The structure of the membranous canal of the cochlea and the spiral organ (diagram). Structure of the inner ear Structure of the membranous canal of the cochlea

The inner ear (auris interna) consists of a bony labyrinth (labyrinthus osseus) and a membranous labyrinth included in it (labyrinthus membranaceus).

The bony labyrinth (Fig. 4.7, a, b) is located deep in the pyramid of the temporal bone. Laterally it borders with the tympanic cavity, to which the windows of the vestibule and cochlea face, medially with the posterior cranial fossa, with which it communicates through the internal auditory canal (meatus acusticus internus), the cochlear aqueduct (aquaeductus cochleae), as well as the blindly ending aqueduct of the vestibule (aquaeductus vestibuli). The labyrinth is divided into three sections: the middle one is the vestibule (vestibulum), behind it is a system of three semicircular canals (canalis semicircularis) and in front of the vestibule is the cochlea (cochlea).

The front, the central part of the labyrinth, is phylogenetically the most ancient formation, which is a small cavity, inside of which two pockets are distinguished: spherical (recessus sphericus) and elliptical (recessus ellipticus). In the first, located near the cochlea, lies the utricle, or spherical sac (sacculus), in the second, adjacent to the semicircular canals, there is an elliptical sac (utriculus). On the outer wall of the vestibule there is a window, covered from the side of the tympanic cavity by the base of the stapes. The anterior part of the vestibule communicates with the cochlea through the scala vestibule, and the posterior part communicates with the semicircular canals.

Semicircular canals. There are three semicircular canals in three mutually perpendicular planes: the external (canalis semicircularis lateralis), or horizontal, is located at an angle of 30° to the horizontal plane; anterior (canalis semicircularis anterior), or frontal vertical, located in the frontal plane; posterior (canalis semicircularis posterior), or sagittal vertical, located in the sagittal plane. Each canal has two bends: smooth and widened - ampullary. The smooth knees of the upper and posterior vertical canals are fused into a common knee (crus commune); all five knees face the elliptical recess of the vestibule.

The lyca is a bony spiral canal, which in humans makes two and a half turns around a bone rod (modiolus), from which a bony spiral plate (lamina spiralis ossea) extends into the canal in a helical manner. This bony plate, together with the membranous basilar plate (basic membrane), which is its continuation, divides the cochlear canal into two spiral corridors: the upper one is the scala vestibule (scala vestibuli), the lower one is the scala tympani (scala tympani). Both scalae are isolated from each other and only at the apex of the cochlea communicate with each other through an opening (helicotrema). The scala vestibule communicates with the vestibule, the scala tympani borders the tympanic cavity through the fenestra cochlea. In the barlban staircase near the cochlear window, the cochlear aqueduct begins, which ends on the lower edge of the pyramid, opening into the subarachnoid space. The lumen of the cochlear aqueduct is usually filled with mesenchymal tissue and possibly has a thin membrane, which apparently acts as a biological filter that converts cerebrospinal fluid into perilymph. The first curl is called the “base of the cochlea” (basis cochleae); he performs in tympanic cavity, forming a cape (promontorium). The bony labyrinth is filled with perilymph, and the membranous labyrinth located in it contains endolymph.

The membranous labyrinth (Fig. 4.7, c) is a closed system of canals and cavities, which basically follows the shape of the bony labyrinth. The membranous labyrinth is smaller in volume than the bone labyrinth, so a perilymphatic space filled with perilymph is formed between them. The membranous labyrinth is suspended in the perilymphatic space by connective tissue cords that pass between the endosteum of the bony labyrinth and the connective tissue membrane of the membranous labyrinth. This space is very small in the semicircular canals and expands in the vestibule and cochlea. The membranous labyrinth forms an endolymphatic space, which is anatomically closed and filled with endolymph.

Perilymph and endolymph represent the humoral system of the ear labyrinth; these liquids differ in electrolyte and bio chemical composition, in particular, endolymph contains 30 times more potassium than perilymph, and it contains 10 times less sodium, which is essential in the formation of electrical potentials. The perilymph communicates with the subarachnoid space through the cochlear aqueduct and is a modified (mainly in protein composition) cerebrospinal fluid. Endolymph, being in closed system The membranous labyrinth does not have direct communication with the cerebral fluid. Both fluids of the labyrinth are functionally closely related to each other. It is important to note that the endolymph has a huge positive resting electrical potential of +80 mV, and the perilymphatic spaces are neutral. Hair cell hairs have a negative charge of -80 mV and penetrate the endolymph with a potential of +80 mV.

A - bone labyrinth: 1 - cochlea; 2 - tip of the cochlea; 3 - apical curl of the cochlea; 4 - middle curl of the cochlea; 5 - main curl of the cochlea; 6, 7 - vestibule; 8 - cochlear window; 9 - window of the vestibule; 10 - ampulla of the posterior semicircular canal; 11 - horizontal leg: semicircular canal; 12 - posterior semicircular canal; 13 - horizontal semicircular canal; 14 - common leg; 15 - anterior semicircular canal; 16 - ampulla of the anterior semicircular canal; 17 - ampulla of the horizontal semicircular canal, b - bone labyrinth ( internal structure): 18 - specific channel; 19 - spiral channel; 20 - bone spiral plate; 21 - scala tympani; 22 - staircase vestibule; 23 - secondary spiral plate; 24 - internal hole of the cochlea water supply, 25 - recess of the cochlea; 26 - lower perforated hole; 27 - internal opening of the vestibule water supply; 28 - mouth of the common south 29 - elliptical pocket; 30 - upper perforated spot.

Rice. 4.7. Continuation.

: 31 - utricle; 32 - endolymphatic duct; 33 - endolymphatic sac; 34 - stirrup; 35 - utero-sac duct; 36 - membrane of the cochlea window; 37 - snail water supply; 38 - connecting duct; 39 - pouch.

With anatomical and physiological points vision in the inner ear, two receptor apparatuses are distinguished: the auditory, located in the membranous cochlea (ductus cochlearis), and the vestibular, uniting the vestibule sacs (sacculus et utriculus) and three membranous semicircular canals.

The membranous cochlea is located in the scala tympani, it is a spiral-shaped canal - the cochlear duct (ductus cochlearis) with a receptor apparatus located in it - the spiral, or organ of Corti (organum spirale). In a transverse section (from the apex of the cochlea to its base through the bone shaft), the cochlear duct has a triangular shape; it is formed by the precursor, outer and tympanic walls (Fig. 4.8, a). The vestibule wall faces the staircase of the prezdzerium; it is a very thin membrane - the vestibular membrane (Reissner's membrane). The outer wall is formed by a spiral ligament (lig. spirale) with three types of stria vascularis cells located on it. Stria vascularis abundantly

A - bony cochlea: 1-apical curl; 2 - rod; 3 - oblong channel of the rod; 4 - staircase vestibule; 5 - scala tympani; 6 - bone spiral plate; 7 - spiral canal of the cochlea; 8 - spiral channel of the rod; 9 - internal auditory canal; 10 - perforated spiral path; 11 - opening of the apical helix; 12 - hook of the spiral plate.

