Inner ear. The structure of the snail

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

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

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

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

AT last years developed a number of techniques for the finest study of the structures of the cochlea, which significantly refined our knowledge in this area. These include in vivo examination through a window made in the cochlea of ​​animals, phase contrast, electron microscopy, study in polarized light, ultraviolet absorption, which allows studying the various phases of nuclear and cytochemical changes in cochlear nerve cells with various types of acoustic stimuli, studies using various histochemical colorful reactions - for polysaccharides, metachromatic reactions, reactions to neutral fat, to glycoprotein, to plasmalogen (fat + aldehyde group), to alkaline phosphatase, etc. In the following presentation, we use new received data.

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

The inner ear, or labyrinth, is located in the thickness of the pyramid temporal bone and consists of a bone capsule and a membranous formation included in it, repeating the structure of the bone labyrinth in shape. There are three divisions of the bony labyrinth:

middle - vestibule (vestibulum);

anterior - snail (cochlea);

posterior - a system of three semicircular canals (canalis semicircularis).

Laterally, the labyrinth is the medial wall of the tympanic cavity, into which the windows of the vestibule and cochlea face, medially borders on the posterior cranial fossa, with which it is connected by the internal ear canal(meatus acusticus internus), vestibule aqueduct (aquaeductus vestibuli) and snail aqueduct (aquaeductus cochleae).

Snail (cochlea) is a bone spiral canal, which in humans has about two and a half turns around the bone rod (modiolus), from which the bone spiral plate (lamina spiralis ossea) extends into the canal. The cochlea in section has the form of a flattened cone with a base width of 9 mm and a height of 5 mm, the length of the spiral bone canal is about 32 mm. The bone spiral plate, together with the membranous basilar plate, which is its continuation, and the vestibular (Reisner) membrane (membrana vestibuli) form an independent canal (ductus cochlearis) inside the cochlea, which divides the canal of the cochlea into two spiral corridors - upper and lower. The upper section of the canal is the scala vestibuli, the lower is the scala tympani. The stairs are isolated from each other throughout, only in the region of the top of the cochlea they communicate with each other through a hole (helicotrema). The scala vestibule communicates with the vestibule, the scala tympani borders the tympanic cavity through the cochlear window and does not communicate with the vestibule. At the base of the spiral plate there is a channel in which the spiral ganglion of the cochlea (gangl. spirale cochleae) is located - here are the cells of the first bipolar neuron of the auditory tract. The bony labyrinth is filled with perilymph, and the membranous labyrinth located in it is filled with endolymph.

vestibule (vestibulum)- the central part of the labyrinth, phylogenetically the most ancient. This is a small cavity, inside of which there are two pockets: spherical (recessus sphericus) and elliptical (recessus ellipticus). In the first, closer to the cochlea, there is a spherical sac (sacculus), in the second, adjacent to the semicircular canals, the uterus (utriculus). The anterior part of the vestibule communicates with the cochlea through the scala vestibulum, the posterior part communicates with the semicircular canals.

Semicircular canals. Three semicircular canals are located in three mutually perpendicular planes: lateral or horizontal (canalis semicircularis lateralis) is at an angle of 30 ° to the horizontal plane; anterior or frontal vertical canal (canalis semicircularis anterior) - in the frontal plane; the posterior or sagittal vertical semicircular canal (canalis semicircularis posterior) is located in the sagittal plane. In each canal, an expanded ampullar and a smooth knee are distinguished, facing the elliptical pocket of the vestibule. The smooth knees of the vertical canals - frontal and sagittal - are merged into one common knee. Thus, the semicircular canals are connected to the elliptical pocket of the vestibule by five foramina. The ampulla of the lateral semicircular canal comes close to the aditus ad antrum, forming its medial wall.

membranous labyrinth It is a closed system of cavities and canals, the shape of which basically repeats the bone labyrinth. The space between the membranous and bony labyrinth is filled with perilymph. This space is very small in the region of the semicircular canals and expands somewhat in the vestibule and cochlea. The membranous labyrinth is suspended inside the perilymphatic space with the help of connective tissue cords. The cavities of the membranous labyrinth are filled with endolymph. Perilymph and endolymph represent the humoral system of the ear labyrinth and are functionally closely related. Perilymph in its ionic composition resembles cerebrospinal fluid and blood plasma, endolymph - intracellular fluid. The biochemical difference concerns primarily the content of potassium and sodium ions: there is a lot of potassium in the endolymph and little sodium, in the perilymph the ratio is reversed. The perilymphatic space communicates with the subarachnoid space through the cochlear aqueduct, the endolymph is located in closed system membranous labyrinth and has no communication with brain fluids.

