At the geniculate ganglion the facial nerve [VII] turns and gives off the greater petrosal nerve, which carries mainly preganglionic parasympathetic (GVE) fibers (Table 8.6).
The facial nerve [VII] continues along the bony canal, giving off the nerve to the stapedius and the chorda tympani, before exiting the skull through the stylomastoid foramen.
The chorda tympani carries taste (SA) fibers from the anterior two-thirds of the tongue and preganglionic parasympathetic (GVE) fibers destined for the submandibular ganglion (Table 8.6).
The vestibulocochlear nerve [VIII] carries SA fibers for hearing and balance, and consists of two divisions: a vestibular component for balance, and a cochlear component for hearing.
The vestibulocochlear nerve [VIII] attaches to the lateral surface of the brainstem, between the pons and medulla, after emerging from the internal acoustic meatus and crossing the posterior cranial fossa (Figs. 8.53 and 8.54). The two divisions combine into the single nerve seen in the posterior cranial fossa within the substance of the petrous part of the temporal bone.
The glossopharyngeal nerve [IX] carries GVA, GSA, SA, GVE, and BE fibers:
The GVA fibers provide sensory input from the carotid body and sinus.
The GSA fibers provide sensory input from the posterior one-third of the tongue, palatine tonsils, oropharynx, and mucosa of the middle ear, pharyngotympanic tube, and mastoid air cells.
The SA fibers are for taste from the posterior one-third of the tongue.
The GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate secretomotor activity in the parotid salivary gland.
The BE fibers innervate the muscle derived from the third pharyngeal arch (the stylopharyngeus muscle).
The glossopharyngeal nerve [IX] arises as several rootlets on the anterolateral surface of the upper medulla oblongata (Fig. 8.54). The rootlets cross the posterior cranial fossa and enter the jugular foramen (Fig. 8.53). Within the jugular foramen, and before exiting from it, the rootlets merge to form the glossopharyngeal nerve.
Within or immediately outside the jugular foramen are two ganglia (the superior and inferior ganglia), which contain the cell bodies of the sensory neurons in the glossopharyngeal nerve [IX].
Branching from the glossopharyngeal nerve [IX] either within or immediately outside the jugular foramen is the tympanic nerve. This branch reenters the temporal bone, enters the middle ear cavity, and participates in the formation of the tympanic plexus. Within the middle ear cavity it provides sensory innervation to the mucosa of the cavity, pharyngotympanic tube, and mastoid air cells.
The tympanic nerve also contributes GVE fibers, which leave the tympanic plexus in the lesser petrosal nerve—a small nerve that exits the temporal bone, enters the middle cranial fossa, and descends through the foramen ovale to exit the cranial cavity carrying preganglionic parasympathetic fibers to the otic ganglion (Table 8.6).
The vagus nerve [X] carries GSA, GVA, SA, GVE, and
BE fibers:
The GSA fibers provide sensory input from the larynx, laryngopharynx, deeper parts of the auricle, part of the external acoustic meatus, and the dura mater in the posterior cranial fossa.
The GVA fibers provide sensory input from the aortic body chemoreceptors and aortic arch baroreceptors, and the esophagus, bronchi, lungs, heart, and abdominal viscera in the foregut and midgut.