Corti's organ structure and function. Spiral (Corti) organ

The spiral organ is located along the entire length of the cochlear canal of the membranous labyrinth filled with endolymph. Above and below the canal of the cochlea are located, respectively, the vestibular and tympanic ladders, filled with perilymph.

The outer wall of the cochlear canal is limited by a vascular strip that grows together with the wall of the cochlear bone. It is separated from the vestibular ladder by the vestibular membrane, and from the tympanic ladder by the basilar plate.

The vascular stria is formed by a layer of stratified epithelium lying on a spiral ligament (thickened periosteum) and penetrated by a dense network of capillaries. In it, the formation of endolymph is carried out, which ensures the transport of nutrients and oxygen to the spiral organ, the maintenance of the ionic composition of the medium, which is optimal for the function of sensorepithelial cells.

As part of the vascular stria, the epithelium contains three types of cells:

Edge cells in contact with endolymph; on the free surface, they have short microvilli, and on the basal surface, folds, which contain thin mitochondria (basal labyrinth). In the basal labyrinth of these cells, there are membrane ion pumps that provide active transport of Na + to the capillaries and its replacement with K +, due to which the endolymph contains high concentrations of K +;

Intermediate cells have processes covering hemocapillaries and penetrating between other cells;

Basal cells- are cambial elements of the vascular stria epithelium.

The vestibular membrane (Reisner) is a thin bilayer plate located between the spiral crest (limbus) and the spiral ligament. From the side of the cochlear canal, it is lined with a single-layer squamous epithelium, in the cytoplasm of which there are many micropinocytic vesicles, indicating its active participation in the transport of water and electrolytes between the peri - and endolymph. The membrane surface facing the vestibular staircase is covered with a layer of squamous epithelial cells.

The basilar plate consists of an amorphous substance, which contains bundles of collagen microfibrils, forming the so-called auditory strings stretched between the spiral ligament and the spiral bone plate, which is the outgrowth of the central bone rod. The different lengths of the strings allow the perception of vibrations of different frequencies.

From the side of the tympanic ladder, the basilar plate is lined with a single-layer squamous epithelium, and from the side of the membranous labyrinth it is located Spiral (Corti) organ, Which contains sensory hair receptor epithelial cells and a variety of supporting cells.

There are two types of hair cells:

Internal hair cells, having a pear-shaped shape, are located in one row and are completely surrounded on all sides by internal phalanx cells. On the apical surface, they have 50-70 stereocilia, located linearly;

Outer hair cells have a prismatic shape. They are located in 3-5 rows in the cup-shaped impressions of the outer phalanx cells in such a way that they come into contact with them only in the region of the basal and apical surfaces; the middle part of these cells is washed by endolymph. On their apical surface there are about 100-300 stereocilia, arranged in 3-4 rows in the form of the letter V. At the same time, they become longer from the base of the cochlea to its apex.

Above the hair cells is a jelly-like integumentary membrane, into which the tops of stereocilia are immersed. The integumentary membrane consists of a dense amorphous substance containing glycoproteins and fibrils. Starting from the spiral limb, it reaches the outer border cells (Hensen), to which it attaches with its edge.

Hair cells are associated with afferent and efferent nerve endings.

Supporting cells are classified into five types: inner and outer pillar cells, inner and outer phalanx cells (Deiters), inner and outer border cells (Hensen), outer supporting cells (Claudius), and Bettcher cells.

Cell-columns (internal and external) with a wide base lie on the basilar plate, and their apical ends converge at an acute angle, limiting the triangular space - a tunnel filled with endolymph, in which the processes of nerve cells pass.

Phalangeal cells (Deiters), internal and external, are tall prismatic cells that lie on the basement membrane.

The inner phalangeal cells completely cover the inner hair cells; nerve fibers penetrate into the spaces between them, forming endings on the hair cells.

The outer phalangeal cells on their apical surface have depressions into which the bases of the hair cells are immersed, and their long finger-like processes (phalanges) lie horizontally adjacent to the apical part of the outer hair cells and, together with the processes of the pillar cells, form a reticular membrane in such a way that they rise above it only hairs. The reticular membrane also passes to the outer border cells (Hensen).

Border cells (Hensen) - internal and external are located on the sides of the internal and external phalanx cells. Their height decreases laterally, where they border on the cells of the inner groove and the outer supporting cells (Claudius).

The outer supporting cells (Claudius) are localized lateral to Henson's cells, have a cubic shape, light cytoplasm, and continue into the cells of the outer groove.

Bettcher's cells are small, with dark cytoplasm, located next to Claudius's cells. They are found only in the basal curls of the cochlea and presumably perform the functions of absorption and secretion.

The inner ear consists of a bony labyrinth and a membranous labyrinth included in it.

The labyrinth is divided into 3 sections - the middle one is the vestibule, posterior to it is the system of semicircular canals, in front of the vestibule is the cochlea.