It is equipped with capillaries, but they do not directly contact the endolymph, ending in the basilar and intermediate cell layers. The epithelial cells of the stria vascularis form the lateral wall of the endocochlear space, and the spiral ligament forms the wall of the perilymphatic space. The tympanic wall faces the scala tympani and is represented by the main membrane (membrana basilaris), which connects the edge of the spiral plate with the wall of the bone capsule. On the main membrane lies a spiral organ - the peripheral receptor of the cochlear nerve. The membrane itself has an extensive network of capillary blood vessels. The cochlear duct is filled with endolymph and communicates with the sac (sacculus) through the connecting duct (ductus reuniens). The main membrane is a formation consisting of elastic, elastic and weakly interconnected transverse fibers (there are up to 24,000 of them). The length of these fibers increases by

Rice. 4.8. Continuation.

: 13 - central processes of the spiral ganglion; 14-spiral ganglion; 15 - peripheral processes of the spiral ganglion; 16 - bone capsule of the cochlea; 17 - spiral ligament of the cochlea; 18 - spiral protrusion; 19 - cochlear duct; 20 - outer spiral groove; 21 - vestibular (Reissner's) membrane; 22 - cover membrane; 23 - internal spiral groove k-; 24 - lip of the vestibular limbus.

Rule from the main curl of the cochlea (0.15 cm) to the apex area (0.4 cm); the length of the membrane from the base of the cochlea to its apex is 32 mm. The structure of the main membrane is important for understanding the physiology of hearing.

The spiral (cortical) organ consists of neuroepithelial inner and outer hair cells, supporting and feeding cells (Deiters, Hensen, Claudius), outer and inner columnar cells , forming the arcs of Corti (Fig. 4.8, b). Inward from the inner columnar cells there is a number of inner hair cells (up to 3500); outside the outer columnar cells are rows of outer hair cells (up to 20,000). In total, humans have about 30,000 hair cells. They are covered by nerve fibers emanating from the bipolar cells of the spiral ganglion. The cells of the spiral organ are connected to each other, as is usually observed in the structure of the epithelium. Between them there are intraepithelial spaces filled with fluid called “cortilymph”. It is closely related to the endolymph and is quite close to it in chemical composition, but it also has significant differences, constituting, according to modern data, the third intracochlear fluid, which determines the functional state of sensitive cells. It is believed that the cortilymph performs the main, trophic function of the spiral organ, since it does not have its own vascularization. However, this opinion must be taken critically, since the presence of a capillary network in the basilar membrane allows for the presence of its own vascularization in the spiral organ.

Above the spiral organ is a covering membrane (membrana tectoria), which, like the main one, extends from the edge of the spiral plate. The integumentary membrane is a soft, elastic plate consisting of protofibrils having a longitudinal and radial direction. The elasticity of this membrane is different in the transverse and longitudinal directions. Hairs of neuroepithelial (external, but not internal) hair cells located on the main membrane penetrate into the integumentary membrane through the cortilymph. When the main membrane oscillates, tension and compression of these hairs occur, which is the moment of transformation of mechanical energy into the energy of an electrical nerve impulse. This process is based on the above-mentioned electrical potentials of labyrinthine fluids.

Membranous semicircular canals and sacs in front of the door. The membranous semicircular canals are located in the bony canals. They are smaller in diameter and repeat their design, i.e. have ampullary and smooth parts (knees) and are suspended from the periosteum of the bone walls by supporting connective tissue cords in which the vessels pass. The exception is the ampoules of the membranous canals, which are almost entirely bone ampoules. The inner surface of the membranous canals is lined with endothelium, with the exception of the ampullae in which receptor cells are located. On the inner surface of the ampullae there is a circular protrusion - the ridge (crista ampullaris), which consists of two layers of cells - supporting and sensitive hair cells, which are peripheral receptors of the vestibular nerve (Fig. 4.9). Long hairs of neuroepithelial cells are glued together, and from them a formation is formed in the form of a circular brush (cupula terminalis), covered with a jelly-like mass (vault). Mechanics

The displacement of the circular brush towards the ampulla or smooth knee of the membranous canal as a result of the movement of the endolymph during angular acceleration is an irritation of neuroepithelial cells, which is transformed into electrical impulse and is transmitted to the endings of the ampullary branches of the vestibular nerve.

In the vestibule of the labyrinth there are two membranous sacs - sacculus and utriculus with otolithic apparatus embedded in them, which, according to the sacs, are called macula utriculi and macula sacculi and are small elevations on the inner surface of both sacs, lined with neuroepithelium. This receptor also consists of supporting cells and hair cells. The hairs of sensitive cells, intertwining their ends, form a network, which is immersed in a jelly-like mass containing a large number of crystals shaped like parallelepipeds. The crystals are supported by the ends of the hairs of sensory cells and are called otoliths, they are composed of phosphate and calcium carbonate (arragonite). The hairs of the hair cells, together with the otoliths and the jelly-like mass, make up the otolithic membrane. The pressure of otoliths (gravity) on the hairs of sensitive cells, as well as the displacement of hairs during linear acceleration, is the moment of transformation of mechanical energy into electrical energy.

Both sacs are connected to each other through a thin canal (ductus utriculosaccularis), which has a branch - the endolymphatic duct (ductus endolymphaticus), or aqueduct of the vestibule. The last one goes to back surface pyramid, where it blindly ends with an expansion (saccus endolymphaticus) in the dura mater of the posterior cranial fossa.

Thus, the vestibular sensory cells are located in five receptor areas: one in each ampulla of the three semicircular canals and one in the two sacs of the vestibule of each ear. Peripheral fibers (axons) from the cells of the vestibular ganglion (scarpe ganglion), located in the internal auditory canal, approach the receptor cells of these receptors; the central fibers of these cells (dendrites) as part of the VIII pair of cranial nerves go to the nuclei in the medulla oblongata.

The blood supply to the internal ear is carried out through the internal labyrinthine artery (a.labyrinthi), which is a branch of the basilar artery (a.basilaris). In the internal auditory canal, the labyrinthine artery is divided into three branches: vestibular (a. vestibularis), vestibulocochlearis (a. vestibulocochlearis) and cochlear (a. cochlearis) arteries. Venous drainage from the inner ear it goes along three routes: the veins of the cochlear aqueduct, the vestibular aqueduct and the internal auditory canal.

Innervation of the internal ear. Peripheral (receptor) section auditory analyzer forms the spiral organ described above. At the base of the bony spiral plate of the cochlea there is a spiral node (ganglion spirale), each ganglion cell of which has two processes - peripheral and central. The peripheral processes go to the receptor cells, the central ones are fibers of the auditory (cochlear) portion of the VIII nerve (n.vestibu-locochlearis). In the region of the cerebellopontine angle, the VIII nerve enters the bridge and at the bottom of the fourth ventricle is divided into two roots: the superior (vestibular) and the inferior (cochlear).

The fibers of the cochlear nerve end in the auditory tubercles, where the dorsal and ventral nuclei are located. Thus, the cells of the spiral ganglion, together with peripheral processes going to the neuroepithelial hair cells of the spiral organ, and central processes ending in the nuclei medulla oblongata, constitute the first neuron of the auditory analyzer. Neuron II of the auditory analyzer begins from the ventral and dorsal auditory nuclei in the medulla oblongata. In this case, a smaller part of the fibers of this neuron goes along the side of the same name, and the majority in the form of striae acusticae passes to the opposite side. As part of the lateral loop, the fibers of neuron II reach the olive, from where

1 - peripheral processes of spiral ganglion cells; 2 - spiral ganglion; 3 - central processes of the spiral ganglion; 4 - internal auditory canal; 5 - anterior cochlear nucleus; 6 - posterior cochlear nucleus; 7 - nucleus of the trapezoid body; 8 - trapezoidal body; 9 - medullary stripes of the fourth ventricle; 10 - medial geniculate body; 11 - nuclei of the inferior colliculi of the midbrain roof; 12 - cortical end of the auditory analyzer; 13 - tegnospinal tract; 14 - dorsal part of the bridge; 15 - ventral part of the bridge; 16 - lateral loop; 17 - posterior leg of the internal capsule.

