The intermediate portion of the facial nerve (also called the intermediate nerve) is a part of the seventh cranial nerve within the facial canal, which carries parasympathetic fibers and sensory (somatic and special) fibers. Therefore, the intermediate nerve is a mixed nerve.

The nerve arises from the facial nerve at the first turn of the facial canal, where the intermediate nerve has its sensory ganglion called the geniculate ganglion.

The sensory fibers arise from pseudounipolar neurons located in the geniculate ganglion. The dendrites of these neurons transmit taste information from the anterior two-thirds of the tongue. The axons of these pseudounipolar neurons travel via the facial nerve to reach the solitary tract nucleus located in the rhomboid fossa below the striae medullares. This nucleus is shared together with the glossopharyngeal nerve (CN IX) and vagus nerve (CN X).

Besides the solitary tract nucleus, this nerve has one more called the superior salivatory nucleus. It is a parasympathetic nucleus located in the rhomboid fossa above the striae medullares, and it innervates the submandibular gland and sublingual gland.

The intermediate nerve divides into two branches right after forming the geniculate ganglion. These branches are:

Greater petrosal nerve - parasympathetic
Chorda tympani - parasympathetic and sensory

Greater petrosal nerve

The greater petrosal nerve carries parasympathetic preganglionic fibers and leaves the facial canal through the hiatus for the greater petrosal nerve.

When reaching the geniculate body, the greater petrosal nerve breaks away and travels anterolaterally to exit the superior surface of the temporal bone through the hiatus for the greater petrosal nerve. The nerve emerges on the anterior surface of the petrous part of the temporal bone and crosses it, going in the anteromedial direction. It goes slightly inferior and passes under the trigeminal cave (a pouch created by the dura mater) towards the foramen lacerum. Then it penetrates the cartilage of the foramen and reaches the external cranial base. In the foramen lacerum, it joins the deep petrosal nerve from the carotid sympathetic plexus, forming the Vidian nerve (nerve of the pterygoid canal).

This nerve innervates the lacrimal gland and the glands and mucous membrane of the nasal cavity and the palate.

The fibers of the greater petrosal nerve originate from the lower part of the pons. The nerve contains not only preganglionic parasympathetic fibers but sympathetic fibers as well. The parasympathetic fibers exit the brainstem as a part of a separate division of the facial nerve known as the intermediate nerve.

Chorda tympani

The chorda tympani is a branch of the facial nerve carrying sensory and parasympathetic preganglionic fibers. It travels almost the entire length of the facial canal and leaves the canal at its descending end part through the canaliculus for chorda tympani, entering the tympanic cavity. In the tympanic cavity, it goes between the malleus and incus. Then the nerve leaves the tympanic cavity, emerging on the external cranial base via the petrotympanic fissure, reaches the infratemporal fossa, and medial to the lateral pterygoid muscle it merges with the lingual nerve (a branch of the mandibular division of the trigeminal nerve (CN V3).

While going together with the lingual nerve, the fibers of the chorda tympani is distributed to the anterior two-thirds of the sides and dorsum of the tongue and these fibers supply fungiform papillae and foliate papillae.

The sensory fibers (afferent special - gustatory) of the chorda tympani transmit taste sensations from the lingual papillae of the anterior two-thirds of the tongue via the lingual nerve, while the efferent parasympathetic preganglionic fibers synapse in the submandibular ganglion to provide secretomotor innervation to the submandibular gland and sublingual gland.

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Intermediate portion of facial nerve