Neuroanatomy Practice Questions

Q: The medulla oblongata receives its blood supply from all of the following arteries except:

Superior cerebellar artery. **Explanation:** The blood supply of the medulla oblongata is derived primarily from the branches of the **vertebral arteries** and their continuation, the **basilar artery**. **Why Superior Cerebellar Artery (SCA) is the correct answer:** The SCA is a branch of the distal part of the basilar artery. It supplies the superior surface of the cerebellum and parts of the **midbrain** and upper pons. It does not descend low enough to supply the medulla oblongata. **Analysis of incorrect options:** * **Anterior Spinal Artery (ASA):** Formed by the union of branches from the vertebral arteries, it supplies the **paramedian** region of the medulla, including the pyramids, medial lemniscus, and hypoglossal nucleus. * **Posterior Inferior Cerebellar Artery (PICA):** A major branch of the vertebral artery, it supplies the **postero-lateral** part of the medulla. Occlusion of this artery leads to **Lateral Medullary Syndrome (Wallenberg Syndrome)**. * **Vertebral Artery:** The medulla is primarily supplied by direct bulbar branches of the vertebral arteries, in addition to the ASA and PICA which originate from it. **High-Yield Clinical Pearls for NEET-PG:** * **Medial Medullary Syndrome (Dejerine Syndrome):** Caused by occlusion of the **Anterior Spinal Artery**. Key features: Ipsilateral 12th nerve palsy and contralateral hemiparesis. * **Lateral Medullary Syndrome (Wallenberg Syndrome):** Caused by occlusion of **PICA** (most common) or the vertebral artery. Key features: Ipsilateral Horner’s syndrome, ataxia, and crossed sensory loss (ipsilateral face, contralateral body). * **Rule of 4s:** Remember that the lower four cranial nerves (IX, X, XI, XII) are associated with the medulla.

Q: Nucleus tractus solitarius receives fibers from all of the following cranial nerves EXCEPT:

Trigeminal. The **Nucleus Tractus Solitarius (NTS)** is a vertical column of grey matter located in the dorsolateral medulla. It serves as the primary sensory receptive center for **visceral afferent** and **taste (gustatory)** signals. ### Why Trigeminal (D) is the Correct Answer The **Trigeminal nerve (CN V)** is primarily responsible for general somatic sensation (touch, pain, temperature) from the face and oral cavity. These fibers terminate in the **Trigeminal Sensory Nuclei** (Principal, Spinal, and Mesencephalic nuclei), not the NTS. Therefore, it does not contribute fibers to the Nucleus Tractus Solitarius. ### Explanation of Other Options The NTS receives inputs from the following nerves, categorized by function: * **Facial Nerve (CN VII):** Carries special visceral afferent (taste) fibers from the anterior 2/3 of the tongue via the chorda tympani [1]. * **Glossopharyngeal Nerve (CN IX):** Carries taste from the posterior 1/3 of the tongue and general visceral afferents from the **carotid body** (chemoreceptors) and **carotid sinus** (baroreceptors) [1], [2]. * **Vagus Nerve (CN X):** Carries taste from the epiglottis and visceral sensations from the base of the tongue, pharynx, larynx, and thoracic/abdominal viscera [2]. ### High-Yield Clinical Pearls for NEET-PG * **Functional Division:** The **rostral** part of the NTS (Gustatory nucleus) handles taste, while the **caudal** part handles cardiorespiratory and gastrointestinal reflexes. * **Vagal Reflexes:** The NTS is the "sensory limb" for several vital reflexes, including the baroreceptor reflex, gag reflex (afferent: IX; efferent: X), and cough reflex. * **Mnemonic:** Remember **"7, 9, 10"** for NTS inputs. * **Output:** The NTS projects to the hypothalamus and the **Area Postrema** (the vomiting center).

Q: Which cranial nerve is involved in the clinical presentation shown below?

Abducent. ***Abducent*** - **Abducent nerve (CN VI)** palsy causes **medial deviation of the eye (esotropia)** due to unopposed action of the **medial rectus muscle**. - Patient presents with **failure of eye abduction** and **horizontal diplopia** that worsens when looking toward the affected side. *Trochlear* - **Trochlear nerve (CN IV)** palsy causes **vertical diplopia** and **superior oblique muscle weakness**. - Patients typically present with **head tilt** to compensate for the vertical misalignment, not horizontal deviation. *Facial* - **Facial nerve (CN VII)** controls **facial muscles** and has **no role in eye movement**. - CN VII palsy presents with **facial weakness**, **inability to close eyelids**, and **loss of facial expression**. *Oculomotor* - **Oculomotor nerve (CN III)** palsy causes **down-and-out eye position** with **ptosis** and **pupil dilation**. - Unlike CN VI palsy, the eye is deviated **laterally and downward**, not medially.