The membranous cochlea is a spiral canal with a receptor apparatus located inside it - a spiral (or Corti organ). In cross section, the cochlear passage has a triangular shape; formed by the vestibular wall (facing the staircase of the vestibule; it is a very thin Reissneri membrane); the outer wall is formed by a spiral ligament with epithelial cells of the vascular stria located on it; the lower tympanic wall faces the tympanic staircase and is represented by the main membrane on which the spiral organ lies - the peripheral receptor of the cochlear nerve.

The spiral (Corti) organ consists of neuroepithelial outer and inner hair cells, supporting cells (Deiters, Hensen, Claudius), outer and inner columnar cells that form Corti's arches. The inner and outer columnar cells form the tunnel of Corti. Inside of the inner columnar cells, there is a number of inner hair cells (up to 3500); outside of the outer columnar cells - 4 rows of outer hair cells (5000 in each row), supported by the cells of Deiters, Hensen and Claudius. Hair cells are enclosed by nerve fibers emanating from the bipolar cells of the spiral ganglion. Between the cells of the organ of Corti there are intraepithelial spaces filled with fluid (cortilymph). It has a connection with peralymph and is quite close to it in chemical composition. It is believed that the main function of cortylymph is trophic (since the organ of Corti does not have its own vascularization).

Above the organ of Corti is the integumentary membrane - a soft, elastic plate, consisting of protofibrils with a longitudinal and radial direction. The elasticity of this membrane is different in the longitudinal and transverse directions. The hairs of neuroepithelial hair cells penetrate into the integumentary membrane. When the main membrane vibrates, tension and compression of these hairs occurs, which serves as the moment of transformation of mechanical energy into the energy of an electrical nerve impulse.

The peripheral receptor of the auditory analyzer is a spiral organ. The dendrites of the spiral ganglion cells located in the cochlea of ​​the labyrinth fit here (to the hair cells). Axons penetrate into the cranial cavity through the internal auditory opening, enter the brain stem in the cerebellopontine angle and end in the ventral and dorsal nuclei of the pons - the second neurons of the auditory tract. The third neuron starts from the olive. Subcortical auditory centers - in the posterior tubercles of the quadruple and the medial geniculate body. The cortical horses of the auditory analyzer are located in the posterior section of the superior temporal gyrus and Heschl's gyrus.

Heimholtz resonance theory.

In the 19th century, when the morphological direction was dominant in medicine, a certain detail of the structure of the auditory organ was taken as the main criterion for determining sound perception. The main membrane on which the spiral organ is located, when viewed with magnifying optics, has a transverse striation, as if it consists of "strings" of different lengths. Based on this fact, Helmholtz in 1863 created the so-called resonant theory of hearing. According to this theory, in the cochlea, mechanical resonance phenomena occur in relation to sound vibrations of various frequencies. By analogy with stringed instruments, high-frequency sounds vibrate a section of the main membrane with short fibers at the base of the cochlea, and low-frequency sounds vibrate a section of the membrane with long fibers at the apex of the cochlea. When complex sounds are presented and perceived, several sections of the membrane begin to vibrate simultaneously. The sensitive cells of the spiral organ perceive these vibrations and transmit them along the nerve to the auditory centers. Based on the study Helmholtz theory, three conclusions can be drawn: 1) the cochlea is the link in the auditory analyzer where the primary analysis of sounds occurs; 2) each simple sound has a certain area on the main membrane; 3) low sounds vibrate the parts of the main membrane located at the apex of the cochlea, and high sounds - at its base.

Thus, Helmholtz's theory was the first to explain the basic properties of the ear, that is, the determination of pitch, strength and timbre. At one time, this theory found many supporters and is still considered classical. Indeed, Helmholtz's conclusion that a primary spatial analysis of sounds occurs in the cochlea is fully consistent with I.P. Pavlov's theory of the ability for primary analysis of both the terminal devices of the afferent nerves and, in particular, the complex receptor apparatus.

The resonance theory of Helmholtz was confirmed in the clinic. A histological examination of the snails of deceased people suffering from insular hearing loss revealed changes in the organ of Corti in the areas corresponding to the lost part of hearing. At the same time, modern knowledge does not confirm the possibility of resonating individual "strings" of the main membrane; hence, more accurate explanations of the spatial reception of sounds in the cochlea are needed.

2. Injuries and foreign bodies of the nasal cavity, rhinolitis. Diagnostics. Methods for removing foreign bodies. Complications.

Material taken from the site www.hystology.ru

The ear is the peripheral part of the auditory and vestibular analyzers. It is a complex complex of structural elements in which receptors are located that provide the perception of sound, vibrational and gravitational signals. The organ of hearing and balance includes the outer, middle and inner ear. Receptor cells are located in certain areas on the inner surface of the cavities and canals of the inner ear, the aggregate of which is called the membranous labyrinth.

