Review Question - QID 106268

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Cranial Nerves Introduction QID: 106268 (M1.NE.14.40)

QID 106268 (Type "106268" in App Search)

A 45-year-old man is brought to the emergency department after being found down in the middle of the street. Bystanders reported to the police that they had seen the man as he exited a local bar, where he was subsequently assaulted. He sustained severe facial trauma, including multiple lacerations and facial bone fractures. The man is taken to the operating room by the ENT team, who attempted to reconstruct his facial bones with multiple plates and screws. Several days later, he complains of the inability to open his mouth wide or to completely chew his food, both of which he seemed able to do prior to the surgery. Where does the affected nerve exit the skull?

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Foramen ovale

51%

248/483

Foramen rotundum

15%

73/483

Superior orbital fissue

28/483

Jugular foramen

13%

61/483

Inferior orbital fissue

36/483

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The man in the clinical vignette likely suffered an iatrogenic injury to the mandibular branch of the trigeminal nerve. CNV3 exits the skull via the foramen ovale.

The divisions of the trigeminal nerve exit the skull via the superior orbital fissue (CNV1), the foramen rotundum (CNV2), and the foramen ovale (CNV3). CNV3 is composed of both motor and sensory components, the motor of which are responsible for the muscles of mastication. Injury to CNV3 would produce symptoms as presented in the question stem.

Speiker describes the well-integrated role of CNV in mastication and its cerebellar control center. He reports that the muscles of mastication work in a coordinated fashion to mix the food bolus with saliva and propel it from the anterior oral cavity into the oropharynyx, where the involuntary swallowing reflex is triggered. The cerebellum controls output for the motor nuclei of cranial nerves V, VII and XII. The entire sequence lasts about one second.

Blumenfeld describes the ophthalmic division of CNV1 as exiting the skull via the superior orbital fissure along with CNIII, CNIV, and CNVI. The maxillary division of the trigeminal nerve exits the skull via the foramen rotundum, and the mandibular division exits via the foramen ovale.

Illustration A shows the major foramen of the skull - be sure to know which cranial nerves exit each foramen for board exams.
Illustration B shows the anatomy of the divisions of the trigeminal nerve.

Incorrect Answers:
Answer 2: The maxillary division of the trigeminal nerve exits the skull via the foramen rotundum.

Answer 3: The ophthalmic division of the trigeminal nerve exits the skull via the superior orbital fissue.

Answer 4: The glossopharnygeal (CNIX), vagus (CNX), and spinal accessory (CNXI) nerves exit the skull via the jugular foramen.

Answer 5: The zygomatic branch of the maxillary nerve transmits via the inferior orbital fissure.

ILLUSTRATIONS:

Evaluating dysphagia.

M R Spieker

Gastrointestinal
- Achalasia

M R Spieker, AFP 2000

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