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The membranous canal of the cochlea is filled with endolymph, which it produces. Webbed snail

HEARING ORGAN

Consists of outer, middle and inner ear.

Outer ear

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 a bone part. The surface of the passage is covered with thin skin containing hair and associated sebaceous glands. Deeper than the sebaceous glands 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. The ceruminous glands are located unevenly along 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 shape. One of the auditory ossicles of the middle ear - the malleus - is fused with the help of its handle to the inner surface of the eardrum. Blood vessels and nerves pass from the malleus to the eardrum. The middle part of the eardrum consists of two layers formed by bundles of collagen and elastic fibers and fibroblasts lying between them. The fibers of the outer layer are arranged radially, and the fibers of the inner layer are arranged circularly. In the upper part of the eardrum, the number of collagen fibers decreases. On its outer surface there is a very thin layer (E0-60 µm) of the epidermis, on the inner surface facing the middle ear there is a mucous membrane about 20-40 µm thick, covered with single-layer squamous epithelium.

Middle ear

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

Tympanic cavity- a flattened space covered with single-layer squamous epithelium, in places turning into cubic or columnar epithelium. There are two openings, or “windows,” on the medial wall of the tympanic cavity. The first is the oval window. It contains the base of the stirrup, which is held in place by a thin ligament around the circumference of the window. The oval window separates the tympanic cavity from the scala vestibularis of the cochlea. The second window is round, located slightly behind the oval one. It is covered with a fibrous membrane. A round window separates the tympanic cavity from the scala tympani of the cochlea.

Auditory ossicles- the hammer, incus, and stirrup, 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.

Eustachian 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 bone wall, and closer to the pharynx it contains islands of hyaline cartilage. The lumen of the tube is lined with multirow prismatic ciliated epithelium. It contains goblet glandular cells. On the surface of the epithelium, ducts of the mucous glands open. The auditory tube regulates air pressure in the tympanic cavity of the middle ear.

Inner ear

The inner ear consists of bony labyrinth and located in it membranous labyrinth, which contains receptor cells - hair sensory epithelial cells of the organ of hearing and balance. They are located in certain areas of the membranous labyrinth: auditory receptor cells are in the spiral organ of the cochlea, and receptor cells of the balance organ are in the elliptical and spherical sacs and ampullary crests of the semicircular canals.

Development. In the human embryo, the organs of hearing and balance are formed together from the ectoderm. A thickening is formed from the ectoderm - auditory placode, which soon turns into auditory fossa, and then in otic vesicle and breaks away from the ectoderm and sinks into the underlying mesenchyme. The auditory vesicle is lined from the inside with multi-row epithelium and is soon divided into 2 parts by a constriction - from one part a spherical sac is formed - the sacculus and the cochlear membranous labyrinth (i.e. the auditory apparatus) is formed, and from the other part - an elliptical sac - the utriculus with semicircular canals and their ampoules (i.e. the organ of balance). In the multirow epithelium of the membranous labyrinth, cells differentiate into sensory sensory cells and supporting cells. The epithelium of the Eustachian tube connecting the middle ear with the pharynx and the epithelium of the middle ear develop from the epithelium of the 1st gill pouch. Somewhat later, the processes of ossification and formation of the bony labyrinth of the cochlea and semicircular canals occur.

Structure of the hearing organ (inner ear)

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

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 vestibuli 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 ones 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 the sensory hair cells. tectorial membrane.

2. SUPPORTING CELLS (SUPPORTING CELLS)

External pillar cells

Internal pillar cells

External phalangeal cells

Inner 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 connective tissue substance, 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 - bone spiral 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. Nerve impulses are generated at the nerve endings 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.

The inner ear (auris interna) consists of the bony and membranous labyrinths (Fig. 559). These labyrinths form the vestibule, three semicircular canals and the cochlea.