It is believed that endolymph is produced by the vascular streak and reabsorbed in the endolymphatic sac. Excessive production of endolymph by the vascular streak and a violation of its absorption can lead to an increase in intralabyrinthine pressure.

From an anatomical and functional point of view, two receptor apparatuses are distinguished in the inner ear:

auditory, located in the membranous cochlea (ductus cochlearis);

vestibular, in vestibular sacs (sacculus and utriculus) and in three ampullae of the membranous semicircular canals.

webbed snail, or cochlear duct (ductus cochlearis) is located in the cochlea between the scala vestibule and the scala tympani. On a transverse section, the cochlear duct has a triangular shape: it is formed by the vestibular, tympanic and outer walls. The upper wall faces the staircase of the vestibule and is formed by a thin, consisting of two layers of flat epithelial cells vestibular (Reissner) membrane (membrana vestibularis).

The floor of the cochlear duct is formed by a basilar membrane that separates it from the scala tympani. The edge of the bone spiral plate through the basilar membrane is connected to the opposite wall of the bone cochlea, where a spiral ligament (lig. spirale) is located inside the cochlear duct, the upper part of which, rich in blood vessels, is called the vascular strip a vascularis). The basilar membrane has an extensive network of capillary blood vessels and is a formation consisting of transverse elastic fibers, the length and thickness of which increases in the direction from the main curl to the top. On the basilar membrane, located spirally along the entire cochlear duct, lies a spiral (Corti) organ - a peripheral receptor for the auditory analyzer. The spiral organ consists of neuroepithelial inner and outer hair cells, supporting and nourishing cells (Deiters, Hensen, Claudius), outer and inner pillar cells that form the arches of Corti.

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

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

Bone labyrinth

Snail (cochlea)

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 noticeably wider in the region of the apex. In the center of the spindle there is a channel for the fibers auditory nerve, from the trunk of which numerous tubules extend to the periphery towards the edge of the bone plate. Through these tubules, the fibers of the auditory nerve approach the spiral (Corti) organ.

vestibule (vestibulum)

1 - elliptical pouch (uterus); 2 - ampulla of the external channel; 3 - endolymphatic sac; 4 - cochlear duct; 5 - spherical bag; 6 - perilymphatic duct; 7 - snail window; 8 - vestibule window

Each bone semicircular canal has two bone legs, one of which is expanded in the form of an ampulla (ampullar bone leg).

membranous labyrinth

cochlear duct

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

On a transverse 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 curl, but another pliable membrane departs at an angle - the vestibular wall of the cochlear duct (vestibular, or vestibular, membrane; Reissner's membrane).

Thus, in the upper staircase - the staircase of the vestibule (scala vestibuli) an independent channel is formed, spirally rising 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 vestibuli there is a fluid - perilymph. It is generated by a particular system of the innermost ear, represented by the vasculature in the perilymphatic space. Through the aqueduct of the cochlea, the perilymph communicates with the cerebral fluid of the subarachnoid space.

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

Endolymph is produced by a vascular strip that occupies the inner surface of the outer wall of the cochlear canal.

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

1 - hole of the cochlea; 2 - ladder vestibule; 3 - membranous labyrinth of the cochlea (cochlear duct); 4 - drum stairs; 5 - bone spiral plate; 6 - bone rod; 7 - vestibular wall of the cochlear duct (Reissner's membrane); 8 - vascular strip; 9 - spiral (main) membrane; 10 - cover membrane; 11 - spiral organ
The spiral, or Corti, organ 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, tighter, more elastic than in areas approaching the dome of the cochlea. There are two groups of cells - sensory and supporting - providing a mechanism for the perception of sounds. There are two rows (internal and external) of supporting, or pillar, cells, as well as external and internal sensory (hair) cells, and there are 3 times more external hair cells than internal ones.

Hair cells resemble an elongated thimble, and their lower edges rest on the bodies of deuters cells. Each hair cell has 20-25 hairs at its upper end. The integumentary membrane (membrana tectoria) extends over the hair cells. It consists of thin, soldered to each other fibers. Hair cells are approached by fibers originating in the cochlear ganglion (cochlear ganglion), located at the base of the bony spiral plate. Internal hair cells carry out "fine" localization and distinction of individual sounds.

