The structure of the auditory analyzer
A modern understanding of the activity of analyzers makes it possible to distinguish three main links of the auditory analyzer:
1) peripheral receptor apparatus - snail with Corti's organ;
2) conducting paths and centers of the cochlear system, including subcortical formations;
3) cortical end of the analyzer.
Peripheral organ of hearing .The auditory organ is divided into two parts: 1) the sound-conducting device - the outer and middle ear and 2) the sound-receiving apparatus - the inner ear.
The outer ear of is represented by the auricle and the auditory passageway, which is separated from the middle ear by a thin dense tendinous eardrum. The middle ear is made up of the tympanum, the eustachian tube and the cells of the mastoid process. The drum cavity is filled with air: pressure equalization in the tympanic cavity occurs through the eustachian tube connecting it with the nasopharyngeal cavity.
On the inner bone wall of the tympanic cavity there are two small holes connecting the middle ear to the inner one: a round window closed by an elastic membrane( m. Secundaris), and an oval window into which a subcutaneous plate of the stapes is inserted.
In the tympanic cavity there is a system of ossicles( a hammer, an anvil and stapes), which are connected with the tympanic membrane and the membrane that closes the window into the labyrinth. The air wave, reaching through the ear canal of the tympanic membrane, leads to its oscillation, and further along the system of ossicles these oscillations are transmitted to the environments of the inner ear.
In the transmission of sound vibrations play the role of the muscles of the tympanum, toning the system of auditory ossicles( m. Stapedius) and tightening the eardrum( M. tensortympani).
The inner ear is located deep in the rocky part of the temporal bone. There are complex bone formations in which the peripheral apparatus of the vestibular and cochlear analyzers are located.
Innervation of all ear formations is carried out due to V, IX and X nerves.
The outer surface of the shell and the initial part of the auditory canal are innervated by n.auricularis from plexus cervicalis. The anterior sections of the auricle and the anterior wall of the external auditory meatus receive twigs n.auriculo-temporalis from n.mandibularis of the third branch of the trigeminal nerve.
In the innervation of the external auditory canal, ramus auricularis n also participates.vagi, which departs from the vagus nerve below the gangl.jugulare, then goes to the fallopian canal and, entering it, goes along with the facial nerve to the exit from the skull: after that it rises up to the ear canal, where the back wall and the eardrum innervate. Availability of endings n.vagi in this area explains the cough reflex when irritating the wall of the ear canal.
Musculature of the auricle receives twigs from n.auricularis posterior, which departs from the facial nerve after exiting it from the ankle-mastoid aperture.
The tympanic membrane has a rich innervation system. As already mentioned, the n branches are suitable to the bottom.auricularis n.vagi and twigs n.auriculo-temporalis from the third branch of the trigeminal nerve;the upper part of the tympanic membrane is innervated by a branch from n.glossopharyngei.
In the middle ear area, the n-branches branch out.facialis and n.glossopharyngeus. The mucosa of the tympanic cavity and the Eustachian tube are innervated by n.tympanicus( from the system n. glossopharyngeus).
The glossopharyngeal nerve, leaving the medulla oblongata, together with n.vagus falls through the foramen jugulare on the surface of the skull and forms two nodes - gangl.superius and gangl.petrosum( the latter lies on the lower edge of the pyramid of the temporal bone).Hence the linguopharyngeal nerve is directed to the tongue and gives n.tympanicus( n. Jacobsoni);branched in the middle ear.
Other than n.tympanicus( from the system. glossopharyngei), in the formation of the plexus tympanicus the branches of n participate.trigemini, which enter the tympanum through n.petrosus superficialis minor from gangl.oticum and sympathetic fibers from the plexus of the carotid artery.
In the tympanic cavity there are also branches from the facial nerve system;Passing near eminentia pyramidalis, gives a branch( n. stapedius), which exits from the bone canal to m.stapedius. Below in the vertical segment from the facial nerve leaves the chorda tympani, penetrating through the bone orifice into the tympanum. Chorda tympani passes in the tympanum from behind in front of the hammer and anvil and through the slot in the front wall comes out, heading along with n.lingualis to the language.
Muscles of the eustachian tube - tensor tympani and tensor ralati mollis - are innervated by the trigeminal nerve, alevator palati mollis - wandering.