Pearls for NEET-PG:** * **Dentate Nucleus:** It has a characteristic "serrated" or tooth-like appearance. It receives fibers from the cerebrocerebellum and sends outputs via the **Superior Cerebellar Peduncle** to the contralateral VL nucleus of the Thalamus [1]. * **Interposed Nuclei:** The Emboliform and Globose nuclei are collectively referred to as the nucleus interpositus. * **Functional Correlation:** Lesions to the deep cerebellar nuclei (especially the dentate) result in **ipsilateral** motor deficits, such as intention tremors and dysmetria.

Q: Ouabain acts by inhibiting which of the following?

Na+K+ ATPase. **Explanation:** The correct answer is **D. Na+K+ ATPase**. [1] **Mechanism of Action:** Ouabain is a cardiac glycoside (similar to Digoxin) derived from the seeds of *Strophanthus gratus*. It acts by specifically binding to and inhibiting the **Na+K+ ATPase pump** (sodium-potassium pump) located on the plasma membrane. [1], [2] This pump normally transports 3 Na+ ions out of the cell and 2 K+ ions into the cell against their concentration gradients. [3] Inhibition leads to an increase in intracellular Na+ concentration, which subsequently decreases the activity of the Na+/Ca++ exchanger. This results in increased intracellular Ca++, leading to increased cardiac contractility (positive inotropy). **Analysis of Incorrect Options:** * **A. Adenyl cyclase:** This enzyme converts ATP to cAMP. It is typically regulated by G-protein coupled receptors (e.g., Beta-receptors), not by cardiac glycosides. * **B. Ca++ channels:** While Ouabain ultimately increases intracellular calcium, it does not act directly on calcium channels (like L-type channels); its effect is secondary to Na+K+ ATPase inhibition. * **C. H+K+ ATPase:** This is the "proton pump" found in the gastric parietal cells. It is inhibited by drugs like Omeprazole, not Ouabain. **High-Yield Facts for NEET-PG:** * **Binding Site:** Ouabain binds to the **alpha (α) subunit** of the Na+K+ ATPase pump on the extracellular side. [2] * **Electrogenic Nature:** The Na+K+ ATPase is electrogenic because it moves more positive charges out than in, helping maintain the resting membrane potential. [3] * **Clinical Use:** While Ouabain is primarily used in research, its relative, **Digoxin**, is used clinically for heart failure and atrial fibrillation. [1] * **Interaction:** Hypokalemia increases the binding of cardiac glycosides to the pump, increasing the risk of toxicity.

Q: Eye examination of a patient revealed lack of upward gaze and dilated pupils fixed to light. What is the MOST probable location of the lesion?

Superior colliculus. The clinical presentation described—**lack of upward gaze** and **dilated pupils fixed to light**—is characteristic of **Parinaud’s Syndrome** (Dorsal Midbrain Syndrome). **1. Why Superior Colliculus is correct:** The superior colliculus and the adjacent pretectal area in the dorsal midbrain house the centers for vertical gaze and the pupillary light reflex [1]. * **Upward Gaze Palsy:** Compression of the **rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF)** or the posterior commissure (near the superior colliculus) disrupts the vertical gaze center. * **Pupillary Abnormalities:** Damage to the **pretectal nuclei** (just anterior to the superior colliculus) disrupts the afferent limb of the light reflex [1], leading to "light-near dissociation" where pupils do not react to light but may react to accommodation [1]. **2. Why other options are incorrect:** * **Optic Chiasm:** Lesions here typically cause bitemporal hemianopia, not vertical gaze palsy. * **Inferior Colliculus:** This is part of the auditory pathway; a lesion here would lead to hearing deficits, not ocular motility issues. * **Edinger-Westphal (EW) Nucleus:** While a lesion here causes a fixed, dilated pupil (parasympathetic loss), it does not explain the lack of upward gaze. Parinaud’s involves the pretectal area *before* the signal reaches the EW nucleus [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Parinaud’s Syndrome Triad:** 1. Upward gaze palsy, 2. Pupillary light-near dissociation, 3. Convergence-retraction nystagmus. * **Common Cause:** **Pineal gland tumors** (Pinealoma) in children/young adults due to direct pressure on the superior colliculus. * **Collier’s Sign:** Eyelid retraction, often seen in this syndrome.

Q: Which of the following neurotransmitters acts on both the sympathetic and parasympathetic divisions of the autonomic nervous system?