The outer hair cells "connect" sounds and contribute to a "complex" sound experience. Weak, quiet sounds are perceived by the outer hair cells, strong sounds are perceived by the inner ones. The outer hair cells are the most vulnerable, are damaged faster, 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, endolymph.

membranous vestibule

The otolithic apparatus in the form of spots (maculae) is located in the elliptical and spherical sacs. 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 ending of the auditory nerve fibers in the "whitish tubercles" of the vestibule. In each sac of the "otolithic apparatus" there are 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 gelatin-like mass that forms an 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 otolith apparatus, a narrow space is defined. The otolithic membrane slides along it and deflects the hair sensitive 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, superior) and sagittal (posterior, inferior) ducts have only independent membranous ampullae, and their simple stalk is united, and therefore only 5 openings open in the vestibule. On the border of the ampulla and the simple stem of each canal, there is an ampullar comb (crista ampularis), which is a receptor for each canal. The space between the expanded, ampullar, part in the region of the scallop is delimited from the lumen of the semi-canal by a transparent dome (cupula gelotinosa). It is a delicate diaphragm and is detected only with special staining of the endolymph. The dome is above the scallop.

1 - endolymph; 2 - transparent dome; 3 - ampullary scallop

The frequency of impulses in the ampullar nerve varies depending on the direction of deviation of the hair bundle, the transparent dome: with a deviation towards the elliptical sac, an increase in impulses, towards the canal, a decrease. The transparent dome contains mucopolysaccharides, which play the role of piezoelectric elements.

Yu.M. Ovchinnikov, V.P. Gamow

Hearing and balance

Registration of two sensory modalities - hearing and balance - occurs in the ear (Fig. 11-1). Both organs (hearing and balance) form a vestibule in the thickness of the temporal bone ( vestibulum) and snail ( cochlea) - vestibulocochlear organ. Receptor (hair) cells (Fig. 11–2) of the hearing organ are located in the membranous canal of the cochlea (organ of Corti), and the balance organ (vestibular apparatus) in the structures of the vestibule - semicircular canals, uterus ( utriculus) and a bag ( sacculus).

Rice . 11 - 1 . Organs of hearing and balance . The outer, middle and inner ear, as well as the auditory and vestibular (vestibular) branches of the vestibulocochlear nerve ( VIII pair cranial nerves).

Rice . 11-2. vestibulocochlear organ and receptor areas (top right, shaded) organs of hearing and balance. The movement of the perilymph from the oval to the round window is indicated by arrows.

Hearing

Organ hearing(Fig. 11-1, 11-2) anatomically consists of the outer, middle and inner ear.

· Outdoor ear represented by the auricle and external auditory canal.

ear sink- elastic cartilage of complex shape, covered with skin, at the bottom of which is the external auditory opening. The form auricle helps to direct sound into the external auditory canal. Some people can move their ears with weak muscles attached to the skull. Outer auditory pass- a blind tube 2.5 cm long, ending at the tympanic membrane. The outer third of the passage is made of cartilage and covered with fine protective hairs. The internal parts of the passage are located in the temporal bone and contain modified sweat glands - ceruminous glands, which produce a waxy secret - earwax - to protect the skin of the passage and fix dust and bacteria.

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

· Internal ear. The vestibule cavity, tympanic and vestibular scala of the cochlea (Fig. 11–3) are filled with perilymph, and the semicircular canals, uterine, sac and cochlear duct (membranous canal of the cochlea) located in the perilymph are filled with endolymph. Between the endolymph and perilymph there is an electrical potential - about + 80 mV (intracochlear, or endocochlear potential).

à Endolymph- a viscous liquid that fills the membranous canal of the cochlea and connects through a special channel ( ductus reuniens) with the endolymph of the vestibular apparatus. K concentration + in endolymph 100 times more than in cerebrospinal fluid (liquor) and perilymph; Na concentration + in endolymph 10 times less than in perilymph.

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

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

Rice . 11–3. The membranous canal and spiral (Corti) organ [11]. The cochlear canal is divided into the tympanic and vestibular scala and the membranous canal (middle scala), in which the organ of Corti is located. The membranous canal is separated from the scala tympani by the basilar membrane. It contains peripheral processes of neurons of the spiral ganglion, which form synaptic contacts with the outer and inner hair cells.

