Chorda tympani
Encyclopedia
The chorda tympani is a nerve
that branches from the facial nerve
(cranial nerve VII) inside the facial canal
, just before the facial nerve exits the skull via the Stylomastoid foramen
. It serves the taste buds in the front of the tongue, runs through the middle ear
, and carries taste
messages to the brain.
The chorda tympani is part of one of three cranial nerves that are involved in taste. The taste system involves a complicated feedback
loop, with each nerve acting to inhibit the signals of other nerves. 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 other nerves.
that carries them to their destinations:
, where it runs from posterior to anterior across the tympanic membrane. It passes between the malleus
and the incus
, on the medial surface of the neck of the malleus.
The nerve continues through the petrotympanic fissure
, after which it emerges from the skull into the infratemporal fossa
. It soon combines with the larger lingual nerve
, a branch of the mandibular nerve
The fibers of the chorda tympani travel with the lingual nerve to the submandibular ganglion
.
Here, the preganglionic fibers of the chorda tympani synapse with postganglionic fibers
which go on to innervate the submandibular
and sublingual
salivary glands.
Special sensory (taste) fibers also extend from the chorda tympani to the anterior 2/3 of the tongue
via the lingual nerve.
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
that branches from the facial nerve
Facial nerve
The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...
(cranial nerve VII) inside the facial canal
Facial canal
The facial canal is a Z-shaped canal running through the temporal bone from the internal acoustic meatus to the stylomastoid foramen. In humans it is approximately 3 centimeters long, which makes it the longest human osseous canal of a nerve...
, just before the facial nerve exits the skull via the Stylomastoid foramen
Stylomastoid foramen
Between the styloid and mastoid processes of the temporal bone is the stylomastoid foramenIt is the termination of the facial canal, and transmits the facial nerve and stylomastoid artery.- Clinical Relevance :...
. It serves the taste buds in the front of the tongue, runs through the middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
, and carries taste
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....
messages to the brain.
The chorda tympani is part of one of three cranial nerves that are involved in taste. The taste system involves a complicated feedback
Feedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...
loop, with each nerve acting to inhibit the signals of other nerves. 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 other nerves.
Nerve fibers
The chorda tympani carries two types of nerve fibers from their origin with the facial nerve to the lingual nerveLingual nerve
The lingual nerve is a branch of the mandibular nerve , itself a branch of the trigeminal nerve, which supplies sensory innervation to the tongue...
that carries them to their destinations:
- Special sensory fibers providing tasteTasteTaste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....
sensation from the anterior two-thirds of the tongueTongueThe tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
. - Presynaptic parasympathetic fibers to the submandibular ganglionSubmandibular ganglionThe submandibular ganglion is part of the human autonomic nervous system. It is one of four parasympathetic ganglia of the head and neck...
, providing secretomotorSecretomotorSecretomotor refers to the capacity of a structure to induce a gland to secrete a substance .Secretomotor nerve endings are frequently contrasted with sensory neuron endings and motor nerve endings. An example of secretomotor activity can be seen with the lacrimal gland, which secretes the aqueous...
innervation to two salivary glands: the submandibular glandSubmandibular glandThe paired submandibular glands are salivary glands located beneath the floor of the mouth. In humans, they account for 70% of the salivary volume and weigh about 15 grams. Unstimulated in humans, the percentage contribution to whole saliva; ~25% Parotid, Submandibular and Sublingual ~ 67% and...
and sublingual glandSublingual glandThe sublingual glands are salivary glands in the mouth.They lie anterior to the submandibular gland under the tongue, beneath the mucous membrane of the floor of the mouth.They are drained by 8-20 excretory ducts called the ducts of Rivinus....
and to the vessels of the tongue, which when stimulated, cause a dilatation of blood vessels of the tongue.
Path
Enters the skull through the internal acoustic meatus as part of the facial nerve, then it travels through the middle earMiddle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
, where it runs from posterior to anterior across the tympanic membrane. It passes between the malleus
Malleus
The malleus or hammer is a hammer-shaped small bone or ossicle of the middle ear which connects with the incus and is attached to the inner surface of the eardrum...
and the incus
Incus
The incus or anvil is the anvil-shaped small bone or ossicle in themiddle ear. It connects the malleus to the stapes. It was first described by Alessandro Achillini of Bologna.The incus transmits sound vibrations from the malleus to the stapes....
, on the medial surface of the neck of the malleus.
The nerve continues through the petrotympanic fissure
Petrotympanic fissure
The petrotympanic fissure is a fissure in the temporal bone that runs from the temporomandibular joint to the tympanic cavity....
, after which it emerges from the skull into the infratemporal fossa
Infratemporal fossa
The infratemporal fossa is an irregularly shaped cavity, situated below and medial to the zygomatic arch.* anteriorly, by the infratemporal surface of the maxilla and the ridge which descends from its zygomatic process...
. It soon combines with the larger lingual nerve
Lingual nerve
The lingual nerve is a branch of the mandibular nerve , itself a branch of the trigeminal nerve, which supplies sensory innervation to the tongue...
, a branch of the mandibular nerve
Mandibular nerve
The mandibular nerve is the largest of the three branches of the trigeminal nerve.-Roots:It is made up of two roots:* a large sensory root proceeding from the inferior angle of the trigeminal ganglion....
The fibers of the chorda tympani travel with the lingual nerve to the submandibular ganglion
Submandibular ganglion
The submandibular ganglion is part of the human autonomic nervous system. It is one of four parasympathetic ganglia of the head and neck...
.
Here, the preganglionic fibers of the chorda tympani synapse with postganglionic fibers
Postganglionic fibers
In the autonomic nervous system, fibers from the ganglion to the effector organ are called postganglionic fibers.-Neurotransmitters:The neurotransmitters used for postganglionic fibers differ:...
which go on to innervate the submandibular
Submandibular gland
The paired submandibular glands are salivary glands located beneath the floor of the mouth. In humans, they account for 70% of the salivary volume and weigh about 15 grams. Unstimulated in humans, the percentage contribution to whole saliva; ~25% Parotid, Submandibular and Sublingual ~ 67% and...
and sublingual
Sublingual gland
The sublingual glands are salivary glands in the mouth.They lie anterior to the submandibular gland under the tongue, beneath the mucous membrane of the floor of the mouth.They are drained by 8-20 excretory ducts called the ducts of Rivinus....
salivary glands.
Special sensory (taste) fibers also extend from the chorda tympani to the anterior 2/3 of the tongue
Tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
via the lingual nerve.
External links
- Photo at Washington University