Q: A 5-day-old infant male presents with an abnormally large head. A CT scan reveals enlarged lateral and third ventricles with a normal-sized fourth ventricle, suggesting stenosis of the cerebral aqueduct (of Sylvius). Which of the following conditions is characteristic of these symptoms?

Obstructive hydrocephalus. The clinical presentation describes **Obstructive (Non-communicating) Hydrocephalus**. This condition occurs when there is a physical blockage within the ventricular system that prevents cerebrospinal fluid (CSF) from flowing into the subarachnoid space [1, 2]. **Why the correct answer is right:** The **Cerebral Aqueduct (of Sylvius)** is the narrowest point of the CSF pathway, connecting the third and fourth ventricles. Stenosis at this site prevents CSF from reaching the fourth ventricle [3]. Consequently, pressure builds up "upstream," leading to the dilation of the **lateral and third ventricles**, while the fourth ventricle remains normal in size [3, 5]. This anatomical discrepancy is a classic diagnostic hallmark of aqueductal stenosis [3]. **Why the incorrect options are wrong:** * **Nonobstructive (Communicating) Hydrocephalus:** This occurs due to impaired CSF absorption by arachnoid granulations or overproduction (e.g., choroid plexus papilloma) [1, 2]. In this case, **all** ventricles (including the fourth) would be symmetrically enlarged. * **Anencephaly:** A neural tube defect characterized by the absence of a major portion of the brain and skull; it does not present with an enlarged head or ventricular dilation. * **Meroanencephaly:** A milder form of anencephaly where some rudimentary brain tissue is present; it is incompatible with the symptoms of hydrocephalus. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site of obstruction:** Cerebral Aqueduct (Stenosis of Sylvius) [5]. * **Flow of CSF:** Lateral Ventricles → *Foramen of Monro* → 3rd Ventricle → *Cerebral Aqueduct* → 4th Ventricle → *Foramina of Luschka & Magendie* → Subarachnoid space [2]. * **Arnold-Chiari Malformation (Type II):** Frequently associated with obstructive hydrocephalus and myelomeningocele. * **Clinical Sign:** "Setting-sun eye" sign (downward gaze) due to pressure on the midbrain tectum [4].

Q: Which cranial nerve is most commonly involved in posterior communicating artery aneurysm?

Oculomotor. The **Oculomotor nerve (CN III)** is the most commonly involved cranial nerve in cases of a **Posterior Communicating (PCom) artery aneurysm**. This is due to the close anatomical proximity: the CN III exits the midbrain and passes directly lateral to the PCom artery as it travels toward the cavernous sinus. An aneurysm at the junction of the Internal Carotid Artery and PCom can compress the nerve, leading to **Oculomotor Nerve Palsy**. **Why the other options are incorrect:** * **Facial Nerve (CN VII):** This nerve emerges from the pontomedullary junction and is more commonly affected by lesions in the cerebellopontine angle (e.g., Acoustic Neuroma) or parotid gland pathologies. * **Optic Nerve (CN II):** While it is near the Circle of Willis, it is more typically compressed by pituitary adenomas or aneurysms of the Anterior Communicating artery. * **Trigeminal Nerve (CN V):** This nerve is located deeper in the pons and Meckel’s cave; it is more frequently associated with Superior Cerebellar Artery compression (Trigeminal Neuralgia). **High-Yield Clinical Pearls for NEET-PG:** 1. **The "Rule of Pupil":** In PCom aneurysms, the **pupil is typically dilated and non-reactive** (Mydriasis) [1]. This is because parasympathetic fibers are located peripherally on the nerve and are compressed first by external pressure. 2. **Medical vs. Surgical CN III Palsy:** Pupil-sparing palsy is usually "medical" (e.g., Diabetes/Hypertension due to microvascular ischemia of the central fibers), whereas **pupil-involving** palsy is "surgical" (e.g., Aneurysm). 3. **Clinical Presentation:** Patients present with "Down and Out" eye deviation, ptosis, and a dilated pupil.

Q: Which of the following vessels do not take part in the Circle of Willis?

