Neuroanatomy — MCQs

Neuroanatomy Indian Medical PG Practice Questions and MCQs

Question 1781: Which of the following cranial nerves is a pure sensory nerve?

A. CN 3
B. CN 5
C. CN 8 (Correct Answer)
D. CN 9

Explanation: ***CN 8*** - The **vestibulocochlear nerve (CN VIII)** is a pure sensory cranial nerve responsible for **hearing** and **balance** [1]. - It consists of two main branches: the **cochlear nerve** (for hearing) and the **vestibular nerve** (for balance and spatial orientation) [1], [2]. *CN 3* - The **oculomotor nerve (CN III)** is primarily a **motor nerve**, controlling most extraocular muscles and the pupil. - It also carries **parasympathetic fibers** to the pupillary sphincter and ciliary muscles, but it is not purely sensory. *CN 5* - The **trigeminal nerve (CN V)** is a **mixed nerve**, containing both sensory and motor components. - Its sensory functions include sensation from the face, while its motor component innervates the muscles of mastication. *CN 9* - The **glossopharyngeal nerve (CN IX)** is a **mixed nerve** with diverse functions. - It carries sensory information from the posterior tongue (taste and general sensation) and pharynx, and motor fibers to the stylopharyngeus muscle, as well as parasympathetic fibers to the parotid gland.

Question 1782: Vidian nerve is also known as?

A. Nerve to pterygoid canal (Correct Answer)
B. Superior petrosal nerve
C. Greater petrosal nerve
D. Auricular branch of vagus nerve

Explanation: ***Nerve to pterygoid canal*** - The **Vidian nerve** is a collective term for the nerve fibers that pass through the **pterygoid canal**, hence its alternative name. - It is formed by the union of the **greater petrosal nerve** (parasympathetic preganglionic fibers) and the **deep petrosal nerve** (sympathetic postganglionic fibers). *Superior petrosal nerve* - This is **not a recognized anatomical structure** - there is no such nerve in standard anatomical nomenclature. - The term may be confused with the **greater petrosal nerve** or the **lesser petrosal nerve**, both of which are actual cranial nerve branches, but neither is an alternative name for the Vidian nerve. *Greater petrosal nerve* - The **greater petrosal nerve** is a component of the Vidian nerve, specifically carrying **parasympathetic fibers** from the facial nerve (CN VII). - It originates from the geniculate ganglion and is one of the two main contributors to the formation of the Vidian nerve, not the Vidian nerve itself. *Auricular branch of vagus nerve* - The **auricular branch of the vagus nerve** (Arnold's nerve) innervates the external auditory canal and part of the auricle. - It is entirely unrelated to the Vidian nerve, which is involved in salivary and lacrimal gland innervation.

Question 1783: From which structure is the deep petrosal nerve formed?

A. Facial nerve
B. Glossopharyngeal
C. Internal carotid plexus (Correct Answer)
D. Greater petrosal nerve

Explanation: ***Internal carotid plexus*** - The **deep petrosal nerve** contains **postganglionic sympathetic fibers** that arise from the **superior cervical ganglion**. - These fibers ascend along the **internal carotid artery** and form the **internal carotid plexus** (sympathetic plexus around the internal carotid). - The **deep petrosal nerve** branches directly from this **internal carotid plexus**. *Greater petrosal nerve* - The **greater petrosal nerve** is a branch of the **facial nerve (CN VII)** carrying **preganglionic parasympathetic fibers**. - It joins with the **deep petrosal nerve** to form the **nerve of the pterygoid canal (Vidian nerve)**, but it does not give rise to the deep petrosal nerve. - These are two separate nerves that converge, not a source structure. *Facial nerve* - The **facial nerve (CN VII)** is primarily involved in facial expression, taste sensation, and parasympathetic innervation. - While it gives rise to the **greater petrosal nerve** (which joins with the deep petrosal nerve), it does not directly form the **deep petrosal nerve** itself. - The deep petrosal nerve carries **sympathetic** fibers, not parasympathetic from CN VII. *Glossopharyngeal* - The **glossopharyngeal nerve (CN IX)** is involved in taste, pharyngeal sensation, and parasympathetic innervation of the parotid gland. - It has no anatomical or functional connection to the formation of the **deep petrosal nerve**.

