Neuroanatomy — MCQs
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From which structure is the greater petrosal nerve formed?
Which artery is the major supply of the medial surface of the cerebral hemisphere?
Which intrinsic ocular muscle responsible for pupillary constriction is supplied by parasympathetic innervation?
Nerve supply of stapedius is:
Which of the following structures is seen in the cavernous sinus?
Secretomotor fibers to parotid gland are through?
The nerve which has the longest intracranial course is:
Which of the following is pure sensory nerve?
What is the longest part of the optic nerve?
Which nerve carries the motor component of the light reflex?
Neuroanatomy Indian Medical PG Practice Questions and MCQs
Question 1731: From which structure is the greater petrosal nerve formed?
- A. Geniculate ganglion (Correct Answer)
- B. Plexus around ICA
- C. Plexus around middle meningeal artery
- D. None of the options
Explanation: ***Geniculate ganglion*** - The **greater petrosal nerve** arises directly from the **geniculate ganglion** of the **facial nerve (cranial nerve VII)**. - This nerve carries **preganglionic parasympathetic fibers** destined for the lacrimal gland and mucous glands of the nose, palate, and pharynx, as well as **taste fibers** from the palate. *Plexus around ICA* - The **plexus around the internal carotid artery (ICA)** typically carries **postganglionic sympathetic fibers**, primarily for structures in the head, including the dilator pupillae muscle. - It does not give rise to the greater petrosal nerve, which is predominantly parasympathetic and sensory. *Plexus around middle meningeal artery* - The **plexus around the middle meningeal artery** consists mainly of **sympathetic fibers** that supply the artery itself and surrounding structures. - It has no direct connection or contribution to the formation of the greater petrosal nerve. *None of the options* - This option is incorrect because the **greater petrosal nerve** does indeed arise from the **geniculate ganglion**.
Question 1732: Which artery is the major supply of the medial surface of the cerebral hemisphere?
- A. Anterior cerebral artery (Correct Answer)
- B. Posterior cerebral artery
- C. Middle cerebral artery
- D. Posterior inferior cerebellar artery
Explanation: ***Anterior cerebral artery*** - The **anterior cerebral artery (ACA)** is a primary branch of the internal carotid artery and is responsible for supplying blood to the **medial surface** of the frontal and parietal lobes of the cerebral hemispheres [1]. - It also supplies the **corpus callosum**, the superior aspect of the frontal and parietal lobes, and parts of the basal ganglia [1]. *Posterior cerebral artery* - The **posterior cerebral artery (PCA)** primarily supplies the **occipital lobe** and the inferior part of the **temporal lobe** [1]. - It also provides blood to parts of the midbrain and the **thalamus** [1]. *Middle cerebral artery* - The **middle cerebral artery (MCA)** is the largest cerebral artery and supplies most of the **lateral surface** of the cerebral hemispheres [1]. - It is crucial for the blood supply to the **motor and sensory cortices** for the face and upper limb, as well as language areas (Broca's and Wernicke's). *Posterior inferior cerebellar artery* - The **posterior inferior cerebellar artery (PICA)** is a branch of the **vertebral artery** and exclusively supplies the **cerebellum** and the lateral medulla. - It is not involved in the blood supply to the cerebral hemispheres.
Question 1733: Which intrinsic ocular muscle responsible for pupillary constriction is supplied by parasympathetic innervation?
- A. Constrictor pupillae (Correct Answer)
- B. Dilator pupillae
- C. Levator palpebrae superioris
- D. Ciliary muscle
Explanation: ***Constrictor pupillae*** - The **constrictor pupillae** (or **sphincter pupillae**) muscle is responsible for **miosis** (pupil constriction) and is innervated by **parasympathetic fibers** from the **oculomotor nerve (CN III)** via the **ciliary ganglion** [1]. - Stimulation of this muscle reduces the pupil size, which is a key part of the **light reflex** and **accommodation reflex** [1]. - This is the **only pupillary muscle** with parasympathetic innervation. *Ciliary muscle* - The **ciliary muscle** is involved in **accommodation**, altering the shape of the lens for focusing on near objects [1]. - While it also receives **parasympathetic innervation** from the ciliary ganglion, it does **not control pupil size**. - Its function is to change **lens curvature**, not pupillary diameter. *Levator palpebrae superioris* - This muscle is responsible for **elevating the upper eyelid**. - It is innervated by the **somatic motor fibers** of the **oculomotor nerve (CN III)**, not parasympathetic fibers. - It is **not an intrinsic ocular muscle** but rather an extraocular muscle. *Dilator pupillae* - The **dilator pupillae** muscle causes **mydriasis** (pupil dilation). - This muscle is innervated by **sympathetic fibers**, originating from the superior cervical ganglion, not parasympathetic fibers.