In the embryonic period, the development of the membranous labyrinth begins with the invagination of the ectoderm into the underlying mesenchyme in the hindbrain region in the form of an auditory fossa, which turns into an auditory vesicle. The latter is connected for some time with the external environment by a narrow endolymphatic canal; with further development, this channel is closed in most animals. The cells of the multilayered epithelial lining of the otic vesicle secrete endolymph, which fills its cavity. The auditory vesicle is divided into two sections and in the upper section an expansion is formed - the utriculus (uterus) and three semicircular canals with ampoules. In the lower part of the bubble, a saccular protrusion appears - a sacculus (sac) and at its end a blind outgrowth, which lengthens and twists into the cochlear canal.

In the epithelium of the utriculus, sacculus and ampullae, areas containing receptor cells are formed, and in the epithelium of the basal part of the cochlear canal, sensitive cells are located in a strip and are part of the spiral (Corti's) organ.

From the surrounding mesenchyme, a cartilaginous capsule first develops, which, in configuration, repeats the complex shape of the parts of the inner ear that have arisen. Later, after the end of ossification, a bone labyrinth is formed.

Outer ear(auris externa) consists of the auricle and the external auditory canal, ending with the tympanic membrane that separates the outer ear from the middle.

Auricle serves as a good sound absorber. This function is especially developed in some species of animals (horses, dogs, cats, bats, etc.), in which reflex control of the auricle facilitates

Rice. 191. Diagram of the structure of the ear:

a- external auditory canal: b - tympanic membrane; in - the tympanic cavity; g - hammer; d- anvil; e- stirrup; g - auditory tube; h - semicircular canal; and - mother; k - pouch; l- the threshold; m- snail; n- oval and O- round windows.

the location of the sound source. In addition, the hairy auricle is a protective organ, preventing insects and particles from entering the external auditory canal. The base of the auricle is elastic cartilage covered with skin, which contains hair roots and sebaceous glands. The muscles that drive the auricle are composed of striated muscle tissue.

External auditory canal in animals it has different lengths and serves to conduct sound vibrations to the tympanic membrane. The basis of the external auditory canal is a tube of elastic cartilage, which passes at the stony bone into bone tissue. The skin of the ear canal contains alveolar sebaceous and modified tubular sweat glands. The latter are lined with a single-layer columnar epithelium that secretes a fluid containing mucus and pigments. A mixture of secretions from the glands and represents earwax.

Eardrum- a weakly stretchable partition with a thickness of 0.1 mm. From the side of the ear canal, it is covered with stratified squamous epithelium, and from the side of the middle ear, it is covered with a single-layer flat epithelium. The basis of the membrane is a fibrous connective tissue containing mainly collagen fibers that form a radial outer layer and a circular inner layer. The handle of the hammer is woven into the connective tissue of the membrane.

Middle ear(auris media) represents the tympanic cavity with the auditory ossicles inside it - the hammer, incus and stapes (Fig. 191). Birds have only one auditory ossicle (column). The bony wall of the cavity is lined with a single-layer cylindrical ciliated epithelium (with the exception of the surface of the tympanic membrane and the auditory ossicles). The wall separating the middle ear from the inner ear has two openings, or "windows". One oval window separates the tympanic cavity from the vestibular ladder of the cochlea .. It is closed by a plate of the stapes and its ligament. Another window is round - it separates the tympanic cavity from the tympanic ladder of the cochlea and is covered with a fibrous membrane. With the help of the auditory ossicles, sound vibrations propagating in the air of the external auditory canal are transmitted to the oval window and are converted into fluid vibrations - perilymphs of the inner ear. The auditory ossicles are interconnected by joints and attached by ligaments to the wall of the tympanic cavity. The middle ear contains a special mechanism consisting of two muscles: one attached to the handle of the hammer, the other to the stapes. The reflex contraction of these muscles under the action of very strong sounds reduces the amplitude of the oscillatory movement of the auditory ossicles, which leads to a decrease in sound pressure in the area of ​​the oval window.

Tympanic cavity the middle ear is connected by the auditory tube (tuba auditiva) with the nasopharyngeal cavity. The part of the tube adjacent to the tympanic cavity consists of bone tissue, and closer to the pharynx of hyaline cartilage. The mucous membrane of the auditory tube is covered with a multi-row ciliated epithelium containing goblet cells. Its own layer has a developed network of elastic fibers and contains mucous or mixed glands, well developed in sheep. In horses, the auditory tube forms a protrusion - a diverticulum, covered from the inside by a mucous membrane with a multi-row ciliated epithelium. The air pressure in the tympanic cavity of the middle ear is regulated through the auditory tube.

Inner ear(auris interna) is located in the rocky part of the petrosal bone of the skull and consists of a system of bony cavities and tortuous channels - a bony labyrinth, inside which there is a system of cavities and channels of smaller sizes and of another shape - a membranous labyrinth. Between the bony labyrinth and the walls of the membranous labyrinth, there are spaces filled with a liquid - perilymph, which resembles cerebrospinal fluid in its ionic composition. The cavity of the membranous labyrinth contains endolymph, which differs from perilymph in the high content of potassium ions.

