VIII pair - vestibulocochlear nerves. Vestibular-cochlear nerve, symptoms of damage Yiii - cochleo-vestibular nerve

Anatomists identify twelve pairs of nerves that have specific functions and are located within the head and neck region. One of them is the vestibulocochlear nerve. It is responsible for special sensitivity: hearing and sense of balance. Violation of its function or anatomy can lead to profound disability of a person.

Structure

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

The nerve originates on the lower surface of the hemispheres, emerging from the gray matter at the olive nuclei in the medulla oblongata and located below the facial nerve. The auditory branch starts from the cochlear node, and its peripheral processes end in the spiral organ, and the central one exits through the apex of the auditory bone pyramid into the brain and reaches the cochlear nuclei.

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

Hearing support

The human sound perception system is quite complex. There are external, middle and inner ears, but the vestibulocochlear nerve innervates the inner part exclusively. First, the sound wave is perceived by the eardrum. Its vibrations are transferred to the hammer, incus and stirrup, connected to each other. From the stapes, the wave affects the oval window, located in the vestibule of the labyrinth. Oscillations cause movements of perilymph and endolymph within the labyrinth. Along with the fluid, sections of the secondary tympanic membrane, or basilar plate, also vibrate. It contains sound-receiving hairs that generate sound and is transmitted to the spiral node located in the inner ear. The processes from the nerve cells that make up the node exit through the opening in the auditory canal and, connecting with the vestibular nerve, go to the bridge, where they end in the substance of the cochlear nuclei in the rhomboid fossa.

The axons of the cochlear neurons cross and form the lateral lemniscus. The fibers are then separated. A small part of them ends on the lower colliculi of the quadrigeminal plate (midbrain). The rest go to the medial geniculate body in the diencephalon or to the median nuclei of the thalamus.

Equilibrium function

The vestibulocochlear nerve is also responsible for the balance of the body in space during movement and at rest. The pattern of its innervation can cause confusion for the uninitiated, since to ensure this function, the synchronous work of many parts of the nervous system is necessary.

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

From the sensory hairs, the peripheral ones are directed to the vestibular 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 pons, the processes of neurons diverge into the spinal cord (to the nuclei of the anterior horns), the cerebellum (cortex of the vermis), the thalamus (vestibular nuclei) and the reticular formation (nuclei of the cranial nerves). All these structures provide friendly reactions of the body to irritation of the vestibular receptors. All information from the subcortical structures enters the area of the middle and inferior temporal gyrus, where the center of motor functions, the center of general sensitivity and the center of the body diagram are located.

Hearing research

What needs to be done to check whether the vestibulocochlear nerve is performing its functions well? Its two branches are examined separately. Hearing tests are carried out by ENT doctors, neurologists and even psychiatrists, so tests that are uniform for all specialties have been developed.

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

The Schwabach test is based on measuring the duration of bone conduction. The tuning fork is turned on and placed on the mastoid process behind the ear. If the patient does not hear the sound, then the problem is in the inner ear, but if the sound is heard longer than necessary, then the pathology is in the middle section of the analyzer.
The Rinne test determines the difference between air and bone conduction. A switched-on tuning fork is placed on the mastoid process, and the patient is asked to say when he stops hearing the sound. After this, the instrument is transferred to the auricle. If the patient is healthy, the sound will still be heard.
Weber test. The newly turned on tuning fork is placed on the parietal region of the person, and the doctor asks which side the sound is heard better. If the patient points to the sore side, then this indicates damage to the middle ear, and if to the healthy side, then the problem is in the inner ear.

Equilibrium Assessment

The vestibulocochlear nerve is also responsible for balance, so neurologists, during a comprehensive examination, often resort to various tests to check the patient’s stability:

- 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 foot rests on the toe of the other. Your arms should be spread out to the sides or straight in front of you. The doctor then asks you to take a few steps forward, first with your eyes open and then with your eyes closed. in the second case, it indicates damage to the inner ear.
Mittelnaer test. The patient walks in place with his eyes closed. If there is damage to the vestibular apparatus, then it will gradually turn towards the lesion.

Damage to the cochlear branch

Damage to the vestibulocochlear nerve in the area responsible for processing auditory impulses has specific clinical manifestations. There are two reduction options:

Impaired sound conduction, or conductive hearing loss (middle ear damage);
- sensorineural hearing loss with damage to the inner ear.

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

Clinically, this is manifested by complaints of noise in the ear, headache, and general hearing loss. If the pathological process is located deep in the brain, then loss of functions of neighboring nerves, such as the vestibular, trigeminal and facial, may be observed. This commonality of symptoms is called “alternating syndrome.”

