Maxillary division
The maxillary division (CN V2) runs forward at the inferior lateral base of the cavernous sinus to enter the foramen rotundum, located just below the superior orbital fissure. Be fore entering the canal, CN V2 gives off the middle meningeal nerve, which supplies the dura of the lateral middle cranial fossa. On the anterior end of the foramen rotundum, CN V2 enters the pterygomaxillary area. This division provides sensation to the cheek as well as the lower eyelid and upper teeth and gums.
Sensory nerve CN V2 has several other branches:
Two large pterygopalatine nerves supply sensation to the nasopharynx, hard and soft palate, and portions of the nasal cavity.
The posterior alveolar nerves supply sensation to the upper gums and molars.
The zygomatic nerve enters the orbit through the inferior orbital fissure and divides into the zygomaticofacial and zygomaticotemporal nerves, which supply sensation to the lateral face.
The maxillary nerve continues anteriorly within a canal between the orbit above and the maxillary sinus below to exit through the infraorbital foramen as the in fraorbital nerve just below the inferior orbital rim. It subsequently divides into the palpebral, nasal, and labial branches.
Mandibular division
The mandibular division (CN V3) enters through the foramen ovale, lateral to the fora men lacerum and medial to the foramen spinosum (carrying the middle meningeal artery). CN V3 innervates the skin of the jaw and carries the motor division of CN V to the muscles of mastication and the neck. Motor paralysis of CN V results in contralateral deviation of the jaw when it is closed (due to weakness of the ipsilateral temporalis) and ipsilateral deviation when protruded (due to weakness in the lateral pterygoid) (Fig 1-43).
Seventh Cranial Nerve
Cranial nerve VII, the facial nerve, is responsible for movement of the facial muscles. Voluntary facial movements, along with other motor activity, originate in the precentral gyrus. White matter tracts pass through the internal capsule and cerebral peduncles along with the other corticobulbar fibers. The motoneurons destined for the upper face receive bilateral innervation, whereas the lower facial musculature receives information only from the contralateral cortex (Fig 1-44). A central or upper motor neuron CN VII palsy causes contralateral lower facial weakness, whereas a peripheral or lower motor neuron CN VII palsy causes ipsilateral upper and lower facial weakness.
The motor fibers of the CN VII nucleus originate in the tegmentum of the caudal pons, ventrolateral to the CN VI nucleus and medial to the spinal nucleus of CN V. The dorsal subnucleus receives bilateral innervation and supplies the upper face; the lateral subnucleus (contralateral innervation) supplies the lower face. The CN VII nucleus receives additional information from BG extrapyramidal connections, which are largely respon sible for involuntary blinking. Abnormal blinking, as present in BG disorders such as Par kinson disease, is probably mediated through altered inhibition of supranuclear control of the blink reflex.
Figure 1-43 The divisions of the trigeminal nerve. (Courtesy of Zoë R. Williams, MD.)
Figure 1-44 Supranuclear, nuclear, and infranuclear anatomy of the facial nerve (CN VII). A, The corticobulbar fibers travel through the internal capsule down into the medial one-third of the corticospinal tracts in the cerebral peduncles of the midbrain. The pathways for the upper one-third of facial function (brow and orbicularis muscles) run parallel to but apparently distinct from the pathways for the lower two-thirds along the pyramidal tracts. The corticobulbar fibers travel in the basis pontis; those that control the lower facial muscles decussate at the level of the pons to synapse on the contralateral CN VII nucleus. Corticobulbar fibers that control the upper facial muscles decussate to synapse on the contralateral CN VII nucleus, and some of the fibers do not cross, reaching the ipsilateral CN VII nucleus. B, CN VII is predominantly motor in function, with its nucleus located in the caudal pons. CN VII courses dorsomedially and encircles the nucleus of CN VI. After bending around the CN VI nucleus, CN VII exits the pons in the cerebellopontine angle close to CNs V, VI, and VIII. CN VIII, the motor root of CN VII, and the nervus intermedius, the sensory and parasympathetic root of CN VII, enter the inter nal auditory meatus. Sensory cells located in the geniculate ganglion continue distally as the chorda tympani nerve, which carries taste fibers. Peripheral fibers of the nervus intermedius portion of CN VII initiate salivary, lacrimal, and mucous secretions. C, After emerging from the parotid gland, CN VII innervates the muscles of facial expression via 5 peripheral branches.
(Part A reprinted from Bhatti MT, Shiffman JS, Pass AF, Tang RA. Neuro-ophthalmologic complications and manifestations of upper and lower motor neuron facial paresis. Curr Neurol Neurosci Rep. 2010;10(6):448–458, with permission from Springer. Part A illustration by Dave Peace; parts B and C illustrations by Christine Gralapp.)
The fascicles of CN VII pass dorsomedially to surround the CN VI nucleus, creating a bump on the floor of the fourth ventricle (the genu of CN VII intra-axially and the collicu lus of CN VII on the floor of the fourth ventricle). CN VII exits the ventrolateral surface of the pons along with fascicles of the nervus intermedius, which contains the facial nerve sensory fibers and the visceral efferent fibers (see the section Parasympathetic Pathways later in this chapter). The subarachnoid portion of the nerve runs anteriorly and laterally to enter the internal auditory meatus along with CN VIII.
Within the petrous bone, CN VII enters the fallopian canal and traverses 3 segments (the labyrinthine, the tympanic, and the mastoid) that run close to the semicircular canals.
CN VII has both sensory and motor functions that are subserved by the following branches in this region:
The parasympathetic fibers destined for the lacrimal gland separate from CN VII in the region of the geniculate ganglion to accompany the greater superficial petrosal nerve (Fig 1-45).
The stapedial nerve enters the pyramidal eminence to innervate the stapedius muscle.
The chorda tympani conducts parasympathetic innervation to the submaxillary gland and afferent fibers from the anterior two-thirds of the tongue. These special afferent fibers are responsible for taste in the anterior tongue and synapse in the geniculate ganglion.