Neuroanatomy — MCQs
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Abnormal regeneration of which nerve is the cause of crocodile tears?
Which of the following nerves does not provide sensory innervation to the palate?
Which of the following muscles is supplied by the cranial part of the accessory nerve?
When a patient says "Ah" and the uvula deviates to the right, which nerve is damaged?
Schirmer's test detects abnormality of which nerve?
Which nerve is the masseteric nerve a branch of?
What is the nerve supply of the angle of the jaw?
Muscles spared by complete transection of the cranial part of the accessory nerve are:
What does right 12th cranial nerve damage lead to?
All of the following muscles are supplied by the accessory nerve except:
Neuroanatomy Indian Medical PG Practice Questions and MCQs
Question 1771: Abnormal regeneration of which nerve is the cause of crocodile tears?
- A. Facial Nerve (Correct Answer)
- B. Glossopharyngeal Nerve
- C. Mandibular Nerve (V3)
- D. Vagus Nerve (CN X)
Explanation: Facial Nerve - **Crocodile tears**, or Bogorad's syndrome, result from aberrant regeneration of the **facial nerve (CN VII)** after injury, often occurring after Bell's palsy or trauma. - During regeneration, parasympathetic secretomotor fibers that should reinnervate salivary glands mistakenly regrow to innervate the **lacrimal gland**, leading to tearing (lacrimation) during salivation or eating. - The mechanism involves misdirected regeneration of fibers from the **greater petrosal nerve** or **chorda tympani** branches of CN VII. *Mandibular Nerve (V3)* - The mandibular nerve is a branch of the **trigeminal nerve (CN V)** and is primarily responsible for motor innervation to the muscles of mastication and sensory innervation to the lower face and mouth. - Its fibers are not involved in **lacrimal gland innervation** nor does its aberrant regeneration lead to crocodile tears. *Vagus Nerve (CN X)* - The vagus nerve is responsible for extensive innervation of the **visceral organs**, including the heart, lungs, and gastrointestinal tract, and plays a role in swallowing and speech. - It does not contain fibers that innervate the **lacrimal gland** or significantly contribute to facial gland secretion. *Glossopharyngeal Nerve* - The glossopharyngeal nerve (CN IX) primarily provides **sensory innervation** to the posterior tongue and pharynx, and motor innervation to the stylopharyngeus muscle. - It also carries parasympathetic fibers to the **parotid salivary gland**, but its aberrant regeneration does not cause lacrimation with salivation.
Question 1772: Which of the following nerves does not provide sensory innervation to the palate?
- A. Glossopharyngeal nerve
- B. Maxillary division of trigeminal nerve
- C. Facial nerve
- D. Hypoglossal nerve (Correct Answer)
Explanation: ***Hypoglossal nerve*** - The **hypoglossal nerve (CN XII)** is primarily a **motor nerve** that innervates the intrinsic and extrinsic muscles of the tongue, controlling tongue movement. - It plays no role in the **sensory innervation of the palate**. *Facial nerve* - The **facial nerve (CN VII)** provides **taste sensation to the soft palate** via the **greater petrosal nerve**, which arises from the geniculate ganglion. - The greater petrosal nerve also carries **parasympathetic fibers** to the palatine glands and contributes to the sensory innervation of the palate. - While primarily known for facial muscle innervation, it also has important sensory and parasympathetic functions related to the oral cavity. *Glossopharyngeal nerve* - The **glossopharyngeal nerve (CN IX)** provides general sensation and taste to the posterior third of the tongue and contributes to the **sensory innervation of the soft palate** and pharynx. - Specifically, it innervates the soft palate's posterior aspect and the fauces. *Maxillary division of trigeminal nerve* - The **maxillary division of the trigeminal nerve (CN V2)** provides general sensory innervation to the hard and soft palates. - This is primarily carried through the **greater, lesser, and nasopalatine nerves**, which are branches of V2.
Question 1773: Which of the following muscles is supplied by the cranial part of the accessory nerve?
- A. Cricothyroid
- B. Levator veli palatini (Correct Answer)
- C. Stylopharyngeus
- D. Tensor veli palati
Explanation: ***Levator veli palatini*** - The **cranial part of the accessory nerve (CN XI)** sends fibers that join the **vagus nerve (CN X)** and are distributed via the **pharyngeal plexus** - These fibers supply the **levator veli palatini** muscle along with other pharyngeal muscles - This muscle is crucial for **elevating the soft palate** during swallowing and speech - This is the **correct answer** as it receives innervation from cranial accessory fibers via the vagus *Cricothyroid* - The **cricothyroid** muscle is supplied by the **external laryngeal nerve**, a branch of the **superior laryngeal nerve** from the vagus - It does NOT receive fibers from the cranial accessory nerve - Functions to **tense the vocal cords** and control pitch *Stylopharyngeus* - The **stylopharyngeus** muscle is uniquely innervated by the **glossopharyngeal nerve (CN IX)** - NOT supplied by the accessory nerve - Involved in **elevating the pharynx and larynx** during swallowing *Tensor veli palati* - The **tensor veli palati** muscle is innervated by the **mandibular nerve (CN V3)**, a branch of the trigeminal nerve - NOT supplied by the accessory nerve - Primary role is to **tense the soft palate** and open the eustachian tube
Question 1774: When a patient says "Ah" and the uvula deviates to the right, which nerve is damaged?
