Corpus: Chorda tympani

The chorda tympani is a mixed nerve branch of the facial nerve (cranial nerve VII) that leaves the nerve in the facial canal and then travels to the tympanic cavity.

The chorda tympani branches off from the facial nerve just before the latter exits the cranial cavity through the stylomastoid foramen. Initially, the chorda passes through the tympanic cavity crossing the upper part of the tympanic membrane from posterior to anterior and passing between the malleus and incus bones.

The nerve then travels through the petrotympanic fissure and emerges in the infratemporal fossa, outside the skull. Here, it joins the lingual nerve and travels with it to the submandibular ganglion. In this ganglion, the preganglionic parasympathetic fibers of the chorda tympani connect to postganglionic neurons, which then innervate the submandibular and sublingual glands. The sensory fibers of the chorda tympani continue with the lingual nerve into the tongue, providing sensation to the anterior two-thirds of the tongue without synapsing in the submandibular ganglion.

The chorda tympani contains preganglionic parasympathetic fibers and sensory fibres.

3.1. Parasympathetic fibres

The preganglionic parasympathetic fibers originate from nerve cells in the superior salivatory nucleus. After synapsing in the submandibular ganglion, these fibers innervate the submandibular and sublingual glands, providing general visceromotor control.

3.2. Sensory fibres

The sensory nerve fibers originate from pseudounipolar nerve cells located in the geniculate ganglion. These fibers supply the anterior two-thirds of the tongue, primarily conveying taste sensation. The sensory afferents terminate in the solitary nucleus of the brainstem.

Unilateral damage to the chorda tympani results in a loss of taste sensation on the affected side in the anterior two-thirds of the tongue. Bilateral damage, which is rare, leads to loss of taste in the anterior two-thirds of the tongue. However, complete ageusia does not occur, as the posterior third of the tongue receives sensory innervation from the glossopharyngeal nerve.