The acoustical centers can be subdivided on trunk, subcrustal and cortical. Being rather young in the phylogenetic relation, the acoustical centers differ in polymorphism of a neural structure and possess rich bonds with phylogenetic old educations (a reticular formation, other touch and motor systems of a brain trunk). Acoustical ways consist of the nervous conductors connecting receptors of hearing to the acoustical centers of all levels. Along with afferent they contain efferent nerve fibrils, value to-rykh it is found insufficiently out. Except vertically directed bunches, as a part of acoustical ways there are horizontal fibers connecting kernels of one level among themselves.
the First neuron of an afferent acoustical way is presented by bipolar neurocytes of a spiral node of a snail (see. Inner ear ). Their peripheral shoots go to spiral body of a snail (kortiyev body) where terminate at outside and internal voloskovy touch cells (see. Kortiyev body ). The central shoots make a cochlear (lower) root of an eighth cranial nerve (see). Almost all of them terminate in the cochlear kernels (ventral and dorsal) lying in myelencephalon (see) on border with the varoliyevy bridge (the bridge of a brain, T.), according to the predoor field (area vestibularis) of a rhomboid pole. In these kernels there are bodies of the 2nd neuron of an acoustical way; the uniform way is divided here into two parts. Ventral (front) cochlear kernel [nucleus cochlearis ventralis (ant.)] phylogenetic older, fibers from it go cross through varoliyev the bridge, forming a trapezoid body (corpus trapezoi-deum). The majority of fibers of a trapezoid body terminates in the front (ventral) and back (dorsal) kernels (nuclei ventrales et dorsales corporis trapezoidei) put in it, and also in an upper olive kernel [nucleus olivaris cranialis (sup.)] the and opposite parties and kernels of a reticular formation of a tire (nuclei tegmenti), other fibers proceed in a lateral loop. Axons of neurocytes of kernels of a trapezoid body and an upper olive kernel (the third neuron) go to a lateral loop of the and opposite parties and, besides, approach kernels of the facial and taking-away nerves, a reticular formation and a part joins them a back longitudinal bunch (fasciculus Jongitudinalis post.). Due to these bonds reflex movements at sound irritations can be carried out. Dorsal (back) cochlear kernel [nucleus cochlearis dorsalis (post.)], phylogenetic younger, gives rise to fibers, to-rye come to a surface of a rhomboid pole in the form of brain strips (striae medullares) going to a median furrow. There they plunge into substance of a brain and form two decussations — superficial (Monakova) and deep (Gel da) then enter a lateral loop (lemniscus lat.). The last represents the main ascending acoustical way of a brain trunk combining fibers from various kernels of acoustical system (back cochlear, upper an olive trapezoid body of kernels). The lateral loop contains both the direct, and crossed fibers; thus the two-way communication of an acoustic organ with the subcrustal and cortical acoustical centers is provided. In a lateral loop own kernel lies (nucleus lemnisci lat.), in Krom a part of its conductors switches.
The lateral loop terminates in the lower hillocks (colliculi inf.) roofs mesencephalon (see) and medial cranked body (corpus geniculatum med.) diencephalon (see). They represent the subcrustal acoustical centers. The lower hillocks play an important role in definition of space localization of a source of a sound and the organization of approximate behavior. Both hillocks are connected by commissure, edges contains, except komissuralny fibers, also the fibers of a lateral loop going to a hillock of the opposite side. Nerve fibrils from the lower hillocks go to upper hillocks (colliculi sup.) or enter directly pokryshechno-spinal and pokryshechno-bulbar ways (tractus tectospi-nalis et tractus tectobulbaris) and in its structure reach motor kernels of craniocereberal and spinal nerves. A part of fibers from the lower hillock goes in its handle (brachium colliculi inf.) to a medial cranked body. In the handle of the lower hillock the kernel is revealed (nucleus brachialis colliculi inf.), a cut, according to a number of researchers, is intermediate «station» of the second, parallel acoustical way which is passing on average a brain and having separate podkorkot vy and cortical projections. The medial cranked body transmits acoustical signals to a cerebral cortex. Shoots of its neurocytes (the fourth neuron) pass in under - a lenticular part of the internal capsule (pars sublenticularis capsulae int.) and, forming acoustical radiance (radiatio acustica), terminate in acoustical area of bark, it is preferential in cross temporal crinkles (a crinkle of Gesh-lya, gyri temporales transversi) where primary acoustic areas are localized (41 and 42). In this area the base units connected through neural groups of subcrustal and trunk kernels with the sites of a snail perceiving sounds of various frequency are allocated (see. Acoustic analyzer ). Secondary acoustic areas (21 and 22) are located on upper and outside surfaces of an upper temporal crinkle, and also take an average temporal crinkle (see Very tectonics of measles of a brain). Acoustical bark is connected by assotsiatsionny fibers with other areas of a cerebral cortex (the back speech field, visual and sensomotor zones). Acoustic areas of two hemispheres connect komissuralny-m fibers which pass in a corpus collosum and front commissure.