Snail and organ of Corti

Conducting sound to the cochlea

The sound pressure transmission chain is as follows: tympanic membrane ® hammer ® incus ® stirrup ® oval window membrane ® perilymph ® basilar and tectorial membranes ® round window membrane (see Fig. 11–2). When the stirrup is displaced, the perilymph moves along the vestibular scala and then through the helicotrema along the scala tympani to the round window. The fluid shifted by the displacement of the membrane of the oval window creates excess pressure in the vestibular canal. Under the action of this pressure, the basilar membrane is displaced towards the scala tympani. An oscillatory reaction in the form of a wave propagates from the basilar membrane to the helicotrema. The displacement of the tectorial membrane relative to the hair cells under the action of sound causes their excitation. The resulting electrical reaction ( microphone Effect) repeats the shape of the audio signal.

· Auditory bones. The sound vibrates the tympanic membrane and transmits the vibrational energy through the system of auditory ossicles to the perilymph of the vestibular scala. If the eardrum and ossicles did not exist, sound could reach the inner ear, but much of the sound energy would be reflected back due to the difference in acoustic impedance ( impedances) air and liquid media. That's why the most important role tympanic membranes and chains auditory bones is in creation compliance between impedances external air environments and liquid environments internal ear. The amplitude of movements of the sole of the stirrup during each sound vibration is only three-quarters of the amplitude of vibrations of the hammer handle. Consequently, the oscillatory lever system of the ossicles does not increase the range of motion of the stirrup. Instead, the lever system reduces the range of oscillations, but increases their strength by about 1.3 times. To this it should be added that the area of ​​the tympanic membrane is 55 mm 2 , while the foot area of ​​the stirrup is 3.2 mm 2 . A 17-fold difference in leverage means that the pressure on the fluid in the cochlea is 22 times higher than the air pressure on the eardrum. Equalization of impedances between sound waves and sound vibrations of a liquid improves the clarity of perception of sound frequencies in the range from 300 to 3000 Hz.

· muscles middle ear. The functional role of the muscles of the middle ear is to reduce the impact of loud sounds on the auditory system. When loud sounds act on the transmitting system and signals enter the central nervous system, a sound-reducing reflex occurs after 40–80 ms, causing contraction of the muscles attached to the stapes and malleus. The malleus muscle pulls the malleus handle forward and down, and the stirrup muscle pulls the stirrup out and up. These two opposing forces increase the rigidity of the ossicular leverage, reducing the conduction of low frequency sounds, especially sounds below 1000 Hz.

· sound-reducing reflex can reduce the transmission of low-frequency sounds by 30-40 dB, while at the same time not affecting the perception of loud voices and whispered speech. The significance of this reflex mechanism is twofold: protection snails from the damaging vibration action of low sound and disguise low sounds in environment. In addition, the muscles of the auditory ossicles reduce the sensitivity of a person's hearing to his own speech at the moment when the brain activates the vocal mechanism.

· Bone conductivity. The cochlea, enclosed in the bony cavity of the temporal bone, is able to perceive the vibrations of a manual tuning fork or the sound of an electronic vibrator applied to the protrusion of the upper jaw or mastoid process. Bone conduction of sound under normal conditions is not activated even by loud airborne sound.

The movement of sound waves in the cochlea

For the material in this section, see the book.

Hair cell activation

For the material in this section, see the book.

Sound characteristics detection

For the material in this section, see the book.

auditory pathways and centers

On fig. 11-6A shows a simplified diagram of the main auditory pathways. Afferent nerve fibers from the cochlea enter the spiral ganglion and from it enter the dorsal (posterior) and ventral (anterior) cochlear nuclei located in the upper part medulla oblongata. Here, the ascending nerve fibers form synapses with second-order neurons, the axons of which partly pass to the opposite side to the nuclei of the superior olive, and partly end on the nuclei of the superior olive of the same side. From the nuclei of the superior olive, the auditory pathways rise up through the lateral lemniscal pathway; part of the fibers ends in the lateral lemniscal nuclei, and most of the axons bypass these nuclei and follow to the inferior colliculus, where all or almost all of the auditory fibers form synapses. From here, the auditory pathway passes to the medial geniculate bodies, where all fibers end in synapses. The auditory pathway finally ends in the auditory cortex, located mainly in the superior gyrus of the temporal lobe (Fig. 11-6B). The basilar membrane of the cochlea at all levels of the auditory pathway is presented in the form of certain projection maps of various frequencies. Already at the level of the midbrain, neurons appear that detect several signs of sound on the principles of lateral and recurrent inhibition.