Damage to the vestibular part

Pathology of the vestibular-cochlear nerve in the area of the vestibular branch will primarily manifest itself with dizziness, nausea (sometimes with vomiting) and nystagmus. This nerve is partly responsible for the position of the eyeballs when the head position changes, so if it is damaged, there may be a change in eye movement. Namely small horizontal or vertical twitches.

In addition, the patient has an unsteady gait and needs to spread his legs wide (as on a ship when rocking) to maintain balance, as well as constantly monitor his legs. Therefore, for such people, the doctor can assume a diagnosis the moment they enter his office.

Neuroma of the vestibulocochlear nerve

The innervation of the vestibular-cochlear nerve suggests that its fibers are covered with a sheath of this kind of insulation, so that the nerve impulse does not pass on to other fibers. But in rare cases (one in one hundred thousand people) a benign tumor can grow from the membrane cells.

It appears slowly and, as a rule, when the tumor has already reached a significant size. Patients complain of hearing loss on one side, dizziness, pain in half of the face, as well as the presence of combined pathology of the facial and facial muscles. This is manifested by speech impairment and difficulties in eating. The tumor compresses the nerve endings, which causes the corresponding clinic.

If neuroma occurs on both sides, then such a patient is recommended to undergo genetic testing for the presence of neurofibromatosis (hereditary connective tissue disease). Treatment is usually surgical.

Meniere's syndrome

The vestibulocochlear nerve may be indirectly damaged in Meniere's disease. The pathology itself is associated with a violation of the production and outflow of fluid in the inner ear. Its excess puts pressure on sensitive hairs, which manifests itself in imbalance.

The disease manifests itself in attacks of dizziness, which are accompanied by tinnitus and a feeling of fullness on the affected side. In addition, patients complain of progressive hearing loss. As they progress, they intensify, and can reach the point that a person cannot get out of bed or turn his head during an attack.

Treatment boils down to relieving discomfort during an attack and taking sedative medications during light periods. If conservative therapy does not help, then resort to a radical remedy and destroy the labyrinth or cross the vestibular branch of the vestibular-cochlear nerve.

The vestibular-cochlear nerve (n. vestibulocochlearis) is formed by two independent anatomically and functionally different sensory nerves. It distinguishes between a system of fibers of the vestibular (n. vestibularis) and cochlear (n. cochlearis) nerves.
1. The vestibular nerve conducts impulses that control the position of the head and body. Together with other sense organs, it participates in indicative reactions. Receptors of the vestibular nerve are located in the otolithic devices of the inner ear: the ampoules of the three semicircular canals, the membranous sac (sacculus) and the utricle (utriculus) of the vestibule. The receptors are associated with the dendrites of the vestibular node, which lies deep in the internal auditory canal of the temporal bone, and form a number of nerves:
a) the elliptical saccular nerve (n. utricularis) makes up the upper part of the vestibular nerve. Starts from the receptors of the elliptical sac of the vestibule of the inner ear;
b) the anterior ampullary nerve (n. ampullaris anterior) together with the elliptic nerve forms the upper part of the vestibular nerve and has receptors in the anterior membranous ampulla of the semicircular canal;
c) the lateral ampullary nerve (n. ampullaris lateralis), like the previous two, is an integral part of the upper section of the vestibular nerve. Contacts the receptors of the lateral ampulla of the semicircular canal;
d) passes in the lower part of the vestibular nerve and its node, the spherical-saccular nerve (n. saccularis) begins from the receptors of the auditory spot of the sac;
e) the posterior ampullary nerve (n. ampullaris posterior) has receptors in the posterior ampulla of the semicircular canal and the lower sensitive spot of the vestibule.

Axons of gangl neurons. vestibuli form the upper root of the VIII pair of nerves emerging from the temporal bone through the internal auditory foramen behind the facial nerve. The superior root passes into the hindbrain between the medullary pons and the cerebellum, without reaching the bottom of the fourth ventricle. The axons of the vestibular nerve are divided into ascending and descending bundles.

The ascending bundles of the vestibular nerve switch in the superior nucleus of the pons and nucl. fastigii of the cerebellum, as well as in the cortex of the vermis.

In the cerebellum there is a direct connection between the vestibular nerves and the motor nuclei. Descending bundles switch in the nucleus of the descending root (inferior nucleus), medial and lateral nuclei (see Pathways of the statokinetic apparatus, p. 214).

2. The cochlear nerve conducts sound stimuli perceived by the receptors of the organ of Corti of the cochlea. Dendrites, emerging through the channels of the spiral plate of the cochlea, reach the cells of the spiral ganglion (gangl. spirale), located in the canal of the cochlea rod. The axons of bipolar cells form the inferior root of the vestibulocochlear nerve, which through the internal carotid foramen of the pyramid of the temporal bone enters the base of the skull, penetrating together with the vestibular nerve between the pons and the cerebellum to the ventral and dorsal nuclei of the hindbrain. In the nuclei there is a switch to the auditory pathway (see).