Middle cerebral. The **Circle of Willis (Circulus Arteriosus)** is a vital polygonal anastomotic network located at the base of the brain in the interpeduncular fossa [3]. It serves as a collateral circulation system between the internal carotid and vertebrobasilar systems. ### 1. Why Middle Cerebral Artery (MCA) is the Correct Answer Although the MCA is the largest terminal branch of the Internal Carotid Artery (ICA), it **does not** form part of the Circle of Willis [1]. It travels laterally into the lateral sulcus (Sylvian fissure) to supply the lateral surface of the cerebral hemispheres. It is considered a "continuation" of the ICA rather than a component of the anastomotic ring itself. ### 2. Analysis of Other Options (Components of the Circle) The Circle of Willis is formed by the following vessels: * **Anterior Cerebral Artery (Option A):** A branch of the ICA that forms the anterolateral segment. * **Anterior Communicating Artery:** Connects the two anterior cerebral arteries (completing the circle anteriorly). * **Posterior Cerebral Artery (Option C):** Terminal branches of the Basilar artery that form the posterior segment. * **Posterior Communicating Artery (Option D):** Connects the ICA with the posterior cerebral artery (completing the circle laterally). * **Internal Carotid Artery:** The source of the anterior and middle cerebral arteries. ### 3. NEET-PG High-Yield Pearls * **Most Common Site of Berry Aneurysm:** Anterior communicating artery (40%), followed by the junction of the ICA and Posterior communicating artery [2]. * **Clinical Correlation:** Rupture of a Berry aneurysm in the Circle of Willis leads to **Subarachnoid Hemorrhage (SAH)**, classically presenting as a "thunderclap headache" [2]. * **Anatomical Variation:** The Circle of Willis is anatomically complete in only about 34–50% of the population.

Q: Which of the following is NOT a consequence of III nerve palsy?

Medial deviation of the eyeball. The **Oculomotor nerve (CN III)** is responsible for supplying the majority of the extraocular muscles, the levator palpebrae superioris, and the parasympathetic fibers to the eye. ### **Why "Medial deviation" is the Correct Answer** In CN III palsy, all extraocular muscles are paralyzed except for the **Lateral Rectus (CN VI)** and the **Superior Oblique (CN IV)**. * The unopposed action of the Lateral Rectus causes the eyeball to be pulled laterally (**Abduction**). * The unopposed action of the Superior Oblique causes the eyeball to move downwards (**Depression**) and outwards (**Intorsion**). * Therefore, the clinical presentation is a **"Down and Out"** gaze, not medial deviation. Medial deviation (Esotropia) occurs in CN VI (Abducens) palsy. ### **Explanation of Other Options** * **Ptosis (A):** Occurs due to paralysis of the **Levator Palpebrae Superioris**, which lifts the upper eyelid. * **Mydriasis (B):** CN III carries parasympathetic fibers to the **Sphincter Pupillae**. Loss of these fibers leads to unopposed sympathetic action, resulting in a fixed, dilated pupil. * **Loss of Pupillary Reflex (D):** Since CN III forms the **efferent limb** of the pupillary light reflex, its damage prevents pupillary constriction in response to light. ### **NEET-PG High-Yield Pearls** * **Rule of Pupil:** In **Surgical** CN III palsy (e.g., PCom artery aneurysm), the pupil is **dilated** (compressive fibers are superficial). In **Medical** CN III palsy (e.g., Diabetes), the pupil is often **spared** (microvascular damage affects deep motor fibers). * **Muscles supplied by CN III:** Superior Rectus, Inferior Rectus, Medial Rectus, Inferior Oblique, and Levator Palpebrae Superioris. * **Formula to remember:** $[LR_6 SO_4]3$ (Lateral Rectus-6, Superior Oblique-4, all others-3).

Q: The bulbocavernosus reflex is elicited by stimulation of which of the following?

Perianal skin. The **Bulbocavernosus Reflex (BCR)** is a polysynaptic reflex used to assess the integrity of the sacral spinal cord segments (**S2–S4**) and the pudendal nerve. [1] ### **Explanation of the Correct Answer** The reflex is elicited by stimulating the **perianal skin** (sensory input via the inferior rectal nerve, a branch of the pudendal nerve) or by squeezing the glans penis/clitoris. The positive response is the **contraction of the external anal sphincter**. In the context of this specific question, while multiple triggers exist, "Perianal skin" is a classic clinical maneuver to test the S4-S5 dermatomes and the integrity of the anal sphincter complex. ### **Analysis of Incorrect Options** * **A & B (Glans penis / Clitoris):** While squeezing the glans or clitoris *does* elicit the BCR, these are typically referred to as the "Glans-anal reflex." In many standardized examinations, if "Perianal skin" is provided as a distinct option, it specifically tests the cutaneous-anal contractile arc. * **C (Tugging of Foley catheter):** This is a common clinical method to elicit the reflex in patients with spinal cord injuries (by stimulating the stretch receptors in the bladder neck/prostatic urethra). However, it is a secondary clinical maneuver rather than the primary anatomical site for eliciting a superficial reflex. [1] ### **High-Yield Clinical Pearls for NEET-PG** * **Spinal Level:** S2, S3, S4 ("Keeps the poop off the floor"). * **Afferent & Efferent Limb:** Both are carried by the **Pudendal Nerve**. * **Clinical Significance:** The BCR is the **first reflex to return** after the resolution of **spinal shock**. [1] Its presence indicates that the injury is "Upper Motor Neuron" (suprasacral) rather than "Lower Motor Neuron" (sacral). * **Absence of Reflex:** If the reflex is absent after the acute phase of injury, it suggests an injury to the conus medullaris or cauda equina.

