The ninth cranial nerve supplies sensory fibers for the middle ear, areas of the tongue and of the pharynx, and motor fibers for the muscles of the pharynx. It contains motor, visceromotor (parasympathetic), viscero-sensory, and taste fibers. It emerges from the medulla oblongata behind the olive right above the vagus nerve and leaves the skull together with the vagus nerve through the jugular foramen (B1). In the foramen, it forms the superior ganglion (B2) and, after passing through it, the larger inferior gan-glion (petrosal ganglion) (B3). Laterally tothe internal carotid artery and the pharynx, it forms an arch to the root of the tongue where it ramifies into several terminal branches.
The motor fibers (AB4) originate from the cranial part of the ambiguous nucleus (AB5), whilethe visceroefferentfibers(secretory fibers) (AB6) originate from the inferior salivatory nucleus (AB7). The cellsof the viscerosensory fibers (AB8) and the tastefibers (AB9) lie in theinferior ganglionanddescend in the solitary tract (B10) to termi-nate at specific levels of the solitary nu-cleus (AB11).
The first branch, the tympanic nerve (B12), originates from the inferior ganglion with viscerosensory and preganglionic secretory fibers in the petrosal fossula. It runs through the tympanic canaliculus into the tympaniccavity, where it receives fibers from theplexus of the internal carotid artery via the caroticotympanic nerve and forms thetym-panic plexus. It supplies sensory fibers to themucosa of tympanic cavity and auditory(eustachian) tube (C). The secretory fibersrun as lesser petrosal nerve to the otic gan-glion.
Apart from connections with the vagus nerve, facial nerve, and sympathetic nervous system, the inferior ganglion gives off the (viscerosensory) branch of the carotidsinus (B13), which descends to the bifurca-tion of the common carotid artery and ter-minates in the wall of the carotid sinus (B14) and in the carotid glomus (B15) .
The nerve transmits impulses of the mechanoreceptors of the sinus and the chemoreceptors of the glomus to themedulla oblongata and via collaterals to the posterior nucleus of the vagus nerve (affer-ent limb of the sinus reflex). Preganglionic fibers run from the vagal nucleus to groups of neurons in the cardiac atria, the axons of which (postganglionic parasympathetic fibers) terminate at the sinoatrial node and the atrioventricular node (efferent limb of the sinus reflex). This system registers and regulates the blood pressure and heart rate.
The nerve also gives off the pharyngealbranches (B16); together with the part of thevagus nerve, they form the pharyngeal plexus and participate in the sensory (E) and motor supply of the pharynx. A motor branch, the stylopharyngeal branch (B17), in-nervates the stylopharyngeal muscle, while some sensory tonsillar branches (D18) extend to the tonsils and the soft palate. The nerve divides below the tonsils into the lingualbranches (D19), which supply the posteriorthird of the tongue including the vallate papillae with sensory as well as taste fibers (D20).