Question 1734: Nerve supply of stapedius is:
- A. Facial nerve (7th nerve) (Correct Answer)
- B. Oculomotor nerve (3rd nerve)
- C. Trigeminal nerve (5th nerve)
- D. Glossopharyngeal nerve (9th nerve)
Explanation: ***Facial nerve (7th nerve)*** - The **facial nerve** is responsible for innervating the **stapedius muscle**, which helps to dampen loud sounds by pulling the stapes away from the oval window. - A lesion in the facial nerve can lead to **hyperacusis** due to the paralysis of the stapedius muscle. *Oculomotor nerve (3rd nerve)* - The **oculomotor nerve** primarily controls **eye movements** and **pupil constriction**. - It does not have any direct involvement in the innervation of middle ear muscles. *Trigeminal nerve (5th nerve)* - The **trigeminal nerve** is responsible for **sensation of the face** and innervates the **muscles of mastication**. - It provides motor supply to the **tensor tympani muscle**, not the stapedius. *Glossopharyngeal nerve (9th nerve)* - The **glossopharyngeal nerve** is primarily involved in **taste sensation** from the posterior tongue, **swallowing**, and mediating the **gag reflex**. - It does not innervate any muscles of the middle ear.
Question 1735: Which of the following structures is seen in the cavernous sinus?
- A. Internal carotid artery (Correct Answer)
- B. Facial nerve
- C. Mandibular division of the trigeminal nerve (V3)
- D. Optic nerve (CN II)
Explanation: ***Internal carotid artery*** - The **internal carotid artery** passes directly through the body of the **cavernous sinus**, making it highly vulnerable to injury or compression in this region. - This artery is surrounded by venous blood within the sinus and is a common site for **carotid-cavernous fistulas** if damaged. *Mandibular division of the trigeminal nerve (V3)* - The **mandibular division (V3)** of the trigeminal nerve does not pass through the cavernous sinus itself; it exits the skull via the **foramen ovale**. - Only the **ophthalmic (V1)** and **maxillary (V2)** divisions are found in the lateral wall of the cavernous sinus. *Facial nerve* - The **facial nerve (CN VII)** has a long and complex course but does not pass through the cavernous sinus. - It travels through the **internal auditory meatus** and then exits the skull via the **stylomastoid foramen**. *Optic nerve (CN II)* - The **optic nerve (CN II)** enters the skull via the **optic canal** and is surrounded by meninges, but it does not traverse the cavernous sinus. - It is located superior and medial to the cavernous sinus, passing into the **middle cranial fossa** to join the optic chiasm.
Question 1736: Secretomotor fibers to parotid gland are through?
- A. Tympanic plexus (Correct Answer)
- B. Greater petrosal nerve
- C. Geniculate ganglion
- D. None of the options
Explanation: This is an easy question, and the expected Bloom's level is low (L1) with an expectation of just remembering the right answer. ***Tympanic plexus*** - The secretomotor fibers to the parotid gland originate from the inferior **salivatory nucleus**, travel via the **glossopharyngeal nerve (CN IX)** to the tympanic plexus. - From the tympanic plexus, these preganglionic parasympathetic fibers form the **lesser petrosal nerve**, which synapses in the otic ganglion, and postganglionic fibers then join the **auriculotemporal nerve** to reach the parotid gland. *Greater petrosal nerve* - The **greater petrosal nerve** carries preganglionic parasympathetic fibers that primarily innervate the **lacrimal gland** and glands of the nasal cavity and palate, not the parotid gland. - It is a branch of the **facial nerve (CN VII)**, whereas secretomotor innervation to the parotid is from the glossopharyngeal nerve (CN IX). *Geniculate ganglion* - The **geniculate ganglion** is a sensory ganglion of the **facial nerve (CN VII)**, containing cell bodies for taste sensation from the anterior two-thirds of the tongue. - It is not directly involved in transmitting secretomotor fibers to the parotid gland. *None of the options* - As the **tympanic plexus** is the correct conduit for the secretomotor fibers to the parotid gland, this option is incorrect. - The pathway involves a specific sequence of nerves and ganglia, which includes the tympanic plexus as a key relay point.
