Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 1721: Nerve injured in Frey’s syndrome is:

A. Auriculotemporal Nerve (Correct Answer)
B. Great auricular nerve
C. Lingual Nerve
D. Inferior alveolar nerve

Explanation: ***Auriculotemporal Nerve*** - Frey's syndrome (also known as **auriculotemporal syndrome**) results from damage and aberrant regeneration of the **auriculotemporal nerve**. - This leads to **sweating and flushing** in the pre-auricular and temporal regions in response to salivary stimuli (e.g., eating). *Great auricular nerve* - The great auricular nerve primarily provides **sensory innervation** to the skin over the parotid gland, mastoid process, and auricle. - While it can be injured during parotid surgery, its damage typically causes **sensory deficits** (numbness) rather than gustatory sweating. *Lingual Nerve* - The lingual nerve provides **general sensation** and **taste** to the anterior two-thirds of the tongue and innervates the submandibular and sublingual glands. - Injury to this nerve leads to issues with **taste and sensation of the tongue**, not gustatory sweating in the face. *Inferior alveolar nerve* - The inferior alveolar nerve provides **sensory innervation** to the lower teeth and lower lip, and its mental branch supplies the chin. - Damage to this nerve is typically associated with **numbness or altered sensation** in the lower dental arch, lip, and chin, not Frey's syndrome.

Question 1722: Stimulation of the external auditory canal leads to cough due to which nerve?

A. Auricular branch of vagus (Correct Answer)
B. Greater auricular nerve
C. Auriculotemporal nerve
D. Facial Nerve

Explanation: ***Auricular branch Vagus*** - The **auricular branch of the vagus nerve (Arnold's nerve)** innervates the posterior and inferior walls of the external auditory canal. - Stimulation of this nerve can trigger the **cough reflex**, as the vagus nerve is also responsible for innervating the larynx, pharynx, and trachea. *Greater auricular nerve* - The **greater auricular nerve** is a cutaneous nerve from the cervical plexus (C2-C3) that supplies sensation to the skin over the mastoid process, posterior auricle, and part of the earlobe. - It does not directly innervate the external auditory canal in a way that would trigger a cough reflex. *Auriculotemporal nerve* - The **auriculotemporal nerve** is a branch of the mandibular nerve (V3) that provides sensory innervation to the temporomandibular joint, skin over the temple, and part of the external ear. - While it innervates part of the ear, its stimulation does not typically elicit a cough reflex. *Facial Nerve* - The **facial nerve** is primarily responsible for motor innervation of the muscles of facial expression and taste sensation to the anterior two-thirds of the tongue. - Although it has a small sensory component to the external ear (via auricular branches), it is not the primary nerve responsible for the cough reflex when the external auditory canal is stimulated.

Question 1723: Contralateral loss of pain and temperature is due to injury to:

A. Anterior spinothalamic tract
B. Lateral spinothalamic tract (Correct Answer)
C. Fasciculus gracilis
D. Fasciculus cuneatus

Explanation: ***Lateral spinothalamic tract*** - The **lateral spinothalamic tract** decussates (crosses over) shortly after entering the spinal cord, so an injury to this tract results in **contralateral loss** of pain and temperature sensation [1]. - This tract is specifically responsible for the transmission of **pain and temperature** information from the periphery to the brain [1]. *Anterior spinothalamic tract* - This tract is primarily responsible for transmitting **crude touch and pressure** sensations, not pain and temperature. - While it also decussates, its injury would lead to contralateral loss of crude touch, not the symptoms described. *Fasciculus gracilis* - This tract is part of the **dorsal column-medial lemniscus pathway**, responsible for **fine touch, vibration, and proprioception** from the lower body [1]. - Injury to this tract would cause **ipsilateral loss** of these sensations, not contralateral pain and temperature. *Fasciculus cuneatus* - Also part of the **dorsal column-medial lemniscus pathway**, it carries **fine touch, vibration, and proprioception** from the upper body [1]. - An injury here would result in **ipsilateral loss** of these specific sensations, not contralateral pain and temperature.

Question 1724: Which of the following is NOT part of the special visceral efferent column?

