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Anatomy & Histology · patient case with 6 questions

Unilateral Facial Weakness

demo: 49-year-old male

chief: “I woke up and the right side of my face was drooping.”

history: Recent upper respiratory infection. No prior neurologic events.

meds: None

findings: Drooping of the right corner of the mouth with inability to purse the lips or retain fluid. Forehead wrinkling and eye closure are preserved on the affected side. No sensory deficit. Nerve pathway illustrated below.

Case image

Question 1

Which muscle group is responsible for the failure to purse the lips and retain fluid?

  1. Masseter
  2. Mylohyoid
  3. Orbicularis oris
  4. Medial pterygoid
Show answer and explanation

Correct answer: C. Orbicularis oris

  • A. Masseter is a muscle of mastication supplied by the mandibular division of the trigeminal nerve; it elevates the mandible.
  • B. Mylohyoid forms the floor of the mouth and is supplied by the nerve to mylohyoid, a trigeminal branch.
  • C. Correct. Orbicularis oris is the sphincter of the mouth, a muscle of facial expression innervated by the facial nerve. Its paralysis produces oral incompetence and drooling.
  • D. The medial pterygoid is likewise trigeminal and involved in mandibular movement, not lip seal.

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Question 2

Which cranial nerve is affected?

  1. Trigeminal nerve (CN V)
  2. Hypoglossal nerve (CN XII)
  3. Glossopharyngeal nerve (CN IX)
  4. Facial nerve (CN VII)
Show answer and explanation

Correct answer: D. Facial nerve (CN VII)

  • A. The trigeminal nerve is sensory to the face and motor to the muscles of mastication; a lesion would produce numbness, which is absent here.
  • B. CN XII moves the tongue; a lesion causes tongue deviation toward the affected side.
  • C. CN IX contributes to swallowing and taste from the posterior third of the tongue, not facial expression.
  • D. Correct. CN VII supplies all the muscles of facial expression. The absence of any sensory loss confirms the trigeminal nerve is intact.

Note: Preserved forehead movement and eye closure point to a central (upper motor neuron) lesion — the forehead has bilateral cortical input. Bell's palsy, a lower motor neuron lesion, paralyzes the whole half of the face including the forehead. Preserved eye closure is a red flag for stroke and warrants urgent medical referral.

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Question 3

Which muscle is innervated by the facial nerve?

  1. Anterior belly of digastric
  2. Lateral pterygoid
  3. Buccinator
  4. Temporalis
Show answer and explanation

Correct answer: C. Buccinator

  • A. The anterior belly of digastric is supplied by the nerve to mylohyoid from CN V3; the posterior belly is supplied by CN VII.
  • B. The lateral pterygoid is also CN V3.
  • C. Correct. Despite its deep position and role in keeping the food bolus on the occlusal table, buccinator is a muscle of facial expression and is supplied by the buccal branch of CN VII.
  • D. Temporalis is a muscle of mastication supplied by CN V3.

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Question 4

Through which foramen does the facial nerve exit the skull?

  1. Jugular foramen
  2. Stylomastoid foramen
  3. Internal acoustic meatus
  4. Foramen ovale
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Correct answer: B. Stylomastoid foramen

  • A. The jugular foramen transmits cranial nerves IX, X, and XI along with the internal jugular vein.
  • B. Correct. The facial nerve enters the internal acoustic meatus, traverses the facial canal, and exits at the stylomastoid foramen, after which it enters the parotid gland and divides into its five terminal branches.
  • C. The internal acoustic meatus is where the facial nerve enters the petrous temporal bone, not where it exits the skull.
  • D. Foramen ovale transmits the mandibular division of the trigeminal nerve.

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Question 5

Which nerve provides secretomotor supply to the submandibular gland, and which carries taste from the anterior two-thirds of the tongue?

  1. The greater petrosal nerve supplies the gland; the facial nerve trunk carries taste
  2. The hypoglossal nerve supplies the gland; the lingual nerve carries taste
  3. The lingual nerve carries the parasympathetic fibers to the gland; the chorda tympani carries taste
  4. The inferior alveolar nerve supplies the gland; the glossopharyngeal nerve carries taste
Show answer and explanation

Correct answer: C. The lingual nerve carries the parasympathetic fibers to the gland; the chorda tympani carries taste

  • A. The greater petrosal nerve supplies the lacrimal gland and the nasal and palatal glands, not the submandibular gland.
  • B. The hypoglossal nerve is purely motor to the tongue muscles.
  • C. Correct. The chorda tympani, a branch of CN VII, joins the lingual nerve. It carries taste from the anterior two-thirds of the tongue and preganglionic parasympathetic fibers that synapse in the submandibular ganglion to supply the submandibular and sublingual glands.
  • D. The inferior alveolar nerve is purely sensory to the mandibular teeth and lip; CN IX carries taste from the posterior third of the tongue only.

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Question 6

The patient is later diagnosed with postherpetic neuralgia. Which medication is appropriate?

  1. Amoxicillin
  2. Nystatin
  3. Gabapentin
  4. Metronidazole
Show answer and explanation

Correct answer: C. Gabapentin

  • A. Antibiotics have no role in a neuropathic pain syndrome of viral origin.
  • B. Nystatin is an antifungal with no analgesic action.
  • C. Correct. Gabapentin and pregabalin are first-line for neuropathic pain, including postherpetic neuralgia following herpes zoster involvement of the geniculate ganglion.
  • D. Metronidazole treats anaerobic and protozoal infection and is irrelevant here.

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