Neuroanatomy Practice Questions

Q: Which of the following causes a loud S1 sound?

Short PR interval. The intensity of the first heart sound (S1) is primarily determined by the position of the atrioventricular (AV) valves (mitral and tricuspid) at the onset of ventricular systole and the rate of pressure rise within the ventricles [1]. **Why "Short PR interval" is correct:** In a **short PR interval** (as seen in WPW syndrome or tachycardia), the time between atrial contraction and ventricular contraction is reduced. This means the mitral valve leaflets do not have enough time to float back toward a semi-closed position [1]. Consequently, the leaflets are still wide open and deep in the ventricular chamber when ventricular systole begins. They must travel a greater distance and close with higher velocity, resulting in a **loud (accentuated) S1**. **Analysis of Incorrect Options:** * **A. Calcified valve:** Severe calcification makes the valve leaflets rigid and immobile, leading to a **soft or muffled S1**. * **B. Mitral valve prolapse (MVP):** MVP is typically associated with a mid-systolic click and a late systolic murmur, but it does not characteristically cause a loud S1. * **D. Dilation/Widening after valvotomy:** If the valve orifice is widened or if there is significant mitral regurgitation, the leaflets may not coapt properly, often leading to a **decreased intensity** of S1. **High-Yield Clinical Pearls for NEET-PG:** * **Loud S1:** Seen in Mitral Stenosis (pliable valve), Short PR interval, Tachycardia, and High-output states (Anemia, Pregnancy, Thyrotoxicosis). * **Soft S1:** Seen in Mitral Regurgitation, Long PR interval (1st-degree heart block), Calcified Mitral Stenosis, and Obesity/COPD (due to sound dampening). * **Variable S1:** A classic sign of **Atrial Fibrillation** and **Complete Heart Block** (due to varying PR intervals).

Q: Which nerve is called the nerve of Wrisberg?

Sensory root of the facial nerve. ### Explanation The **Nerve of Wrisberg** is the **sensory root of the facial nerve (CN VII)**. The facial nerve emerges from the brainstem as two distinct roots: a large medial motor root and a smaller lateral root, which is the nerve of Wrisberg (nervus intermedius). **Why Option C is Correct:** The nerve of Wrisberg carries three types of fibers: 1. **Special Visceral Afferent (SVA):** Taste sensations from the anterior two-thirds of the tongue (via the chorda tympani). 2. **General Visceral Efferent (GVE):** Parasympathetic secretomotor fibers to the lacrimal, submandibular, and sublingual glands. 3. **General Somatic Afferent (GSA):** Sensory fibers from the external auditory canal and parts of the auricle. **Analysis of Incorrect Options:** * **Option A:** The **motor root** is the larger division of the facial nerve supplying the muscles of facial expression. It is not referred to as the nerve of Wrisberg. * **Option B:** The tympanic branch of the glossopharyngeal nerve (CN IX) is known as **Jacobson’s nerve**. It forms the tympanic plexus and eventually becomes the lesser petrosal nerve. * **Option D:** The **greater auricular nerve** (C2, C3) is a branch of the cervical plexus providing sensation to the skin over the parotid gland and the lower part of the auricle. **Clinical Pearls for NEET-PG:** * **Nomenclature Confusion:** Do not confuse the *Nerve of Wrisberg* (Sensory root of CN VII) with the *Ligament of Wrisberg* (Posterior meniscofemoral ligament in the knee) or the *Cartilage of Wrisberg* (Cuneiform cartilage of the larynx). * **Geniculate Ganglion:** This is where the cell bodies of the sensory fibers of the nerve of Wrisberg are located. * **Ramsay Hunt Syndrome:** Herpes Zoster Oticus involves the nerve of Wrisberg, leading to vesicles in the ear canal and taste loss.

Q: Which muscle is innervated by the Abducens nerve?

Lateral rectus. ***Lateral rectus***- The **Abducens nerve (CN VI)** specifically innervates only the **lateral rectus muscle** [1].- This muscle is responsible for moving the eyeball **laterally**, a movement known as **abduction** [1].*Medial rectus*- This muscle is innervated by the **Oculomotor nerve (CN III)**, not the Abducens nerve [1].- The primary action of the medial rectus is **adduction** (moving the eye medially) [1].*Superior oblique*- This muscle is innervated by the **Trochlear nerve (CN IV)**, which is unique among cranial nerves.- Its primary functions are **intorsion** (internal rotation) and **depression** of the eye.*Inferior oblique*- This muscle is innervated by the **Oculomotor nerve (CN III)**, along with the other recti (except lateral) and the levator palpebrae superioris.- Its main actions are **extorsion** (external rotation) and **elevation** of the eye [1].

