Anatomy & Histology · patient case question
The nerve providing MOTOR innervation to the lower lip passes through which structure?
Patient case: Persistent lower lip lesion
Patient: Female, 44 years old
Chief complaint: “There's a small lump on my lower lip that hasn't gone away.”
History: Reports occasional hoarseness of the voice over the past two months. No systemic disease.
Findings: A small, firm, well-defined nodule on the labial mucosa of the lower lip, present for more than five months and unchanged in size.
Show answer and explanation
Correct answer: D. The parotid gland
- A. The infratemporal fossa contains V3, the maxillary artery, the pterygoid muscles and the pterygoid venous plexus. The facial nerve does not traverse it.
- B. The submandibular gland lies below the mandible near the marginal mandibular branch, which is why the nerve is at risk during submandibular surgery, but the nerve passes SUPERFICIAL to the gland rather than through it.
- C. The pterygomaxillary fissure transmits the maxillary artery and the maxillary division of the trigeminal nerve into the pterygopalatine fossa. It is a V2 route, not a facial nerve one.
- D. CORRECT. Motor supply to the lower lip comes from the MARGINAL MANDIBULAR branch of the facial nerve. The facial nerve exits the skull at the stylomastoid foramen, enters the PAROTID GLAND, and divides within it into its five terminal branches — temporal, zygomatic, buccal, marginal mandibular and cervical. The marginal mandibular branch then runs forward, often below the inferior border of the mandible, to reach depressor anguli oris, depressor labii inferioris and mentalis.
Note: Surgical relevance: the marginal mandibular branch is the most frequently injured facial nerve branch in submandibular and neck procedures. Injury produces an asymmetric smile with the lower lip failing to depress — without any loss of sensation.
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