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In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear from the middle ear. Its function is to transmit changes in pressure of sound from the air to the ossicles inside the middle ear, and thence to the oval window in the ...
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.
Within the facial canal, chorda tympani branches off the facial nerve and enters the lateral wall of the tympanic cavity within the middle ear, where it runs across the tympanic membrane (from posterior to anterior) and medial to the neck of the malleus. [3]
Pressure waves move the tympanic membrane which in turns moves the malleus, the first bone of the middle ear. The malleus articulates to incus which connects to the stapes. The footplate of the stapes connects to the oval window, the beginning of the inner ear.
The vibratory portion of the tympanic membrane (eardrum) is many times the surface area of the footplate of the stapes (the third ossicular bone which attaches to the oval window); furthermore, the shape of the articulated ossicular chain is a complex lever, the long arm being the long process of the malleus, the fulcrum being the body of the ...
The vestibular membrane and the basilar membrane develop to separate the cochlear duct from the vestibular duct and the tympanic duct, respectively. [18] Molecular regulation. Most of the genes responsible for the regulation of inner ear formation and its morphogenesis are members of the homeobox gene family such as Pax, Msx and Otx homeobox genes.
The tympanic reflex helps prevent damage to the inner ear by muffling the transmission of low frequency vibrations from the tympanic membrane to the oval window. The reflex has a response time of 40 milliseconds, not fast enough to protect the ear from sudden loud noises such as an explosion or gunshot.
The tympanic nerve then travels through the inferior tympanic canaliculus to the tympanic cavity forming the tympanic plexus. From here, the sensory axons provide innervation of the middle ear and internal surface of the tympanic membrane.