Embryogenesis. The development of the vestibulocochlear nerve begins at the end of the 3rd week of the embryonic period. Neuroblasts are formed along with the facial nerve ganglion. This commonality of development is explained from a phylogenetic point of view by the fact that they are nerves derived from the lateral line. Simultaneously with the node, the membranous labyrinth is formed in the form of a thickening of the surface ectoderm on the sides of the neural tube, called the auditory placode. At the 4th week, the placode thickens and turns into the otic fossa, which closes into the otic vesicle. During the formation of the auditory vesicle, the common nerve ganglion is divided into three: gangl. geniculi (VII pair), vestibularis, spiralis (VIII pair). At the same time, the auditory vesicle differentiates into semicircular canals, which phylogenetically represent the more ancient part, since they already appear in fish and snails. Dendrites of neuroblast gangl. vestibuli grow into the semicircular canals and vestibule, and the dendrites of gangl cells. spirale - into the snail. Only in the third month of embryonic development are receptors formed in the organ of Corti.

Phylogenesis. In aquatic animals, the VIII nerve does not exist independently, but is part of the VII nerve and the lateral line. The vestibular nerve is the first to differentiate due to the appearance of the organ of balance. In terrestrial animals, the facial, vestibular and auditory nerves have completely acquired independent significance.

The vestibulocochlear nerve (VIII pair) is sensitive. It consists of two independent nerves - the vestibular and cochlear, which have different functions.

The cochlear nerve (n. cochlearis) is auditory; it conducts sound stimulation from the auditory receptors of the spiral organ of the cochlea. The auditory analyzer pathway consists of three neurons. The first neurons are bipolar cells located in the spiral ganglion of the cochlea (gangl. spirale). The dendrites of these neurons come from the auditory hair cells of the spiral (corti) organ, which perceive vibrations of the endolymph and convert them into nerve impulses. The axons of bipolar cells form the cochlear nerve, which, together with the vestibular and facial nerves, enters the cranial cavity through the internal auditory canal and enters the upper parts of the medulla oblongata and lower parts of the pons at the cerebellopontine angle. In the brain stem, the cochlear nerve is separated from the vestibular nerve and ends in the ventral and dorsal auditory nuclei (nucl. cochlearis ventralis et f dorsalis), where the second neurons of the auditory analyzer are located. From these nuclei, auditory fibers, to which conductors from additional formations of the gray matter (superior olive, nucleus of the trapezoid body) join, partially moving to the opposite side, partially on their side rise upward in the brain stem, forming a lateral loop (lemniscus lateralis). The lateral loop, consisting of crossed and uncrossed fibers, rises upward and ends in the subcortical auditory centers, the internal geniculate body and the inferior tubercle of the midbrain roof plate. The third neuron starts from the internal geniculate body, passes through the internal capsule and corona radiata to the cortical part of the auditory analyzer, located in Heschl's gyrus in the region of the posterior part of the superior temporal gyrus. Partial decussation of auditory fibers ensures bilateral communication of the hearing organ with the subcortical and cortical auditory centers. The fibers that end in the inferior tubercle of the roof plate are connected to the subcortical motor centers and play an important role in the spatial localization of the sound source and providing motor responses to auditory stimuli.

1 - spiral (Corti) node of the cochlea; 2 - spiral (Corti) organ; 3 - cochlear nerve; 4 - dorsal auditory nucleus; 5 - trapezoid body and its nuclei; 6 - ventral auditory nucleus; 7 - nucleus of the lateral loop of the midbrain; 8 - lower colliculus of the midbrain roof plate; 9 - medial geniculate body; 10 - side (lateral) loop; 11 - thalamus; 12 - cortical section of the auditory analyzer.

The study of the function of the cochlear nerve includes clarification of the patient's complaints, examination of hearing acuity, bone and air conduction. It is necessary to find out whether the patient is bothered by tinnitus, hearing loss, distortion of sound perception in the form of changes in its timbre, strength, or whether there are auditory hallucinations. Hearing acuity is examined for each ear separately using whispered and loud speech. The patient closes the second ear with his finger. With eyes closed, the patient must repeat words or phrases that are whispered from a distance of 6-7 m. It is from this distance that the healthy ear hears whispered speech. A healthy person hears loud speech from a distance of 20 m. They try to establish the maximum distance from which words are perceived correctly. With hearing loss, the distance to correctly perceive speech decreases. More precisely, hearing acuity is examined using audiography. It is necessary to take into account that the patient’s hearing may be reduced if the sound-receiving apparatus and other parts of the auditory analyzer (spiral organ, auditory nerve and its nuclei) are damaged, as well as in the presence of pathology of the sound-conducting apparatus in the middle ear.

