Chorda tympani

Topography and fiber course

The chorda tympani is formed within the facial canal (Fallopian canal). It branches off from the main trunk after the greater petrosal nerve (n. petrosus major) and the nerve to the stapedius (n. stapedius) have separated from it.

• Exit from the skull: the nerve leaves the skull through the petrotympanic fissure (fissura petrotympanica).
• Joining the lingual nerve: in the infratemporal fossa, at the level of the upper border of the medial pterygoid muscle, the chorda tympani joins the lingual nerve (n. lingualis — a branch of the mandibular nerve from CN V).
• Further path: the fibers of the chorda run within the lingual nerve in a caudal direction. They pass superior to the submandibular salivary gland along the lateral surface of the hyoglossus muscle and weave into the lateral surface of the tongue.

Fiber composition and innervation

The chorda tympani carries two types of nerve fibers:

• Gustatory (afferent) fibers: provide taste sensitivity for the anterior 2/3 of the tongue. Receptors are located in taste buds (caliculi gustatorii). Impulses pass in transit via the lingual nerve and chorda tympani to the cell bodies of the first sensory neurons located in the geniculate ganglion (ganglion geniculi). Further along the intermediate nerve, the signal enters the brainstem to the main sensory center — the nucleus of the solitary tract (nucleus tractus solitarii). From there, the central pathway as part of the medial lemniscus (lemniscus medialis) proceeds to the thalamus and terminates in the cerebral cortex (insula and lower part of the postcentral gyrus).
• Secretomotor (parasympathetic) fibers: originate from the superior salivatory nucleus (nucleus salivatorius superior) in the brainstem. Passing through the geniculate ganglion in transit, the preganglionic fibers reach the submandibular ganglion (ganglion submandibulare) via the chorda, where they form synapses. Postganglionic fibers innervate the submandibular (glandula submandibularis) and sublingual (glandula sublingualis) salivary glands, stimulating salivation.

Clinical significance and topical diagnosis

Damage to the fibers of the chorda tympani leads to ageusia (loss of taste) on the anterior 2/3 of the tongue and decreased saliva secretion. Total loss of taste is extremely rare, as the posterior third and the root of the tongue are innervated by the glossopharyngeal (IX) and vagus (X) nerves.

The function of the chorda tympani is used for topical diagnosis of facial nerve lesions:

• Lesion proximal to the branching of the chorda (but distal to the branching of n. stapedius): causes peripheral palsy of facial expression muscles combined with impaired taste and salivation. Hearing and lacrimation remain intact.
• Lesion distal to the branching of the chorda (at the level of the stylomastoid foramen and below): presents as an isolated paresis of facial muscles. Taste and salivation are not affected.

Dysfunction of the chorda tympani can also occur due to compression of the facial nerve by a growing acoustic neuroma (tumor of CN VIII) or in idiopathic facial neuropathy (Bell's palsy), where MRI reveals pathological contrast enhancement along the course of the nerve.

Physiological experiments

In experimental physiology, the chorda tympani is used to study the autonomic nervous system. When the central end of the vagus nerve is surgically anastomosed with the chorda tympani trunk, efferent vagal fibers grow into the submandibular gland. As a result of this experiment, the dynamics of salivation begin to reflect the activity of the vagal nucleus associated with hunger and satiety.

Class and exam questions

What else to study on this topic

• Facial nerve (cranial nerve VII)
• Lingual nerve (n. lingualis)
• Submandibular ganglion (ganglion submandibulare)
• Nucleus of the solitary tract (nucleus tractus solitarii)

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.