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Question:

A 35-year-old man comes to the office due to a painful tongue sore.  For the past 2 weeks he has had a fever and has experienced myalgias and arthralgias.  He has no known medical problems.  The patient works as a driver for a local delivery service.  He had unprotected sex with a stranger approximately 1 month ago.  Physical examination shows a rash over his trunk and cervical lymphadenopathy.  An ulcer is located on the median sulcus of the tongue and is 2 cm anterior to the foramen cecum.  Blood is drawn for an HIV test.  The pain sensation from his ulcer is most likely carried by which of the following nerves?

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Explanation:

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Acute HIV can present with rash, lymphadenopathy, fever, and painful oral ulcers on the tongue.  Innervation of the tongue is complex, as there are motor, general sensory, and gustatory (taste) components.

  1. Motor innervation of the tongue is provided by the hypoglossal nerve (cranial nerve [CN] XII) with the exception of the palatoglossus muscle, which is innervated by the vagus nerve (CN X).
  2. General sensory innervation of the tongue (including touch, pain, pressure, and temperature sensation) is provided by:
    • Anterior 2/3 of the tongue: mandibular branch of trigeminal nerve (CN V3)
    • Posterior 1/3 of the tongue: glossopharyngeal nerve (CN IX)
    • Posterior area of the tongue root: vagus nerve (CN X)
  3. Gustatory innervation (taste buds) is as follows:
    • Anterior 2/3 of the tongue: chorda tympani branch of facial nerve (CN VII)
    • Posterior 1/3 of the tongue: glossopharyngeal nerve (CN IX)
    • Posterior area of the tongue root and taste buds of the larynx and upper esophagus: vagus nerve (CN X)

Any lesion anterior to the terminal sulcus and foramen cecum, including this patient's oral ulcer, would be located on the anterior 2/3 of the tongue.  Pain from this region (as well as sensations of touch, pressure, and temperature) is transmitted by the mandibular branch of the trigeminal nerve.

(Choices A, B, and E)  The chorda tympani branch of the facial nerve (CN VII) transmits gustatory sensation from the anterior 2/3 of the tongue but not painful stimuli.  The glossopharyngeal nerve (CN IX) transmits taste, pain, temperature, and touch stimuli from the posterior 1/3 of the tongue.  The vagus nerve (CN X) innervates the far posterior area of the tongue root, transmitting both gustatory and general sensory stimuli.

(Choice D)  The maxillary division of the trigeminal nerve (CN V2) does not participate in tongue innervation.

Educational objective:
General sensation from the anterior 2/3 of the tongue is carried by the mandibular division of the trigeminal nerve.  Gustatory innervation of the anterior 2/3 of the tongue is provided by the chorda tympani branch of the facial nerve.