| Chorda tympani | |
|---|---|
 The right tympanic membrane with the malleus and the chorda tympani, viewed from within the tympanic cavity (medial). | |
| Details | |
| From | Facial nerve |
| Innervates | Taste (anterior 2/3 of tongue)Sublingual gland |
| Identifiers | |
| Latin | nervus chorda tympani |
| MeSH | D002814 |
| TA98 | A14.2.01.084 A14.2.01.118 |
| TA2 | 6292 |
| FMA | 53228 |
| Anatomical terms of neuroanatomy | |
Chorda tympani is a branch of thefacial nerve that carriesgustatory (taste) sensory innervation from the front of the tongue andparasympathetic (secretomotor) innervation to thesubmandibular andsublingualsalivary glands.[1]
Chorda tympani has a complex course from thebrainstem, through thetemporal bone andmiddle ear, into theinfratemporal fossa, and ending in theoral cavity.[2]
Chorda tympani fibers emerge from thepons of thebrainstem as part of theintermediate nerve of thefacial nerve. The facial nerve exits thecranial cavity through theinternal acoustic meatus and enters thefacial canal. In the facial canal, the chorda tympani branches off thefacial nerve and enters the lateral wall of thetympanic cavity inside themiddle ear where it runs across thetympanic membrane (from posterior to anterior) and medial to theneck of the malleus.[3]
The chorda then exits the skull by descending through thepetrotympanic fissure into theinfratemporal fossa just lateral to thestyloid bone. Here it joins thelingual nerve, a branch of themandibular nerve (CN V3). Traveling with thelingual nerve, the fibers of chorda tympani enter thesublingual space to reach theanterior 2/3 of the tongue andsubmandibular ganglion.[4]
The chorda tympani carries two types of nerve fibers from their origin from the facial nerve to thelingual nerve that carries them to their destinations:
The chorda tympani is one of three cranial nerves that are involved intaste. The taste system involves a complicatedfeedback loop, with each nerve acting to inhibit the signals of other nerves.
There are similarities between the tastes the chorda tympani picks up in sweeteners between mice andprimates, but not rats. Relating research results to humans is therefore not always consistent.[5]Sodium chloride is detected and recognized most by the chorda tympani nerve.[5] The recognition and responses to sodium chloride in the chorda tympani is mediated byamiloride-sensitive sodium channels.[6] The chorda tympani has a relatively low response toquinine and varied responses tohydrochloride. The chorda tympani is less responsive tosucrose than is thegreater petrosal nerve.[7]
The chorda tympani nerve carries its information to thenucleus of solitary tract, and shares this area with thegreater petrosal,glossopharyngeal, andvagus nerves.[8] When the greater petrosal and glossopharyngeal nerves are cut, regardless of age, the chorda tympani nerve takes over the space in the terminal field. This takeover of space by the chorda tympani is believed to be the nerve reverting to its original state before competition and pruning.[9] The chorda tympani, as part of theperipheral nervous system, is not as plastic in early ages. In a study done by Hosley et al. and a study done by Sollars, it has been shown that when the nerve is cut at a young age, the relatedtaste buds are not likely to grow back to full strength.[10][11] In a bilateral transection of the chorda tympani in mice, the preference for sodium chloride increases compared to before the transection. Also avoidance of higher concentrations of sodium chloride is eliminated.[5] The amiloride-sensitive channels responsible for salt recognition and response is functional in adult rats but not neonatal rats. This explains part of the change in preference of sodium chloride after a chorda tympani transection.[6]The chorda tympani innervates thefungiform papillae on the tongue.[11] According to a study done by Sollars et al. in 2002, when the chorda tympani has been transected early in postnatal development some of the fungiform papillae undergo a structural change to become more "filiform-like".[12] When some of the other papillae grow back, they do so without a pore.[11]
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Injury to the chorda tympani nerve leads to loss or distortion of taste from anterior 2/3 oftongue.[13] However, taste from the posterior 1/3 of tongue (supplied by the glossopharyngeal nerve) remains intact.
The chorda tympani appears to exert a particularly strong inhibitory influence on other taste nerves, as well as on pain fibers in the tongue. When the chorda tympani is damaged, its inhibitory function is disrupted, leading to less inhibited activity in the othernerves.[citation needed]
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