The third neuron begins, going to the nuclei of the quadrigeminal and medial geniculate body. The IV neuron goes to the temporal lobe of the brain and ends in the cortical part of the auditory analyzer, located mainly in the transverse temporal gyrus (Heschl’s gyrus) (Fig. 4.10).

The vestibular analyzer is constructed in a similar way.

The vestibular ganglion (ganglion Scarpe) is located in the internal auditory canal, the cells of which have two processes. The peripheral processes go to the neuroepithelial hair cells of the ampullary and otolith receptors, and the central ones form the vestibular portion of the VIII nerve (n. cochleovestibularis). The first neuron ends in the nuclei of the medulla oblongata. There are four groups of nuclei: lateral nuclei

CHAPTER 11. HEARING AND BALANCE

CHAPTER 11. HEARING AND BALANCE

The recording of two sensory modalities - hearing and balance - occurs in the ear. Both organs (hearing and balance) form the vestibule in the thickness of the temporal bone (vestibulum) and a snail (cochlea)- vestibulocochlear organ. The receptor (hair) cells (Fig. 11-1) of the organ of hearing are located in the membranous canal of the cochlea (organ of Corti), and the organ of balance (vestibular apparatus) in the structures of the vestibule - the semicircular canals, the utricle (utriculus) and a bag (sacculus).

Rice. 11-1. Vestibulocochlear organ and receptor areas(top right, blackened) organs of hearing and balance. The movement of perilymph from the oval to the round window is indicated by arrows

HEARING

HEARING ORGAN anatomically consists of the outer, middle and inner ear.

Outer ear presented auricle and external ear canal.

Middle ear. Its cavity communicates with the nasopharynx using the Eustachian (auditory) tube and is separated from the external auditory canal by a tympanic membrane with a diameter of 9 mm, and from the vestibule and scala tympani of the cochlea by oval and round windows, respectively. Eardrum transmits sound vibrations to three small interconnected auditory ossicles: the malleus is attached to the tympanic membrane, and the stapes is attached to the oval window. These bones vibrate in unison and amplify the sound twenty times. The auditory tube maintains air pressure in the middle ear cavity at atmospheric pressure.

Inner ear. The cavity of the vestibule, tympanic and vestibular scala of the cochlea (Fig. 11-2) are filled with perilymph, and the semicircular canals, utricle, saccule and cochlear duct (membranous canal of the cochlea) located in the perilymph are filled with endolymph. There is an electrical potential between the endolymph and perilymph - about +80 mV (intracochlear, or endocochlear potential).

❖ Endolymph- viscous liquid, fills the membranous canal of the cochlea and is connected through a special channel (ductus reuniens) with endolymph of the vestibular apparatus. The concentration of K+ in the endolymph is 100 times higher than in the cerebrospinal fluid (CSF) and perilymph; the concentration of Na+ in the endolymph is 10 times less than in the perilymph.

❖ Perilymph its chemical composition is close to blood plasma and cerebrospinal fluid and occupies an intermediate position between them in terms of protein content.

❖ Endocochlear potential. The membranous canal of the cochlea is positively charged (+60-+80 mV) relative to the other two scalae. The source of this (endocochlear) potential is the stria vascularis. Hair cells are polarized by the endocochlear potential to a critical level, which increases their sensitivity to mechanical stress.

Uligka and organ of Corti

Snail- spirally twisted bone canal - forms 2.5 curls about 35 mm long. The basilar (main) and vestibular membranes, located inside the cochlear canal, divide

Rice. 11-2. Membranous canal and spiral organ of Corti. The cochlear canal is divided into the scala tympani and vestibular canal and the membranous canal (middle scala), in which the organ of Corti is located. The membranous canal is separated from the scala tympani by a basilar membrane. It contains peripheral processes of neurons of the spiral ganglion, forming synaptic contacts with outer and inner hair cells

The canal cavity is divided into three parts: scala tympani (scala tympani), scala vestibular (scala vestibuli) and membranous canal of the cochlea (scala media, middle scala, cochlear duct). Endolymph fills the membranous canal of the cochlea, and perilymph fills the vestibular and tympanic scala. In the membranous canal of the cochlea, on the basilar membrane, there is a receptor apparatus of the cochlea - the organ of Corti (spiral) organ. Organ of Corti(Figs. 11-2 and 11-3) contains several rows of support and hair cells. All cells are attached to the basilar membrane; hair cells are connected to the integumentary membrane with their free surface.

Rice. 11-3. Hair receptor cells of the organ of Corti

Hair cells- receptor cells of the organ of Corti. They form synaptic contacts with the peripheral processes of sensory neurons of the spiral ganglion. There are inner and outer hair cells, separated by a cell-free space (tunnel).

❖ Inner hair cells form one row. On their free surface there are 30-60 immobile micro-processes - stereocilia, passing through the integumentary membrane. The stereocilia are arranged in a semicircle (or V-shaped), open towards the external structures of the organ of Corti. The total number of cells is about 3500; they form approximately 95% of synapses with the processes of sensory neurons of the spiral ganglion.

❖ Outer hair cells arranged in 3-5 rows and also have stereocilia. Their number reaches 12 thousand, but together they form no more than 5% of synapses with afferent fibers. However, if the outer cells are damaged but the inner cells are intact, noticeable hearing loss will still occur. Perhaps the outer hair cells somehow control the sensitivity of the inner hair cells for different sound levels.

basilar membrane, separating the middle and scala tympani, contains up to 30 thousand basilar fibers coming from the bony shaft of the cochlea (modiolus) towards its outer wall. Basilar fibers - tight, elastic, reed-like - are attached to the cochlear shaft at only one end. As a result, the basilar fibers can vibrate harmoniously. Basilar fiber length increases from the base to the apex of the cochlea - the helicotrema. In the area of ​​the oval and round windows their length is about 0.04 mm; in the area of ​​the helicotrema they are 12 times longer. Diameter of basilar fibers decreases from the base to the top of the cochlea by about 100 times. As a result, short basilar fibers near the oval window vibrate better at high frequencies, while long fibers near the helicotrema vibrate better at low frequencies (Fig. 11-4). Consequently, high-frequency resonance of the basilar membrane occurs near the base where sound waves enter the cochlea through the oval window, and low-frequency resonance occurs near the helicotrema.

Conduction of sound to the cochlea

The chain of sound pressure transmission looks like this: tympanic membrane - malleus - incus - stapes - membrane of the oval window - perilymph - basilar and tectorial membranes - membrane of the round window (see Fig. 11-1). When the stapes is displaced, the perilymph moves along the scala vestibularis and then through the helicotrema along the scala tympani to the round window. Fluid displaced by the displacement of the oval window membrane creates excess pressure in the vestibular canal. Under the influence of this pressure, the basilar membrane moves towards the scala tympani. The oscillatory reaction in the form of a wave propagates from the basilar membrane to the helicotrema. The displacement of the tectorial membrane relative to the hair cells under the influence of sound causes their excitation. The resulting electrical reaction (microphone effect) repeats the shape of the sound signal.

