The tympanic nerve ( Jacobson's nerve) is a branch of the glossopharyngeal nerve passing through the petrous part of the temporal bone to reach the middle ear. It provides sensory innervation for the middle ear, the Eustachian tube, the parotid gland, and mastoid cells. It also carries parasympathetic fibers destined for the parotid gland.
Structure
The tympanic nerve contains sensory axons to the
middle ear (including the internal surface of the
Eardrum) whose cell bodies are lodged in the superior ganglion of the glossopharyngeal nerve.
It also contains parasympathetic axons which continue as the lesser petrosal nerve to the otic ganglion, which itself gives off postganglionic parasympathetic neurons.
Origin
The tympanic nerve arises from the inferior ganglion of the glossopharyngeal nerve (CN IX)
in the
jugular fossa.
Course
It passes through the petrous part of the temporal bone within the tympanic canaliculus that is situated within the bony ridge separating the
carotid canal and the
jugular foramen to reach the
middle ear.
In the tympanic cavity of the middle ear, it ramifies upon the promontory of tympanic cavity to form the tympanic plexus.
Distribution
Sensory
The tympanic nerve provides sensation to the
middle ear (
tympanic cavity).
This includes the internal surface of the
Eardrum. It also supplies the
Eustachian tube, the
parotid gland, and
Mastoid cells.
Parasympathetic autonomic
The tympanic nerve is also the parasympathetic root of the
otic ganglion.
These neurons then provide secretomotor innervation of the
parotid gland via the auriculotemporal nerve.
It is involved in the salivatory reflex to increase
salivation during
chewing.
Variation
The tympanic nerve usually arises from the inferior ganglion of the glossopharyngeal nerve. Rarely, it may arise from a higher part.
Rarely, it may provide no parasympathetic fibres to the otic ganglion.
Clinical significance
The tympanic nerve is involved in a reflex, where stimulation of the
ear canal increases
salivation.
Cancer
The tympanic nerve may be involved by
paraganglioma, in this location referred to as a glomus tympanicum tumour.
This causes a soft mass in the
middle ear (
tympanic cavity).
There may also be pulsatile tinnitus,
hearing loss or
hearing problems, and some cardiac abnormalities.
History
The tympanic nerve is also known as the nerve of Jacobson, or Jacobson's nerve.
== Additional images ==
and superior cervical ganglia.]]
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