Q: A 45-year-old patient presents with difficulty reacting to bright light. On examination, the pupillary light reflex is absent but the near reflex is preserved. Where is the lesion likely located?

Pretectal area of the midbrain. ***Pretectal area of the midbrain*** This clinical presentation describes **light-near dissociation** (Argyll Robertson pupil), where the pupillary light reflex is absent but the near (accommodation) reflex is preserved [2]. **Pathway Analysis:** - **Light reflex pathway**: Retina → optic nerve → optic tract → pretectal nucleus → bilateral Edinger-Westphal nuclei → pupillary constriction [1]. - **Near reflex pathway**: Visual cortex → frontal eye fields → Edinger-Westphal nucleus (bypasses pretectal area) **Why this lesion causes the finding:** A lesion in the **pretectal area** interrupts the light reflex pathway while sparing the near reflex pathway (which doesn't pass through the pretectal area), resulting in the characteristic light-near dissociation [2]. **Clinical significance:** - Classic finding in neurosyphilis (tabes dorsalis) [1] - Also seen in diabetes mellitus, multiple sclerosis, and midbrain lesions [1] - Pupils are typically small, irregular, and show poor light response *Incorrect - Edinger-Westphal nucleus* - This is the parasympathetic nucleus that provides the **final common pathway** for BOTH light and near reflexes [2] - A lesion here would abolish **both reflexes**, not cause dissociation *Incorrect - Optic nerve* - Lesion would cause an **afferent pupillary defect** (Marcus Gunn pupil) - Light reflex would be impaired in the affected eye, but near reflex would remain intact in both eyes - This doesn't explain bilateral light-near dissociation *Incorrect - Oculomotor nerve* - Carries parasympathetic fibers from Edinger-Westphal nucleus to the eye [2] - Lesion would cause **efferent defect** affecting both light AND near reflexes - Would also cause ptosis, ophthalmoplegia, and pupil dilation

Q: A corneal wisp test was performed, and the corneal reflex was elicited. Which of the following nerves is responsible for the afferent limb of this reflex?

Trigeminal Nerve. ***Trigeminal Nerve*** - The **afferent limb** (sensory input) of the corneal reflex is mediated by the **ophthalmic division (V1)** of the Trigeminal Nerve (CN V). - Sensory stimulation of the cornea sends impulses to the main sensory nucleus of CN V in the **pons**. *Facial Nerve* - The Facial Nerve (CN VII) constitutes the **efferent limb** of the corneal reflex, transmitting the motor signal. - This motor signal causes the eyelid closure reaction (blinking) by innervating the **orbicularis oculi** muscle. *Oculomotor Nerve* - The Oculomotor Nerve (CN III) is primarily responsible for most ocular movements and the **pupillary light reflex** (efferent limb), but not corneal sensation. [1] - It innervates the **levator palpebrae superioris** muscle, which controls eyelid opening, the opposite action of the reflex blink. *Abducens Nerve* - The Abducens Nerve (CN VI) is solely responsible for innervating the **lateral rectus** muscle, controlling lateral eye movement. - It plays no role in either the afferent (sensory) or efferent (motor) component of the corneal reflex pathway.

Q: Which of the following lesions will develop after lesion in the area marked as $X$ ?

Left homonymous superior quadrantopic hemianopia. ***Left homonymous superior quadrantopic hemianopia*** - The area marked 'X' represents the **inferior optic radiation (Meyer's loop)** on the right side, located in the **temporal lobe**. - The inferior optic radiation carries information from the **superior visual field** of the contralateral side. - A lesion in the right inferior optic radiation results in a **left homonymous superior quadrantopia**, affecting the superior quadrant of the visual field in the left hemifield of both eyes. - **Key principle**: Inferior radiation lesion → Superior field defect (contralateral side). *Left homonymous inferior quadrantopic hemianopia* - This visual field defect is caused by a lesion in the **superior optic radiation** (parietal lobe) on the right side, not the inferior radiation. - The superior optic radiation carries information from the **inferior visual field**. - A lesion at 'X' is in the inferior radiation, which would cause a superior field defect, not an inferior one. *Right homonymous superior quadrantopic hemianopia* - This lesion results from damage to the **inferior optic radiation** on the **left side**, not the right side as indicated by 'X'. - The visual field defect would be on the opposite side from the lesion location. *Right homonymous inferior quadrantopic hemianopia* - This visual field defect is caused by a lesion in the **superior optic radiation** on the **left side**. - The lesion at 'X' is on the right side, so it cannot produce a right-sided visual field defect. - Remember: lesions affect the **contralateral** visual field.

