The autonomic component of the facial nerve is parasympathetic and supplies a variety of glands and the smooth muscle within the walls of blood vessels.
The origin of the parasympathetic fibres is the superior salivatory nucleus which lies rostral to the pontomedullary junction in the brainstem. It receives input from the hypothalamus and the reticular formation. Preganglionic fibres pass from the superior salivatory nucleus to the geniculate ganglion within the sensory root of the facial nerve. From here, the fibres divide into three bundles.
The first bundle passes anteriorly as the greater petrosal nerve in the temporal bone before joining the sympathetic deep petrosal nerve to form the nerve of the pterygoid canal. This penetrates into the pterygoid fossa to synapse with the pterygopalatine ganglion. Postganglionic fibres from the latter site innervate glands and smooth muscle in the oral cavity, the nasal mucosa, and the tear-producing lacrimal gland.
The second branch of parasympathetic fibres passes from the geniculate ganglion laterally to join the tympanic branch of cranial nerve IX. Combined, this is the lesser petrosal nerve which travels forwards to the foramen ovale, descending through it to synapse with the otic ganglion. Postganglionic fibres leave the otic ganglion to innervate the parotid gland.
The third branch of parasympathetic fibres from the geniculate ganglion joins the facial nerve in the facial canal. Within the canal these fibres turn anteriorly to form the chorda tympani nerve which traverses the malleus ossicle before joining the lingual nerve. The lingual nerve projects forwards on the inner aspect of the mandible to synapse with the submandibular ganglion. Postganglionic fibres innervate the nearby submandibular and sublingual salivary glands.
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