- A. Left X CN (Correct Answer)
- B. Left XII CN
- C. Right X CN
- D. Right XII CN
Explanation: ***Left X CN*** - The **vagus nerve (CN X)** innervates the muscles of the soft palate, including the **levator veli palatini**, which elevates the soft palate and uvula. - When one side of the vagus nerve is damaged, the intact side pulls the uvula towards the **healthy side** during phonation ("Ah"). Therefore, if the uvula deviates to the right, the **left vagus nerve** is paretic. *Right X CN* - If the **right vagus nerve** were damaged, the uvula would deviate to the **left side**, as the intact left vagus nerve would pull it in that direction. - This option incorrectly identifies the side of the lesion that would cause rightward deviation. *Left XII CN* - The **left hypoglossal nerve (CN XII)** primarily controls the muscles of the **tongue**, not the soft palate or uvula. - Damage to this nerve would cause deviation of the tongue, not the uvula, to the **affected side** (left). *Right XII CN* - The **right hypoglossal nerve (CN XII)** also controls the muscles of the tongue. - Damage to this nerve would cause the tongue to deviate to the **right side** upon protrusion, but would not affect uvular movement.
Question 1775: Schirmer's test detects abnormality of which nerve?
- A. Facial (Correct Answer)
- B. Oculomotor
- C. Hypoglossal
- D. Glossopharyngeal
Explanation: Facial - Schirmer's test measures **tear production**, which is primarily innervated by the **lacrimal gland** through parasympathetic fibers originating from the facial nerve (CN VII). - Abnormalities in tear production, as detected by this test, can indicate dysfunction of the facial nerve or its associated pathways. Oculomotor - The oculomotor nerve (CN III) is responsible for controlling most **extraocular muscles** and **pupillary constriction**, not tear production. - Damage to this nerve typically causes symptoms like **ptosis**, **diplopia**, and **mydriasis**. Hypoglossal - The hypoglossal nerve (CN XII) primarily controls the **movements of the tongue**. - Dysfunction of this nerve would manifest as difficulties with **speech** and **swallowing**, not tear deficiency. Glossopharyngeal - The glossopharyngeal nerve (CN IX) is involved in **taste**, **salivation**, and controlling muscles of the **pharynx**. - It does not have a direct role in lacrimal gland function or tear production.
Question 1776: Which nerve is the masseteric nerve a branch of?
- A. Buccal nerve
- B. Mandibular division of the trigeminal nerve (Correct Answer)
- C. Maxillary nerve
- D. Facial nerve
Explanation: ***Mandibular division of the trigeminal nerve*** - The **masseteric nerve** is a branch of the **anterior trunk** of the mandibular division (V3) of the trigeminal nerve. - It supplies motor innervation to the **masseter muscle**, which is one of the muscles of mastication. *Buccal nerve* - The **buccal nerve** is primarily a **sensory nerve** that provides sensation to the skin of the cheek, the buccal mucosa, and the gingiva of the mandibular molars. - While it is also a branch of the mandibular division of the trigeminal nerve, it does not directly give rise to the masseteric nerve. *Maxillary nerve* - The **maxillary nerve** (V2) is the second division of the trigeminal nerve and is **purely sensory**. - It provides sensation to the midface, upper teeth, and palate, and does not innervate muscles of mastication. *Facial nerve* - The **facial nerve** (CN VII) is responsible for motor innervation of the **muscles of facial expression**, not the muscles of mastication. - Damage to the facial nerve would affect facial movements like smiling or frowning, not chewing.
Question 1777: What is the nerve supply of the angle of the jaw?
- A. Mandibular nerve
- B. Greater auricular nerve (Correct Answer)
- C. Maxillary nerve
- D. Lesser occipital nerve
Explanation: Greater auricular nerve - The greater auricular nerve, a branch of the cervical plexus (C2, C3), supplies cutaneous sensation to the skin over the angle of the mandible, the parotid gland, and the mastoid process. - This nerve is often involved in conditions like parotid surgery or neck dissections, leading to numbness in its distribution. Mandibular nerve - The mandibular nerve (V3) provides sensory innervation to the lower teeth, chin, lower lip, and part of the cheek, and motor innervation to the muscles of mastication. - While it innervates areas close to the jaw, its primary cutaneous distribution does not include the skin directly over the angle of the jaw. Maxillary nerve - The maxillary nerve (V2) is responsible for sensory innervation to the midface, upper teeth, nasal cavity, and hard palate. - Its cutaneous distribution is primarily above the lower jaw, specifically the nose, upper lip, and cheekbone area. Lesser occipital nerve - The lesser occipital nerve, another branch of the cervical plexus (C2), primarily supplies sensation to the skin over the mastoid process and the posterosuperior aspect of the auricle. - Its innervation is mainly posterior to the ear and does not extend to the angle of the jaw.