Bone labyrinth (labyrinthus osseus)

The vestibule (vestibulum) is a cavity that communicates behind 5 openings with the semicircular canals and in front with the openings of the cochlear canal. On the labyrinthine wall of the tympanic cavity, i.e. on the lateral wall of the vestibule, there is an opening of the vestibule (fenestra vestibuli), where the base of the stapes is placed. On the same wall of the vestibule there is another opening of the cochlea (fenestra cochleae), covered with a secondary membrane. The cavity of the vestibule of the inner ear is divided by a comb (criita vestibuli) into two recesses: an elliptical recess (recessus ellipticus), - posterior, communicates with the semicircular canals; spherical recess (recessus sphericus) - anterior, located closer to the cochlea. The aqueduct of the vestibule (aqueductus vestibuli) originates from the elliptical depression with a small hole (apertura interna aqueductus vestibuli).

The aqueduct of the vestibule passes through the bone of the pyramid and ends in a hole on the posterior surface with an opening (apertura externa aqueductus verstibuli). Bone semicircular canals (canales semicirculares ossei) are located mutually perpendicular in three planes. However, they are not parallel to the main axes of the head, but are at an angle of 45° to them. When the head is tilted forward, the fluid of the anterior semicircular canal (canalis semicircularis anterior), located vertically in the sagittal cavity, moves. When the head is tilted to the right or left, fluid currents arise in the posterior semicircular canal (canalis semicircularis posterior). It is also vertical in the frontal plane. When the head rotates, fluid movement occurs in the lateral semicircular canal (canalis semicircularis lateralis), which lies in the horizontal plane. The five openings of the canal pedicles communicate with the vestibule, since one end of the anterior canal and one end of the posterior canal are connected into a common pedicle. One leg of each canal at the junction with the vestibule of the inner ear expands in the shape of an ampoule.

The cochlea (cochlea) consists of a spiral canal (canalis spiralis cochleae), limited by the bony substance of the pyramid. It has 2 ½ circular strokes (Fig. 558). In the center of the cochlea there is a complete bone rod (modiolus), located in the horizontal plane. A bony spiral plate (lamina spiralis ossea) protrudes into the lumen of the cochlea from the side of the rod. In its thickness there are openings through which blood vessels and auditory nerve fibers pass to the spiral organ. The spiral plate of the cochlea, together with the formations of the membranous labyrinth, divides the cochlear cavity into two parts: the scala vestibule (scala vestibuli), connecting to the cavity of the vestibule, and the scala tympani (scala tympani). The place where the scala vestibule transitions into the scala tympani is called the lucid foramen of the cochlea (helicotrema). The fenestra cochleae opens into the scala tympani. The cochlear aqueduct originates from the scala tympani and passes through the bony substance of the pyramid. On the lower surface of the posterior edge of the pyramid of the temporal bone there is an external opening of the aqueduct of the cochlea (apertura externa canaliculi cochleae).

Membranous labyrinth

The membranous labyrinth (labirynthus membranaceus) is located inside the bony labyrinth and almost repeats its outline (Fig. 559).

The vestibular part of the membranous labyrinth, or vestibule, consists of a spherical sac (sacculus), located in the recessus sphericus, and an elliptical sac (utriculus), located in the recessus ellipticus. The sacs communicate one with

another through the connecting duct (ductus reuniens), which continues into the ductus endolymphaticus, ending in the connective tissue sac (sacculus). The sac is located on the posterior surface of the pyramid of the temporal bone at the apertura externa aqueductus vestibuli.

The semicircular canals also open into the elliptical sac, and the canal of the membranous part of the cochlea opens into the ventricle.

In the walls of the membranous labyrinth of the vestibule in the area of ​​the sacs, there are areas of sensitive cells - spots (maculae). The surface of these cells is covered with a gelatinous membrane containing calcium carbonate crystals - otoliths, which irritate gravity receptors by the movement of fluid when the position of the head changes. The auditory spot of the uterus is the place where the perception of irritations associated with changes in body position relative to the center of gravity, as well as vibration vibrations, occurs.

