Trigeminal nerve

The trigeminal nerve is the fifth cranial nerve and its primary role is relaying sensory information from the face and head, although it does provide motor control to the muscles of mastication. It is both large and complicated and has multiple brainstem nuclei (sensory and motor) as well as many interconnections with other cranial nerves. It swaps parasympathetic fibers and taste fibers somewhat haphazardly, and divides into numerous terminal branches.

Gross anatomy

Nuclei

There are three sensory and one motor nuclei. The sensory nuclei are arranged in a column which spans from the midbrain through the pons and medulla and into the upper cervical cord.

1. mesencephalic nucleus: proprioceptive fibers for muscles of the face, orbit, mastication, and tongue
2. main sensory nucleus: located in the upper pons, lateral to the motor nucleus is responsible for touch sensation for all three trigeminal divisions
3. spinal nucleus: lower pons to upper cervical cord is responsible for pain and temperature; additionally it receives afferent fibers from the glossopharyngeal nerve and vagus nerve.

The motor nucleus is located in the upper pons and gives off the smaller motor root which bypasses the trigeminal ganglion and innervates the muscles of mastication as well as mylohyoid and tensor palatini.

Intracranial component

The trigeminal nerve exits at the mid pons anteriorly, courses through the prepontine cistern (cisternal portion) to enter Meckel cave (cavernous portion) where its fibers form the trigeminal ganglion, which is also known as the Gasserian or semilunar ganglion. It then divides into three main branches known as divisions:

Ophthalmic division / nerve (V1 or Va)

Courses anteriorly in the lateral wall of the cavernous sinus inferior to trochlear nerve. Just before entering the orbit, the tentorial nerve arises and ascends to supply a large portion of the falx and supratentorial dura. The ophthalmic division then divides into 3 terminal branches before each passes through the superior orbital fissure separately:

• frontal nerve (superior orbital fissure outside the tendinous ring)
  • supraorbital nerve (supraorbital notch)
  • supratrochlear nerve (supratrochlear notch)
• lacrimal nerve (superior orbital fissure outside the tendinous ring)
• nasociliary nerve (superior orbital fissure though the tendinous ring)
  • small communicating branch to the ciliary ganglion
  • short ciliary nerves
  • long ciliary nerves
  • infratrochlear nerve
  • posterior ethmoidal nerve (posterior ethmoidal foramen)
  • anterior ethmoidal nerve (anterior ethmoidal foramen then the cribriform plate)

Maxillary division / nerve (V2 or Vb)

Courses anteriorly low in the lateral wall of the cavernous sinus inferior to trochlear nerve. Just before exiting the skull it runs along the floor of the middle cranial fossa and gives off the middle meningeal nerve which ascends to supply the anterior dura of the middle cranial fossa. It then passes through the foramen rotunda in the greater wing of the sphenoid bone to exit skull and enter the superior aspect of the pterygopalatine fossa. It gives branches to pterygopalatine ganglion but also receives parasympathetic nerves from the ganglion via the greater petrosal nerve.  It then divides into the:

• zygomatic nerve (inferior orbital fissure)
  • zygomaticotemporal nerve (zygomaticotemporal foramen)
  • zygomaticofacial nerve (zygomaticofacial foramen)
• infraorbital nerve (inferior orbital fissure then infraorbital foramen)
  • posterior superior alveolar nerve (pterygomaxillary fissure)
  • middle superior alveolar nerve
  • anterior superior alveolar nerve
• nasopalatine nerve (sphenopalatine foramen)
• posterior superior nasal nerves (sphenopalatine foramen)
• greater palatine nerve (greater palatine foramen)
  • lateral posterior inferior nasal nerve (un-named foramina)
• lesser palatine nerve (lesser palatine foramen)
• pharyngeal nerve (palatovaginal canal)

Mandibular division / nerve (V3 or Vc)

Courses inferiorly through the foramen ovale to enter the infratemporal fossa, hence does not pass through the cavernous sinus. It consists of a sensory root and a smaller motor root, the later which bypasses the trigeminal ganglion inferiorly. These roots pass through the foramen ovale separately and then unite just below the foramen. It immediately gives off nervus spinosus and nerve to medial pterygoid from the main trunk. It then descends in the infratemporal fossa passing between the tensor veli palatini and lateral pterygoid muscles before dividing into anterior and posterior divisons:

• anterior division (4 branches, all motor except one)
  • deep temporal nerves
  • lateral pterygoid nerves
  • masseteric nerve
  • buccal nerve
• posterior division (3 branches, all sensory except one)
  • auriculotemporal nerve
  • lingual nerve
  • inferior alveolar nerve
    • nerve to mylohyoid
    • incisive nerve
    • mental nerve

Related pathology

• trigeminal neuralgia
• trigeminal schwannoma