A. Nucleus ambiguus
B. Accessory nerve (Correct Answer)
C. Glossopharyngeal n
D. Vagus nerve

Explanation: ***Accessory nerve*** - The **accessory nerve (CN XI)** has two components: a **cranial part** and a **spinal part**. - The **spinal part** (which forms the main functional component) carries **somatic efferent fibers** to the **sternocleidomastoid** and **trapezius muscles** and is **NOT part of the special visceral efferent column**. - The cranial part briefly joins the vagus nerve and is functionally part of the vagus; the spinal accessory is the clinically and anatomically distinct component. - SVE specifically innervates muscles derived from **pharyngeal arches**, not muscles like SCM and trapezius. *Glossopharyngeal n* - The **glossopharyngeal nerve (CN IX)** contains **special visceral efferent fibers** that innervate the **stylopharyngeus muscle**, which is derived from the **third pharyngeal arch**. - These fibers originate from the **nucleus ambiguus**. *Nucleus ambiguus* - The **nucleus ambiguus** is a brainstem nucleus that contains the cell bodies of **special visceral efferent neurons**. - These neurons send axons through the **glossopharyngeal (CN IX), vagus (CN X)**, and **cranial part of accessory (CN XI) nerves** to innervate muscles of the pharynx and larynx derived from pharyngeal arches. *Vagus nerve* - The **vagus nerve (CN X)** carries **special visceral efferent fibers** that innervate muscles of the **pharynx** and **larynx** involved in swallowing and speech. - These fibers originate from the **nucleus ambiguus** and supply muscles derived from the **fourth and sixth pharyngeal arches**.

Question 1725: Traumatic optic neuropathy due to closed head trauma commonly affects which part of the optic nerve?

A. Optic canal (Correct Answer)
B. Intraocular part
C. Intracranial part
D. Optic tract

Explanation: ***Optic canal*** - The **optic nerve** is highly susceptible to injury within the **optic canal** due to its tight anatomical confines and the close proximity of the optic nerve to rigid bone. - Trauma to this region can lead to direct compression, shearing injury, or ischemia from damage to surrounding vasculature, resulting in significant visual impairment. *Intra ocular part* - The intraocular part of the optic nerve, including the **optic disc**, is typically protected by the globe and orbit against blunt trauma. - Direct intraocular trauma, such as a penetrating injury, would be required to significantly affect this segment, which is not usually the cause in closed head trauma. *Intracranial part* - The intracranial part of the optic nerve is relatively mobile within the cerebrospinal fluid and is less prone to direct compression or shearing forces from closed head trauma compared to the optic canal. - While it can be affected by diffuse axonal injury or mass effects within the cranium, it is not the most commonly affected segment for traumatic optic neuropathy in closed head injuries. *Optic tract* - The **optic tract** lies posterior to the optic chiasm and is part of the central nervous system pathways for vision, not the optic nerve itself. - Injuries to the optic tract are more likely to cause homonymous hemianopia rather than the profound unilateral vision loss characteristic of traumatic optic neuropathy, and are generally less vulnerable to direct mechanical trauma from closed head injury.

Question 1726: Pupillary reflex pathway - All of the following are a part except?

A. Edinger Westphal nucleus
B. Medial geniculate body (Correct Answer)
C. Pretectal nuclei
D. Retinal ganglion cell

Explanation: ***Medial geniculate body*** - The **medial geniculate body** is part of the **auditory pathway**, involved in processing sound information [2]. - It does not play a role in the **afferent** or **efferent** limbs of the pupillary light reflex. *Edinger Westphal nucleus* - The **Edinger-Westphal nucleus** is the **parasympathetic nucleus** of cranial nerve III (**oculomotor nerve**) [1]. - It provides preganglionic parasympathetic fibers that lead to pupillary constriction via the **ciliary ganglion** [1]. *Pretectal nuclei* - The **pretectal nuclei** receive input from the **retina** and are critical for the **afferent limb** of the pupillary light reflex [1], [3]. - They send fibers to the **Edinger-Westphal nuclei** bilaterally, mediating the direct and consensual light reflexes [1]. *Retinal ganglion cell* - **Retinal ganglion cells** are responsible for transmitting visual information from the **retina** to the brain [4]. - A subset of these cells, containing **melanopsin**, are photosensitive and specifically mediate the input for the **pupillary light reflex** [3].

Question 1727: Myelination in peripheral nervous system is done by

A. Astrocytes
B. Oligodendrocytes
C. Ependymal cells
D. Schwann cells (Correct Answer)

Explanation: ***Schwann cells*** - **Schwann cells** are glial cells found in the **peripheral nervous system (PNS)** that wrap around axons to form the myelin sheath [4]. - The **myelin sheath** insulates the axon and increases the speed of nerve impulse conduction [1]. *Astrocytes* - **Astrocytes** are star-shaped glial cells found in the **central nervous system (CNS)** [2]. - They play roles in structural support, nutrient supply, and blood-brain barrier formation, but not myelination. *Oligodendrocytes* - **Oligodendrocytes** are glial cells responsible for **myelination in the central nervous system (CNS)** [1], [3]. - Each oligodendrocyte can myelinate multiple axons or multiple segments of the same axon [3]. *Ependymal cells* - **Ependymal cells** are glial cells that line the ventricles of the brain and the central canal of the spinal cord in the **CNS**. - They are involved in the production and circulation of **cerebrospinal fluid (CSF)**.

Question 1728: 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 1729: 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 1730: 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.

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