The semicircular canals of the membranous labyrinth connect to the elliptical sacs of the vestibule. At the confluence there are expansions of the membranous labyrinth (ampullae). This labyrinth is suspended from the walls of the bone labyrinth with the help of connective tissue fibers. It has auditory ridges (criitae ampullares) that form folds in each ampulla. The direction of the scallop is always perpendicular to the semicircular canal. Scallops have hairs of receptor cells. When the position of the head changes, when the endolymph moves in the semicircular canals, irritation of the receptor cells of the auditory crests occurs. This causes a reflex contraction of the corresponding muscles, which aligns the position of the body and coordinates the movements of the external eye muscles.

The vestibule of the membranous labyrinth and part of the semicircular canals contain sensory cells located in the auditory spots and auditory crests, where endolymph currents are perceived. From these formations the statokinetic analyzer originates, ending in the cerebral cortex.

Membranous part of the cochlea

The cochlear part of the labyrinth is represented by the cochlear duct (ductus cochlearis). The duct begins from the vestibule in the region of recessus cochlearis and ends blindly near the apex of the cochlea. In cross-section, the cochlear duct has a triangular shape and most of it is located closer to the outer wall. Thanks to the cochlear duct, the cavity of the bony duct of the cochlea is divided into two parts: the upper one - the scala vestibuli (scala vestibuli) and the lower one - the scala tympani (scala tympani). They communicate with each other at the apex of the cochlea by a cleared opening (helicotrema) (Fig. 558).

The outer wall (stria vascularis) of the cochlear duct fuses with the outer wall of the bony duct of the cochlea. The upper (paries vestibularis) and lower (membrana spiralis) walls of the cochlear duct are a continuation of the bony spiral plate of the cochlea. They originate from its free edge and diverge towards the outer wall at an angle of 40-45°. On the membrana spiralis there is a sound-receiving apparatus - a spiral organ.

The spiral organ (organum spira1e) is located throughout the entire cochlear duct and is located on a spiral membrane, which consists of thin collagen fibers. Sensitive hair cells are located on this membrane. The hairs of these cells, as usual, are immersed in a gelatinous mass called the membrane tectoria. When a sound wave swells the basilar membrane, the hair cells standing on it sway from side to side and their hairs, immersed in the covering membrane, bend or stretch to the diameter of the smallest atom. These atom-sized changes in the position of the hair cells produce a stimulus that generates the generator potential of the hair cells. One reason for the high sensitivity of hair cells is that the endolymph maintains a positive charge of about 80 mV relative to the perilymph. The potential difference ensures the movement of ions through the pores of the membrane and the transmission of sound stimuli.

Sound wave paths. Sound waves, meeting the resistance of the elastic eardrum, together with it vibrate the handle of the hammer, which displaces all the auditory ossicles. The base of the stapes presses on the perilymph of the vestibule of the inner ear. Since the fluid practically does not compress, the perilymph of the vestibule displaces the fluid column of the scala vestibule, which moves through the opening at the apex of the cochlea (helicotrema) into the scala tympani. Its liquid stretches the secondary membrane covering the round window. Due to the deflection of the secondary membrane, the cavity of the perilymphatic space increases, which causes the formation of waves in the perilymph, the vibrations of which are transmitted to the endolymph. This leads to displacement of the spiral membrane, which stretches or bends the hairs of sensory cells. Sensory cells are in contact with the first sensory neuron.

For the conduction pathways of the hearing organ, see section I. Extroceptive pathways of this publication.

Development of the vestibulocochlear organ

Development of the outer ear. The outer ear develops from the mesenchymal tissue surrounding the first branchial groove. In the middle of the second month of embryonic development, three tubercles are formed from the tissue of the first and second gill arches. Due to their growth, the auricle is formed. Developmental anomalies are the absence of the auricle or improper formation of the outer ear due to uneven growth of individual tubercles.

Middle ear development. At the second month, the middle ear cavity develops from the distal part of the first branchial groove in the embryo. The proximal part of the sulcus is transformed into the auditory tube. In this case, the ectoderm of the gill furrow and the endoderm of the pharyngeal pouch are located close to each other. Then the blind end of the bottom of the pharyngeal pouch extends from its surface and is surrounded by mesenchyme. The auditory ossicles form from it; Until the ninth month of the intrauterine period, they are surrounded by embryonic connective tissue and the tympanic cavity as such is absent, as it is filled with this tissue.