There are three parts in the bone labyrinth: the vestibule, three semicircular canals and the cochlea, inside which are the corresponding membranous parts. The membranous part of the vestibule is represented by two sacs - the utriculus and the sacculus. The utriculus communicates with the membranous semicircular canals located in three mutually perpendicular planes. One end of each channel is flask-shaped and is called an ampoule. The sacculus is connected through a small duct to the membranous canal of the cochlea. In the wall of each sac there are elevations called spots, or macules, and in the wall of the ampullae, there are elevations called scallops (crista ampullaris). Macula - spots of utriculus and sacculus and scallops - cristae of the ampullae of the semicircular canals are those sensitive devices in which signals arise when the position of the head or body in space changes. These specialized areas of the vestibular apparatus are lined with

Rice. 192. Scheme of the structure of the static macular spot (according to Colmer):

1 - supporting cells; 2 - receptor cells; 3 - hairs of receptor cells; 4 - gelatinous substance; 5 - otoliths; 6 - nerve fibers.

epithelium, in which there are two types of cells: receptor (hair) and supporting (Fig. 192). High supporting cells with their expanded bases are located on the basement membrane. At their apical pole, reaching the free surface of the epithelial layer, microvilli are developed. Hair sensitive cells are placed between the supporting cells, alternating correctly, which do not reach the basal plate with their bases. Their base is in contact with afferent and efferent nerve endings, and on the apical surface there are from 40 to 100 hairs - cilia. Among the hairs, one is mobile and the longest is the kinocilium, the rest are motionless and are arranged stepwise in height - stereocilia. Receptor cells are classified into two types. Cells of the first type are in the form of cones with a rounded base, enclosed in a cupped extended end of the afferent nerve fiber, with which synaptic contacts are formed. Cells of the second type are cylindrical in shape and afferent and efferent nerve endings are adjacent to their base, forming characteristic synapses (Fig. 193).

The surface of the epithelium of the macula is covered with a jelly-like mass - an otolith membrane, which includes calcite crystals - otoliths, or statoconia. When the body moves in space, the otolith membrane shifts, bends the hairs of the receptor cells, which leads to their excitation or inhibition. The deviation of hairs from the stereocilium to the kinocilium causes an exciting effect, and from the kinocilium to the stereocilium - inhibitory.

In the epithelium of the macula, differently polarized hair cells are located in groups, as a result of which, during the sliding of the otolith membrane in one direction, only a certain group of cells is stimulated, which regulates the tone of certain muscles of the trunk.

The surface of the epithelium of the scallops is covered with a gelatinous substance in the form of a dome (cupula) up to 1 mm high and capable of closing the lumen of the ampulla. The substance of the dome contains hairs of receptor cells, the fine structure of which and their innervation are similar to those of the macula (Fig. 194). The stimulus for the receptor cells of the scallops of the semicircular canals is the angular acceleration of the head in the plane of this canal. When the head is turned in the semicircular canal, the endolymph moves. The resulting displacement of the dome bends the hairs

Rice. 193.

Diagram of the ultramicroscopic structure of macular cells (A- in mammals, B- in birds):
a - type I hairy receptor cell; b - cupped afferent nerve ending; v- multicellular contacts of nerve fibers in the macula of birds; G- type II receptor cell; d- motionless hairs (stereocilia); e- mobile cilium (kinocilia); f- supporting cells; h - their microvilli.

receptor cells, which entails an increase or decrease in the frequency of impulses of these cells, which is transmitted to the nerve endings approaching the hair cells.

Unlike the receptors of the semicircular canals that respond to angular acceleration, the otolith receptors of the utriculus and sacculus respond to linear acceleration.

Excitation from the receptor cells of the vestibular apparatus spreads along the dendrites of bipolar cells, the bodies of which are located in the vestibular ganglion. The axons of these cells as part of the fibers of the vestibular nerve go to the nerve cells of the vestibular nuclei of the medulla oblongata on their side. The complex of the vestibular nuclei of the medulla oblongata is the first point where the primary processing of information about the movement and position of the body and head in space takes place. From the cells of the vestibular nuclei, processes follow to the nerve cells of the optic hillock, the neurons of which, through

Rice. 194. Diagram of the structure of the scallop of the ampoule (according to Colmer):

1 - epithelial supporting cells; 2 - receptor hair cells; 3 - hairs of receptor cells; 4 - a gelatinous substance in the form of a dome; 5 - nerve fibers.

axons are associated with nerve cells in the temporal region of the cerebral cortex, which is the center of the balance analyzer.

Snail- the part of the inner ear where the receptors that receive sound vibrations are located. The cochlea in the form of a bony spiral channel inside the stony bone is twisted in the form of a shell around the axial bone and forms up to five turns in animals. Parts of the cochlea directed towards the axis are designated internal, and those directed in the opposite direction - external. Along the entire length, on the inner part of the canal wall, there is a bony protrusion - a spiral plate with a thickened periosteum - a spiral limbus. The latter is divided into two lips: upper - vestibular and lower - tympanic. The depression between them is called a spiral groove. A spiral ganglion is located at the base of the spiral plate.

