Trigeminal Nerve (CN V)

Summary

The trigeminal nerve, also known as the 5th cranial nerve or cranial nerve 5 (CN V), has both motor and sensory functions. The nerve emerges from the brainstem at the level of the pons, and then divides into 3 branches, known as the V1, V2, and V3 divisions of the trigeminal nerve.

V1, also known as the ophthalmic nerve, provides sensory innervation to the forehead and upper eye areas in the upper 3rd of the face. It is the sensory arm of the corneal and lacrimal reflex, and nerve fibers travel through the superior orbital fissure.

V2, also known as the maxillary nerve, carries sensation from the cheek area and the middle 3rd of the face. Fibers of the maxillary nerve enter the skull through the foramen rotundum.

V3, also known as the mandibular nerve, provides sensory innervation to the jaw area and lower 3rd of the face, as well as sensation to the anterior 2/3rds of the tongue. The mandibular nerve is also responsible for motor innervation to the muscles of mastication, and therefore serves as the motor arm of the jaw jerk reflex. V3 also carries motor innervation to the tensor tympani muscle, which works to dampen loud noises. Finally, V3 fibers either enter or exit the cranium through the foramen ovale depending on nerve fiber direction.


Key Points

• Trigeminal Nerve (Cranial Nerve V)
  • Nerve Type
    • Motor
    • Sensory
  • Nerve Entry/Exit
    • Exits brainstem from pons
      • At lateral mid-pons at level of the middle cerebellar peduncle
        • May be affected by schwannomas affecting cerebellopontine angle (although CN VIII is more commonly affected)
      • Trigeminal nucleus extends from midbrain to high cervical spinal cord
  • 3 branches
    • V1 (ophthalmic)
      • Function
        • Facial sensation
          • Innervates sensation in ophthalmic distribution
      • Foramina
        • Superior orbital fissure
      • Reflexes
        • Corneal (afferent sensory carried by V1)
          • CN VII carries efferent motor
        • Lacrimal (afferent sensory carried by V1)
          • CN VII carries efferent motor
    • V2 (maxillary)
      • Function
        • Facial sensation
          • innervates sensation in maxillary distribution
      • Foramina
        • Foramen rotundum
          • Branches also pass through the inferior orbital fissure
    • V3 (mandibular)
      • Function
        • Controls muscles of mastication 
          • innervates masseter, temporalis, and lateral/medial pterygoids
          • Test with symmetrical jaw clench palpation/jaw opening against resistance
        • Tongue sensation
          • Sensation on anterior ⅔ of the tongue
          • Lingual nerve branches from V3
        • Loud noise dampening 
          • Via tensor tympani branch from V3
        • Facial sensation
          • Sensation in mandibular distribution
            • Including area around ear, most of the external auditory canal via auriculotemporal branch (Except for posterior external auditory canal, which is innervated by CN X)
            • Test with light touch with cotton swab
      • Foramina        
        • Foramen ovale
          • The meningeal (recurrent) branch also passes through the foramen spinosum to carry sympathetic fibers to the dura mater
      • Reflexes
        • Jaw jerk (afferent sensory and efferent motor carried by V3)
  • Other information
    • Trigeminal neuralgia is caused by aberrant neuronal activity in the V2 and V3 branches, leading to electric sharp pains in these distributions
      • Treated by carbamazepine