Movement of sound waves in the cochlea

When the sole of the stapes moves inward against the oval window, the round window bulges outward because the cochlea is surrounded on all sides by bone tissue. The initial effect of a sound wave entering the oval window is manifested in the deflection of the basilar membrane at the base of the cochlea in the direction of the round

Rice. 11-4. The nature of waves along the basilar membrane. A, B and C show the scala vestibular (top) and scala tympani (bottom) in the direction from the oval (top left) through the helicotrema (right) to the round (bottom left) window; the basilar membrane in A-G is the horizontal line dividing the named ladders. The middle staircase is not taken into account in the model. Left: high wave movement (A), medium- (B) and low frequency (IN) sounds along the basilar membrane. On right: correlation between sound frequency and vibration amplitude of the basilar membrane depending on the distance from the base of the cochlea

window. However, the elastic tension of the basilar fibers creates a wave of fluid that runs along the basilar membrane in the direction of the helicotrema (Fig. 11-4).

Each wave starts out relatively weak, but becomes stronger when it reaches that part of the basilar membrane where the membrane's own resonance becomes equal to the frequency of the sound wave. At this point the basilar membrane can vibrate freely back and forth, i.e. the energy of the sound wave is dissipated, the wave is interrupted at this point and loses the ability to move along the basilar membrane. Thus, a high frequency sound wave travels a short distance along the basilar membrane before it reaches its resonant point and disappears; medium-frequency sound waves travel approximately halfway and then stop; finally, very low frequency sound waves travel along the membrane almost to the helicotrema.

Hair cell activation

Fixed and elastic stereocilia are directed upward from the apical surface of the hair cells and penetrate the integumentary membrane (Fig. 11-3). At the same time, the basal part of the hair receptor cells is fixed to the basilar fibers containing

membrane Hair cells are excited as soon as the basilar membrane begins to vibrate along with the cells attached to it and the covering membrane. And this excitation of hair cells (generation of receptor potential) begins in stereocilia.

Receptor potential. The resulting tension on the stereocilia causes mechanical transformations that open 200 to 300 cation channels. K+ ions from the endolymph enter the stereocilium, causing depolarization of the hair cell membrane. At the synapses between the receptor cell and the afferent nerve ending, a fast-acting neurotransmitter - glutamate - is released, it interacts with glutamate receptors, depolarizes the postsynaptic membrane and generates action potentials.

Directional sensitivity. When the basilar fibers bend toward the scala vestibularis, the hair cells depolarize; but when the basilar membrane moves in the opposite direction, they become hyperpolarized (the same directional sensitivity, which determines the electrical response of the receptor cell, is characteristic of the hair cells of the balance organ, see Fig. 11-7A).

Sound Characteristics Detection

Frequency the sound wave is rigidly “tied” to a specific area of ​​the basilar membrane (see Fig. 11-4). Moreover, there is a spatial organization of nerve fibers throughout the entire auditory pathway - from the cochlea to the cerebral cortex. Registration of signals in the auditory tract of the brain stem and in the auditory field of the cerebral cortex shows that there are special brain neurons excited by specific sound frequencies. Therefore, the main method used by the nervous system to determine sound frequencies is to determine which part of the basilar membrane is most stimulated - the so-called "place principle".

Volume. The auditory system uses several mechanisms to determine loudness.

❖ Loud sound increases the amplitude of vibrations of the basilar membrane, which increases the number of excited hair cells, and this leads to spatial summation of impulses and transmission of excitation along many nerve fibers.

❖ The outer hair cells are not excited until the vibration of the basilar membrane reaches a high intensity

intensity. Stimulation of these cells can be assessed by the nervous system as an indication of a truly loud sound. ❖ Loudness estimation. There is no direct proportional relationship between the physical strength of sound and its apparent loudness, i.e. the sensation of increasing sound volume does not strictly parallel the increase in sound intensity (sound power level). To estimate the sound power level, use the logarithmic indicator of the actual sound intensity: 10-fold increase in sound energy - 1 white(B). 0.1 B is called decibel(dB) 1 dB - increase in sound energy by 1.26 times - sound intensity relative to the threshold (2x10 -5 dyn/cm 2) (1 dyn = 10 -5 N). In normal sound perception during communication, a person can distinguish changes in sound intensity of 1 dB.

Auditory pathways and centers

In Fig. Figure 11-5A shows a simplified diagram of the main auditory pathways. Afferent nerve fibers from the cochlea enter the spiral ganglion and from it enter the dorsal (posterior) and ventral (anterior) cochlear nuclei, located in the upper part of the medulla oblongata. Here, ascending nerve fibers form synapses with second-order neurons, the axons of which

Rice. 11-5. A. Main auditory pathways(posterior view of the brainstem, cerebellum and cerebral cortex removed). B. Auditory cortex

partly they pass to the opposite side to the nuclei of the superior olive, and partly they end on the nuclei of the superior olive of the same side. From the superior olive nuclei, the auditory tract ascends through the lateral lemniscal tract; some of the fibers end in the lateral lemniscal nuclei, and most of the axons bypass these nuclei and follow to the inferior colliculus, where all or almost all auditory fibers form synapses. From here, the auditory pathway passes to the medial geniculate body, where all fibers end at synapses. The auditory pathway finally ends in the auditory cortex, located mainly in the superior gyrus of the temporal lobe (Fig. 11-5B). The basilar membrane of the cochlea at all levels of the auditory pathway is presented in the form of certain projection maps of various frequencies. Already at the level of the midbrain, neurons appear that detect several signs of sound based on the principles of lateral and recurrent inhibition.

Auditory cortex

The projection areas of the auditory cortex (Fig. 11-5B) are located not only in the upper part of the superior temporal gyrus, but also extend to the outer side of the temporal lobe, capturing part of the insular cortex and parietal operculum.

Primary auditory cortex directly receives signals from the internal (medial) geniculate body, while auditory association area secondarily excited by impulses from the primary auditory cortex and thalamic areas bordering the medial geniculate body.

Tonotopic maps. In each of the 6 tonotopic maps, high-frequency sounds excite neurons in the back of the map, while low-frequency sounds excite neurons in the front of the map. It is assumed that each separate area perceives its own specific features sound. For example, one large map in the primary auditory cortex almost entirely discriminates against sounds that appear high-pitched to the subject. Another map is used to determine the direction of sound arrival. Some areas of the auditory cortex detect special qualities of sound signals (for example, unexpected onset of sounds or modulations of sounds).

Audio frequency range, to which neurons of the auditory cortex respond narrower than for neurons of the spiral ganglion and brain stem. This is explained, on the one hand, high degree specialization of cortical neurons, and on the other hand, the phenomenon of lateral and recurrent inhibition, enhancing the

the decisive ability of neurons to perceive the required sound frequency.

