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Trigeminal Nerve Anatomy

Gross Anatomy

The trigeminal nerve is the largest and most complex of the 12 cranial nerves (CNs). It supplies sensations to the face, mucous membranes, and other structures of the head. It is the motor nerve for the muscles of mastication and contains proprioceptive fibers. It exits the brain by a large sensory root and a smaller motor root coming out of the pons at its junction with the middle cerebral peduncle. It passes laterally to join the gasserian (semilunar) ganglion in the Meckel cave. (See the image below.)

Schematic representation of the trigeminal nerve w

Schematic representation of the trigeminal nerve with its central connections.

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Nuclei

The sensory nucleus, located in the pons, is quite extensive. It receives ordinary sensations from the main 3 branches of the trigeminal. The ophthalmic division is in the lower part of the nucleus, and the mandibular branch is in the upper part. The large rostral head is the main sensory nucleus. The caudal tapered part is the spinal tract, which is continuous with substantia gelatinosa of Rolando in the spinal cord. The spinal tract is the sensory nucleus, primarily for pain and temperature. The main sensory nucleus serves mostly for discrimination sense.

The motor nucleus is ventromedial to the sensory nucleus. It lies near the lateral angle of the fourth ventricle in the rostral part of the pons. The mesencephalic nucleus is in the midbrain and receives proprioceptive fibers from all muscles of mastication.

Connections

The main sensory nucleus receives its afferents (as the sensory root) from the semilunar ganglion through the lateral part of the pons ventral surface. Its axons cross to the other side, ascending to the thalamic nuclei to relay in the postcentral cerebral cortex. The descending sensory fibers from the semilunar ganglion course through the pons and medulla in the spinal tract of CN V to end in the nuclei of this tract (as far as the second cervical segment). (See tables 1 and 2, below.)

The axons of these nuclei cross to the opposite side, ascending in the spinothalamic tract, to relay in the thalamic nuclei; from there, they end in the cerebral cortex. The sensory nucleus of CN V is connected to other motor nuclei of the pons and medulla. In addition, the descending sensory spinal tract receives somatic sensory fibers from CNs VII, IX, and X.

The proprioceptive fibers of CN V arise from the muscles of mastication and the extraocular muscles. They terminate in the mesencephalic nucleus. This nucleus has connections to the motor nucleus of CN V.

The motor nucleus of CN V receives cortical fibers for voluntary control of the muscles of mastication. These fibers are mostly crossed. It also receives input from the mesencephalic and sensory nuclei. The axons emerge anterior to the sensory root from the lateral surface of the pons. This motor root joins the semilunar ganglion together with the sensory root.

The semilunar (gasserian or trigeminal) ganglion is the great sensory ganglion of CN V. It contains the sensory cell bodies of the 3 branches of the trigeminal nerve (the ophthalmic, mandibular, and maxillary divisions). The ophthalmic and maxillary nerves are purely sensory. The mandibular nerve has sensory and motor functions.

The gasserian ganglion lies in a depression on the petrous apex, within a dural fold called the Meckel cave. The sensory roots of the 3 branches of CN V are received anteriorly. They then pass from the posterior aspect of the ganglion to the pons. The motor root passes under the ganglion to join the sensory division of the mandibular nerve and exits the skull through foramen ovale. The carotid plexus contributes sympathetic fibers to the gasserian ganglion.

Burkett et al successfully visualized trigeminal fibers entering the pons at the nerve root entry zone (NREZ) and descending through the spinal trigeminal tract using robust diffusion-tensor imaging (DTI). Such protocols contribute to our understanding of the anatomical distribution within the brainstem and is a potentially new neurosurgical planning tool.

Table 1. Summary of the Components, Function, Central Connections, Cell Bodies, and Peripheral Distribution of CN V. (Open Table in a new window)

Components

Function

Central connection

Cell bodies

Peripheral distribution

Afferent general somatic

General sensibility

Sensory nucleus V

Gasserian ganglion

Sensory branches of the ophthalmic, maxillary, and mandibular nerves to skin, mucous membranes of the face and head

Efferent special visceral

Mastication

Motor nucleus V

Motor nucleus V

Branches to temporalis, masseter, pterygoids, mylohyoid, tensor tympani, and palati

Afferent proprioceptive

Muscular sensibility

Mesencephalic nucleus V

Mesencephalic nucleus V

Sensory endings in muscles of mastication

Table 2. Summary of the Types of Fibers, Function, and Pathways of the Trigeminal Nerve. (Open Table in a new window)

Type

Function

Pathway

Branchial motor

Motor to muscles of mastication

CN V innervates the muscles of mastication, mylohyoid, tensor tympani, tensor veli palate, anterior belly of digastric

General sensory

Sensory from surface of head and neck, sinuses, meninges and TM

The Gasserian ganglion receives the ophthalmic, maxillary and mandibular divisions of CN V and sympathetic fibers from the carotid plexus and sends branches to the dura. The four accessory ganglia are anatomically but not functionally associated with CN V

 

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