Pre-cochlear nerve: description, structure and anatomy

The anatomies distinguish twelve pairs of nerves, which have specific functions and are located within the region of the head and neck. One of them is the pre-cochlear nerve. He is responsible for the special sensitivity: hearing and a sense of balance. Violation of its function or anatomy can lead to a person's deep disability.

Structure

What is the pre-cochlear nerve? Its anatomy is quite complicated, since, based on the name, it includes two separate spines, which have different functions. The first - the vestibular, is responsible for the balance and innervates the semicircular canals of the inner ear. The second one, the auditory one, conducts impulses from the labyrinth of the cochlea to its root.

The nerve takes its beginning on the lower surface of the hemispheres, emerging from the gray matter in the olive nuclei in the medulla oblongata and being located below the facial nerve. The auditory branch starts from the snail's nodule, and its peripheral processes terminate in a spiral organ, and the central branch leaves through the apex of the pyramid of the auditory bone into the brain and reaches the cochlear cores.

The second, vestibular, branch also begins with a nodule that is located in the inner ear. The dendrites of these neurons go to semicircular canals, spherical and elliptical sacs. And the axon as a part of the vestibular root is sent to the rhomboid fossa and ends there on the vestibular nuclei.

Hearing Protection

The system of perception of sound in humans is rather complicated. There is an external, middle and inner ear, but the pre-cochlear nerve innervates the inner part only. First, the sound wave is perceived by the tympanic membrane. Its vibrations are transferred to the hammer, anvil and stapes, connected together. From the stapes, the wave touches the oval window located on the threshold of the labyrinth. Oscillations cause the movement of the perilymph and the endolymph inside the labyrinth. Together with the fluid, the areas of the secondary tympanic membrane, or basilar plate, also oscillate. It contains sound-sensing hairs that generate a nerve impulse. It is transferred to a spiral node located in the inner ear. The processes from the nerve cells that make up the node go through the hole in the ear canal and, connecting with the vestibule nerve, go to the bridge, where they end in the substance of the cochlear nuclei in the rhomboid fossa.

The axons of cochlear neurons cross and form a lateral loop. Then the fibers are separated. A small part of them ends on the lower hills of the plate of the quadruple (middle brain). The rest go to the medial geniculate bodies in the intermediate brain or to the middle nuclei of the thalamus.

The equilibrium function

For the equilibrium of the body in space during movement and at rest, also corresponds to the pre-collateral nerve. The scheme of its innervation in the uninitiated can cause a shock, because to ensure this function requires the synchronous operation of many departments of the nervous system.

The main function of the vestibular apparatus is to analyze the position of the head in space at any time and adjust the position of the body and muscle tone. The organ responsible for the balance is next to the labyrinth in the middle ear and represents three intersecting canals of an oval shape that end in elliptical and spherical sacs. Within these structures are hairs that are sensitive to changes in the position of the head, angular and linear acceleration, as well as changes in gravity.

From the sensitive hairs, the peripheral processes of the neurons are directed to the pre-door node located at the bottom of the temporal bone. Entering the substance of the brain, the nerve is directed into the rhomboid fossa to the vestibular nuclei. From the bridge, the processes of the neurons diverge into the spinal cord (to the nuclei of the anterior horns), the cerebellum (the cortex of the worm), the thalamus (vestibular nuclei) and the reticular formation (the nucleus of the cranial nerves). All these structures provide friendly body responses to the irritation of the vestibular receptors. All information from the subcortical structures enters the region of the middle and lower temporal gyrus, where the center of motor functions is located, the center of general sensitivity and the center of the body scheme.

Hearing Research

What should I do to check whether the pre-cochlear nerve is performing well? Two of its branches are examined separately. Hearing studies are performed by ENT doctors, neuropathologists and even psychiatrists, therefore, tests for all specialties have been developed.

It all starts with a simple hearing test. Normally, a person should hear a whisper speech addressed to him from a distance of five meters. Hearing loss or lack of it can cause not only damage to the outer or middle ear, but also the inner ear. Therefore, it is so important to understand the causes of the disease.