To determine which of the systems (sound-receiving or sound-conducting) is damaged, tuning fork tests are carried out. A set of tuning forks with a frequency of 128, 512 and 2048 vibrations per 1 s is used. Air and bone conduction in a neurological clinic are usually examined using a tuning fork with an oscillation frequency of 128 per 1 s.

Rinne's experience. The stem of the sounding tuning fork is placed on the mastoid process of the pyramid of the temporal bone. After the patient stops feeling the vibration of the tuning fork through the bone, without dampening the vibration, the jaws of the tuning fork are brought to the external auditory canal at a distance of 1-2 cm. A healthy person perceives sound through the air almost 2 times longer than through the bone. This result of the experience is assessed as positive and interpreted as Rinne + (positive). If the sound of a tuning fork is felt through the bone longer than through the air, this indicates damage to the sound-conducting apparatus (for example, otitis media, otosclerosis, etc.). This result is interpreted as Rinne - (negative).

Weber's experience makes it possible to distinguish between damage to the sound-conducting and sound-receiving apparatuses. The stem of a vibrating tuning fork is placed in the middle of the crown, forehead or bridge of the patient’s nose. Normally, the sound of a tuning fork is perceived equally by both ears or in the middle, i.e., “lateralization” of the sound is not observed. In case of unilateral damage to the sound-conducting apparatus (for example, otitis media), bone conduction will be better than air conduction, so the patient will better feel the sound of the tuning fork in the affected ear (“lateralization” of sound into the affected ear). If the sound-receiving apparatus (spiral organ, cochlear nerve) is damaged on one side, the sound of the tuning fork will be better perceived by the healthy ear (“lateralization” of the sound into the healthy ear). The “lateralization” of sound during the Weber test can be demonstrated by artificially disconnecting the sound-conducting apparatus (closing one ear canal with your finger). The sound will be better perceived with a closed ear. Damage to the sound-conducting apparatus is characterized by hearing impairment for low tones and preservation of bone conduction; damage to the sound-receiving apparatus is characterized by hearing impairment to high tones and loss of bone conduction.

Pathology of the auditory analyzer. There are the following hearing disorders: complete hearing loss, deafness (anacusis), decreased hearing (hypacusis), increased perception (hyperacusis). Irritation by the pathological process of the neuroreceptor auditory apparatus in the inner ear or the cochlear nerve is accompanied by noise, whistling, ringing in the ear and head. Unilateral decrease or absence of hearing is possible only with pathology of the labyrinth of the inner ear, cochlear nerve or its nuclei (in neurological practice, more often with neuropathy of the cochlear nerve or its neuroma in the cerebellopontine angle). Unilateral damage to the lateral lemniscus, subcortical auditory center or cortical auditory analyzer does not cause noticeable hearing disorders due to the fact that the nuclei of the cochlear nerve have a bilateral connection with the cortical auditory centers. In such cases, there may be only a slight decrease in hearing on both sides. If the pathological process irritates the cortical part of the auditory analyzer, auditory hallucinations occur, which can sometimes be the aura of a generalized convulsive epileptic attack.

The vestibular nerve (n. vestibularis) is an integral part of the vestibular analyzer, which perceives and analyzes information about the position and movements of the head and body in space. The vestibular nerve carries stimuli from the receptors of the semicircular canals of the inner ear and the otolithic apparatus. The body of the peripheral neuron of the vestibular analyzer is located in the vestibular node, located in the inner ear. The dendrites of the cells of this node end in the ampoules of the semicircular canals and in the otoliths; the axons as part of the root of the vestibular nerve are directed together with the cochlear nerve through the internal auditory canal to the brain stem. In the brain stem, the vestibular nerve is divided into bundles of ascending and descending fibers, heading to its four nuclei, where they end: ascending fibers - in the superior vestibular nucleus (Bechterew's nucleus), descending fibers - in the medial vestibular nucleus (Schwalbe nucleus), lateral vestibular nucleus (nucleus Deiters) and the inferior vestibular nucleus (Roller's nucleus). These nuclei contain the bodies of the second neurons of the vestibular analyzer, the axons of which go in different directions, providing connections between the vestibular apparatus and the cerebellum, the nuclei of the nerves of the oculomotor group through the system of the medial longitudinal fasciculus, with the anterior horns of the spinal cord, the reticular formation of the brain stem, the nucleus of the vagus nerve and others structures. Numerous connections of the vestibular analyzer explain the presence of various symptoms in its pathology. The cortical section of the vestibular analyzer is located in the cortex of the temporal lobe, near the auditory projection area.

The study of the function of the vestibular analyzer is carried out mainly in the otolaryngology clinic, it includes checking for the presence of spontaneous nystagmus, balance disorders, performing coordination tests, determining the excitability of the vestibular analyzer using caloric and rotational tests, electronystagmography and other studies.