Efferent fibers are available in all links of acoustical ways. From a cerebral cortex there are two systems of the descending conductors; shorter terminate in a medial cranked body and the lower hillocks, longer are traced to an upper olive kernel. From the last to a snail there passes the olivoulitkovy way (tractus olivocochlearis Rasmussen) which contains straight lines and the crossed fibers. That and others reach spiral body of a snail and terminate on its outside and internal voloskovy cells.
At S.'s defeat c., items develop neurosensory disturbances, to-rye divide on cochlear and retrocochlear. Cochlear disturbances are connected with defeat of the neuroreceptor device in a cochlear labyrinth of an inner ear, and retrocochlear — with damage of an acoustical nerve and its root, conduction paths and the centers.
At cochlear defeat hearing (see) suffers preferential on high-pitch tones, perception of a sound evenly decreases both at air, and at bone conductivity. At the same time curves of air and bone conductivity on a tone audiogramma are located in parallel, close to one from another. At a research of bone conductivity from parietal area a tuning fork of C128 (see. opit Weber ) and an ultrasonic radiator at 98 thousand fluctuations in 1 sec. the sound in both cases is heard on the party, opposite struck. On the party of defeat hypersensitivity to increase of volume of sound (the phenomenon of the accelerated increase of loudness happens positive), especially in an initial stage of a disease of Menyer is observed (see. Menyera disease ). At cochlear decrease in hearing usually are absent any nevrol. symptoms, but can join vestibular disturbances owing to involvement of a vestibular labyrinth (see. Vestibulyarny symptom complex ) or to be surprised the nerves passing in a temporal bone (flavoring fibers for lobbies 2/3 languages, a facial nerve).
At cochlear defeat subjective noise are very strong and painful for the patient, are localized in an ear; at noise audiometriya (see) hearing decreases, but it is not sharp; rechetonalny dissociation is expressed poorly; in the presence of several sources of a sound perception of the speech decreases slightly; the hyperacusia is observed in one ear, quite often on it hearing is reduced (at the same time there is no sensitization to irritation in other analyzers); disturbance of localization of a sound corresponds to unilateral decrease in hearing; auditory hallucinations do not happen.
At retrocochlear defeat decrease in hearing accurately depends on localization of a tsrotsess in a brain. The most often unilateral deafness (see) or unilateral falloff of hearing is noted at defeat in area of a mostomozzhechkovy corner (radicular defeat), side departments of a varoliyev of the bridge (nuclear defeat). At defeat of a mesencephalon there is a bilateral decrease in hearing.
Retrocochlear decrease in hearing is characterized by a number of features. At it most often and considerably hearing on high frequencies (4000 — 8000 Hz) in parallel on bone and air conductivity decreases. Therefore on character tone audiogramm it is impossible to distinguish cochlear decrease in hearing from retrocochlear.
At retrocochlear unilateral relative deafness (see) or deafness there is no lateralization of a sound in Weber's experience (see. Weber experience ), what is the main sign for differentiation of cochlear and retrocochlear decrease in hearing. At the same time ultrasound lateralizutsya accurately in better the hearing ear at any form of neurosensory unilateral relative deafness. It is characteristic, especially of defeat of a mesencephalon, rechetonalny dissociation with preferential disturbance of legibility of the speech. At increase of intensity of a sound to 110 dB paradoxical decrease in legibility of the speech is often noted. Existence of several sources of a sound, accession of noise, frequent giving of audibles signal sharply reduce perception of tones and especially the speech. At the central defeat many features of a hearing disorder are connected not so much with defeat of the acoustic analyzer how many with change of century of N of.
At retrocochlear defeat subjective noise at patients are poorly expressed, are localized in the head; at a noise audiometriya hearing strongly decreases; rechetonalny dissociation is shown in very sharp form, and, the level of defeat of acoustical ways is higher, the vyrazhenny this symptom is shown; giperakuzpya it is observed in both ears at normal hearing that is followed often by hypersensitivity in other analyzers (a gyaperosmiya, a hyperesthesia); at normal hearing space hearing on the party opposite of localizations of the center of defeat in a cerebral hemisphere is broken.
