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Diseases of the auditory nerve, pathways and auditory centers in the brain

Lesions of the conduction department of the auditory analyzer can occur on any part of it. The most common are diseases of the first neuron, united in a group called the auditory nerve neuritis. This name is somewhat arbitrary, since this group includes not only diseases of the auditory nerve trunk, but also lesions of nerve cells that make up the spiral nerve node, as well as some pathological processes in the cells of the Corti organ.

The bipolar nerve cells of the spiral node are very sensitive to all kinds of harmful influences. They easily undergo degeneration (degeneration) when exposed to chemical poisons, in particular, intoxication with certain medicinal substances, household and industrial poisons (quinine, streptomycin, salicylic drugs, arsenic, lead, mercury, nicotine, alcohol, carbon monoxide, etc.). Some of these substances (quinine and arsenic) have a special affinity for the nerve elements of the auditory organ and act on these elements as if selectively, just as, for example, methyl alcohol (wood alcohol) acts selectively on the nerve endings in the eye and causes blindness due to atrophy of the optic nerve.

Intoxication of cells, the spiral nerve node occurs not only when poisoning with chemical poisons, but also exposure to bacterial poisons (toxins) circulating in the blood in many diseases, such as meningitis, scarlet fever, influenza, typhoid, mumps, etc. As a result of intoxication as chemical poisons, and bacterial death of all or part of the cells of the spiral node occurs with subsequent complete or partial loss of auditory function. The death of the bipolar nerve cells of the spiral node leads to deafness primarily due to a break in the passage of the nerve impulse from the peripheral receptor to the cortical end of the auditory analyzer. In addition, in these cases usually occurs the so-called descending degeneration, i.e., atrophy of those processes of bipolar nerve cells that are directed to the Corti's organ, and the death of the corresponding hair cells.

The degeneration process sometimes becomes upward and spreads to the central processes of bipolar cells, i.e. to the nerve fibers that make up the very trunk of the auditory nerve. Diseases of the trunk of the auditory nerve also arise due to the transition of the inflammatory process from the meninges to the nerve membrane during meningitis. Such a transition usually occurs in the place where the auditory nerve leaves the internal auditory canal and enters the brain, penetrating through the meninges. As a result of the inflammatory process, death of all or part of the fibers of the auditory nerve occurs and, accordingly, complete or partial hearing loss occurs.

Conductive auditory tracts in the brain can suffer from congenital malformations and various diseases and brain injuries. In all cases, such lesions are usually not isolated, that is, they are not limited to violations of the auditory tract only, but are also accompanied by other brain disorders. Of the diseases, hemorrhages, tumors, inflammatory processes in the brain tissue (encephalitis) in various infectious diseases (meningitis, syphilis, etc.) should be noted here. The nature of the auditory dysfunction depends on the location of the lesion. In those cases when the process develops in one half of the brain and captures the auditory pathways to their intersection, hearing in the corresponding ear is impaired; if at the same time all the auditory fibers die, then there is a complete loss of hearing in this ear, with a partial loss of the auditory tract - a greater or lesser decrease in hearing, but again only in the corresponding ear. With unilateral lesions of the pathways above the intersection, bilateral hearing loss occurs, more pronounced on the side opposite to the lesion; complete loss of hearing even in one ear does not occur in these cases, since impulses from both receptors will be conducted to the central end of the analyzer along the preserved pathways of the opposite side.

Diseases of the auditory region of the cerebral cortex, as well as diseases of the conduction tract, can occur with hemorrhages, tumors, encephalitis. Unilateral lesions lead to a decrease in hearing in both ears, more to the opposite.

As for bilateral lesions of the conduction pathways and the central end of the auditory analyzer, then if they can take place, then in practice their number can hardly be any significant.
In fact, it is hard to imagine that any congenital anomaly of the brain or any disease of the brain tissue captured only auditory regions in isolation and symmetry. Therefore, severe degrees of persistent hearing impairment, due to its origin in congenital or acquired lesions of the central parts of the auditory analyzer, if they occur, it is usually only with extensive brain lesions and are accompanied by such profound impairments of other brain functions that the hearing loss in the overall picture of the lesion is put off by background.