The thickening of the periosteum on the outer surface of the wall of the bony cochlear canal is called the spiral ligament.

Between the spiral plate and the spiral ligament, two connective tissue membranes are stretched, which in the form of a spiral stretch along the entire cochlear canal. One of them - the basilar membrane from the inside passes into the tympanic lip of the limbus. The other - the vestibular membrane on one side is connected to the vestibular lip, and on the other to the spiral ligament at some distance from the place of attachment of the basilar membrane. At the base of the basilar membrane are thin collagen fibers, longer at the apex of the cochlea and shorter at its base. Between the fibers and fibrils there is a basic homogeneous substance containing glycosaminoglycans. Thus, along its entire length, almost to the very apex of the cochlea, the bony canal is divided by two membranes into three canals, or ladders. Upper channel - the vestibular staircase originates from the oval window and

Rice. 195. Diagram of the structure of a part of the curl of a snail in a cross section:

A - spiral plate; 1 - limb; a - vestibular lip; b- the tympanic lip; v- spiral chute; d - spiral ganglion; B - spiral ligament; 2 - basilar membrane; 3 - vestibular membrane; 4 - vestibular ladder; 5 - drum ladder; 6 - membranous canal of the cochlea; 7 - vascular strip; 8 - unilamellar squamous epithelium; 9 - endothelium; V- spiral (Corti's) organ; d- inner cage-pillar; e- outer pillar cage; f- tunnel; h - inner hair cell; and- outer hair cells; k - external phalanx cells; l- outer border cells; m- external supporting cells; n- tectorial integumentary plate (Fig. Kozlov).

continues to the top of the snail. The lower channel - the tympanic ladder starts from the round window, and at the top at the junction of the vestibular and basilar membranes through a narrow opening - the helicotremu communicates with the vestibular ladder. Both stairs are filled with perilymph.

The middle ladder, or membranous canal of the cochlea, does not communicate with the cavity of other canals and is filled with endolymph. In cross section, the cochlear canal has the shape of a triangle (Fig. 195), the sides of which are formed by the vestibular membrane, the basilar membrane and the vascular strip lying on the outer wall of the bony cochlea. The vascular stria is represented by a multi-row epithelial layer located on the basal lamina. Among the high epithelial cells, there are many blood capillaries in it. It is believed that the epithelium of the vascular stria performs a secretory function - it produces endolymph.

The vestibular membrane from the side of the cavity of the membranous canal is covered with a single-layer squamous epithelium, and from the side of the vestibular ladder - endothelium, passing into the endothelium of the periosteum. The basilar plate on the side of the tympanic ladder is also covered with a thin layer of endothelium, under which blood capillaries meet. From the side of the cavity of the middle, that is, the membranous canal of the cochlea, a specialized epithelium is located on the basilar plate, which forms the sound-receiving apparatus of the auditory analyzer - the spiral (Corti) organ.

Corti's organ consists of two types of internal and external cells: receptor (hair) and supporting (supporting). The latter, with their bases, are located on the basal plate located between the complex of epithelial cells of the spiral organ and the connective tissue part of the basilar membrane. There are several types of supporting cells. The supporting cells-pillars along the length of the spiral organ are located in two rows: a row of inner and a row of outer pillars. The extended base of these cells lies on the basement membrane, and the apical poles of the cells are inclined obliquely to each other and form a kind of vault that covers a triangular canal - a tunnel filled with endolymph. Myelin-free nerve fibers containing dendrites of the spiral ganglion neurons pass through the tunnel. The cytoplasm of the pillars is highly elastic due to the presence of a large number of tonofibrils in it.

In the immediate vicinity of the outer cells of the pillars, there are three rows of outer phalanx cells. These cylindrical cells at the apical end have a cup-shaped depression and a phalangeal process that reaches the surface of the spiral organ and ends in a plate. The phalangeal plates, joining one another, form a mesh membrane, in the holes of which are the upper ends of the auditory cells, and their body is adjacent to the inner side of the phalangeal process (Fig. 196). Thus, the receptor cells are separated from one another by the processes of phalangeal cells. In the cytoplasm, a bundle of tonofibrils passes along the length of the cell, continuing into the process.

Border cells are located outside the phalangeal cells. On the apical surface of these cells there are a large number of microvilli, and in the cytoplasm there are drops of lipoids, vacuoles, glycogen, which indicates their trophic function. Gradually decreasing in height, bordering outer cells pass into low supporting cells that cover the rest of the basilar membrane and pass into the epithelium of the vascular stria. On the inner side - one row of phalangeal cells and then internal bordering cylindrical cells, which, decreasing in height, pass into the cubic epithelium of the spiral groove.

Receptor - hair cells are located on both sides of the pillar cells, while the inner hair cells are located in one row, the outer ones in three rows. Along the length of the spiral organ, there are up to 20,000 receptor cells.