Rice . 11–6. BUT . Main auditory pathways (back view of the brainstem, cerebellum and cerebral cortex removed). B . auditory cortex.

auditory cortex

The projection areas of the auditory cortex (Fig. 11-6B) are located not only in the upper part of the superior temporal gyrus, but also extend to the outer side of the temporal lobe, capturing part of the insular cortex and parietal tegmentum.

Primary auditory bark directly receives signals from the internal (medial) geniculate body, while auditory associative region secondarily excited by impulses from the primary auditory cortex and thalamic regions bordering the medial geniculate body.

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

· Range sound frequencies, to which the neurons of the auditory cortex respond narrower than for the neurons of the spiral ganglion and brain stem. This is explained, on the one hand, by the high degree of specialization of cortical neurons, and, on the other hand, by the phenomenon of lateral and recurrent inhibition, which enhances the resolving ability of neurons to perceive the required sound frequency.

· Many neurons in the auditory cortex, especially in the auditory association cortex, respond to more than just specific sound frequencies. These neurons "associate" sound frequencies with other types of sensory information. Indeed, the parietal part of the auditory association cortex overlaps somatosensory area II, which makes it possible to associate auditory information with somatosensory information.

Determining the direction of sound

· Direction source sound. Two ears working in unison can detect the source of a sound by the difference in volume and the time it takes for it to reach both sides of the head. A person determines the sound coming to him in two ways.

à by time delays between admission sound in one ear and in opposite ear. The sound first arrives at the ear closest to the sound source. Low-frequency sounds go around the head due to their considerable length. If the sound source is located on the midline in front or behind, then even a minimal shift from the midline is perceived by a person. Such a subtle comparison of the minimum difference in sound arrival time is performed by the CNS at points where auditory signals converge. These points of convergence are the superior olives, the inferior colliculus, and the primary auditory cortex.

à difference between intensity sounds in two ears. At high sound frequencies, the size of the head noticeably exceeds the wavelength of the sound wave, and the wave is reflected by the head. This results in a difference in the intensity of the sounds coming to the right and left ears.

auditory sensations

· Range frequencies, which a person perceives, includes about 10 octaves of the musical scale (from 16 Hz to 20 kHz). This range gradually decreases with age due to a decrease in the perception of high frequencies. distinction frequencies sound characterized by the minimum difference in frequency of two close sounds, which is still captured by a person.

· Absolute threshold auditory sensitivity- the minimum sound intensity that a person hears in 50% of the cases of its presentation. The threshold of hearing depends on the frequency of the sound waves. Maximum sensitivity hearing human situated in areas from 5 00 before 4000 Hz. Within these limits, a sound is perceived that has an extremely low energy. In the range of these frequencies, the area of ​​​​sound perception of human speech is located.

· Sensitivity to sound frequencies below 500 Hz progressively declining. This protects a person from the possible constant sensation of low-frequency vibrations and noises produced by his own body.

Spatial orientation

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

vestibular apparatus

The vestibular (pre-door) apparatus, or the organ of balance (Fig. 11-2) is located in the stony part of the temporal bone and consists of the bone and membranous labyrinths. The bony labyrinth is a system of semicircular ducts ( canales semicirculares) and a cavity communicating with them - the vestibule ( vestibulum). Membranous labyrinth- a system of thin-walled tubes and sacs located inside the bony labyrinth. In the bone ampullae, the membranous canals expand. Each ampullar dilatation of the semicircular canal contains scallops (crista ampullaris). On the eve of the membranous labyrinth, two interconnected cavities are formed: matochka into which the membranous semicircular canals open, and pouch. The sensitive areas of these cavities are spots. The membranous semicircular canals, the uterus and the sac are filled with endolymph and communicate with the cochlea, as well as with the endolymphatic sac located in the cranial cavity. Scallops and spots - the perceiving areas of the vestibular organ - contain receptor hair cells. In the semicircular canals, rotational movements are registered ( angular acceleration), in the uterus and pouch - linear acceleration.

· sensitive spots and scallops(Fig. 11-7). In the epithelium of spots and scallops there are sensitive hair and supporting cells. The epithelium of the spots is covered with a gelatinous otolithic membrane containing otoliths - calcium carbonate crystals. The scallop epithelium is surrounded by a jelly-like transparent dome (Figs. 11–7A and 11–7B), which is easily displaced by endolymph movements.

Rice . 11–7. Receptor area of ​​the organ of balance . Vertical sections through the scallop (A) and spots (B, C). OM - otolithic membrane, O - otoliths, PC - supporting cell, RC - receptor cell.