At the third month after birth, the embryonic connective tissue of the middle ear is resorbed, releasing the auditory ossicles.

Development of the inner ear. Initially, the membranous labyrinth is formed. At the beginning of the 3rd week of embryonic development, at the head end on the sides of the neural groove in the embryo, an auditory plate is laid in the ectoderm, which at the end of this week is immersed in the mesenchyme, and then laced off in the form of an auditory vesicle (Fig. 560). At the 4th week, an endolymphatic duct grows in the direction of the ectoderm from the dorsal part of the auditory vesicle, which maintains a connection with the vestibule of the inner ear. The cochlea develops from the ventral part of the auditory vesicle. The semicircular canals are formed at the end of the 6th week of the intrauterine period. At the beginning of the third month, the utricle and saccule separate in the vestibule.

At the time of differentiation of the membranous labyrinth, mesenchyme gradually concentrates around it, which turns into cartilage and then into bone. Between the cartilage and the membranous labyrinth there remains a thin layer filled with mesenchymal cells. They turn into connective tissue cords that suspend the membranous labyrinth.

Developmental anomalies. There is a complete absence of the auricle and external auditory canal, their small or large size. A common anomaly is the accessory helix and tragus. Possible underdevelopment of the inner ear with atrophy of the auditory nerve.

Age characteristics. In a newborn, the auricle is relatively smaller than in an adult, and does not have pronounced convolutions and tubercles. Only by the age of 12 does it reach the shape and size of the auricle of an adult. After 50-60 years, the cartilage becomes numb. The external auditory canal in a newborn is short and wide, and the bony part consists of a bony ring. The size of the eardrum in a newborn and an adult is almost the same. The eardrum is located at an angle of 180° to the upper wall, and in an adult - at an angle of 140°. The tympanic cavity is filled with fluid and connective tissue cells; its lumen is small due to the thick mucous membrane. In children under 2-3 years of age, the upper wall of the tympanic cavity is thin, has a wide stony-scaly gap filled with fibrous connective tissue with numerous blood vessels. With inflammation of the tympanic cavity, infection may penetrate through the blood vessels into the cranial cavity. The posterior wall of the tympanic cavity communicates through a wide opening with the cells of the mastoid process. The auditory ossicles, although they contain cartilaginous points, correspond to the size of an adult. The auditory tube is short and wide (up to 2 mm). The cartilaginous part easily stretches, so when the nasopharynx in children becomes inflamed, the infection easily penetrates into the tympanic cavity. The shape and size of the inner ear do not change throughout life.

Phylogenesis. The statokinetic apparatus in lower animals is presented in the form of ectodermal pits (statocysts), which are lined with mechanoreceptors. The role of statoliths is performed by a grain of sand (otolith), which enters the ectodermal pit from the outside. Otoliths irritate the receptors on which they lie, and impulses arise that enable orientation in body position. When a grain of sand is displaced, impulses will appear that inform the body on which side the body needs support in order to avoid falling or turning over. It is assumed that these organs are also hearing aids.

In insects, the hearing apparatus is represented by a thin cuticular membrane, under which the tracheal bladder is located; between them lie the receptors of sensory cells.

The spinal auditory system originates from the lateral line nerves. A pit appears near the head, which gradually detaches from the ectoderm and turns into the semicircular canals, vestibule and cochlea.

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 of the endolymph, which is positively charged in relation to the 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 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 scala 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. In the Organ of Corti, the primary formation of the analysis of sound signals begins.

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.

The mechanism of sound vibrations in the cochlea

Sound waves are picked up by the auricle and sent through the ear canal to the eardrum. Vibrations of the eardrum, through the system of auditory ossicles, are transmitted through the stapes to the membrane of the oval window, and through it are transmitted to the lymphatic fluid. Depending on the vibration frequency, only certain fibers of the main membrane respond to fluid vibrations (resonate). The hair cells of the organ of Corti are excited when the fibers of the main membrane touch them and are transmitted through the auditory nerve into impulses, where the final sensation of sound is created.

is a unique organ not only in its structure, but also in the functions it performs. Thus, it perceives sound vibrations, is responsible for maintaining balance and has the ability to hold the body in space in a certain position.

