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Anatomy & Histology · patient case with 2 questions

A lesion on the side of the tongue

Patient: Male, 63 years old

Chief Complaint: “There is a rough patch on the side of my tongue.”

Background: Forty pack-year smoking history, daily alcohol. No prior oral lesions.

Findings: A 1.5 cm indurated white and red lesion on the posterior lateral border of the tongue on the left. Incisional biopsy performed under local anaesthesia. At review the patient reports altered taste and reduced sensation over the area.

Question 1

Which nerve carries TASTE from the posterior one-third of the tongue?

  1. Chorda tympani branch of the facial nerve (CN VII)
  2. Glossopharyngeal nerve (CN IX)
  3. Hypoglossal nerve (CN XII)
  4. Lingual branch of the mandibular nerve (V3)
Show answer and explanation

Correct answer: B. Glossopharyngeal nerve (CN IX)

  • A. The chorda tympani carries taste from the ANTERIOR two-thirds. It is a branch of CN VII that hitches a ride with the lingual nerve.
  • B. CORRECT. The GLOSSOPHARYNGEAL nerve carries BOTH taste and general sensation from the posterior one-third of the tongue — it is the one region where a single nerve does both jobs. This matters for a posterior lateral lesion: infiltration at its base can produce taste loss as well as numbness.
  • C. The hypoglossal nerve is purely motor to the intrinsic and most extrinsic tongue muscles, with no sensory or gustatory function.
  • D. The lingual nerve carries GENERAL sensation — touch, temperature, pain — from the anterior two-thirds, but not taste from that region; it merely conveys the chorda tympani fibres.

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Question 2

Taste and general sensation from the ANTERIOR two-thirds of the tongue are carried, respectively, by:

  1. Chorda tympani (CN VII) and lingual nerve (V3)
  2. Glossopharyngeal (CN IX) and lingual nerve (V3)
  3. Chorda tympani (CN VII) and glossopharyngeal (CN IX)
  4. Lingual nerve (V3) and chorda tympani (CN VII)
Show answer and explanation

Correct answer: A. Chorda tympani (CN VII) and lingual nerve (V3)

  • A. CORRECT. The anterior two-thirds has a split supply: TASTE travels in the CHORDA TYMPANI, a branch of the facial nerve, while GENERAL sensation travels in the LINGUAL NERVE from V3. The chorda tympani joins the lingual nerve in the infratemporal fossa, which is why a lingual nerve injury during third molar surgery can cost the patient taste as well as touch on that side.
  • B. CN IX serves the posterior third, not the anterior two-thirds.
  • C. The taste half is right, but general sensation anteriorly is the lingual nerve, not CN IX.
  • D. This reverses the two. The lingual nerve is the general sensory nerve; the chorda tympani is the taste nerve.

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