Trigeminal nerve

Sensory function

Sensory innervation of face and head.

Motor function

Motor innervation of the following muscles:

  • Temporal
  • Masseter
  • Medial pterygoid
  • Lateral pterygoid
  • Mylohyoid
  • Digastric (anterior belly)
  • Tensor veli palatini
  • Tensor tympani

Anatomy

1. Intra-axial segment

There are 4 trigeminal nuclei (3 sensory, 1 motor) in the brainstem.

The mesencephalic nucleus is a thin elongated nucleus from the level of the inferior colliculus to the pons, located anterior to the cerebral aqueduct and upper 4th ventricle. It receives proprioceptive afferents from teeth, temporomandibular joint and soft palate. it gives off efferents to the motor nucleus (see below) that regulate the force of bite and coordinate mastication.

The principal sensory nucleus lies lateral to the root entry zone in the caudal pons and receives afferents for tactile sensation from the face.

The motor nucleus lies anteromedial to the main sensory nucleus. It supplies efferents to the muscles of mastication (temporalis, masseter, pterygoids) as well as the mylohyoid, anterior belly of digastric and tensor tympani/veli palatini.

The spinal nucleus extends from the principal sensory nucleus in the pons to the upper cervical cord (C2-4 levels) and receives afferents mediating pain and temperature sensation from the teeth, face and head.

2. Cisternal (preganglionic) segment

Exits the lateral mid-pons ventrally. It consists of a larger sensory and a smaller motor root that course in the prepontine cistern.

It enters the middle cranial fossa and passes through the dura (porus trigeminus) to enter Meckel’s cave.

3. Intradural segment

Meckel’s cave is formed by dura lined by a fold of arachnoid and is filled with CSF. The trigeminal nerve is covered by pia in Meckel’s cave.

The trigeminal (or Gasserian or semilunar) ganglion is located at the bottom of Meckel’s cave.

4. Post-ganglionic divisions of trigeminal nerve

The ophthalmic nerve (V1) courses within the lateral wall of the cavernous sinus inferior to the trochlear nerve. It exits the skull through the superior orbital fissure. Inside the orbit it divides into three branches:

  • The frontal nerve (largest of the three) receives sensory afferents from the skin of the forehead, upper eyelids and mucosa of frontal sinus.

  • The lacrimal nerve receives sensory afferents from the conjuctiva and lacrimal gland.

  • The nasociliary nerve gives off the following branches: 1) the anterior and posterior ethmoidal nerves receive sensory afferents from the nasal mucosa, ethmoidal cells and sphenoidal sinus mucosa 2) the infratrochlear nerve receives sensory afferents from the skin of the upper eyelids and the bridge of the nose, conjuctiva and lacrimal gland. 3) The long ciliary nerves receive sensory afferents from the cornea, sclera and iris and also contain sympathetic fibers from the superior cervical ganglion. 4) sensory fibers from the ciliary ganglion that contain afferents from the cornea, iris and ciliary body.

    The maxillary nerve (V2) courses within the cavernous sinus wall, inferior to V1 and exits the skull through the foramen rotundum. It traverses the roof of the pterygopalatine fossa and runs as the infraorbital nerve in the floor of the orbit. It exits the orbit through the infraorbital foramen and supplies sensory innervation to the skin of the cheek and the upper teeth.

    The mandibular nerve (V3) exits directly from Meckel’s cave inferiorly through foramen ovale. It gives the following branches:

  • Branches to medial pterygoid, tensor tympani and tensor veli palatini muscles.

  • The lateral pterygoid nerve (motor) to the lateral pterygoid muscle.

  • The masticator nerve (motor) to masseter and temporalis muscles.

  • The mylohyoid nerve (motor) to mylohyoid and anterior belly of digastric muscles.

  • The buccal nerve (sensory) to the skin of the cheek.

  • The inferior alveolar (sensory) to the lower teeth.

  • The lingual nerve (sensory) supplies sensory innervation to the anterior 2/3 of the tongue and also carries fibers from the facial nerve which mediate taste information from the anterior 2/3 of the tongue.

  • The auriculotemporal nerve (sensory) supplies the auricle, external acoustic meatus, external side of the tympanic membrane, the skin in the temporal region and also receives some afferents from the temporomandibular joint.

Clinical implications

  • The most common symptoms in lesions of the trigeminal nerve is either facial pain or numbness.
  • Lesions affecting the motor (V3) division cause weaknes of mastication.
  • Trigeminal neuralgia is sometimes caused by neurovascular conflict between the trigeminal nerve and the superior cerebellar (SCA) or aterior inferior cerebellar (AICA) arteries.
  • Other causes of trigeminal dysfunction include compression by tumor or aneurysm, syringobulbia, stroke, trauma with fracture of the middle cranial fossa and thrombosis of the cavernous sinus.