Rice. 196. Receptor and supporting cells of the spiral organ (according to Kolmer):

a- pillar cells; b - phalangeal cells; c - phalanx process; g - phalanx plate; d- mesh membrane; e- outdoor and f- inner hair cells; s- nerve fibers that form synapses on the auditory cells; and - synapses on the auditory cells; To- spiral tunnel.

Each receptor cell with its rounded base adjoins a depression on the apical surface of the phalangeal cell. Thus, the auditory cells do not have direct contact with the lamina basalis. The nuclei in these cells are located at the basal pole. They have a significant amount of mitochondria and glycogen in their cytoplasm. On the apical surface of the receptor cells there is a cuticular plate with hairs - stereocilia. Electron microscopic methods have established that there are 30 - 60 short hairs on the inner cells, arranged in the form of a rectilinear brush. Each outer receptor cell has up to 120 longer hairs arranged in a curved (Y-shaped) brush.

Above the tops of the hair cells is a ribbon-like plate of a jelly-like consistency - an integumentary membrane consisting of a transparent basic substance containing glycosaminoglycans and thin fibers. One edge of the integumentary membrane is connected to the upper side of the vestibular lip of the spiral limbus, and the other edge, which has a tongue-shaped cross-section, is in contact with the hair cells along its entire length; the hairs of the latter are immersed in the membrane substance.

Rice. 197. Schematic of the analyzer of hearing and balance:

a - static spot (macula); b - sensitive neuron of the vestibular ganglion; v- neuron of the vestibular nucleus of the medulla oblongata; d - neurons of the optic hillocks; d- the end of their axons in the cerebral cortex; e- sensitive neurons of the spiral ganglion; f- neurons of the auditory tubercle of the medulla oblongata; s- neurons of the auditory analyzer in the visual hillocks; and - the end of their axons on the pyramidal cells of the cortex; To- a spiral organ.

During sound exposure, the vibrations of the tympanic membrane through the system of the auditory ossicles of the middle ear set the membrane of the oval window and the pelemphus of the vestibular and tympanic stairs in vibrational motion. Oscillations of the peralmph are transmitted to the vestibular membrane, and then to the cavity of the membranous canal of the cochlea, setting in motion the endolymph and the basilar membrane. It has been shown that each pitch of sound corresponds to a certain length of a section of the basilar membrane covered by an oscillatory process. When low-frequency sounds act on the ear, the basilar membrane is displaced along its entire length from the base to the apex of the cochlea. In this case, the hairs are displaced relative to the integumentary (tectorial) membrane and the receptor cells are excited. Under the action of high-frequency sounds, the basilar membrane is involved in the oscillatory process only in a limited area near the oval window. Accordingly, a smaller number of receptor cells will be excited - only those that are located on the basilar membrane at the base of the cochlea.

Hearing analyzer (fig. 197). From the auditory cells of the spiral (Corti's) organ, stimulation is transmitted to the cells of the spiral ganglion. The axons of these cells enter the fibers of the cochlear nerve, which in the internal auditory canal connects with the vestibular nerve to form one statoacoustic nerve. After entering the cranial cavity, the nerve fibers belonging to the cells of the spiral ganglion are again separated, enter the medulla oblongata and end on the cells of the auditory tubercle. These cells, which serve as the second neurons of the analyzer, send processes to the medial geniculate bodies of the optic tubercles. Here are multipolar neurocytes, the axons of which reach the cells of the cerebral cortex. The descending paths of the auditory analyzer begin from the latter.

ORGAN OF HEARING

Comprises outer, middle and inner ear.

Outer ear

The outer ear includes auricle, external auditory canal and eardrum.

Auricle consists of a thin plate of elastic cartilage covered with skin with a few fine hairs and sebaceous glands. There are few sweat glands in its composition.

External auditory canal formed by cartilage, which is a continuation of the elastic cartilage of the shell, and the bone part. The surface of the passage is covered with thin skin containing hair and associated sebaceous glands. Deeper than the sebaceous glands, there are tubular ceruminous glands that secrete earwax. Their ducts open independently on the surface of the ear canal or into the excretory ducts of the sebaceous glands. Ceruminous glands are located unevenly along the course of the auditory tube: in the inner two-thirds they are present only in the skin of the upper part of the tube.

Eardrum oval, slightly concave. One of the auditory ossicles of the middle ear - the malleus - is fused with the help of its handle with the inner surface of the tympanic membrane. Blood vessels and nerves pass from the malleus to the eardrum. The tympanic membrane in the middle part consists of two layers formed by bundles of collagen and elastic fibers and fibroblasts lying between them. The fibers of the outer layer are located radially, and the inner ones are circular. In the upper part of the tympanic membrane, the amount of collagen fibers decreases. On its outer surface there is a very thin layer of E0-60 microns) the epidermis, on the inner surface facing the middle ear is a mucous membrane with a thickness of about 20-40 microns, covered with a single-layer squamous epithelium.