Question 1778: Muscles spared by complete transection of the cranial part of the accessory nerve are:
- A. Cricopharyngeus
- B. Palatopharyngeus
- C. Stylopharyngeus (Correct Answer)
- D. Salpingopharyngeus
Explanation: ***Stylopharyngeus*** - The stylopharyngeus muscle is innervated by the **glossopharyngeal nerve (CN IX)**, not the cranial part of the accessory nerve. - Therefore, a complete transection of the cranial accessory nerve would spare its function. *Cricopharyngeus* - The cricopharyngeus muscle is innervated by the **pharyngeal plexus**, which receives input from the **vagus nerve (CN X)** and the cranial part of the accessory nerve. - Damage to the cranial accessory nerve would likely affect its function. *Palatopharyngeus* - The palatopharyngeus muscle is innervated by the **pharyngeal plexus**, which receives contributions from the **vagus nerve (CN X)** and the cranial part of the accessory nerve. - Its function would be compromised by a complete transection of the cranial accessory nerve. *Salpingopharyngeus* - The salpingopharyngeus muscle is innervated by the **pharyngeal plexus**, which includes fibers from the **vagus nerve (CN X)** and the cranial part of the accessory nerve. - Transection of the cranial accessory nerve would therefore affect this muscle.
Question 1779: What does right 12th cranial nerve damage lead to?
- A. Scanning speech defects
- B. Tongue deviation to left on protrusion
- C. Nasal twang to voice
- D. Tongue deviation to right on protrusion (Correct Answer)
Explanation: ***Tongue deviation to right on protrusion*** - Damage to the **right 12th cranial nerve (hypoglossal nerve)** causes weakness or paralysis of the **right genioglossus muscle**. - When the tongue is protruded, the **unopposed action of the left genioglossus muscle** pushes the tongue to the **right**, towards the side of the lesion. *Tongue deviation to left on protrusion* - This symptom would occur with damage to the **left 12th cranial nerve**, as the unopposed right genioglossus muscle would push the tongue to the left. - The **genioglossus muscle** is primarily responsible for tongue protrusion and moving the tongue to the opposite side. *Nasal twang to voice* - A **nasal twang** or **hypernasality** is typically associated with **palatal weakness**, often due to damage to the **vagus nerve (CN X)** or a **velopharyngeal insufficiency**. - The **hypoglossal nerve** (CN XII) does not directly control the muscles involved in soft palate movement or phonation in this manner. *Scanning speech defects* - **Scanning speech**, characterized by a slow, hesitant, and dysarthric pattern with abnormally long pauses, is a classic sign of **cerebellar dysfunction**. - It is not directly caused by isolated damage to the **hypoglossal nerve**, which primarily affects tongue movement and articulation.
Question 1780: All of the following muscles are supplied by the accessory nerve except:
- A. Palatopharyngeus
- B. Musculus uvulae
- C. Palatoglossus
- D. Stylopharyngeus (Correct Answer)
Explanation: ***Stylopharyngeus*** - The stylopharyngeus muscle is supplied by the **glossopharyngeal nerve (CN IX)**, making it the exception. - This muscle is responsible for **elevating the pharynx and larynx** during swallowing. - **All other options are pharyngeal muscles supplied by the vagus nerve (CN X) via the pharyngeal plexus, NOT by the accessory nerve.** *Palatopharyngeus* - The palatopharyngeus muscle is supplied by the **vagus nerve (CN X)** via the **pharyngeal plexus**. - It depresses the **soft palate** and elevates the **pharynx and larynx**. - **Note:** The accessory nerve does NOT supply pharyngeal muscles. *Palatoglossus* - The palatoglossus muscle is supplied by the **vagus nerve (CN X)** via the **pharyngeal plexus**. - It elevates the **posterior part of the tongue** and depresses the **soft palate**. - **Note:** The accessory nerve does NOT supply pharyngeal muscles. *Musculus uvulae* - The musculus uvulae is supplied by the **vagus nerve (CN X)** via the **pharyngeal plexus**. - This muscle **shortens and elevates the uvula**. - **Note:** The accessory nerve does NOT supply pharyngeal muscles. **Clinical Pearl:** The accessory nerve (CN XI) actually supplies the **sternocleidomastoid** and **trapezius** muscles, not pharyngeal muscles. The cranial part of CN XI joins the vagus but does not independently innervate pharyngeal musculature.
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