Determining the direction of sound

Direction of the sound source. Two ears working in unison can detect the source of a sound by the difference in volume and the time it takes to reach both sides of the head. A person determines the sound coming to him in two ways. The time delay between the arrival of sound in one ear and the opposite ear. Sound travels first to the ear closest to the sound source. Low frequency sounds bend around the head due to their considerable length. If the sound source is located on the midline in front or behind, then even a minimal shift from the midline is perceived by a person. This subtle comparison of the minimum difference in the time of sound arrival is carried out by the central nervous system at the points where auditory signals converge. These convergence points are the superior olive, inferior colliculus, and primary auditory cortex. The difference between the intensity of sounds in the two ears. At high sound frequencies, the size of the head noticeably exceeds the length of the sound wave, and the wave is reflected by the head. This results in a difference in the intensity of sounds coming to the right and left ears.

Auditory sensations

Frequency range, that a person perceives includes about 10 octaves of the musical scale (from 16 Hz to 20 kHz). This range gradually decreases with age due to a decrease in the perception of high frequencies. Sound frequency discrimination characterized by a minimal difference in frequency between two close sounds, which can still be detected by a person.

Absolute hearing threshold- the minimum sound intensity that a person hears in 50% of cases when it is presented. The hearing threshold depends on the frequency of sound waves. The maximum sensitivity of human hearing is located in the region from 500 to 4000 Hz. Within these boundaries, sound is perceived as having extremely low energy. The region of sound perception of human speech is located in the range of these frequencies.

Sensitivityto sound frequencies below 500 Hz progressively decreases. This protects a person from the possible constant sensation of low-frequency vibrations and noise produced by his own body.

SPATIAL ORIENTATION

The spatial orientation of the body at rest and in movement is largely ensured by reflex activity originating in the vestibular apparatus of the inner ear.

Vestibular apparatus

The vestibular (vestibulary) apparatus, or organ of balance (Fig. 11-1) is located in the petrous part of the temporal bone and consists of the bony and membranous labyrinths. Bone labyrinth - system of semicircular ducts (canales semicirculares) and the cavity communicating with them - the vestibule (vestibulum). Membranous labyrinth- a system of thin-walled tubes and sacs located inside the bone labyrinth. In the bone ampullae, the membranous canals expand. In each ampullary extension of the semicircular canal there are scallops(crista ampullaris). In the vestibule of the membranous labyrinth, two interconnected cavities are formed: little mother, into which the membranous semicircular canals open, and pouch. The sensitive areas of these cavities are spots. The membranous semicircular canals, the utricle and the sac are filled with endolymph and communicate with the cochlea, as well as with the endolymphatic sac located in the cranial cavity. The ridges and spots, the receptive areas of the vestibular organ, contain receptor hair cells. Rotational movements are recorded in the semicircular canals (angular acceleration), in the uterus and pouch - linear acceleration.

Sensitive spots and scallops(Figure 11-6). The epithelium of the spots and scallops contains sensory hair cells and supporting cells. The epithelium of the spots is covered with a gelatinous otolithic membrane containing otoliths - crystals of calcium carbonate. The scallop epithelium is surrounded by a jelly-like transparent dome (Fig. 11-6A and 11-6B), which easily moves with the movements of the endolymph.

Hair cells(Fig. 11-6 and 11-6B) are located in the crests of each ampulla of the semicircular canals and in the spots of the vestibular sacs. Hair receptor cells in the apical part contain 40-110 immobile hairs (stereocilia) and one mobile eyelash (kinocilium), located on the periphery of the bundle of stereocilia. The longest stereocilia are located near the kinocilium, and the length of the rest decreases with distance from the kinocilium. Hair cells are sensitive to the direction of stimulus (directional sensitivity, see fig. 11-7A). When the irritating effect is directed from stereocilia to

Rice. 11-6. Receptor area of ​​the balance organ. Vertical sections through the comb (A) and spots (B, C). OM - otolith membrane; O - otoliths; PC - supporting cell; RK - receptor cell

kinocilia, the hair cell is excited (depolarization occurs). When the stimulus is directed in the opposite direction, the response is suppressed (hyperpolarization).

Stimulation of the semicircular canals

The receptors of the semicircular canals perceive rotational acceleration, i.e. angular acceleration (Fig. 11-7). At rest, there is a balance in the frequency of nerve impulses from the ampullae of both sides of the head. An angular acceleration of about 0.5° per second is sufficient to displace the dome and bend the cilia. Angular acceleration is recorded due to the inertia of the endolymph. When the head turns, the endolymph remains in the same position, and the free end of the dome deviates in the direction opposite to the turn. Movement of the dome bends the kinocilium and sterocilia embedded in the jelly-like structure of the dome. The tilt of the stereocilia toward the kinocilium causes depolarization and excitation; the opposite direction of tilt results in hyperpolarization and inhibition. When excited, a receptor potential is generated in the hair cells and acetylcholine is released, which activates the afferent endings of the vestibular nerve.

Rice. 11-7. Physiology registration of angular acceleration. A- different reactions of hair cells in the scallops of the ampullae of the left and right horizontal semicircular canals when turning the head. B- Successively increasing images of the perceptive structures of the scallop

Body reactions caused by stimulation of the semicircular canals.

Stimulation of the semicircular canals causes subjective sensations in the form of dizziness, nausea and other reactions associated with excitation of the autonomic nervous system. Added to this are objective manifestations in the form of changes in tone eye muscles(nystagmus) and tone of anti-gravity muscles (falling reaction). Dizziness is a spinning sensation and can cause imbalance and falls. The direction of the rotation sensation depends on which semicircular canal was stimulated. In each case, the dizziness is oriented in the direction opposite to the displacement of the endolymph. During rotation, the feeling of dizziness is directed in the direction of rotation. The sensation experienced after the rotation stops is directed in the direction opposite to the actual rotation. As a result of dizziness, vegetative reactions occur - nausea, vomiting, pallor, sweating, and with intense stimulation of the semicircular canals, a sharp drop in blood pressure is possible (collapse).

Nystagmus and muscle tone disorders. Stimulation of the semicircular canals causes changes in muscle tone, manifested in nystagmus, disruption of coordination tests and the fall reaction.

❖ Nystagmus- rhythmic twitching of the eye, consisting of slow and fast movements. Slow movements are always directed towards the movement of the endolymph and are a reflex reaction. The reflex occurs in the crests of the semicircular canals, impulses enter the vestibular nuclei of the brain stem and from there are switched to the muscles of the eye. Fast movements determined by the direction of nystagmus; they arise as a result of central nervous system activity (as part of the vestibular reflex from the reticular formation to the brainstem). Rotation in the horizontal plane causes horizontal nystagmus, rotation in the sagittal plane causes vertical nystagmus, rotation in the frontal plane causes rotational nystagmus.

❖ Rectifying reflex. Violation of the pointing test and the fall reaction are the result of changes in the tone of the anti-gravity muscles. The tone of the extensor muscles increases on the side of the body where the displacement of the endolymph is directed, and decreases on the opposite side. So, if the gravitational forces are directed to the right foot, then the head and body of a person deviate to the right, displacing the endolymph to the left. The resulting reflex will immediately cause extension of the right leg and arm and flexion of the left arm and leg, accompanied by deviation of the eyes to the left. These movements are a protective righting reflex.

