Chorda Tympani — Course and Distribution
Overview
The chorda tympani is a branch of the facial nerve (CN VII) that travels with the mandibular nerve’s lingual branch. It carries two functional components:
- Taste from anterior 2/3 of tongue (special visceral afferent, SVA)
- Preganglionic parasympathetic to submandibular and sublingual glands (general visceral efferent, GVE)
Course
| Segment | Details |
|---|---|
| Origin | Arises from the facial nerve in the facial canal (descending part), approximately 6 mm above the stylomastoid foramen |
| Middle ear | Passes forward and upward, enters the middle ear cavity, runs across the medial surface of the tympanic membrane (between the fibrous and mucous layers) — lies medial to the handle of malleus |
| Exit from skull | Passes through the petrotympanic fissure (Glaserian fissure) to emerge on the medial surface of the spine of sphenoid |
| Infratemporal fossa | Crosses the infratemporal fossa medially, passes between the two pterygoid muscles |
| Joining lingual nerve | Joins the posterior border of the lingual nerve at an acute angle, approximately at the level of the lower border of lateral pterygoid |
| Distribution | Travels with lingual nerve to tongue and submandibular region |
Functional Distribution
| Function | Fibres | Distribution |
|---|---|---|
| Taste | SVA (from geniculate ganglion of CN VII) | Anterior 2/3 of tongue (fungiform papillae) |
| Preganglionic parasympathetic | GVE | Relay in submandibular ganglion → postganglionic to submandibular gland and sublingual gland |
Submandibular Ganglion
- Suspended from the lingual nerve by two roots
- Receives chorda tympani preganglionic fibres (via lingual nerve)
- Postganglionic fibres supply: submandibular gland (secretomotor) and sublingual gland (secretomotor)
- Sympathetic fibres from facial artery plexus pass through without relay
Pathway Summary
CN VII facial nerve (in petrous bone)
→ Chorda tympani (branches off in facial canal)
→ Crosses middle ear (over tympanic membrane)
→ Petrotympanic fissure
→ Infratemporal fossa
→ Joins lingual nerve (V3 posterior division)
→ [TASTE fibres] → anterior 2/3 tongue
→ [PARASYMPATHETIC fibres] → submandibular ganglion → submandibular + sublingual glands
Applied Anatomy
Middle Ear Surgery:
- Chorda tympani crosses the middle ear and is vulnerable during myringotomy, ossicular chain surgery, and mastoidectomy
- Injury → loss of taste on anterior 2/3 of tongue on same side + reduced salivation from submandibular and sublingual glands
Dry Mouth (Xerostomia):
- Bilateral chorda tympani damage (e.g., bilateral parotid surgery, radiation) → significant reduction in submandibular and sublingual saliva → severe dry mouth
Bell’s Palsy:
- Facial nerve oedema in the facial canal above the origin of chorda tympani → loss of taste on anterior 2/3 tongue + hyperacusis (if nerve to stapedius also involved) + facial palsy
- Helps localise the level of facial nerve lesion
Frey’s Syndrome:
- Cross-reference: aberrant regeneration of parasympathetic fibres (via auriculotemporal nerve not chorda tympani) → gustatory sweating
Mandibular Nerve | Branches of Mandibular Nerve — Posterior Division | Otic Ganglion — Relations to Mandibular Nerve