Question 1784: Sensory afferent fibers from the fallopian tubes ascend to:

A. T 8
B. T 10 (Correct Answer)
C. L 2
D. L 4

Explanation: ***T 10*** - The **fallopian tubes** and **ovaries** share sensory innervation primarily through the **T10** and **T11** spinal segments. [2] - This is consistent with the **visceral pain** referral pattern often experienced in the periumbilical region during pain originating from these organs. [2] *T 8* - Sensory innervation to **T8** primarily covers the epigastric region, which is typically associated with organs higher in the abdomen, such as the stomach and gallbladder. [1] - Pain from the fallopian tubes is generally referred lower than the epigastrium. *L 2* - The **L2** spinal segment mainly innervates structures in the lower abdomen and upper thigh, like parts of the colon and the hip joint. [1] - This dermatomal level is too low to be the primary sensory afferent pathway for the fallopian tubes. *L 4* - **L4** sensory innervation is largely associated with the knee and medial calf regions. - It does not correspond to the visceral sensory pathways from pelvic organs like the fallopian tubes.

Question 1785: Intratemporal lesion of chorda tympani nerve results in -

A. Loss of secretomotor fibers to the submandibular salivary gland
B. Loss of taste sensations from anterior 2/3rd of tongue (Correct Answer)
C. Loss of taste sensations from posterior 1/3rd of tongue
D. Loss of taste sensations from papillae of tongue

Explanation: Loss of taste sensations from anterior 2/3rd of tongue - The chorda tympani nerve, a branch of the facial nerve (CN VII), carries special visceral afferent (taste) fibers from the anterior two-thirds of the tongue. - An intratemporal lesion of the chorda tympani will result in loss of taste sensation from the anterior two-thirds of the tongue, which is a clinically significant and easily detectable finding [1]. - The chorda tympani exits the facial canal through the petrotympanic fissure and travels through the middle ear (intratemporal course) before joining the lingual nerve. Loss of secretomotor fibers to the submandibular salivary gland - While the chorda tympani also carries parasympathetic secretomotor fibers to the submandibular and sublingual salivary glands, this function is less clinically apparent. - Although secretomotor loss does occur with an intratemporal lesion, both taste loss and secretomotor loss occur together, but the question format requires selecting the most clinically significant and testable consequence. - In standard medical examinations, taste loss from the anterior 2/3 of tongue is the classic association tested with chorda tympani lesions. Loss of taste sensations from posterior 1/3rd of tongue - Taste sensation from the posterior one-third of the tongue is carried by the glossopharyngeal nerve (CN IX), not the chorda tympani. - An intratemporal lesion of the chorda tympani would not affect this region. Loss of taste sensations from papillae of tongue - This option is too vague and non-specific. - While taste loss does affect taste papillae, this option doesn't specify which part of the tongue, making it imprecise compared to the specific anatomical distribution (anterior 2/3) affected by the chorda tympani [1].

Question 1786: Which one of the following structures is not a part of the auditory pathway?

A. Inferior colliculus
B. Medial geniculate body
C. Lateral lemniscus
D. Medial lemniscus (Correct Answer)

Explanation: ***Medial lemniscus*** - The **medial lemniscus** is a major ascending sensory pathway responsible for transmitting **fine touch, vibration, and proprioception** from the body to the cerebral cortex [2]. - It is part of the **somatosensory system** and does not play a role in auditory processing. *Lateral lemniscus* - The **lateral lemniscus** is a key ascending auditory pathway in the brainstem that transmits information from the **cochlear nuclei** to higher auditory centers [1]. - It plays a crucial role in the processing of **auditory information**, including sound localization. *Inferior colliculus* - The **inferior colliculus** is a principal nucleus in the midbrain that serves as a major integrative and relay center for virtually all **auditory information** ascending from lower brainstem nuclei [1]. - It is involved in **sound localization**, frequency discrimination, and the startle reflex. *Medial geniculate body* - The **medial geniculate body (MGB)** is the auditory nucleus of the **thalamus** that serves as a crucial relay station for auditory information between the **inferior colliculus** and the primary auditory cortex [1]. - It is involved in various aspects of auditory processing, including **sound localization** and attention.

Question 1787: The facial nerve supplies motor fibers to which of the following muscles?

A. Stapedius (Correct Answer)
B. Mylohyoid
C. Anterior belly of the digastric
D. Geniohyoid

Explanation: ***Stapedius*** - The **facial nerve (CN VII)** provides motor innervation to the **stapedius muscle**, which plays a role in dampening loud sounds by pulling the stapes away from the oval window. - Dysfunction of this innervation can lead to **hyperacusis** (increased sensitivity to sound). *Mylohyoid* - The **mylohyoid muscle** is innervated by the **nerve to mylohyoid**, which is a branch of the **inferior alveolar nerve** (a branch of the mandibular division of the trigeminal nerve, CN V3). - It forms the floor of the mouth and elevates the **hyoid bone** and tongue during swallowing and speaking. *Anterior belly of the digastric* - The **anterior belly of the digastric muscle** is innervated by the **nerve to mylohyoid**, a branch of the **inferior alveolar nerve** (CN V3). - This muscle helps in depressing the mandible and elevating the hyoid bone. *Geniohyoid* - The **geniohyoid muscle** is innervated by fibers from the **C1 spinal nerve** that travel briefly with the **hypoglossal nerve (CN XII)**. - It elevates and protracts the hyoid bone, aiding in swallowing.