Question 1737: The nerve which has the longest intracranial course is:
- A. Trochlear nerve (Fourth cranial nerve) (Correct Answer)
- B. Oculomotor nerve (Third cranial nerve)
- C. Abducens nerve (Sixth cranial nerve)
- D. Trigeminal nerve (Fifth cranial nerve)
Explanation: The nerve which has the longest intracranial course is: ***Trochlear nerve (Fourth cranial nerve)*** - This nerve has the **longest intracranial course** of all the cranial nerves, emerging from the dorsal aspect of the midbrain. - Its long path makes it particularly susceptible to **injury** from head trauma or increased intracranial pressure. *Oculomotor nerve (Third cranial nerve)* - While significant in length, the **oculomotor nerve** does not have the longest intracranial course; it emerges from the ventral midbrain. [1] - It controls most of the **extraocular muscles**, but its intracranial path is shorter than that of the trochlear nerve. *Abducens nerve (Sixth cranial nerve)* - The **abducens nerve** has a relatively long course within the pons and across the clivus but is not the longest. - It is often impacted in conditions causing **elevated intracranial pressure** or skull base fractures due to its path. *Trigeminal nerve (Fifth cranial nerve)* - The **trigeminal nerve** has a large sensory ganglion and extensive peripheral branches but its intracranial course is comparatively short, emerging from the pons. - It is primarily responsible for **facial sensation** and mastication.
Question 1738: Which of the following is pure sensory nerve?
- A. Trigeminal
- B. Abducent
- C. Trochlear
- D. Olfactory (Correct Answer)
Explanation: ***Olfactory*** - The **olfactory nerve (Cranial Nerve I)** is exclusively responsible for the sense of **smell**, making it a pure **sensory nerve** [1]. - It transmits impulses from the **olfactory receptors** in the nasal cavity to the brain. *Trigeminal* - The **trigeminal nerve (Cranial Nerve V)** is a **mixed nerve**. - It has both **sensory functions** (face sensation) and **motor functions** (mastication). *Abducent* - The **abducent nerve (Cranial Nerve VI)** is a **motor nerve**. - It innervates the **lateral rectus muscle**, responsible for moving the eye laterally. *Trochlear* - The **trochlear nerve (Cranial Nerve IV)** is primarily a **motor nerve**. - It innervates the **superior oblique muscle**, which depresses and intorts the eyeball.
Question 1739: What is the longest part of the optic nerve?
- A. Intracanalicular
- B. Intraorbital (Correct Answer)
- C. Intraocular
- D. Intracranial
Explanation: ***Intraorbital*** - The **intraorbital segment** is the **longest portion** of the optic nerve, measuring approximately **25-30 mm**. - It extends from the posterior pole of the eyeball to the **optic canal** and is characterized by a curved, **S-shaped course** within the orbit. - This excess length (approximately 8 mm more than the distance it spans) allows for **free eye movements** without putting tension on the nerve. *Intracranial* - The **intracranial portion** extends from the **optic canal** to the **optic chiasm**, measuring approximately **10-16 mm**. - While often mistakenly thought to be the longest, it is actually the **second longest segment**. - This segment is crucial for the formation of the **optic chiasm** where partial decussation of fibers occurs. *Intracanalicular* - The **intracanalicular portion** passes through the **optic canal** within the sphenoid bone, measuring approximately **4-10 mm**. - This segment is relatively short and constricted, making it vulnerable to compression in conditions like optic nerve gliomas or meningiomas. *Intraocular* - The **intraocular portion** (optic disc) is the **shortest segment**, measuring only about **1 mm**. - It passes through the **lamina cribrosa** of the sclera and is visible on fundoscopy as the optic disc.
Question 1740: Which nerve carries the motor component of the light reflex?
- A. 1st nerve
- B. 2nd nerve
- C. 3rd nerve (Correct Answer)
- D. 4th nerve
Explanation: ***3rd nerve*** - The **oculomotor nerve** (3rd cranial nerve) carries the **efferent motor pathway** of the pupillary light reflex [1]. - It innervates the **sphincter pupillae muscle**, causing pupillary constriction (miosis) [1]. *1st nerve* - The **olfactory nerve** (1st cranial nerve) is responsible for the sense of **smell**. - It is not involved in vision or the pupillary light reflex. *2nd nerve* - The **optic nerve** (2nd cranial nerve) carries the **afferent sensory pathway** of the pupillary light reflex, detecting light [1]. - While essential for the reflex, it is not the motor component that causes pupillary constriction [1]. *4th nerve* - The **trochlear nerve** (4th cranial nerve) innervates the **superior oblique muscle** of the eye [2]. - Its primary function is eye movement, specifically depression and intorsion, and it has no role in the pupillary light reflex [2].
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