Q: Arrange the following in the sequence of auditory pathway: 1. Cochlear nucleus 2. Spiral ganglion 3. Superior olivary nucleus 4. Inferior colliculus 5. Medial geniculate body

2-1-3-4-5. ***2-1-3-4-5*** - The auditory pathway begins with the **spiral ganglion**, which contains the cell bodies of the first-order neurons that innervate the hair cells of the cochlea. - Signals then proceed to the **cochlear nucleus** in the brainstem, followed by the **superior olivary nucleus**, the **inferior colliculus**, and finally the **medial geniculate body** in the thalamus before reaching the auditory cortex [1]. *5-4-3-2-1* - This sequence represents a nearly reverse order of the ascending auditory pathway, starting from a higher processing center (medial geniculate body) and moving backward, which is incorrect for sensory input. - The **medial geniculate body** is the thalamic relay for auditory information, receiving input from lower centers and projecting to the auditory cortex [1]. *3-4-5-1-2* - This sequence incorrectly places the **superior olivary nucleus** as the initial processing stage, preceding the lower-level **spiral ganglion** and **cochlear nucleus**. - Auditory information must first be transduced by hair cells and then relayed by the spiral ganglion neurons to the cochlear nucleus before further processing in the olivary complex. *1-2-3-4-5* - This sequence incorrectly places the **cochlear nucleus** before the **spiral ganglion**. - The **spiral ganglion** contains the primary afferent neurons that receive input from the hair cells and project their axons to the cochlear nucleus.

Q: Match the following: A) Glossopharyngeal nerve B) Spinal accessory nerve C) Facial nerve D) Mandibular nerve 1) Shrugging of shoulder 2) Touch sensation from the posterior one-third of the tongue 3) Chewing 4) Taste from the anterior two-thirds of the tongue

A-2 , B-1 , C-4 , D-3. ***A-2 , B-1 , C-4 , D-3*** - **A) Glossopharyngeal nerve (CN IX)** is responsible for **general sensation and taste from the posterior one-third of the tongue** [1]. (2). - **B) Spinal Accessory nerve (CN XI)** innervates the **sternocleidomastoid** and **trapezius muscles**, which are involved in shrugging the shoulders (1). - **C) Facial nerve (CN VII)** carries **taste sensation from the anterior two-thirds of the tongue** [1] (4) via the chorda tympani. - **D) Mandibular nerve (V3)**, a branch of the trigeminal nerve, innervates the muscles of mastication, enabling **chewing** (3). *A-3 , B-1 , C-4 , D-2* - This option incorrectly associates the **glossopharyngeal nerve** with chewing, which is a function of the mandibular nerve (V3). - It also incorrectly associates the **mandibular nerve** with touch sensation from the posterior one-third of the tongue, which is a function of the glossopharyngeal nerve [1]. *A-2 , B-3 , C-4 , D-1* - This option incorrectly links the **spinal accessory nerve** with chewing; this nerve primarily controls shoulder and neck movements. - It also incorrectly assigns shrugging of the shoulder to the **mandibular nerve** instead of the spinal accessory nerve. *A-4 , B-1 , C-2 , D-3* - This choice incorrectly attributes **taste from the anterior two-thirds of the tongue** to the glossopharyngeal nerve, which supplies the posterior one-third [1]. - It also incorrectly links **touch sensation from the posterior one-third of the tongue** to the facial nerve, which is involved in taste from the anterior two-thirds [1].

Q: A 45-year-old patient presents with difficulty speaking and swallowing following a stroke. MRI reveals an infarct in the medulla. Which of the following cranial nerve nuclei is most likely affected?

Nucleus ambiguus. ***Nucleus ambiguus*** - The **nucleus ambiguus** is located in the **medulla** and contains motor neurons that innervate muscles involved in **speaking** and **swallowing**, specifically those of the pharynx, larynx, and soft palate via cranial nerves IX, X, and XI [1]. - An infarct in the medulla causing difficulty speaking and swallowing strongly implicates damage to this nucleus, leading to **dysarthria** and **dysphagia** [1]. *Vestibulocochlear nucleus* - This nucleus is primarily involved in **hearing** and **balance**, which would manifest as dizziness, hearing loss, or nystagmus, not directly difficulty speaking and swallowing. - While located in the brainstem, damage to this nucleus typically does not cause the specific symptoms of dysarthria and dysphagia described. *Trigeminal nerve nucleus* - The trigeminal nerve is responsible for sensory innervation of the face, and motor innervation for **mastication** (chewing). - Damage would primarily affect facial sensation or jaw movement, not the act of deglutition or phonation. *Facial nerve nucleus* - This nucleus, located in the **pons**, controls the muscles of **facial expression** and taste for the anterior two-thirds of the tongue. - Damage would lead to facial weakness or paralysis, not the profound difficulty with speaking and swallowing affecting pharyngeal and laryngeal function.