Pathology of the vestibular analyzer. Vestibular disorders occur when the vestibular analyzer is damaged at any level: with diseases of the inner ear, damage to the vestibular nerve, especially in the cerebellopontine angle, pathology of the brain stem, cerebral cortex. The close connection of the vestibular analyzer with vegetative formations, the nuclei of the oculomotor nerves determines the occurrence of dizziness, nausea, vomiting, instability when standing, unsteadiness of gait, nystagmus, changes in the rhythm of breathing, pulse, blood pressure, and increased sweating when it is irritated. The leading symptoms of vestibular dysfunction are systemic dizziness and nystagmus. Dizziness is a feeling of rotation of surrounding objects in one direction (clockwise or counterclockwise). Vestibular nystagmus is an involuntary rhythmic, rapidly repeated twitching of the eyeballs.

vestibular-cochlear nerve, n. vestibulocochlearis, formed by sensitive nerve fibers coming from the organ of hearing and balance. On the anterior surface of the brain, the vestibulocochlear nerve emerges behind the pons, lateral to the root of the facial nerve. The nerve then enters the internal auditory canal and is divided into the vestibular and cochlear parts, according to the presence of the vestibular and cochlear nodes (see “Inner ear”).

The bodies of nerve cells that make up vestibular part,pars [nervus] vestibuldris, vestibulocochlear nerve, lie in vestibular node, ganglionvestibulare, which is located at the bottom of the internal auditory canal. The peripheral processes of these cells form anterior, posterior and lateral ampullary nerves, pp. ampulldresanterior, posterioretlaterdlis, and elliptical saccular ampullary nerve, n. utriculoampullaris, And spherical saccular nerve, n. sacculdris, which end in receptors in the membranous labyrinth of the inner ear. The central processes of the cells of the vestibular ganglion are directed to the nuclei of the same name, which lie in the region of the vestibular field of the rhomboid fossa, forming the vestibular part of the vestibulocochlear nerve.

cochlear part,pars (ne r vus) cochledris, vestibulocochlear nerve is formed by the central processes of neurons cochlear ganglion(spiral cochlear ganglion), ganglioncochleare (ganglionspiralecochleae), lying in the spiral canal of the cochlea. The peripheral processes of the cells of this node end in the spiral organ of the cochlear duct, and the central ones reach the cochlear nuclei, which lie in the pons and project into the vestibular field of the rhomboid fossa [see. “Vestibular-cochlear organ (organ of hearing and balance)

vestibulocochlear nerve(lat. nervus vestibulocochlearis) - (VIII pair of cranial nerves) a nerve of special sensitivity, responsible for the transmission of auditory impulses and impulses emanating from the vestibular part of the inner ear.

Contents [show]

[edit]Anatomy

The vestibulocochlear nerve is a nerve of special sensitivity, consisting of two roots with different functions: the vestibular root (lat. radix vestibularis), carrying impulses from the static apparatus, represented by the semicircular ducts of the vestibular labyrinth, and the cochlear root (lat. radix cochlearis), conducting auditory impulses from the spiral organ of the cochlear labyrinth.

On the lower surface of the brain it appears below the facial nerve (lat. n.facialis), outward from the olive medulla oblongata.

Peripheral fibers (dendrites) radix cochleare originate from the cochlear ganglion (lat. ganglion cochleare) and end in the spiral organ, which is the perceptive device of the auditory pathway.

The central processes (axons) of the cochlear ganglion cells form the radix cochleare, which exits the pyramid of the temporal bone through the internal auditory opening and enters the substance of the brain. It ends in the posterior and anterior cochlear nuclei.

The vestibular root begins from the vestibular ganglion (lat. ganglion vestibulare), located in the cleft of the internal auditory canal. The vestibular ganglion is divided into two parts: superior and inferior.

The peripheral processes (dendrites) of the cells of the ganglion vestibulare approach the receptor cells of the spherical sac, elliptical sac and semicircular ducts. The central processes (axons) are part of the vestibular root and approach the vestibular nuclei of the vestibular field of the rhomboid fossa (lat. fossa rhomboidea).

[edit]Function

[edit]Auditory system

The auditory system consists of the outer, middle and inner ear. Only the inner ear, consisting of the cochlea (lat. cochlea), containing the organ of Corti and the spiral organ (lat. organum spirale), and the auditory nerve. Sound waves coming from the outer ear are transformed into nerve impulses in the organ of Corti. In addition to air conduction, there is also bone conduction (transmission of sound vibrations through the bones of the skull). From the Corti ganglion come postganglionic fibers of the spiral ganglion, which are directed to this node and switch in it, forming the auditory nerve. The auditory nerve, in turn, joins the vestibular nerve on its way through the internal auditory foramen of the temporal bone. In the region of the cerebellopontine angle, both nerves enter the brainstem immediately behind the inferior cerebellar peduncle (lat. pedunculus cerebellaris inferior). In the brain stem there are the second neurons of the auditory nerve, represented by the anterior and posterior cochlear nuclei (lat. nuclei cochleares ventralis et dorsalis), which occupy the most lateral position of the vestibular field of the rhomboid fossa.