Q: All of the following are found in the floor of the third ventricle, except:

Oculomotor nerve. The **third ventricle** is a slit-like cavity located between the two thalami. Understanding its boundaries is high-yield for neuroanatomy. ### **Why Oculomotor Nerve is the Correct Answer** The **Oculomotor nerve (CN III)** emerges from the midbrain (specifically the interpeduncular fossa) and is located in the **subarachnoid space** at the base of the brain [1]. It is **not** a structural component of the ventricular system or the floor of the third ventricle. ### **Analysis of the Floor of the Third Ventricle** The floor is formed by structures belonging to the **diencephalon** and the **midbrain**. From anterior to posterior, these include: 1. **Optic Chiasma (Option D):** Forms the most anterior part of the floor. 2. **Infundibulum (Option A):** The stalk connecting the hypothalamus to the pituitary gland. 3. **Tuber Cinereum:** A gray matter elevation between the optic chiasma and mammillary bodies. 4. **Mammillary Bodies (Option C):** Pair of small round swellings belonging to the limbic system. 5. **Posterior Perforated Substance:** A layer of gray matter pierced by central branches of the posterior cerebral artery. 6. **Tegmentum of Midbrain:** Forms the posterior-most part of the floor. ### **NEET-PG High-Yield Pearls** * **Anterior Wall:** Formed by the **Lamina terminalis**, anterior commissure, and columns of the fornix. * **Roof:** Formed by the **Ependyma** (covered by the vascular tela choroidea). * **Communication:** The third ventricle communicates with the lateral ventricles via the **Foramen of Monro** and with the fourth ventricle via the **Aqueduct of Sylvius** [1]. * **Clinical Correlation:** Tumors in the floor of the third ventricle (like craniopharyngiomas) can lead to **Diabetes Insipidus** or visual field defects due to proximity to the hypothalamus and optic chiasma.

Question 1

The medulla oblongata receives its blood supply from all of the following arteries except:

Accepted Answer

Superior cerebellar artery

Answer

Anterior spinal artery

Answer

Posterior inferior cerebellar artery

Answer

Vertebral artery

Question 2

Nucleus tractus solitarius receives fibers from all of the following cranial nerves EXCEPT:

Accepted Answer

Trigeminal

Answer

Glossopharyngeal

Answer

Vagus

Answer

Facial

Question 3

Which cranial nerve is involved in the clinical presentation shown below?

Accepted Answer

Abducent

Answer

Trochlear

Answer

Facial

Answer

Oculomotor

Question 4

A 5-day-old infant male presents with an abnormally large head. A CT scan reveals enlarged lateral and third ventricles with a normal-sized fourth ventricle, suggesting stenosis of the cerebral aqueduct (of Sylvius). Which of the following conditions is characteristic of these symptoms?

Accepted Answer

Obstructive hydrocephalus

Answer

Nonobstructive hydrocephalus

Answer

Anencephaly

Answer

Meroanencephaly

Question 5

Which cranial nerve is most commonly involved in posterior communicating artery aneurysm?

Accepted Answer

Oculomotor

Answer

Facial

Answer

Optic

Answer

Trigeminal

Question 6

Which of the following statements is NOT true regarding the 5th cranial nerve?

Accepted Answer

Supplies parasympathetic fibers to salivary glands

Answer

Arises from the hindbrain

Answer

Provides sensory innervation to the whole face

Answer

Innervates muscles of mastication

Question 7

Which of the following vessels do not take part in the Circle of Willis?

Accepted Answer

Middle cerebral

Answer

Anterior cerebral

Answer

Posterior cerebral

Answer

Posterior communicating

Question 8

Which of the following is NOT a consequence of III nerve palsy?

Accepted Answer

Medial deviation of the eyeball

Answer

Ptosis

Answer

Mydriasis

Answer

Loss of pupillary reflex

Question 9

The bulbocavernosus reflex is elicited by stimulation of which of the following?

Accepted Answer

Perianal skin

Answer

Glans penis

Answer

Clitoris

Answer

Tugging of Foley catheter

Question 10

All of the following are found in the floor of the third ventricle, except:

Accepted Answer

Oculomotor nerve

Answer

Infundibulum

Answer

Mammillary body

Answer

Optic chiasma

Neuroanatomy — MCQs

Neuroanatomy — MCQs

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