Sensory Root of Facial Nerve (Right)

Origin

The sensory root of the facial nerve, or intermediate nerve, together with the facial nerve proper, exits the pons at the ventrolateral pontomedullary junction, just ventral to the vestibulocochlear nerve.

Parasympathetic fibers of the intermediate nerve originate in the superior salivatory nucleus of the pons. Sensory fibers of the intermediate nerve have cell bodies that are located in the geniculate ganglion in the petrous temporal bone. These fibers terminate on the nucleus solitarius in the pons.

Course

From its exit from the brainstem, the intermediate nerve courses laterally to enter the facial canal of the temporal bone via the internal acoustic meatus. At the level of the geniculate ganglion, the greater petrosal nerve branches off. The remainder of the intermediate nerve continues down the facial canal before penetrating the tympanic cavity as the chorda tympani (Myckatyn & Mackinnon, 2004).

Branches

The intermediate nerve gives rise to two nerves, the greater petrosal nerve and the chorda tympani. The greater petrosal nerve conveys parasympathetic innervation to the nasal, lacrimal, and palatine glands.

The chorda tympani conveys taste sensation from the anterior two thirds of the tongue and sends parasympathetic fibers to the oral cavity to innervate the submandibular and sublingual glands.

Supplied Structures

The intermediate nerve is a mixed nerve supplying sensory and parasympathetic innervation to cavities and glands of the face.

Special visceral afferent fibers from the anterior two thirds of the tongue send taste information back towards the brainstem by way of the chorda tympani nerve.

General visceral efferent fibers of the intermediate nerve send preganglionic parasympathetic innervation to targets throughout the face.

—The greater petrosal nerve innervates the nasal, lacrimal, and palatine glands. The preganglionic parasympathetic fibers of the greater petrosal nerve synapse with postganglionic neurons in the pterygopalatine ganglion.

—The chorda tympani nerve innervates the submandibular and sublingual glands. For both, the preganglionic parasympathetic fibers of the chorda tympani run with the lingual nerve (CN V3) before synapsing with postganglionic parasympathetic neurons in the submandibular ganglion (Myckatyn and Mackinnon, 2004).

List of Clinical Correlates

—Loss of taste

—Reduced salivation

—Dry eye

—Geniculate neuralgia

References

Myckatyn, T. M. & Mackinnon, S. E. (2004) A review of facial nerve anatomy. Semin Plast Surg, 18(1), 5-12.