Anatomy & Histology · patient case question
Which nerve provides SENSORY innervation to the lower lip?
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: A. The mental nerve
- A. CORRECT. The MENTAL NERVE is the terminal branch of the inferior alveolar nerve, emerging from the mental foramen between the mandibular premolar apices. It divides into labial branches supplying the mucosa and skin of the lower lip and the chin. This is why a mental block anaesthetises the lower lip, and why lower lip numbness after surgery or trauma localises to the mental foramen region.
- B. The lingual nerve supplies the anterior two-thirds of the tongue, the floor of mouth and the lingual gingiva.
- C. The long buccal nerve supplies the buccal mucosa and buccal gingiva of the mandibular molars — the cheek, not the lip.
- D. The marginal mandibular branch of the facial nerve is MOTOR to the lower lip muscles. Injuring it paralyses the lip but leaves sensation intact — the distinction this case is built around.
Note: Both nerves are V3-related in a sense but they are entirely different systems: sensory lip = mental nerve from V3; motor lip = facial nerve, CN VII.
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