Noise lesions. With prolonged exposure to noise, degenerative changes in the hair cells of the Corti's organ develop, spreading to nerve fibers and cells of the spiral nerve node. As a result of this process, progressive hearing impairment occurs, which in some cases reaches a sharp degree. Such a prolonged exposure to loud noise is observed in some industries. A harmful effect on the organ of hearing is exerted not only by strong sound irritation, but also by the concussion of the floor, which occurs in noisy workshops during the operation of moving mechanisms; these tremors are transmitted to the inner ear through the body and, causing displacement of the liquid in the labyrinth and the main membrane, are superimposed on sound vibrations.

Hearing damage among workers in noisy industries is common. Measures to protect the labor of workers in noisy industries (reducing noise and shaking, introducing special plugs, etc.), as well as eliminating production processes accompanied by loud noise, by replacing them with other, less noisy or even almost noiseless ones (for example, replacing rivets with electric welding) in to a large extent can prevent the development of this type of deafness and hearing loss.

Air contusion. Air contusion (the word "concussion" means a bruise) arising from the action of a blast wave is accompanied by various changes in the body and causes, in particular, a number of disturbances in the auditory analyzer. The action of a blast wave, i.e., a sudden sharp fluctuation in atmospheric pressure, is usually combined with the influence of strong sound irritation that accompanies any explosion. As a result of the simultaneous action of both of these factors, pathological changes can occur in all departments of the auditory analyzer. There are ruptures of the eardrum, hemorrhages in the middle and inner ear, displacement and destruction of the cells of the organ of Corti. The result of this kind of damage is a persistent damage to auditory function. Hearing impairment can reach varying degrees depending on the location and extent of the damage.

Functional hearing impairment. In air contusion, in addition to persistent hearing impairment resulting from anatomical damage to the peripheral parts of the auditory analyzer, temporary auditory dysfunctions are often observed, sometimes combined with speech impairment. These disorders are usually observed immediately after a concussion, often reaching a degree of complete deafness and complete lack of speech. They learned the name of surdomutism (from lat. Surditas - deafness and mutismus - lack of speech). The word “mutism”, included in this composite term, emphasizes the temporary, functional nature of the lesion, in contrast to the term “deaf-numbness” (surdomutitas), which refers to persistent hearing loss and lack of speech. Concussion surdomutism is associated with the development of transcendental protective inhibition (according to I.P. Pavlov), which occurs in the cortical centers of hearing and speech in response to the action of an extreme stimulus in the form of a powerful sound wave, a deafening sound of a shot and a strong concussion. In most cases, the phenomena of dementitis quickly pass under the influence of disinhibition treatment, and sometimes without any treatment.

In some cases, the inhibitory process takes a long, protracted nature.

Functional hearing impairment also includes hysterical deafness, which develops in people with a weak nervous system under the influence of strong irritants (fear, fear). Cases of hysterical deafness are sometimes observed in children.
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Diseases of the auditory nerve, pathways and auditory centers in the brain

  1. Activation of the auditory center
    The well-known Russian physiologist, academician P. Anokhin, in his studies, established that sometimes situations arise in the activity of the human brain when all its structures are activated. In this case, they work as a whole and perform the task most effectively. To create just such a situation, we developed special exercises involving in the processes
  2. Auditory Nerve Neuroma
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  5. Auditory Disorders
    Hearing disorders - deafness, hearing loss, auditory agnosia - are associated with damage to the auditory analyzer, which consists of a peripheral receptor - the Corti organ, which is located in the cochlea of ​​the inner ear, the auditory nerve that extends from it, the auditory tract continues in the brain, and the cortical auditory center in the cortex of the temporal lobe. Hearing impairment in childhood more often
  6. Central, or cortical, section of the auditory analyzer
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  7. Sound conducting and sound receiving functions of the auditory analyzer
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  10. Peripheral Hearing Analyzer
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