Q: During an examination of the cranial nerves, a patient shows inability to move their eye laterally past the midline. Which of the following structures in the cavernous sinus is most likely affected?

Abducens nerve. ***Abducens nerve*** - The **abducens nerve (CN VI)** innervates the **lateral rectus muscle**, responsible for **abduction** (lateral movement) of the eye [1]. - Inability to move the eye laterally past the midline indicates paralysis or weakness of the lateral rectus muscle, directly implicating the abducens nerve [1]. *Oculomotor nerve* - The **oculomotor nerve (CN III)** controls most **extraocular muscles** (superior, inferior, medial rectus, inferior oblique) and the levator palpebrae superioris, as well as pupillary constriction [1], [2]. - Damage to this nerve would primarily affect **adduction**, elevation, depression, and eyelid opening, not isolated lateral gaze. *Trochlear nerve* - The **trochlear nerve (CN IV)** innervates the **superior oblique muscle**, which depresses and internally rotates the eye [1]. - A lesion here typically presents with **vertical diplopia**, particularly when reading or descending stairs, due to impaired eye depression and intorsion. *Ophthalmic nerve* - The **ophthalmic nerve (V1)** is one of the three divisions of the trigeminal nerve and is purely **sensory**. - It provides sensation to the forehead, upper eyelid, cornea, and nose, and does not control any eye movements.

Question 1

Which of the following causes a loud S1 sound?

Accepted Answer

Short PR interval

Answer

Calcified valve

Answer

Mitral valve prolapse (MVP)

Answer

Dilation or widening of the mitral valve after valvotomy

Question 2

Which nerve is called the nerve of Wrisberg?

Accepted Answer

Sensory root of the facial nerve

Answer

Motor root of the facial nerve

Answer

Tympanic branch of the glossopharyngeal nerve

Answer

Greater auricular nerve

Question 3

Which muscle is innervated by the Abducens nerve?

Accepted Answer

Lateral rectus

Answer

Medial rectus

Answer

Inferior oblique

Answer

Superior oblique

Question 4

A 45-year-old patient presents with difficulty reacting to bright light. On examination, the pupillary light reflex is absent but the near reflex is preserved. Where is the lesion likely located?

Accepted Answer

Pretectal area of the midbrain

Answer

Edinger–Westphal nucleus

Answer

Optic nerve

Answer

Oculomotor nerve

Question 5

A corneal wisp test was performed, and the corneal reflex was elicited. Which of the following nerves is responsible for the afferent limb of this reflex?

Accepted Answer

Trigeminal Nerve

Answer

Abducens Nerve

Answer

Oculomotor Nerve

Answer

Facial Nerve

Question 6

Which of the following lesions will develop after lesion in the area marked as $X$ ?

Accepted Answer

Left homonymous superior quadrantopic hemianopia

Answer

Right homonymous superior quadrantopic hemianopia

Answer

Left homonymous inferior quadrantopic hemianopia

Answer

Right homonymous inferior quadrantopic hemianopia

Question 7

Arrange the following in the sequence of auditory pathway:

1. Cochlear nucleus
2. Spiral ganglion
3. Superior olivary nucleus
4. Inferior colliculus
5. Medial geniculate body

Accepted Answer

2-1-3-4-5

Answer

5-4-3-2-1

Answer

3-4-5-1-2

Answer

1-2-3-4-5

Question 8

Match the following:
A) Glossopharyngeal nerve
B) Spinal accessory nerve
C) Facial nerve
D) Mandibular nerve

1) Shrugging of shoulder
2) Touch sensation from the posterior one-third of the tongue
3) Chewing
4) Taste from the anterior two-thirds of the tongue

Accepted Answer

A-2 , B-1 , C-4 , D-3

Answer

A-3 , B-1 , C-4 , D-2

Answer

A-2 , B-3 , C-4 , D-1

Answer

A-4 , B-1 , C-2 , D-3

Question 9

A 45-year-old patient presents with difficulty speaking and swallowing following a stroke. MRI reveals an infarct in the medulla. Which of the following cranial nerve nuclei is most likely affected?

Accepted Answer

Nucleus ambiguus

Answer

Vestibulocochlear nucleus

Answer

Trigeminal nerve nucleus

Answer

Facial nerve nucleus

Question 10

During an examination of the cranial nerves, a patient shows inability to move their eye laterally past the midline. Which of the following structures in the cavernous sinus is most likely affected?

Accepted Answer

Abducens nerve

Answer

Oculomotor nerve

Answer

Trochlear nerve

Answer

Ophthalmic nerve

Neuroanatomy — MCQs

Neuroanatomy — MCQs

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