Stimulation of the uterus and sac

Static balance. The spot of the uterus, lying horizontally on its lower surface, reacts to linear acceleration in the horizontal direction (for example, in a lying position); the saccule spot, located vertically on the lateral surface of the sac (Fig. 11-7B), determines the linear acceleration in the vertical direction (for example, in a standing position). Tilt of the head displaces the sac and uterus to some angle between the horizontal and vertical positions. The force of gravity of the otoliths moves the otolith membrane relative to the surface of the sensory epithelium. The cilia, embedded in the otolithic membrane, bend under the influence of the otolithic membrane sliding along them. If the cilia bend towards the kinoci-

Lia, then there is an increase in impulse activity; if in the other direction from the kinocilium, then impulse activity decreases. Thus, the function of the sac and utricle is to maintain static balance and orient the head relative to the direction of gravity. Equilibrium during linear acceleration. The spots of the utricle and sac are also involved in determining linear acceleration. When a person unexpectedly receives a push forward (acceleration), the otolithic membrane, which has an inertia much greater than the surrounding fluid, is displaced back by the cilia of the hair cell. This causes entry into nervous system a signal about an imbalance in the body, and the person feels that he is falling backwards. Automatically, a person leans forward until this movement causes an equally equal sensation of falling forward, because the otolithic membrane, under the influence of acceleration, returns to its place. At this point, the nervous system determines a state of suitable balance and stops the forward tilt of the body. Therefore, the spots control the maintenance of equilibrium during linear acceleration.

Projection pathways of the vestibular apparatus

The vestibular branch of the VIII cranial nerve is formed by the processes of approximately 19 thousand bipolar neurons, forming a sensory ganglion. The peripheral processes of these neurons approach the hair cells of each semicircular canal, utricle, and sac, and the central processes are sent to the vestibular nuclei of the medulla oblongata (Fig. 11-8A). Axons of second-order nerve cells are connected to the spinal cord (vestibulospinal tract, olivospinal tract) and rise as part of the medial longitudinal fascicles to the motor nuclei of the cranial nerves, which control eye movements. There is also a pathway that carries impulses from the vestibular receptors through the thalamus to the cerebral cortex.

The vestibular system is part of a multimodal system(Fig. 11-8B), including visual and somatic receptors that send signals to the vestibular nuclei either directly or through the vestibular nuclei of the cerebellum or the reticular formation. Input signals are integrated in the vestibular nuclei, and output commands affect the oculomotor and spinal systems motor control. In Fig. 11-8B

Rice. 11-8. A Ascending pathways of the vestibular apparatus(posterior view, cerebellum and cerebral cortex removed). B. Multimodal system of spatial orientation of the body.

shows the central and coordinating role of the vestibular nuclei, connected by straight lines and feedback with the main receptor and central systems of spatial coordination.

The inner ear contains the receptor apparatus of two analyzers: the vestibular (vestibular and semicircular canals) and the auditory, which includes the cochlea with the organ of Corti.

The bony cavity of the inner ear, containing a large number of chambers and passages between them, is called labyrinth . It consists of two parts: the bony labyrinth and the membranous labyrinth. Bone labyrinth- a series of cavities located in the dense part of the bone; three components are distinguished in it: the semicircular canals are one of the sources of nerve impulses that reflect the position of the body in space; vestibule; and the snail - an organ.

Membranous labyrinth enclosed within the bony labyrinth. It is filled with a fluid, endolymph, and is surrounded by another fluid, perilymph, which separates it from the bony labyrinth. The membranous labyrinth, like the bony labyrinth, consists of three main parts. The first corresponds in configuration to the three semicircular canals. The second divides the bony vestibule into two sections: the utricle and the saccule. The elongated third part forms the middle (cochlear) scala (spiral canal), repeating the bends of the cochlea.

Semicircular canals. There are only six of them - three in each ear. They have an arched shape and begin and end in the uterus. The three semicircular canals of each ear are located at right angles to each other, one horizontally and two vertically. Each channel has an extension at one end - an ampoule. The six channels are arranged in such a way that for each there is an opposite channel in the same plane, but in a different ear, but their ampoules are located at mutually opposite ends.

Cochlea and organ of Corti. The name of the snail is determined by its spirally convoluted shape. This is a bone canal that forms two and a half turns of a spiral and is filled with fluid. The curls go around a horizontally lying rod - a spindle, around which a bone spiral plate is twisted like a screw, pierced by thin canaliculi, where the fibers of the cochlear part of the vestibulocochlear nerve - the VIII pair of cranial nerves - pass. Inside, on one wall of the spiral canal along its entire length there is a bony protrusion. Two flat membranes extend from this protrusion to the opposite wall so that the cochlea is divided along its entire length into three parallel channels. The two external ones are called the scala vestibuli and the scala tympani; they communicate with each other at the apex of the cochlea. Central, so-called the spiral canal of the cochlea ends blindly, and its beginning communicates with the sac. The spiral canal is filled with endolymph, the scala vestibule and scala tympani are filled with perilymph. Perilymph has a high concentration of sodium ions, while endolymph has a high concentration of potassium ions. The most important function endolymph, which is positively charged in relation to perilymph, is the creation of an electrical potential on the membrane separating them, which provides energy for the process of amplifying incoming sound signals.

The scala vestibule begins in a spherical cavity, the vestibule, which lies at the base of the cochlea. One end of the scala through the oval window (the window of the vestibule) comes into contact with the inner wall of the air-filled cavity of the middle ear. The scala tympani communicates with the middle ear through the round window (window of the cochlea). Liquid

cannot pass through these windows, since the oval window is closed by the base of the stapes, and the round window by a thin membrane separating it from the middle ear. The spiral canal of the cochlea is separated from the scala tympani so-called. the main (basilar) membrane, which resembles a miniature string instrument. It contains a number of parallel fibers of varying lengths and thicknesses stretched across a helical channel, with the fibers at the base of the helical channel being short and thin. They gradually lengthen and thicken towards the end of the cochlea, like the strings of a harp. The membrane is covered with rows of sensitive, hair-equipped cells that make up the so-called. the organ of Corti, which performs a highly specialized function - converts vibrations of the main membrane into nerve impulses. Hair cells are connected to the endings of nerve fibers that, upon exiting the organ of Corti, form the auditory nerve (cochlear branch of the vestibulocochlear nerve).

Membranous cochlear labyrinth, or duct, has the appearance of a blind vestibular protrusion located in the bony cochlea and blindly ending at its apex. It is filled with endolymph and is a connective tissue sac about 35 mm long. The cochlear duct divides the bony spiral canal into three parts, occupying the middle of them - the middle staircase (scala media), or cochlear duct, or cochlear canal. The upper part is the vestibular staircase (scala vestibuli), or the vestibular staircase, the lower part is the tympanic or tympanic staircase (scala tympani). They contain peri-lymph. In the area of ​​the dome of the cochlea, both staircases communicate with each other through the opening of the cochlea (helicotrema). The scala tympani extends to the base of the cochlea, where it ends at the round window of the cochlea, closed by the secondary tympanic membrane. The scala vestibule communicates with the perilymphatic space of the vestibule. It should be noted that perilymph in its composition resembles blood plasma and cerebrospinal fluid; it has a predominant sodium content. Endolymph differs from perilymph in its higher (100 times) concentration of potassium ions and lower (10 times) concentration of sodium ions; in its chemical composition it resembles intracellular fluid. In relation to the peri-lymph, it is positively charged.