Each of these functions is performed by one of three parts of the ear: external and internal. Next, we will talk specifically about the internal section, and more specifically about one of its components - the cochlea.

The structure of the cochlea of ​​the inner ear

Structure presented labyrinth, consisting of a bone capsule and a membranous formation that repeats the shape of the same capsule.

Location of the cochlea in the bony labyrinth of the inner ear

The bony labyrinth consists of the following sections:

  • semicircular canals;
  • vestibule;
  • snail.

Snail in the ear- this is a bone formation that has the appearance of a volumetric spiral in 2.5 turns around the bone shaft. The width of the base of the cochlea cone is 9 mm, and in height – 5 mm. The length of the bone spiral is 32 mm.

Reference. The cochlea consists of a relatively durable material; according to some scientists, this material is one of the most durable in the entire human body.

Starting its path in the bone core, spiral plate goes inside the labyrinth. This formation at the beginning of the cochlea is wide, and towards its completion it gradually begins to narrow. The plate is all dotted with channels in which dendrites of bipolar neurons.

Section of the cochlea of ​​the inner ear

Thanks to main (basilar) membrane, located between the unused edge of this plate and the wall of the cavity, occurs division of the cochlear canal into 2 passages or stairs:

  1. Superior canal or scala vestibule- originates at the oval window and extends all the way to the apical point of the cochlea.
  2. Inferior canal or scala tympani- extends from the apical point of the cochlea up to the round window.

Both canals at the apex of the cochlea are connected by a narrow opening - helicotrem. Also both cavities are filled perilymph, which has characteristics similar to cerebrospinal fluid.

The vestibular (Reissner's) membrane divides the upper canal into 2 cavities:

  • stairs;
  • membranous canal, called the cochlear duct.

IN cochlear duct located on the basilar membrane organ of corti– sound analyzer. It consists of supporting and auditory receptor hair cells, above which is located cover membrane, resembling a jelly-like mass in its appearance.

The structure of the organ of Corti, responsible for the beginning of sound processing

Functions of the cochlea of ​​the inner ear

The main function of the cochlea in the ear- this is the transmission of nerve impulses coming from the middle ear to the brain, while the organ of Corti is a very important link in the chain, since it is here that the primary formation of the analysis of sound signals begins. What is the sequence of performing such a function?

So, when sound vibrations reach the ear, they hit the membrane of the eardrum, thereby causing vibration in it. Then the vibration reaches 3 auditory ossicles(maleus, incus, stapes).

Connected with snail stapes affects fluid in the areas: scala vestibule and scala tympani. In this case, the liquid affects the basilar membrane, which includes the auditory nerves, and creates vibration waves on it.

From the generated vibration waves cilia of hair cells in the sound analyzer (organ of Corti) come into motion, irritating the plate located above them like a canopy (covering membrane).

Then this process comes to the final stage, where hair cells transmit impulses about the characteristics of sounds to the brain. Moreover, the latter is like a complex logic processor begins to separate useful audio signals from background noise, distributing them into groups according to various characteristics and looking for similar images in memory.

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The inner ear (auris interna) is divided into three parts: the vestibule, the cochlea, and the semicircular canal system. Phylogenetically, the organ of balance is a more ancient formation.

The inner ear is represented by the outer bone and inner membranous (formerly called leathery) sections - labyrinths. The cochlea belongs to the auditory analyzer, the vestibule and semicircular canals belong to the vestibular analyzer.

Bone labyrinth

Its walls are formed by the compact bone substance of the pyramid of the temporal bone.

Snail (cochlea)

Fully lives up to its name and is a curled canal of 2.5 turns, twisting around a bone cone-shaped rod (modiolus), or spindle. From this spindle into the lumen of the helix, a bone plate extends in the form of a spiral, which has an unequal width as it moves from the base of the cochlea to the dome of the cochlea: at the base it is much wider and almost touches the inner wall of the helix, and at the apex it is very narrow and disappears.