Acetylcholine. The correct answer is **Acetylcholine (ACh)**. To understand why, one must look at the functional anatomy of the Autonomic Nervous System (ANS). Acetylcholine is the universal neurotransmitter for **all preganglionic neurons** in both the sympathetic and parasympathetic divisions [1]. It acts on nicotinic receptors at the autonomic ganglia. Additionally, it is the neurotransmitter for all **parasympathetic postganglionic** fibers and a specific subset of sympathetic postganglionic fibers (those supplying sweat glands). **Analysis of Options:** * **A. Atropine:** This is a competitive antagonist of muscarinic acetylcholine receptors, not a neurotransmitter [2]. It is a drug used to block parasympathetic effects. * **B. Pilocarpine:** This is a cholinergic agonist (parasympathomimetic drug) used clinically (e.g., in glaucoma), not an endogenous neurotransmitter [2]. * **D. Adrenaline (Epinephrine):** While it is a primary hormone/neurotransmitter of the sympathetic system (released by the adrenal medulla), it does not play a role in the parasympathetic division [1]. **NEET-PG High-Yield Pearls:** 1. **The "Exception" Rule:** All sympathetic postganglionic neurons release Norepinephrine **except** those to eccrine sweat glands and some blood vessels in skeletal muscle, which release Acetylcholine. 2. **Receptor Types:** ACh acts on **Nicotinic (Nn)** receptors at all autonomic ganglia and **Muscarinic (M)** receptors at parasympathetic effector organs [2]. 3. **Adrenal Medulla:** Consider the adrenal medulla a "modified sympathetic ganglion"; it is stimulated by preganglionic sympathetic fibers using Acetylcholine to release Adrenaline into the blood [1].

Q: Fluidity of the cell membrane is primarily maintained by which of the following components?

Cholesterol. The cell membrane follows the **Fluid Mosaic Model**, where the lipid bilayer acts as a dynamic, fluid structure. **Cholesterol** is the key regulator of this fluidity, acting as a "fluidity buffer" [1]. 1. **Why Cholesterol is Correct:** Cholesterol molecules are interspersed between phospholipids. At high temperatures, they stabilize the membrane by restraining the movement of phospholipids, preventing it from becoming too fluid. At low temperatures, they prevent the fatty acid chains from packing too tightly (crystallizing), thereby maintaining fluidity [2]. Without cholesterol, the membrane would be too brittle at cold temperatures and too liquid at body temperature [1]. 2. **Why Other Options are Incorrect:** * **Carbohydrates:** These are found on the outer surface (as glycoproteins or glycolipids) forming the **glycocalyx**. Their primary roles are cell recognition, signaling, and protection, not the regulation of internal membrane fluidity. * **Proteins:** While proteins (integral and peripheral) perform functions like transport, enzymatic activity, and structural support, they do not determine the baseline fluidity of the lipid bilayer; rather, their own mobility is *dependent* on the fluidity provided by lipids and cholesterol [3]. **High-Yield Facts for NEET-PG:** * **Flip-Flop Movement:** Phospholipids can move laterally or rotate easily, but "flip-flop" (transverse) movement is rare and requires enzymes like **flippases**. * **Lipid Rafts:** These are specialized microdomains rich in cholesterol and sphingolipids that serve as platforms for cell signaling [2]. * **Ratio:** The fluidity is also influenced by the ratio of **saturated to unsaturated fatty acids**; a higher proportion of unsaturated fatty acids (which have "kinks") increases membrane fluidity.

Question 1

What effect does UV radiation have on cells?

Accepted Answer

Stimulates formation of pyrimidine dimers

Answer

Prevents formation of pyrimidine dimers

Answer

Prevents formation of purine dimers

Answer

All the above

Question 2

A 54-year-old chronic alcoholic presents with progressively increasing abdominal distension over the past 3 months. Paracentesis reveals straw-colored, clear fluid with a protein content of 2.3 g/dL. Which of the following is a major contributor to the fluid accumulation in this patient?

Accepted Answer

Decreased oncotic pressure

Answer

Blockage of lymphatics

Answer

Decreased capillary permeability

Answer

Inflammatory exudate

Question 3

At what age is the pincer grasp typically attained?

Accepted Answer

10 months

Answer

4 months

Answer

12 months

Answer

18 months

Question 4

Which of the following is a cerebellar nucleus?

Accepted Answer

Dentate

Answer

Caudate

Answer

Subthalamic

Answer

Globus pallidus

Question 5

Ouabain acts by inhibiting which of the following?

Accepted Answer

Na+K+ ATPase

Answer

Adenyl cyclase

Answer

Ca++ channels

Answer

H+K+ ATPase

Question 6

Eye examination of a patient revealed lack of upward gaze and dilated pupils fixed to light. What is the MOST probable location of the lesion?

Accepted Answer

Superior colliculus

Answer

Optic chiasm

Answer

Inferior colliculus

Answer

Edinger Westphal nucleus

Question 7

Which of the following is true about graft versus host disease?

Accepted Answer

Associated with solid organ transplantation

Answer

Graft must contain immunocompetent T cells

Answer

It is seen in immunosuppressed persons

Answer

Also called as runt disease

Question 8

Which of the following neurotransmitters acts on both the sympathetic and parasympathetic divisions of the autonomic nervous system?

Accepted Answer

Acetylcholine

Answer

Atropine

Answer

Pilocarpine

Answer

Adrenaline

Question 9

Which of the following decreases the fluidity of the cell membrane?

Accepted Answer

Stearic acid

Answer

Carbohydrates

Answer

Linoleic acid

Answer

Cholesterol

Question 10

Fluidity of the cell membrane is primarily maintained by which of the following components?

Accepted Answer

Cholesterol

Answer

Carbohydrates

Answer

Proteins

Answer

None of the above

Neuroanatomy — MCQs

Neuroanatomy — MCQs

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