Middle ear

The middle ear consists of tympanic cavity, ossicles and auditory tube.

Tympanic cavity- a flattened space, covered with a single-layer squamous epithelium, sometimes turning into a cubic or columnar epithelium. On the medial wall of the tympanic cavity, there are two holes, or "windows". The first is an oval window. The base of the stapes is located in it, which is held with a thin ligament around the circumference of the window. An oval window separates the tympanic cavity from the vestibular ladder of the cochlea. The second window is round, slightly behind the oval one. It is covered with a fibrous membrane. A round window separates the tympanic cavity from the snail's tympanic ladder.

Auditory bones- the hammer, incus, stapes, as a system of levers, transmit vibrations of the eardrum of the outer ear to the oval window, from which the vestibular staircase of the inner ear begins.

Auditory tube connecting the tympanic cavity with the nasal part of the pharynx has a well-defined lumen with a diameter of 1-2 mm. In the area adjacent to the tympanic cavity, the auditory tube is surrounded by a bony wall, and closer to the pharynx contains islets of hyaline cartilage. The lumen of the tube is lined with multi-row prismatic ciliated epithelium. It contains goblet glandular cells. On the surface of the epithelium, the ducts of the mucous glands open. The air pressure in the tympanic cavity of the middle ear is regulated through the auditory tube.

Inner ear

The inner ear consists of bone labyrinth and located in it webbed labyrinth, in which there are receptor cells - hairy sensory epithelial cells of the organ of hearing and balance. They are located in certain areas of the membranous labyrinth: the auditory receptor cells are in the cochlear spiral organ, and the receptor cells of the equilibrium organ are in the elliptical and spherical sacs and ampullary crests of the semicircular canals.

Development. In the human embryo, the organ of hearing and balance is laid together, from the ectoderm. A thickening is formed from the ectoderm - auditory placode which soon turns into auditory fossa and then in auditory vesicle and breaks off from the ectoderm and plunges into the underlying mesenchyme. The auditory vesicle is lined from the inside with a multi-row epithelium and soon it is divided into 2 parts by a constriction - a spherical sac is formed from one part - a sacculus and a cochlear membranous labyrinth (i.e. a hearing aid) is laid, and from the other part - an elliptical sac - an utriculus with semicircular canals and their ampoules (i.e. organ of balance). In the multilayered epithelium of the membranous labyrinth, cells differentiate into receptor sensoryepithelial cells and supporting cells. The epithelium of the Eustachian tube connecting the middle ear to the pharynx and the epithelium of the middle ear develop from the epithelium of the 1st branchial pocket. Somewhat later, the processes of ossification and the formation of the bone labyrinth of the cochlea and semicircular canals occur.

The structure of the organ of hearing (inner ear)

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

1 - membranous canal of the cochlea; 2 - vestibular ladder; 3 - drum ladder; 4 - spiral bone plate; 5 - spiral assembly; 6 - spiral comb; 7 - dendrites of nerve cells; 8 - vestibular membrane; 9 - basilar membrane; 10 - spiral ligament; 11 - epithelium lining 6and slave another staircase; 12 - vascular strip; 13 - blood vessels; 14 - integumentary plate; 15 - external sensorepithelial cells; 16 - internal sensorepithelial cells; 17 - internal supporting epithelialitis; 18 - external supporting epithelialitis; 19 - pillar cells; 20 - tunnel.

The structure of the organ of hearing (inner ear). The receptor part of the organ of hearing is inside webbed labyrinth, located in turn in the bone labyrinth, in the form of a cochlea - a bone tube spiral-twisted in 2.5 turns. A membranous labyrinth runs along the entire length of the bony cochlea. On a transverse section, the labyrinth of the bone 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. superior medial wall- formed vestibular membrane (8)... It is a thin fibrillar connective tissue plate covered with a single-layer squamous epithelium facing the endolymph and the endothelium facing the perilymph.

2. outer wall- formed vascular stripe (12) lying on spiral ligament (10)... The vascular stria is a multi-row epithelium, which, unlike all epitheliums of the body, has its own blood vessels; this epithelium secretes endolymph that 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 from the base of the cochlea to the apex. Each string is capable of resonating to a strictly defined vibration frequency - strings closer to the base of the cochlea (shorter strings) resonate to higher vibration frequencies (to higher sounds), strings closer to the top of the cochlea - to lower vibration frequencies (to lower sounds) ...

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

Spiral organ or Corti's organ - receptor part of the organ of hearing , located on the basilar membrane. It consists of sensitive, supportive cells and an integumentary membrane.

1. Sensory hair epithelial cells - Slightly elongated cells with a rounded base, at the apical end have microvilli - stereocilia. The dendrites of 1 neurons of the auditory tract, whose bodies lie in the thickness of the bone shaft - the spindle of the bone cochlea in the spiral ganglia, approach the base of the sensory hair cells and form synapses. Sensory hair epithelial cells are divided into internal pear-shaped and outdoor prismatic. The outer hair cells form 3-5 rows, while the inner ones only 1 row. Internal hair cells receive about 90% of all innervation. A tunnel of Corti is formed between the inner and outer hair cells. Overhanging the microvilli of sensory hair cells tectorial membrane.