In this regard, at the base of the cochlea the distance between the edge of the bony spiral plate and the inner surface of the cochlea is very small, and in the area of ​​the apex it is noticeably wider. In the center of the spindle there is a canal for the fibers of the auditory nerve, from the trunk of which numerous tubules extend to the periphery towards the edge of the bone plate. Through these tubules, the auditory nerve fibers approach the spiral (corti) organ.

vestibule (vestibulum)

The bony vestibule is a small, almost spherical cavity. Its outer wall is almost entirely occupied by the opening of the fenestra vestibule; on the anterior wall there is an opening leading to the base of the cochlea; on the posterior wall there are five openings leading to the semicircular canals. Small openings are visible on the inner wall, through which the fibers of the vestibular cochlear nerve approach the receptor sections of the vestibule in the area of ​​small depressions on this wall of a spherical and elliptical shape.


1 - elliptical sac (uterus); 2 — ampoule of the external canal; 3 - endolymphatic sac; 4 - cochlear duct; 5 - spherical bag; 6 - perilymphatic duct; 7 — cochlear window; 8 - window of the vestibule


Bone semicircular canals (canales semicircularesossei) are three arched thin tubes. They are located in three mutually perpendicular planes: horizontal, frontal and sagittal and are called lateral, anterior and posterior. The semicircular canals are not located strictly in the indicated planes, but deviate from them by 300, i.e. the lateral one is deflected from the horizontal plane by 300, the anterior one is turned to the middle by 300, the rear one is deflected posteriorly by 300. This should be taken into account when conducting a study of the function of the semicircular canals.

Each bony semicircular canal has two bony pedicles, one of which is expanded in the form of an ampulla (ampullary bone pedicle).

Membranous labyrinth

It is located inside the bone and completely follows its contours: cochlea, vestibule, semicircular ducts. All sections of the membranous labyrinth are connected to each other.

Cochlear duct

From the free edge of the bony spiral plate along its entire length towards the inner surface of the cochlear curls, the fibers of the “string” of the basilar plate (membrane) extend, and thus the cochlear curl is divided into two floors.

The upper floor - the staircase of the vestibule (scala vestibuli) begins in the vestibule, rises spirally to the dome, where through the opening of the cochlea (helicotrema) it passes into another, lower floor - the scala tympani (scala tympani), and also spirals down to the base of the cochlea. Here the lower floor ends with a cochlear window covered by a secondary tympanic membrane.

On a cross section, the membranous labyrinth of the cochlea (cochlear duct) has the shape of a triangle.

From the place of attachment of the basilar plate (membrana basillaris), also towards the inner surface of the helix, but at an angle, another pliable membrane extends - the vestibular wall of the cochlear duct (vestibular, or vestibular, membrane; Reissner's membrane).

Thus, in the upper staircase, the staircase vestibule (scala vestibuli), an independent canal is formed, spiraling upward from the base to the dome of the cochlea. This is the cochlear duct. Outside of this membranous labyrinth in the scala tympani and in the scala vestibule there is a fluid - perilymph. It is generated by a specific system of the inner ear itself, represented by the vascular network in the perilymphatic space. Through the cochlear aqueduct, the perilymph communicates with the cerebral fluid of the subarachnoid space.

Inside the membranous labyrinth there is endolymph. It differs from perilymph in the content of K+ and Na+ ions, as well as in electrical potential.

Endolymph is produced by the vascular strip, which occupies the inner surface of the outer wall of the cochlear passage.



a - section of the cochlea of ​​the rod axis; b - membranous labyrinth of the cochlea and spiral organ.

1 - cochlear opening; 2 - staircase vestibule; 3 - membranous labyrinth of the cochlea (cochlear duct); 4 - scala tympani; 5 - bone spiral plate; 6 - bone rod; 7 - vestibular wall of the cochlear duct (Reisner's membrane); 8 - vascular strip; 9 — spiral (main) membrane; 10 - covering membrane; 11 - spiral organ
The spiral, or organ of Corti, is located on the surface of the spiral membrane in the lumen of the cochlear duct. The width of the spiral membrane is not the same: at the base of the cochlea, its fibers are shorter, more stretched, and more elastic than in areas approaching the dome of the cochlea. There are two groups of cells—sensory and supporting—that provide the mechanism for perceiving sounds. There are two rows (inner and outer) of supporting, or pillar, cells, as well as outer and inner sensory (hair) cells, with 3 times more outer hair cells than inner ones.

