ABSTRACT
The facial nerve is the nerve of the second branchial arch, and as such innervates structures derived from Reichert’s cartilage (see “Embryology,” chap. 9). Five populations of fibers contribute to the facial nerve trunk (189, 190): (1) special visceral efferent fibers, which supply the striated muscles of facial expression, the stapedius muscle, the stylohyoid muscle, and the posterior belly of the digastric muscle; (2) general visceral efferent fibers (preganglionic secretory fibers) which are distributed to the lacrimal and seromucinous glands of the nasal cavity via the greater superficial petrosal nerve (see also Nervus Intermedius, p. 187) and to the submaxillary and sublingual glands through the chorda tympani nerve; (3) special sensory fibers for taste from the anterior two-thirds of the tongue through the chorda tympani nerve and from the tonsillar fossae and palate via the greater superficial petrosal nerve; (4) somatic sensory fibers supplying the external auditory canal and adjacent conchal region, as well as conveying proprioceptive information from the facial muscles; and (5) visceral afferent fibers serving the mucosa of the nose, pharynx, and palate. Three nuclei supply the fibers to the facial nerve: (1) The motor nucleus is located in the caudal aspect of the pons. Its superior part, which supplies the frontal and orbicularis oculi muscles, receives both crossed and uncrossed fibers from the precentral gyrus (motor cortex). The inferior part of the facial motor nucleus receives only homolateral, uncrossed cortical information to innervate the remainder of the facial musculature, save for the levator palpebrae superioris. The blink reflex and stapedius reflex are mediated through internuclear connections in the medulla oblongata (191). (2) The superior salivatory nucleus is situated dorsal to the motor nucleus and carries parasympathetic secretory stimuli to the submaxillary, sublingual, lacrimal, nasal, and palatine glands. (3) The nucleus of the solitary tract which is located in the medulla oblongata receives the taste, proprioceptive, and cutaneous sensory fibers of the facial nerve.