· hair cells(Fig. 11-7 and 11-7B) are found in the scallops of each ampulla of the semicircular canals and in the spots of vestibular sacs. Hair receptor cells in the apical part contain 40–110 immobile hairs ( stereocilia) and one mobile eyelash ( kinocilia) located on the periphery of the bundle of stereocilia. The longest stereocilia are located near the kinocilium, while the length of the rest decreases with distance from the kinocilium. Hair cells are sensitive to the direction of the stimulus ( directional sensitivity, see fig. 11–8A). When the stimulus is directed from the stereocilia to the kinocilium, the hair cell is excited (depolarization occurs). With the opposite direction of the stimulus, the response is suppressed (hyperpolarization).

à There are two types of hair cells. Type I cells are usually located in the center of the scallops, while type II cells are located along their periphery.

Ú Cells type I have the shape of an amphora with a rounded bottom and are placed in the goblet-shaped cavity of the afferent nerve ending. Efferent fibers form synaptic endings on afferent fibers associated with type I cells.

Ú Cells type II have the form of cylinders with a rounded base. A characteristic feature of these cells is their innervation: the nerve endings here can be both afferent (most) and efferent.

à In the epithelium of spots, kinocilia are distributed in a special way. Here the hair cells form groups of several hundred units. Within each group, the kinocilia are oriented in the same way, but the orientation of the kinocilia is different between different groups.

Stimulation of the semicircular canals

The receptors of the semicircular canals perceive the acceleration of rotation, i.e. angular acceleration (Fig. 11–8). At rest, there is a balance in the frequency of nerve impulses from the ampullae of both sides of the head. An angular acceleration on the order of 0.5° per second is sufficient to displace the dome and bend the cilia. Angular acceleration is recorded due to the inertia of the endolymph. When the head is turned, the endolymph remains in the same position, and the free end of the dome deviates in the direction opposite to the turn. Movement of the dome bends the kinocilium and sterocilia embedded in the jelly-like structure of the dome. The inclination of the stereocilia towards the kinocilium causes depolarization and excitation; the opposite direction of tilt leads to hyperpolarization and inhibition. When excited, a receptor potential is generated in the hair cells and an emission occurs, which activates the afferent endings of the vestibular nerve.

Rice . 11–8. Physiology of Registration of Angular Acceleration. BUT - different reaction of hair cells in the crests of the ampullae of the left and right horizontal semicircular canals when the head is turned. B - Sequentially enlarged images of scallop receptive structures.

The semicircular canals detect turning or rotation of the head. When the head suddenly begins to turn in any direction (this is called angular acceleration), then the endolymph in the semicircular canals, due to its large inertia, remains for some time in a stationary state. The semicircular canals at this time continue to move, which causes the endolymph flow in the direction opposite to the rotation of the head. This leads to the activation of the vestibular nerve endings, and the frequency of nerve impulses exceeds the frequency of spontaneous impulses at rest. If the rotation continues, the pulse frequency gradually decreases and returns to its original level within a few seconds.

Reactions organism, caused stimulation semicircular channels. Stimulation of the semicircular canals causes subjective sensations in the form of dizziness, nausea and other reactions associated with the excitation of the autonomic nervous system. To this are added objective manifestations in the form of a change in the tone of the eye muscles (nystagmus) and the tone of anti-gravity muscles (fall reaction).

· Dizziness is a sensation of rotation and can cause unbalance and fall. The direction of sensation of rotation depends on which semicircular canal was stimulated. In each case, the vertigo is oriented in the opposite direction to the displacement of the endolymph. During rotation, the feeling of dizziness is directed towards the direction of rotation. The sensation experienced after the rotation stops is directed in the opposite direction from the actual rotation. As a result of dizziness, vegetative reactions occur - nausea, vomit, pallor, sweating, and with intensive stimulation of the semicircular canals, a sharp drop in blood pressure is possible ( collapse).

· nystagmus and violations muscular tone. Stimulation of the semicircular canals causes changes in muscle tone, manifested in nystagmus, impaired coordination tests, and a fall reaction.

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

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

Stimulation of the uterus and sac

For the material in this section, see the book.

projection pathways of the vestibular apparatus

The vestibular branch of the VIII cranial nerve is formed by the processes of about 19 thousand bipolar neurons that form a sensory ganglion. The peripheral processes of these neurons approach the hair cells of each semicircular canal, uterus, and sac, and the central processes go to the vestibular nuclei of the medulla oblongata (Fig. 11-9A). The axons of nerve cells of the second order are connected with the spinal cord (pre-door-spinal tract, olivo-spinal tract) and rise as part of the medial longitudinal bundles to the motor nuclei of the cranial nerves that control eye movements. There is also a pathway that conducts impulses from the vestibular receptors through the thalamus to the cerebral cortex.