Axons originating from the anterior cochlear nucleus mostly pass to the opposite side in the form of “trapezoidal” fibers and participate in the formation of the trapezoidal body, located on the border between the base and the tegmentum of the pons. Axons originating from the posterior cochlear nucleus run dorsally from the inferior cerebellar peduncle to the opposite side, partly as part of the medullary striae of the fourth ventricle (lat. striae medullares ventriculi quarti), partly as part of the reticular formation.

The crossed fibers transmit impulses to the trapezius nucleus, superior olivary nucleus, lateral lemniscus nucleus, or reticular formation. Fibers that have not undergone decussation generally end in the upper olives of the same side. Thus, the bodies of the third neurons of the auditory pathways are located in the superior olive and nuclei of the trapezoid body. Their axons form a lateral or auditory loop, consisting of crossed and uncrossed auditory tracts, which rises upward and reaches the subcortical auditory centers - the medial geniculate bodies and the inferior colliculi.

The last auditory axons originate from the cells of the subcortical auditory centers, which pass through the posterior leg of the internal capsule and corona radiata, ending in the temporal lobe of the cerebral cortex (the posterior section of the superior temporal gyrus and the transverse gyri of Herschl, located in the depths of the Sylvian fissure).

The primary cortical field is surrounded by secondary projection fields in which auditory stimuli are analyzed, identified, and compared. They are also interpreted and recognized as noises, tones, melodies, vowels and consonants, words and sentences, in other words, symbols of speech. If these cortical areas are damaged in the dominant hemisphere, the ability to recognize sounds and understand speech is lost (sensory aphasia).

On the way from the organ of Corti to the cortex, the fibers of the auditory pathway make 4-6 switches (in the nucleus of the superior olive, neurons of the reticular formation, nucleus of the lateral lemniscus, inferior colliculi, medial geniculate bodies). At these points they give off collaterals, which are part of the reflex arcs. Some collaterals are connected to the cerebellum. Others pass along the medial longitudinal fasciculus to the nuclei that innervate the muscles of the eyes and are involved in organizing the friendly rotation of the eyes in the direction of sound (see eye movement). Some of the fibers go through the lower and upper colliculi of the roof of the midbrain to the pretectal nucleus and from it, as part of the tectobulbar tract, to the nuclei of various cranial nerves, including the nucleus of the facial nerve (to adjust the tone of the stapedius muscle (lat. m.stapedius)), as well as to the motor cells of the anterior horns of the cervical spinal cord. The last connection ensures that the head turns towards or away from the sound source. Collaterals sending impulses to the ascending activating system of the reticular formation contribute to the organization of the awakening process. Some impulses descend as part of the lateral loop to interneurons, which have a regulatory, presumably partially inhibitory, effect on the tone of the basement membrane. These neurons are thought to provide the ear with the ability to focus on specific sound frequencies by simultaneously suppressing nearby frequencies.

[edit]Equilibrium system

The vestibular analyzer receptors are located in the semicircular canals and in the otolithic apparatus of the inner ear. From here, impulses follow along the dendrites of the first neurons of the vestibular pathways to the vestibular ganglion of Scarpa (lat. ganglion vestibulare), lying in the internal auditory canal. The bodies of the first sensory neurons are located in it. From here, impulses follow along the axons of the same cells passing as part of the common trunk of the VIII nerve. Entering the substance of the brain, the central processes of the Scarpe ganglion follow to the vestibular nuclei, which are located in the projection of the vestibular field of the rhomboid fossa on the border with the pons and medulla oblongata.

The vestibular nuclei complex includes

1. Superior vestibular nucleus (Bechterew's nucleus)

2. Lateral vestibular nucleus (Deiters nucleus)

3. Medial vestibular nucleus (Schwalbe nucleus)

4. Inferior vestibular nucleus (Roller's nucleus)

The fibers of the vestibular nerve divide before approaching certain cell groups of the vestibular nuclei, where the second neurons begin. Some of its fibers transmit impulses directly, without switching, to the cerebellum, and to its oldest ontogenetic part - archicerebellum. Efferent impulses from the nucleus fastigii (archicerebellum) return to the vestibular nuclei and then along the vestibular nerve to the hair cells of the labyrinth, exerting a regulatory, predominantly inhibitory effect.

