Trigeminal Nerve (Left)

Origin

The trigeminal nerve originates in the pons. It emerges from the lateral surface of the pons, roughly where the middle cerebellar peduncle enters the brainstem. Motor axons of the trigeminal nerve originate in the pons in the motor nucleus of the trigeminal nerve.

The sensory neurons of the trigeminal nerve have cell bodies located in the trigeminal ganglion. The nuclei targeted by these sensory axons are the pontine or main sensory nucleus of the trigeminal nerve, the mesencephalic nucleus of the trigeminal nerve, and the spinal nucleus of the trigeminal nerve.

Course

The trigeminal nerve is the largest of the cranial nerves and provides motor and sensory innervation to derivatives of the first pharyngeal arch.

The trigeminal nerve exits the pons laterally in the body of the middle cerebellar peduncle. From here, the trigeminal nerve runs anteriorly and laterally, crossing over the anterior portion of the petrous ridge of the temporal bone. Just after crossing over, and near the foramen lacerum, the trigeminal nerve runs into the trigeminal ganglion. This is located in the trigeminal impression of the temporal bone, also known as trigeminal (or Mekel’s) cave.

Branches

The trigeminal nerve has three branches. The ophthalmic nerve, also referred to as CN V1, conveys sensory innervation from the forehead and face above the eyes. The maxillary nerve, also referred to as CN V2, conveys sensory innervation from the middle of the face. The mandibular nerve, also referred to as CN V3, conveys sensory innervation from the lower face and sends motor nerves to the muscles of mastication.

Supplied Structures

The trigeminal nerve is a mixed nerve conveying sensory innervation from the face and facial cavities and sending motor innervation to the muscles of mastication. All three branches convey sensory information but only the mandibular nerve contains motor fibers. Some branches peripheral to the trigeminal nerve will transmit parasympathetic fibers, but these fibers come from other sources and are not present in the trigeminal nerve or its three divisions.

The ophthalmic nerve travels into the orbit and conveys general sensory information from the skin of the upper face, roughly from the anterior nose and upper half of the eye, superiorly to the top of the head. This nerve also conveys sensation to the cornea, the mucosa of ethmoid air cells, frontal sinus, and sphenoid sinus, and small portions of the dural folds.

The maxillary nerve travels into the pterygopalatine fossa and innervates the skin of the middle face, roughly from the lower half of the eyes down to the upper lip with its territory arcing up as it moves posteriorly. Other tissues supplied by the maxillary nerve are the maxillary teeth and gingiva, the palate, the nasal cavity, the maxillary sinus, the nasopharynx, the lower lateral nose, and portions of the cranial dura mater.

The mandibular nerve travels into the infratemporal fossa and innervates the skin of the lower face, from the lower lips down to the lower margins of the mandible. Its territory arcs posteriorly and upward, just anterior to the ear. Other tissues innervated by sensory fibers of the mandibular nerve include the mucous membrane lining the cheek, mandibular gingiva, mandibular teeth, and anterior two thirds of the tongue.

The motor fibers of the mandibular nerve innervate the muscles of mastication, including the: temporalis, masseter, medial pterygoid, and lateral pterygoid muscles. It also innervates the tensor veli palatini, tensor tympani, mylohyoid, and the posterior digastric muscles.

Although not fibers of the trigeminal nerve, many sympathetic and parasympathetic fibers will travel to their targets by joining the trigeminal nerve. Chiefly among these are the parasympathetic fibers of the oculomotor nerve, the facial nerve, and the glossopharyngeal nerve, which innervate the pupillary constrictors, the anterior tongue taste fibers, and the glands of the face, respectively.

List of Clinical Correlates

—Corneal reflex

—Trigeminal neuralgia

—Herpes zoster