The cochlear duct in cross section has a triangular shape. The upper - vestibular wall of the cochlear duct, facing the staircase of the vestibule, is formed by a thin vestibular (Reissner) membrane (membrana vestibularis), which is covered from the inside with single-layer squamous epithelium, and on the outside - by endothelium. Between them there is fine fibrillar connective tissue. The outer wall fuses with the periosteum of the outer wall of the bony cochlea and is represented by a spiral ligament, which is present in all curls of the cochlea. On the ligament there is a vascular strip (stria vascularis), rich in capillaries and covered with cubic cells that produce endolymph. The lower - the tympanic wall, facing the scala tympani - is most complexly structured. It is represented by the basilar membrane, or plate (lamina basilaris), on which the spiral, or organ of Corti, which produces sounds, is located. The dense and elastic basilar plate, or basilar membrane, is attached at one end to the spiral bone plate, and at the opposite end to the spiral ligament. The membrane is formed by thin, weakly stretched radial collagen fibers (about 24 thousand), the length of which increases from the base of the cochlea to its apex - near the oval window, the width of the basilar membrane is 0.04 mm, and then towards the apex of the cochlea, gradually expanding, it reaches end 0.5 mm (i.e. the basilar membrane expands where the cochlea narrows). The fibers consist of thin fibrils anastomosing among themselves. The weak tension of the fibers of the basilar membrane creates conditions for their oscillatory movements.

The organ of hearing itself, the organ of Corti, is located in the bony cochlea. The organ of Corti is a receptor part located inside the membranous labyrinth. In the process of evolution, it arises on the basis of the structures of the lateral organs. It perceives vibrations of fibers located in the canal of the inner ear and transmits them to the auditory cortex, where sound signals are formed. Begins in the Organ of Corti primary formation analysis of sound signals.

Location. The organ of Corti is located in the spirally curled bone canal of the inner ear - the cochlear passage, filled with endolymph and perilymph. The upper wall of the passage is adjacent to the so-called. staircase vestibule and is called Reisner's membrane; the lower wall bordering the so-called. scala tympani, formed by the main membrane attached to the spiral bone plate. The organ of Corti is composed of supporting, or supporting, cells, and receptor cells, or phonoreceptors. There are two types of supporting cells and two types of receptor cells - external and internal.

External supporting cells lie further from the edge of the spiral bone plate, and internal- closer to him. Both types of supporting cells converge at an acute angle to each other and form a triangular-shaped canal - an internal (Corti) tunnel filled with endo-lymph, which runs spirally along the entire organ of Corti. The tunnel contains unmyelinated nerve fibers coming from the neurons of the spiral ganglion.

Phonoreceptors lie on supporting cells. They are secondary sensory (mechanoreceptors) that transform mechanical vibrations into electrical potentials. Phonoreceptors (based on their relationship to the tunnel of Corti) are divided into internal (flask-shaped) and external (cylindrical) which are separated from each other by the arcs of Corti. The inner hair cells are arranged in a single row; their total number along the entire length of the membranous canal reaches 3500. Outer hair cells are arranged in 3-4 rows; their total number reaches 12,000-20,000. Each hair cell has an elongated shape; one of its poles is close to the main membrane, the second is located in the cavity of the membranous canal of the cochlea. At the end of this pole there are hairs, or stereocilia (up to 100 per cell). The hairs of the receptor cells are washed by the endolymph and come into contact with the integumentary, or tectorial, membrane (membrana tectoria), which is located above the hair cells along the entire course of the membranous canal. This membrane has a jelly-like consistency, one edge of which is attached to the bony spiral plate, and the other ends freely in the cavity of the cochlear duct a little further than the external receptor cells.

All phonoreceptors, regardless of location, are synaptically connected to 32,000 dendrites of bipolar sensory cells located in the spiral nerve of the cochlea. These are the first auditory pathways, which form the cochlear (cochlear) part of the VIII pair of cranial nerves; they transmit signals to the cochlear nuclei. In this case, signals from each inner hair cell are transmitted to bipolar cells simultaneously along several fibers (probably this increases the reliability of information transmission), while signals from several outer hair cells converge on one fiber. Therefore, about 95% of the auditory nerve fibers carry information from the inner hair cells (although their number does not exceed 3500), and 5% of the fibers transmit information from the outer hair cells, the number of which reaches 12,000-20,000. These data highlight the enormous physiological importance of inner hair cells in sound reception.

To hair cells Efferent fibers - axons of neurons of the superior olive - are also suitable. The fibers coming to the inner hair cells do not end on these cells themselves, but on afferent fibers. They are hypothesized to have an inhibitory effect on auditory signal transmission, promoting increased frequency resolution. Fibers coming to the outer hair cells affect them directly and, by changing their length, change their phono sensitivity. Thus, with the help of efferent olivo-cochlear fibers (Rasmussen's bundle fibers), higher acoustic centers regulate the sensitivity of phonoreceptors and the flow of afferent impulses from them to the brain centers.

Conduction of sound vibrations in the cochlea . Sound perception is carried out with the participation of phonoreceptors. Under the influence of a sound wave, they lead to the generation of a receptor potential, which causes excitation of the dendrites of the bipolar spiral ganglion. But how is the frequency and intensity of sound encoded? This is one of the most complex issues in the physiology of the auditory analyzer.

The modern idea of ​​coding the frequency and intensity of sound comes down to the following. A sound wave, acting on the system of auditory ossicles of the middle ear, sets into oscillatory motion the membrane of the oval window of the vestibule, which, bending, causes wave-like movements of the perilymph of the upper and lower canals, which gradually attenuate towards the apex of the cochlea. Since all fluids are incompressible, these oscillations would be impossible if it were not for the membrane of the round window, which bulges when the base of the stapes is pressed on the oval window and returns to its original position when the pressure is released. Vibrations of the perilymph are transmitted to the vestibular membrane, as well as to the cavity of the middle canal, setting the endolymph and basilar membrane in motion (the vestibular membrane is very thin, so the fluid in the upper and middle canals vibrates as if both canals are one). When the ear is exposed to low frequency sounds (up to 1000 Hz), the basilar membrane is displaced along its entire length from the base to the apex of the cochlea. As the frequency of the sound signal increases, the oscillating column of liquid, shortened in length, moves closer to the oval window, to the most rigid and elastic part of the basilar membrane. When deformed, the basilar membrane displaces the hairs of the hair cells relative to the tectorial membrane. As a result of this displacement, an electrical discharge occurs in the hair cells. There is a direct relationship between the amplitude of the displacement of the main membrane and the number of auditory cortex neurons involved in the excitation process.

1 - membranous canal of the cochlea; 2 - vestibular staircase; 3 - scala tympani; 4 - spiral bone plate; 5 - spiral knot; 6 - spiral ridge; 7 - dendrites of nerve cells; 8 - vestibular membrane; 9 - basilar membrane; 10 - spiral ligament; 11 - epithelium lining 6 and another staircase; 12 - vascular strip; 13 - blood vessels; 14 - cover plate; 15 - outer sensoroepithelial cells; 16 - internal sensoroepithelial cells; 17 - internal supporting epithelialitis; 18 - external supporting epithelialitis; 19 - pillar cells; 20 - tunnel.

The structure of the hearing organ (inner ear). The receptor part of the hearing organ is located inside membranous labyrinth, located in turn in the bone labyrinth, having the shape of a snail - a bone tube spirally twisted into 2.5 turns. A membranous labyrinth runs along the entire length of the bony cochlea. On a cross section, the labyrinth of the bony cochlea has a rounded shape, and the transverse labyrinth has a triangular shape. The walls of the membranous labyrinth in cross section are formed by:

1. superomedial wall- educated vestibular membrane (8). It is a thin fibrillar connective tissue plate covered with single-layer squamous epithelium facing the endolymph and endothelium facing the perilymph.