Question 1788: Which nerve is responsible for supplying the posterior semicircular canal?

A. Superior vestibular nerve supplying posterior semicircular canal
B. Superior vestibular nerve supplying anterior semicircular canal
C. Inferior vestibular nerve supplying posterior semicircular canal (Correct Answer)
D. Inferior vestibular nerve supplying anterior semicircular canal

Explanation: ***Inferior vestibular nerve supplying posterior semicircular canal*** - The **inferior vestibular nerve** innervates the **posterior semicircular canal** and the saccule. - This nerve transmits information about changes in **angular acceleration** in the plane of the posterior canal and **linear acceleration** from the saccule [1]. - This is the correct answer to the question. *Superior vestibular nerve supplying posterior semicircular canal* - This is **anatomically incorrect**. - The **superior vestibular nerve** innervates the **anterior (superior) and lateral (horizontal) semicircular canals** and the utricle. - It does **not** supply the posterior semicircular canal. *Superior vestibular nerve supplying anterior semicircular canal* - While this statement is **anatomically correct**, it does not answer the question. - The question specifically asks for the nerve supplying the **posterior semicircular canal**, not the anterior canal. - The superior vestibular nerve does supply the anterior semicircular canal, but this is irrelevant to the question asked. *Inferior vestibular nerve supplying anterior semicircular canal* - This is **anatomically incorrect**. - The **inferior vestibular nerve** supplies the **posterior semicircular canal** and the saccule only. - The **anterior semicircular canal** is innervated by the **superior vestibular nerve**, not the inferior vestibular nerve.

Question 1789: A young girl presents with symptoms of nasal and palatal dryness. Which ganglion is likely affected?

A. Otic ganglion
B. Nodose ganglion
C. Submandibular ganglion
D. Pterygopalatine ganglion (Correct Answer)

Explanation: ***Pterygopalatine ganglion*** - The **pterygopalatine ganglion** is the primary source of **parasympathetic innervation** for the **nasal** and **palatal mucosa**, including their glands that produce secretions for moisture. - Damage to this ganglion would impair the secretomotor function, leading to **dryness in these regions**. *Nodose ganglion* - The **nodose ganglion** is a **sensory ganglion of the vagus nerve (CN X)**, primarily involved in visceral sensation from the thoracic and abdominal organs. - It does not directly innervate glands of the nasal or palatal mucosa, so its damage would not cause dryness in these areas. *Otic ganglion* - The **otic ganglion** provides **parasympathetic innervation** to the **parotid gland**, controlling saliva production from this gland. - Lesion to the otic ganglion would primarily affect parotid gland function, leading to symptoms like dry mouth, but not specifically nasal or palatal dryness. *Submandibular ganglion* - The **submandibular ganglion** provides **parasympathetic secretomotor innervation** to the **submandibular** and **sublingual salivary glands**. - Damage would lead to reduced saliva production from these glands, causing dry mouth, but not specifically nasal or palatal dryness.

Question 1790: In adults, the spinal cord normally ends at what level?

A. Lower border of L3
B. Lower border of S1
C. Lower border of L5
D. Lower border of L1 (Correct Answer)

Explanation: ***Lower border of L1*** - In adults, the **spinal cord** typically terminates at the level of the **L1 vertebral body**, or specifically, its lower border [1]. - This marks the anatomical transition from the solid spinal cord to the **conus medullaris**, which then continues as the **cauda equina** [1]. *Lower border of L3* - While the spinal cord in **newborns** can extend as low as L3, it retracts with growth, and this level is incorrect for adults. - An adult spinal cord ending at L3 would be considered an **abnormal finding**, potentially indicating a **tethered cord syndrome**. *Lower border of S1* - The spinal cord never extends to the S1 level in healthy individuals, even in newborns. - The **sacrum (S1-S5)** is well below the normal termination point of the spinal cord. *Lower border of L5* - The spinal cord typically terminates well above L5 in adults. - The **cauda equina**, not the spinal cord itself, extends through the lumbar and sacral regions to L5 and beyond.

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