à vestibule–spinal path (tractus vestibulospinalis). The lateral vestibular tract starts from the lateral vestibular nucleus (Deiters), passes through the anterior funiculus, and reaches the anterior horns. a - and g - motor neurons. Axons of neurons of the medial vestibular nucleus (Schwalbe) join the medial longitudinal beam (fasciculus longitudinalis medialis) and go down in the form of a medial vestibulo-spinal tract to thoracic spinal cord.

à Olivo–spinal path (tractus olivospinalis). The nerve fibers of the bundle start from the olive nucleus, pass in the anterior funiculus of the cervical spinal cord and end in the anterior horns.

Rice . 11–9. Ascending pathways of the vestibular apparatus (posterior view, cerebellum and cerebral cortex removed). B . Multimodal system spatial body orientation.

Vestibular apparatus is part multimodal systems(Fig. 11-9B), which includes visual and somatic receptors that send signals to the vestibular nuclei either directly or through the vestibular nuclei of the cerebellum or the reticular formation. Input signals are integrated in the vestibular nuclei, and output commands act on the oculomotor and spinal systems motor control. On fig. 11-9B shows the central and coordinating role of the vestibular nuclei connected by direct and feedback connections with the main receptor and central systems of spatial coordination.

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

Bone labyrinth (labyrinthus osseus)

The vestibule (vestibulum) is a cavity that communicates behind with 5 holes with the semicircular canals and in front with the holes of the cochlear canal. On the labyrinth wall of the tympanic cavity, that is, on the lateral wall of the vestibule, there is an opening of the vestibule (fenestra vestibuli), where the base of the stirrup is placed. On the same wall of the vestibule 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 scallop (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. From the elliptical recess originates the water supply of the vestibule (aqueductus vestibuli) 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 back surface with a hole (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 flows occur in the posterior semicircular canal (canalis semicircularis posterior). It is also vertical in the frontal plane. When the head rotates, the movement of fluid occurs in the lateral semicircular canal (canalis semicircularis lateralis), which lies in a horizontal plane. Five openings of the canal legs communicate with the vestibule, since one end of the anterior canal and one end of the posterior canal are connected into a common leg. One leg of each canal at the junction with the vestibule of the inner ear expands in the form of an ampulla.

The cochlea (cochlea) consists of a spiral canal (canalis spiralis cochleae), limited by the bone substance of the pyramid. It has 2 ½ circular moves (Fig. 558). In the center of the cochlea is a complete bone rod (modiolus), located in a horizontal plane. A bone spiral plate (lamina spiralis ossea) protrudes into the lumen of the cochlea from the side of the rod. In its thickness there are holes through which blood vessels and fibers of the auditory nerve 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 vestibuli, which connects to the vestibule cavity, and the scala tympani (scala tympani). The place where the staircase of the vestibule passes into the tympanic staircase is called the clarified foramen of the cochlea (helicotrema). The fenestra cochleae opens into the scala tympani. From the scala tympani originates the aqueduct of the cochlea, passing through the bone substance of the pyramid. On the lower surface of the posterior edge of the pyramid of the temporal bone is the external opening of the cochlear aqueduct (apertura externa canaliculi cochleae).

membranous labyrinth

The membranous labyrinth (labirynthus membranaceus) is located inside the bone 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 recessus sphericus, and an elliptical sac (utriculus), lying in recessus ellipticus. The sacs communicate one with

to others through a connecting duct (ductus reuniens), which continues into the ductus endolymphaticus, ending in a connective tissue sac (sacculus). The pouch is located on the posterior surface of the pyramid of the temporal bone in 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 region 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 with fluid movement when the head position changes. The auditory spot of the uterus is the place where the perception of irritations associated with a change in the position of the body in relation to the center of gravity, as well as vibrational vibrations.

The semicircular canals of the membranous labyrinth connect with the elliptical sacs of the vestibule. At the confluence there are extensions 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 crests (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 scallops occurs. This causes a reflex contraction of the corresponding muscles, leveling the position of the body and coordinating the movements of the external eye muscles.

The vestibule of the membranous labyrinth and part of the semicircular canals contain sensitive 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.