2. outer wall- educated vascular strip (12), lying on spiral ligament (10). The stria vascularis is a multirow epithelium that, unlike all epithelia in the body, has its own blood vessels; this epithelium secretes endolymph, which fills the membranous labyrinth.

3. Bottom wall, base of the triangle - basilar membrane (lamina) (9), consists of individual stretched strings (fibrillar fibers). The length of the strings increases in the direction from the base of the cochlea to the top. Each string is capable of resonating at a strictly defined vibration frequency - strings closer to the base of the cochlea (shorter strings) resonate at higher vibration frequencies (higher sounds), strings closer to the top of the cochlea - at lower vibration frequencies (lower sounds) .

The space of the bony cochlea above the vestibular membrane is called vestibular staircase (2), below the basilar membrane - drum ladder (3). The scala vestibular and scala tympani are filled with perilymph and communicate with each other at the apex of the bony cochlea. At the base of the bony cochlea, the scala vestibular ends in an oval opening closed by the stapes, and the scala tympani ends in a round opening closed by an elastic membrane.

Spiral organ or organ of Corti - receptive part of the hearing organ , located on the basilar membrane. It consists of sensory cells, supporting cells and a covering membrane.

1. Sensory hair epithelial cells - slightly elongated cells with a rounded base, at the apical end they have microvilli - stereocilia. The dendrites of the first neurons of the auditory pathway approach the base of the sensory hair cells and form synapses, the bodies of which lie in the thickness of the bone rod - the spindle of the bony cochlea in the spiral ganglia. Sensory hair epithelial cells are divided into internal pear-shaped and external prismatic. The outer hair cells form 3-5 rows, while the inner hair cells form only 1 row. Inner hair cells receive about 90% of all innervation. The tunnel of Corti is formed between the inner and outer hair cells. Hangs over the microvilli of sensory hair cells. tectorial membrane.

2. SUPPORTING CELLS (SUPPORTING CELLS)

External pillar cells

Internal pillar cells

External phalangeal cells

Internal phalangeal cells

Supporting phalangeal epithelial cells- located on the basilar membrane and are a support for sensory hair cells, supporting them. Tonofibrils are found in their cytoplasm.

3. COVERING MEMBRANE (TECTORIAL MEMBRANE) - gelatinous formation consisting of collagen fibers and amorphous substance connective tissue, extends from the upper part of the thickening of the periosteum of the spiral process, hangs over the organ of Corti, the tips of the stereocilia of hair cells are immersed in it

1, 2 - external and internal hair cells, 3, 4 - external and internal supporting (supporting) cells, 5 - nerve fibers, 6 - basilar membrane, 7 - openings of the reticular (reticular) membrane, 8 - spiral ligament, 9 - spiral bone plate, 10 - tectorial (cover) membrane

Histophysiology of the spiral organ. The sound, like air vibration, vibrates the eardrum, then the vibration is transmitted through the hammer and anvil to the stapes; the stapes through the oval window transmits vibrations to the perilymph of the scala vestibularis; along the vestibular scala, vibrations at the apex of the bony cochlea pass into the perilymph of the scala tympani and spiral downwards and rest against the elastic membrane of the round opening. Vibrations of the perilymph of the scala tympani cause vibrations of the strings of the basilar membrane; When the basilar membrane oscillates, the sensory hair cells oscillate in the vertical direction and their hairs touch the tectorial membrane. Bending of the microvilli of hair cells leads to the excitation of these cells, i.e. the potential difference between the outer and inner surfaces of the cytolemma changes, which is sensed by the nerve endings on the basal surface of the hair cells. IN nerve endings Nerve impulses are generated and transmitted along the auditory pathway to the cortical centers.

As determined, sounds are differentiated by frequency (high and low sounds). The length of the strings in the basilar membrane changes along the membranous labyrinth; the closer to the apex of the cochlea, the longer the strings. Each string is tuned to resonate at a specific vibration frequency. If the sounds are low, the long strings resonate and vibrate closer to the top of the cochlea and the cells sitting on them are accordingly excited. If high-pitched sounds resonate, short strings located closer to the base of the cochlea resonate, and the hair cells sitting on these strings are excited.

VESTIBULAR PART OF THE MEMBRANUS LABYRINTH - has 2 extensions:

1. Pouch - a spherical extension.

2. Uterus - an extension of an elliptical shape.

These two extensions are connected to each other by a thin tubule. Three mutually perpendicular semicircular canals with extensions are associated with the uterus - ampoules. Most of the inner surface of the sac, utricle and semicircular canals with ampoules is covered with single-layer squamous epithelium. At the same time, in the saccule, uterus and in the ampoules of the semicircular canals there are areas with thickened epithelium. These areas of thickened epithelium in the sac and utricle are called spots or macules, and in ampoules - scallops or cristae.

As already indicated, to the free end bone The spiral plate extending from the spindle (modiolus) is attached to a membranous plate - membrane basilaris, reaching the inner surface of the outer wall of the cochlea. The bony and membranous plates divide the cochlear canal along its entire length into the scala tympani, facing the base of the cochlea, and the scala vestibuli, facing its apex.

In the staircase vestibule from the bony spiral records, near the attachment of the membranous spiral plate to it, another thin membranous plate, membrana Reissneri, extends off at an angle of 45°. Both membranous plates, together with the outer wall of the cochlea, are lined with lig. spirale (spiral ligament), form the middle staircase (scala media) or cochlear duct (ductus cochlearis), which has the shape of a triangle in cross section.

Upper (vestibular) wall forms Reissner's membrane, and the lower (tympanic) is the main membrane. While the scala vestibule and tympanum are filled with perilymph, the cochlear duct is filled with endolymph. Ductus cochlearis, like the bony cochlea, makes 2.5 or 23/4 turns, forming the main (basal), middle and upper (apical) curls of the cochlea. The initial part of the ductus cochlearis - coecum vestibuli (at the base of the cochlea) - and the final part - coecum cupulae (at the apex) - end blindly.

Through ductus reunien Henseni, opening anterior to the coecum vestibuli, the ductus cochlearis communicates with the rest of the endolymphatic space (vestibule and semicircular canals). The endolymphatic space, as already indicated, is anatomically closed.

IN last years developed a number of methods for the finest study of the structures of the cochlea, which significantly refined our knowledge in this area. This includes intravital research through a window made in the cochlea of ​​animals, phase contrast, electron microscopy, study in polarized light, ultraviolet absorption, which makes it possible to study the various phases of nuclear and cytochemical changes in cochlear nerve cells during various types acoustic stimulation, studies using various histochemical colorful reactions - to polysaccharides, metachromatic reactions, reactions to neutral fat, to glycoprotein, to plasmalogen (fat + aldehyde group), to alkaline phosphatase, etc. In the further presentation we use the new data obtained .

Membrana basilaris(basic membrane), spirally curled, increases in width from the base to the apex due to the fact that the spiral bone plate decreases in width from the base to the apex. The organ of Corti is located on the basilar membrane. It is divided into an internal zone - zona arcuata - covered by part of the organ of Corti - arcs, a middle zone - zona tecta - covered by the rest of the organ of Corti and continuing to the last cell of Hensen, and an external zone - zona pectinate - passing into the lig. spirale