Chapter 13: Facial Sensory and Motor Pathways & Approach to Facial Sensory and Motor Deficits: Cranial Nerves 5 & 7

TRIGEMINAL NERVE (CRANIAL NERVE 5)

The principal clinically relevant functions of the trigeminal nerve are facial somatic sensation and innervation of the muscles of mastication. The trigeminal nerve also innervates one palate muscle (tensor veli palitini) and one inner ear muscle (tensor tympani).

The trigeminal nerve supplies somatic sensation to the face, the inside of the mouth (although not taste), the sinuses, and most of the dura mater (including all supratentorial dura and the tentorium cerebelli; the rest of the posterior fossa dura mater is supplied by cranial nerve 10). The three divisions of the trigeminal nerve and the regions for which they supply sensation are:

1. Ophthalmic division (V₁): forehead, upper lid, upper half of cornea

2. Maxillary division (V₂): cheek, lower lid, lower half of cornea, roof of mouth, upper gums/teeth/lip

3. Mandibular division (V₃): lower gums/teeth/lip, lower jaw, anterior tongue

The muscles of mastication innervated by CN 5 are:

• Masseter

• Pterygoids

• Anterior belly of the digastric (the posterior belly of the digastric is innervated by 7)

• Mylohyoid (the stylohyoid is innervated by CN 7)

See Table 14–1 for a summary of the functions shared between CNs 5, 7, 9, and 10.

Trigeminal Pathways

Trigeminal Sensory Pathways

The facial sensory pathways of the trigeminal nerve are analogous to those for the body: All sensory information travels back to a ganglion, and pain and temperature sensation travel separately from other modalities (Fig. 13–1). The sensory ganglion of CN 5 is called the gasserian ganglion, which resides in Meckel’s cave (mnemonic: ganglion for cranial nerve V resides in Meckel’s cave). The gasserian ganglion receives somatosensory input from the face and transmits that information to the brainstem at the level of the pons. Distal to the gasserian ganglion, the trigeminal nerve divides into three branches: ophthalmic (V₁), maxillary (V₂), and mandibular (V₃). V₁ and V₂ pass through the cavernous sinus, whereas V₃ does not pass though the cavernous sinus. V₁ exits the skull through the superior orbital fissure, V₂ through the foramen rotundum, and V₃ through the foramen ovale.

Proximal to the gasserian ganglion, the somatosensory information from CN 5 enters the brainstem at the level of the pons. Although the point of entry of CN 5 into the brainstem is at the level of the pons (as would be expected for the 5-6-7-8 schema ...