2. SUPPORT CELLS (SUPPORT CELLS)

Outer pillar cages

Inner pillar cells

External phalanx cells

Internal phalanx cells

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

3. COVERING MEMBRANE (TECTORIAL MEMBRANE) - a gelatinous formation, consisting of collagen fibers and an amorphous substance of connective tissue, departs from the upper part of the thickening of the periosteum of the spiral process, hangs over the organ of Corti, the tops 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 - holes of the reticular (mesh) membrane, 8 - spiral ligament, 9 - bone spiral plate, 10 - tectorial (integumentary) membrane

Histophysiology of the spiral organ. The sound, like the vibration of the air, vibrates the eardrum, then the vibration through the malleus, the incus is transmitted to the stapes; the stapes through the oval window transmits vibrations to the perilymph of the vestibular staircase; along the vestibular staircase, the vibration at the apex of the bone cochlea passes into the peremphus of the tympanic staircase and descends in a spiral downward and abuts against the elastic membrane of the round opening. Oscillations of the pelemphus of the tympanic ladder cause oscillations of the strings of the basilar membrane; when the basilar membrane vibrates, the hairy sensory cells vibrate in the vertical direction and the hairs touch the tectorial membrane. Flexion of hair cell microvilli leads to excitation of these cells, i.e. the potential difference between the outer and inner surfaces of the cytolemma changes, which is captured by the nerve endings on the basal surface of the hair cells. In the 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 low sounds, long strings resonate and vibrate closer to the apex of the cochlea and, accordingly, the cells sitting on them are excited. If high sounds resonate short strings located closer to the base of the cochlea, the hair cells sitting on these strings are excited.

VESTIBULAR SECTION OF THE REPRAPED LABYRINTH - has 2 extensions:

1. The pouch is a spherical extension.

2. The uterus is an extension of the 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, uterus and semicircular canals with ampoules is covered with a single-layer squamous epithelium. At the same time, there are areas with thickened epithelium in the sac, uterus and in the ampullae of the semicircular canals. These areas with thickened epithelium in the sac and uterus are called spots or macula and in ampoules - scallops or cristae.

The spiral, or Corti, organ is located on the basilar plate of the membranous labyrinth of the cochlea. This epithelial formation follows the course of the cochlea. Its area expands from the basal cochlear curl to the apical one.

Vascular streak and its meaning:

The spiral ligament from the side of the cochlear passage is lined with the so-called vascular stripe. It is formed by a layer of high epithelium, under which there are several more layers of epithelial cells, the deepest of which is built of lower cells. A large number of capillaries and precapillaries pass between the layers of the epithelium. In the deep layers of the epithelium of the vascular stria, numerous capillaries pass in two layers, which are in close contact with epithelial cells, without a layer of connective tissue. The vascular stripe produces endolymph, provides transport of nutrients and oxygen to the organ of Corti, maintains the ionic composition of endolymph necessary for normal function hair cells

The structure of the basilar plate:

The basis of the wall of the cochlear canal, on which the organ of Corti lies, is the basilar membrane, covered from the sides of the tympanic ladder with a flat epithelium. The basilar membrane consists of thin collagen fibers - auditory strings. These strings are stretched between a spiral bone plate extending from the cochlear modiolus and a spiral ligament lying on the outer wall of the cochlea. The basilar membrane from the side of the cochlear canal is covered with a border basement membrane on which the spiral organ of Corti lies.

Cellular composition of Corti's organ:

Consists of two groups of cells - sensorepithelial (hairy) and supporting. Each of these groups of cells is subdivided into inner and outer. The two groups are separated by a tunnel (consisting of internal and external columnar epithelial cells)

Internal sensoryepithelial cells are pitcher-shaped and lie in one row on supporting internal phalangeal epithelial cells.

External sensorepithelial cells have a cylindrical shape, lie in 3-4 rows on the depressions of the supporting external phalangeal epithelial cells.

The supporting epithelial cells of the spiral organ, in contrast to the sensory ones, are directly located on the basement membrane with their bases. Internal phalangeal epithelial cells, lying under the internal sensorepithelial cells, are interconnected by tight and slit-like contacts. The outer phalangeal cells are also located on the basilar membrane. They lie in 3-4 rows in the immediate vicinity of the outer columnar cells. These cells are prismatic.

Sound reception:

During sound impact on the tympanic membrane, its vibrations are transmitted to the malleus, incus and stapes, and then through the oval window to the perilymph, basilar and tectorial membranes. This movement strictly matches the frequency and intensity of the sounds. In this case, a deviation of stereocilia and excitation of receptor cells occur. All this leads to the emergence of a receptor potential (microphone effect). Afferent information along the auditory nerve is transmitted to the central parts of the auditory analyzer.