1. The Schwabach test is based on measuring the duration of bone conduction. The tuning fork is turned on and mounted on the mastoid process behind the ear. If the patient does not hear the sound, then the problem is in the inner ear, if the sound is heard longer than necessary, the pathology is in the middle section of the analyzer.
2. The Rinne test determines the difference between air and bone conduction. The tuning fork is placed on the mastoid process, and the patient is asked to say when he ceases to hear the sound. After this, the instrument is transferred to the auricle. In the case where the patient is healthy, the sound will still be heard.
3. Weber's test. The newly inserted tuning fork is placed on the parietal area of the person, and the doctor asks where the sound is heard better. If the patient points to the sore side, then it speaks in favor of damage to the middle ear, and if to a healthy one, then the problems are in the inner ear.

Estimation of balance

The pre-cochlear nerve also responds to the balance, so neuropathologists in the course of a comprehensive examination often resort to various tests to check the patient for stability:

1. Romberg's pose is one of the most common options. The patient is asked to stand exactly so that the feet are on the same line, and the heel of one leg rests against the toe of the second. Hands should be diluted to the sides or straightened before themselves. Then the doctor asks to take a few steps forward first with his eyes open, and then with closed. The shakiness of the gait in the second case indicates the defeat of the inner ear.
2. Mittwater's test. The patient walks on the spot with his eyes closed. If there is a lesion of the vestibular apparatus, then gradually it will turn toward the hearth.

Defeat of cochlear branch

The defeat of the anterior-cochlear nerve in the area responsible for the processing of auditory impulses has specific clinical manifestations. There are two options for reducing:

- Violation of sound transmission, or conductive hearing loss (defeat of the middle ear);
- sensorineural hearing loss in case of internal ear damage.

In the first case, the causes of the condition may be inflammatory processes, sclerosis of tissues or neoplastic diseases. The second variant of the disease can also be caused by inflammatory phenomena, neurinoma, as well as damage to the brain substance in the locations of the nuclei of the eighth pair of cranial nerves.

Clinically, this is manifested by complaints of noise in the ear, headache, a general decrease in hearing. If the pathological process is located in the thickness of the brain, then loss of functions and neighboring nerves, such as vestibular, trigeminal and facial, can be observed. Such a commonality of symptoms is called "alternating syndrome".

The defeat of the vestibular part

The pathology of the anterior-cochlear nerve on the site of the vestibular branch will first of all manifest itself in vertigo, nausea (sometimes with vomiting), and nystagmus. This nerve is partly responsible for the position of the eyeballs when the position of the head changes, so when it is injured, there may be a change in the movement of the eyes. Namely, small horizontal or vertical twitchings.

In addition, the patient has an unstable gait, and he needs to spread his legs widely (as on the ship during pitching) in order to keep his balance, and also constantly monitor his legs. Therefore, in such people the doctor can presume a diagnosis at the moment when they go into his office.

Neurinoma of the pre-cochlear nerve

Innervation of the pre-cochlear nerve suggests that its fiber is covered by a shell of Schwann cells. This is a kind of isolation, so that the nerve impulse does not pass to other fibers. But from the skin cells in rare cases (one for one hundred thousand people) a benign tumor can grow.

It manifests itself slowly and, as a rule, when the neoplasm has already reached considerable dimensions. Patients complain of hearing loss on one side, dizziness, pain in half of the face, as well as the presence of a combined pathology of the facial and abduction nerve. This is manifested by speech disorders, difficulties in eating. The tumor squeezes the nerve endings, which causes the corresponding clinic.

If the neurinoma has arisen from both sides, then such a patient is recommended to undergo a genetic examination for the presence of neurofibromatosis (hereditary connective tissue disease). Treatment, as a rule, operative.

Meniere's syndrome

The pre-cochlear nerve can be indirectly damaged by Ménière's disease. The pathology itself is associated with impaired production and outflow of fluid in the inner ear. Her overabundance puts pressure on sensitive hairs, which is manifested in a violation of equilibrium.

The disease manifests dizziness, which is accompanied by a noise in the ears and a feeling of bursting from the affected side. In addition, patients complain of progressive hearing loss. As the disease progresses, the symptoms intensify, and it can go so far that a person during an attack can not get out of bed or turn his head.

Treatment is reduced to stopping unpleasant sensations during an attack and taking sedative medications at light intervals. If conservative therapy does not help that they resort to a radical remedy and destroy the labyrinth or cross the vestibular branch of the pre-collar nerve.