At decrease in hearing the level of defeat of acoustical ways is established by comparison of acoustical disturbances to data of inspection of vestibular function, taste and other neurologic symptoms.
Various on character and localization of a disease have nek-ry features in manifestation of acoustical disturbances. Most often and strongly hearing at defeat of a mostomozzhechkovy corner, cochlear (acoustical) kernels in side departments of a varoliyev of the bridge decreases and at processes on average a brain. For defeat in area of a mostomozzhechkovy corner at a tumor preddverno-ulitko-vogo a nerve (cm. Mostomozzhechkovy corner, pathology ) unilateral decrease in hearing, and quite often full unilateral deafness is characteristic at long full safety of hearing on other ear. Arachnoiditis (see) mostomozzhechkovy a corner usually is followed by bilateral decrease in hearing preferential in the range of high frequencies (4000 — 8000 Hz). At defeat in area of a mostomozzhechkovy corner usually taste on front 2/3 languages at the same time decreases or drops out, function of the trigeminal, taking-away and facial nerves is broken, vestibular excitability changes, quite often there is horizontal spontaneous nystagmus (see).
Defeat of cochlear kernels at unilateral tumors or lateral heart attacks of a varoliyev of the bridge (see. Bridge of a brain ) is followed by unilateral falloff of hearing or the unilateral deafness which is combined with paresis and paralyzes of a look towards a tumor alternating syndromes (see), the expressed spontaneous nystagmus. Median tumors of a varoliyev of the bridge usually do not cause decrease in hearing.
Defeat of a mesencephalon (see) proceeds often with sharp bilateral decrease in hearing (sometimes to full deafness) that can be combined with the converging spontaneous nystagmus expressed by increase in a caloric nystagmus, easing or loss of a railroad nystagmus, disturbance of pupillary tests (see. Pupillary reflexes ), extrapyramidal symptoms (see. Extrapyramidal system ).
At hemilesion of the internal capsule and a temporal share of a brain (see) hearing does not decrease since acoustical ways are located in parencephalons far apart, and each acoustical way in these departments has straight lines and the crossed ways. When patol. the center is located in a temporal share, there are acoustical hallucinations (see), perception of short audibles signal is broken, perception of the distorted and accelerated speech with switching off of high-pitch tones and speeches with submission of various words in the right and left ear (dikhotichesky hearing) especially decreases; the ear for music changes. Patol. the centers in temporoparietal departments of a brain and the lower parietal segment cause disturbances of space perception of hearing on the opposite side (at normal hearing on both ears). At the big tumors of a temporal share of a brain for the second time influencing a mesencephalon decrease in hearing can be noted.
Most often decrease in hearing is observed owing to neuritis of the eighth cranial nerve developing after flu, acute respiratory diseases, epidemic parotitis, an arachnoiditis with preferential localization in a mostomozzhechkovy corner, cerebrospinal meningitis, use of the antibiotics possessing ototoksichesky action (Neomycinum, Kanamycinum, Monomycinum, gentamycin, streptomycin) and also furosemide at intoxication by lead, arsenic, phosphorus, mercury, at long impact of noise (at weavers, hammerers, etc.), at tumors of an acoustical nerve (a cochlear part of an eighth cranial nerve, T.), changes of a pyramid of a temporal bone, patients with vascular, inflammatory or tumoral defeat of lateral departments have a varoliyeva of the bridge.
In an acute stage of neuritis of an eighth cranial nerve treatment includes intravenous administration of 40% of solution of hexamethylenetetramine (urotropin) with glucose, use of antibiotics (except for ototoksichesky), a prozerina, Dibazolum, a komplamin, Stugeronum, Nospanum or other vasodilators, vitamin of Vkh, 0,1% of solution of strychnine of nitrate in the increasing doses (from 0,2 to 1 ml), only 20 — 30 injections, acupuncture, inhalations of Carbogenum, an injection of ATP. Favorable results are yielded by the treatment begun in the first 3 — 5 days from the beginning of a disease; the treatment begun 3 months later from the beginning of a disease, malorezultativno. Treatment of neuritis of the eighth cranial nerve caused by use of ototoksichesky antibiotics, ineffectively; for the purpose of prevention of neuritis it is necessary to limit their use (only according to strict indications), not to appoint at the same time and consistently two different ototoksichesky antibiotics, to limit their prescription to children and elderly people.
Treatment of tumors of an eighth cranial nerve operational (see. Eighth cranial nerve ).
Recovery of hearing at encephalitis, tumoral and vascular damages of a brain depends on efficiency of treatment of a basic disease.
See also Conduction paths .
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