Archicerebellum also receives secondary fibers from the vestibular nuclei. It sends efferent impulses back to the vestibular nucleus complex, as well as to the spinal cord to motor neurons along the cerebellar-reticular and reticulospinal connections. The lateral vestibular nucleus (Deiters nucleus) is where the important lateral vestibulospinal tract begins. It descends ipsilaterally in the anterior funiculus to the γ- and α-motoneurons of the spinal cord, reaching the sacral segments. This pathway has a facilitative effect on extensor reflexes and maintains muscle tone high enough to maintain balance.

Fibers from the medial vestibular nucleus (Schwalbe's nucleus) join on each side of the medial longitudinal fasciculus, communicate with the motor cells of the anterior horns of the cervical segments of the spinal cord and descend as the medial vestibulospinal tract to the rostral (upper) part of the thoracic spinal cord. These fibers are located near the anterior median sulcus of the cervical spinal cord. They form the fasciculus sulcomarginalis, which descends and ends in the rostral part of the thoracic spinal cord. These fibers influence the tone of the neck muscles according to different head positions. It is also possible that they take part in reflex arcs that help maintain balance through initial compensatory movements of the arms.

All vestibular nuclei are connected to the nuclei of the oculomotor nerves through the medial longitudinal fasciculus. Thanks to the vestibulo-oculomotor connections, consistency in the movements of the eyeballs and gaze fixation is achieved when the position of the head changes. Impaired impulse conduction along them leads to the appearance of vestibular nystagmus. Some fibers have been shown to contact the interstitial nucleus of Cajal and the nucleus of Darshkevich and continue to the thalamus optic.

Some of the axons of the vestibular nuclei come into contact with the formations of the autonomic nervous system and, in particular, with the posterior nucleus of the vagus nerve and with the nuclei of the hypothalamic region. The presence of these connections explains the appearance of pronounced autonomic reactions in pathology of the vestibular analyzer in the form of nausea, vomiting, paleness or redness of the skin, sweating, increased intestinal motility, decreased blood pressure, bradycardia, hyperglycemia, etc.

138Glossopharyngeal nerve; nuclei, zones of innervation. Inferior salivary nucleus. Innervation of the parotid salivary gland.

The element responsible for transmitting impulses from the hearing organs to the brain is the vestibulocochlear nerve. Its dendritic processes are also part of the vestibular nucleus, and therefore the nerve performs several functions at once. Questions about its location and signal transmission mechanism should be considered in more detail.

Nerve location and auditory function

The vestibulocochlear nerve is located in the inner ear and has many branches that cover elements of this part of the auditory nerve. The processes connect and extend to the temporal part of the brain, adjacent to the gray matter.

Looking in more detail, the anatomy of the location of the vestibulocochlear nerve is as follows:

Peripheral dendrites, responsible for transmitting auditory impulses, begin in the cochlear ganglion. Then they pass through the spiral organ and transmit the impulse to the central canal.
The second part of the nerve covers the nuclei of the vestibular apparatus and transmits a static signal. The vestibular ganglion has two components: an upper and lower part.
The dendrites enter into a central process that extends into the gray matter of the brain.

The vestibular-cochlear organ should be considered in more detail in terms of the functions it performs. It's worth starting with hearing. Parts of the inner ear such as the spiral and organ of Corti of the cochlea also participate in the process of sound perception.

The anatomy of impulse transmission is extremely simple: sound vibrations irritate hair receptors and are transformed into a nerve impulse in the organ of Corti. Through transmission to the spiral ganglion, they are converted into a stream of information that is perceived by the nerve nuclei.

After the processes of the auditory nerve receive the transformed sound impulse, the signal path begins to the cortical center of the brain. On its way, it passes the nuclei of the superior olive and lateral lemniscus, switching up to 6 times. As a result, a person gains the ability to recognize speech, the nature of sound, and the source of its production. It is worth noting here the ability to concentrate auditory perception at frequencies of a certain range.

Vestibular function

The second part of the nerve's activity is its penetration into the vestibular apparatus and the reception of signals about the position of the body. This system is quite complex, since on its way the impulse bypasses the nuclei of the organ and is transformed many times.

The vestibulocochlear organ passes through the following nuclei:

upper (Bechterev);
lateral (Deiters);
medial (Schwalbe);
lower (Roller).

The anatomy of signal transmission is based on the fact that individual fibers depart from the dendrites of the vestibular part of the nerve, which cover the indicated nuclei and convert the signal into them, splitting and reuniting into a single line. To achieve the goal, the impulse from the nucleus needs to connect with that part of the process that is responsible for the auditory function. Next, the signal enters the brain through the central channel, and from there a system of fibers diverges, which covers the spinal cord, muscle tissue and adjacent nerve endings responsible for oculomotor function, etc.

As a result, the autonomic nervous system is formed, which, based on signals received from the vestibular organ, sends commands to the brain and perceives a response. Thus, a person can control the position of his body in space, make movements and react to sound physically.