The membranous part of the cochlea

The cochlear part of the labyrinth is represented by the cochlear duct (ductus cochlearis). The duct starts from the vestibule in the area of ​​recessus cochlearis and ends blindly near the top of the cochlea. On the transverse section, the cochlear duct has a triangular shape and most of it is located closer to the outer wall. Thanks to the cochlear passage, the cavity of the bony passage of the cochlea is divided into two parts: the upper one is the scala vestibuli and the lower one is the scala tympani. They communicate with each other at the top of the cochlea with an enlightened hole (helicotrema) (Fig. 558).

The outer wall (vascular strip) of the cochlear duct fuses with the outer wall of the cochlear osseous duct. 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-perceiving apparatus - a spiral organ.

The spiral organ (organum spira1e) is located throughout the cochlear duct and is located on a spiral membrane, which consists of thin collagen fibers. Sensory hair cells are located on this membrane. The hairs of these cells, as usual, are immersed in a gelatinous mass called the integumentary membrane (membrana 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 integumentary membrane, bend or stretch to the diameter of the smallest atom. These atom-sized changes in the position of hair cells produce a stimulus that generates a hair cell generator potential. 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 tympanic membrane, together with it they vibrate the handle of the malleus, which displaces all the auditory ossicles. The base of the stirrup presses on the perilymph of the vestibule of the inner ear. Since the liquid practically does not compress, the perilymph of the vestibule displaces the liquid column of the vestibule ladder, which advances through the opening at the top of the cochlea (helicotrema) into the scala tympani. Its liquid stretches the secondary membrane that closes 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 sensitive cells. The sensitive cells are in contact with the first sensitive neuron.

Conducting pathways of the organ of hearing, 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 gill groove I. In the middle of the second month of embryonic development, three tubercles are formed from the tissue of the I and II gill arches. Due to their growth, the auricle is formed. Anomalies of development are the absence of the auricle or the incorrect formation of the outer ear due to the uneven growth of individual tubercles.

middle ear development. For the second month, the middle ear cavity develops in the embryo from the distal part of the gill sulcus I. The proximal part of the sulcus is transformed into the auditory tube. In this case, the ectoderm of the gill groove and the endoderm of the pharyngeal pocket are located close to each other. Then the blind end of the bottom of the pharyngeal pocket moves away from its surface and is surrounded by mesenchyme. The auditory ossicles are formed from it; up to the 9th month of the intrauterine period, they are surrounded by embryonic connective tissue and the tympanic cavity as such is absent, since 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 laid. At the beginning of the 3rd week of embryonic development, at the head end, on the sides of the neural groove in the embryo, the auditory plate is laid in the ectoderm, which at the end of this week is immersed in the mesenchyme, and then laces off in the form of an auditory vesicle (Fig. 560). On the 4th week, in the direction of the ectoderm from the dorsal part of the auditory vesicle, the endolymphatic duct grows, 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 laid at the end of the 6th week of the intrauterine period. At the beginning of the third month, the uterus and the sac separate out in the vestibule.

At the moment 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 remains a thin layer filled with mesenchymal cells. They turn into connective tissue strands that hang the membranous labyrinth.

Anomalies of development. Meets complete absence auricle and external auditory canal, small or large. A frequent anomaly is an additional curl and tragus. Possible underdevelopment of the inner ear with atrophy of the auditory nerve.

Age features. 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, her cartilage begins to harden. The external auditory canal in a newborn is short and wide, and the bone part consists of a bone ring. The size of the eardrum in a newborn and an adult is almost the same. The tympanic membrane 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 up to 2-3 years upper wall the tympanic cavity is thin, has a wide stony-scaly fissure filled with fibrous connective tissue with numerous blood vessels. With inflammation of the tympanic cavity, infection can enter the cranial cavity through the blood vessels. The posterior wall of the tympanic cavity is connected by a wide opening with the cells of the mastoid process. The auditory ossicles, although containing cartilaginous points, correspond to the size of an adult. The auditory tube is short and wide (up to 2 mm). The cartilaginous part is easily stretched, therefore, with inflammation of the nasopharynx in children, 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 fossa from the outside. Otoliths irritate the receptors on which they lie, and impulses arise that make it possible to orientate in the position of the body. When a grain of sand is displaced, impulses will arise 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 auditory apparatus is represented by a thin cuticular membrane, under which the tracheal bladder is located; between them lie the receptors of the sensory cells.

The auditory apparatus of the vertebrae originates from the lateral line nerves. A fossa appears near the head, which gradually detaches from the ectoderm and turns into the semicircular canals, the vestibule and the cochlea.