The hair cells resemble an elongated thimble, and their lower edges rest on the bodies of the Deuterian cells. Each hair cell has 20-25 hairs at its upper end. A covering membrane (membrana tectoria) extends over the hair cells. It consists of thin fibers fused to each other. The hair cells are approached by fibers that originate in the cochlear ganglion (spiral ganglion of the cochlea), located at the base of the bony spiral plate. Inner hair cells carry out “fine” localization and discrimination of individual sounds.

Outer hair cells “connect” sounds and contribute to a “complex” sound experience. Weak, quiet sounds are perceived by the outer hair cells, strong sounds by the inner ones. The outer hair cells are the most vulnerable and are damaged more quickly, and therefore, when the sound analyzer is damaged, the perception of weak sounds first suffers. Hair cells are very sensitive to the lack of oxygen in the blood and endolymph.

Membranous vestibule

It is represented by two cavities occupying a spherical and elliptical recess on the medial wall of the bony vestibule: a spherical sac (sacculus) and an elliptical sac, or utricle (utriculus). These cavities contain endolymph. The spherical sac communicates with the cochlear duct, the elliptical sac communicates with the semicircular ducts. Both sacs are also connected to each other by a narrow duct, which turns into an endolymphatic duct - the aqueduct of the vestibule (agueductus vestibuli) and ends blindly in the form of an endolymphatic sac (sacculus endolymphaticus). This small sac is located on the posterior wall of the pyramid of the temporal bone, in the posterior cranial fossa and can be a collector of endolymph and stretch when it is in excess.

The elliptical and spherical sacs contain the otolithic apparatus in the form of spots (maculae). A. Scarpa was the first to draw attention to these details in 1789. He also pointed out the presence of “pebbles” (otoliths) in the vestibule, and also described the course and termination of the auditory nerve fibers in the “whitish tubercles” of the vestibule. Each sac of the “otolithic apparatus” contains terminal nerve endings of the vestibulocochlear nerve. The long fibers of the supporting cells form a dense network in which the otoliths are located. They are surrounded by a gelatinous mass that forms the otolithic membrane. Sometimes it is compared to wet felt. Between this membrane and the elevation, which is formed by the cells of the sensitive epithelium of the otolithic apparatus, a narrow space is defined. The otolithic membrane slides along it and deflects sensitive hair cells.

The semicircular ducts lie in the semicircular canals of the same name. The lateral (horizontal or external) duct has an ampulla and an independent leg, with which it opens into an elliptical sac.

The frontal (anterior, upper) and sagittal (posterior, lower) ducts have only independent membranous ampoules, and their simple stalk is combined, and therefore only 5 openings open into the vestibule. At the border of the ampulla and the simple stalk of each canal there is an ampullar ridge (crista ampularis), which is a receptor for each canal. The space between the expanded, ampullary part in the scallop area is delimited from the lumen of the semi-canal by a transparent dome (cupula gelotinosa). It is a delicate diaphragm and is revealed only with special staining of the endolymph. The dome is located above the scallop.



1 - endolymph; 2 — transparent dome; 3 - ampullary comb


The impulse occurs when the movable gelatin dome moves along the comb. It is assumed that these displacements of the dome can be compared with fan-shaped or pendulum-like movements, as well as with oscillations of a sail when the direction of air movement changes. One way or another, under the influence of the endolymph current, the transparent dome, moving, deflects the hairs of sensitive cells and causes them to be excited and triggered.

The frequency of impulses in the ampullary nerve changes depending on the direction of deviation of the hair bundle, the transparent dome: when deviated towards the elliptical sac - an increase in impulses, towards the canal - a decrease. The transparent dome contains mucopolysaccharides that act as piezoelements.

Yu.M. Ovchinnikov, V.P. Gamow