Diagnosis of the condition

Since the vestibular-cochlear nerve is responsible for hearing and transmission of vestibular signals, any deviations in the functioning of the chain of hearing organs can lead to a failure in the perception of information. It is worth considering possible situations.

If auditory function is impaired, the scenario can develop in the following directions:

Conductive hearing loss. Deviations are localized in the outer or middle ear. They can be caused by congenital defects, injuries, tumors or previous diseases. In this case, the flow of information of a certain kind is blocked.
Sensorineural hearing loss. It is directly related to nervous perception and the condition of the organs of the inner ear.

If the perception of sound waves and vibrations is impaired, an inflammatory process can be detected. If a pathological noise occurs, we have to talk about a neuroma or damage to the cochlea. Typically, deafness develops only on the side of the affected ear.

Symmetrical disorders are observed with damage to the thalamus or temporal lobe of the brain. Then auditory hallucinations may occur, sounds are perceived as excessively loud, agnosia occurs, and sharp stimuli cause pain.

When violations of the vestibular process are detected, nystagmus of the eyeballs is often observed. At the same time, orientation in space deteriorates, dizziness and fainting occur, and hearing gradually decreases.

The causes of such pathologies can be tumors in the inner ear or brain along the path of the nerve junction. Also, such disorders can be a consequence of syphilis, multiple sclerosis, Meniere's syndrome, vertebrobasilar insufficiency, etc. Vestibular function is affected by the state of the labyrinth of the inner ear. Coordination disorders with concomitant disorders of auditory function are observed in cases of serious intoxication of the body. Poisoning can be caused by pesticides, potent drugs, chemical compounds, inflammation, etc.

Neuroma and its treatment

The most well-known problem in medical practice associated with damage to the nucleus and connections of the vestibular-cochlear nerve is neuroma. This pathology represents the occurrence of a tumor that blocks the normal activity of the element. If it is large in size, it also affects other centers of the body’s functioning, which can lead to death due to respiratory arrest or cessation of cardiac function.

The first symptoms of neuroma development are the standard signs of hearing loss, noise and other discomfort. The disease occurs in four stages:

Otiatric. The tumor is localized in the internal auditory canal. It puts pressure on nerve endings, which causes disruption of corresponding functions and distortion of human sensations. In this case, vestibular disorders may be absent.
Otoneurological. Symptoms intensify, the tumor affects neighboring nerves. The tumor spreads beyond the inner ear and extends to the cerebellopontine ganglion. Paresis of the facial nerve, loss of orientation in space, and deafness on the side of the affected ear may be observed.
Neurological. The tumor puts pressure on the brain, specifically on the pons, brainstem and cerebellum. On the part of the neoplasm, paresis of more and more new ligaments develops. In this case, the eyes suffer, as nystagmus increases, congestion occurs, and the corneal reflex is absent. Increased intracranial pressure is added to the symptoms.
Terminal. During this period, the tumor degenerates into a cyst-like formation filled with a yellowish liquid. Pressure is exerted on the vital centers of the brain that regulate breathing and heartbeat. If left untreated, cerebral edema develops and the patient dies.

To diagnose neuroma, standard examinations are performed. To clarify the size and position of the tumor, detailed radiography is necessary. Additionally, cerebrospinal fluid samples are taken. If cancer is suspected, a biopsy is performed.

The essence of treatment is surgical removal of the neuroma. The sooner it is identified and excised, the lower the risk of complications and brain damage.

Elimination and prevention of malfunctions

To eliminate other disorders of the vestibulocochlear nerve, you need to seek help from a neurologist. After a thorough diagnosis of the condition and clarification of the causes of the ailment, treatment will be prescribed. It necessarily contains a set of measures, which will include the following actions and procedures:

Taking medications. With the help of certain medications, depending on the diagnosis, it is possible to relieve swelling that blocks the normal functioning of the nerve, stop inflammation, eliminate infection, etc. It may also be necessary to stimulate nervous activity and blood circulation in the receiving part of the brain.
Physiotherapy. The use of radiation and electrical impulses can have a beneficial effect on the entire nervous system, and when the direction is localized, it can activate the necessary connections.
Nutrition. The diet involves giving up salt at least for the period of normalization of the patient’s condition. You also need to eliminate all junk food, introduce more clean water and give up bad habits.
Operation. To remove problematic formations, surgical, radio wave intervention or the gamma knife technique is traditionally used. In this way, tumors that interfere with the functioning of organs associated with the vestibulocochlear nerve are excised. If the functioning of the process connecting the nuclei of the vestibular apparatus is disrupted, an approach based on its dissection is used.

Surgery for pathologies of the vestibulocochlear nerve is associated with the risk of damage to adjacent endings or hearing loss. If the auditory process or labyrinth is damaged, a person becomes deaf, so radical methods are used in patients with already developed deafness. In some situations, it is more advisable to use a wait-and-see method, without specific actions.