The second ear in humans. Human anatomy: structure of the inner, middle and outer ear

Date of: 04.04.2019

The outer ear is a whole system that is located in the outer part of the auditory organ and enters it. The visible part is the auditory conch. What comes next? What functions do all the elements of a complex system called the outer ear perform?

The visible part of our hearing aid is auricle. It is in it that sound waves fall, which then go into the Eustachian tube and are brought to the eardrum - a thin membrane that reproduces sound impulses and sends them further - and the inner ear.

Sink

The auricle in different people can have different shapes and sizes. But its structure is the same for everyone. This is the cartilaginous area covered with skin, in which there are many nerve endings. Cartilage is absent only in the earlobe, where adipose tissue is in a kind of skin sac.

Structure

The outer ear consists of 3 main parts:

Auricle.
Eustachian tube.
Eardrum.

Consider in detail all the components of each organ.

The auricle consists of:

Darwin's tubercle is the most external convex cartilaginous formation of the ear.
The triangular fossa is closer to the temporal part of the inner recess of the shell.
Rooks - deepening after the ear tubercle outside.
Curl legs - cartilage on the auditory opening closer to the face.
The cavity of the auricle is a tubercle above the opening.
An antihelix is \u200b\u200ba cartilage protruding above the auditory opening outside.
Curl the outer part of the shell.
Anti-tragus - the lower convex cartilage above the lobe.
Ear lobe - earlobe.
Interstitial notch is the lower part of the auditory opening.
Tragus - protruding cartilage closer to the temporal zone.
The suprapelvic tubercle is a semicircular cartilage above the auditory opening.
Curl-tragus furrow - the upper part of the ear arch.
Legs antihelix - recesses and heights in the upper part of the shell.

Auditory trumpet

The channel connecting the external shell and the eardrum - Eustachian or auditory tube. It is along it that a sound goes that causes certain impulses in the thin membrane of the outer ear. Behind the eardrum, the system begins.

Eardrum

It consists of the mucous membrane, squamous cells, fibrous fibers. Thanks to the latter, the membrane is plastic and elastic.

Functions of departments, their location and features

Auricle - the department that we see outside. Its main function is sound perception.. Therefore, it should always be clean and without obstacles to transmit sound waves.

If the auricle is clogged with sulfuric plug or pathogenic microelements during the inflammatory process, then a visit to the otolaryngologist is necessary. External damage to the auricle may be associated with:

Chemical exposure.
Thermal impact.
Mechanical.

Any damage and deformations of the ear zone must be quickly treated, because the hearing organ is an important system that should work smoothly. Otherwise, diseases may occur - up to complete deafness.

Eustachian tube performs several functions:

Conducts a sound.
Protects the inner ear from damage, infections, foreign objects.
It stabilizes the pressure.
Drainage - spontaneous cleaning of the pipe from excess cells and tissues.
Provides ventilation for the auditory organ.

Common diseases of this organ are inflammatory processes, in particular - tubootitis. With any discomfort in the ear area or partial temporary loss of hearing, contacting an otolaryngologist is a must.
Eardrum performs the functions of:

Sound conduction.
Inner ear receptor protection.

A lot of pressure, sudden loud noise, getting an object in the ear can provoke its rupture. Then the person loses hearing and in some cases is required surgical intervention. In most cases, the membrane recovers itself over time.

Photo and diagram with a description

It is the eardrum located on the border of the outer and middle ear. Near the membrane are: hammer, anvil and stirrup. It contains nerve endings that are divided into fibers leading deep into the organ of hearing. In the epithelium of the membrane, blood vessels are located that provide nutrition to the tissues of the auditory organ. The eardrum is tensioned using the muscular-tubal canal.

The outer ear is connected through the auditory tube to the nasopharynx. That is why from any inflammatory disease of the nasopharynx, the infection can spread to the ear through the Eustachian tube. ENT organs - the ear, throat, nose - should be protected in general, since they are closely related.

With the disease of one of them, pathogens quickly spread to neighboring tissues and organs. Often, otitis media begins with a common cold. When treatment did not start on time, and the infection spread to the middle ear.

A complex system

The entire outer ear performs not only the function of perceiving sound. But it also controls its adaptation in the auditory area, being a kind of resonator of sound power.

The outer ear also protects all other parts of the ear zone from injuries, deformities, inflammations, etc.

To monitor the condition of the outer ear is within the power of any person. It is necessary to perform the basic. In case of any discomfort - consult a doctor.

Experts advise Do not clean the sink deeply, as there is a possibility of violating the integrity of the auditory membrane.

With colds, it is necessary to carry out competent manipulations to release mucus from the nose. For instance. It is necessary to blow your nose properly so that the pathogenic mucus does not get into the sinuses. And from there - into the Eustachian tube and into the middle ear. Then otitis of 1, 2, 3 degrees can develop.

Any disease of the ear zone requires diagnosis and treatment. Hearing organs are a complex system. In violation of any of its departments, irreversible processes occur that lead to deafness.

Prevention of diseases of the ear zone is simply necessary. Enough for this:

Boost immunity.
Do not supercool.
Avoid injuries of any kind.
Properly clean your ears.
Observe personal hygiene.

Then your hearing will be completely safe.

Useful video

Familiarize yourself visually with the structure of the outer ear of a person below:

A cross section of the peripheral part of the auditory system is divided into the outer, middle and inner ear.

Outer ear

The outer ear consists of two main components: the auricle and the external auditory canal. It performs various functions. First of all, a long (2.5 cm) and narrow (5-7 mm) external auditory meatus performs a protective function.

Secondly, the external ear (auricle and external auditory meatus) have their own resonant frequency. Thus, the external auditory meatus in adults has a resonant frequency of approximately 2500 Hz, while the auricle is equal to 5000 Hz. This provides amplification of the incoming sounds of each of these structures at their resonant frequency up to 10-12 dB. An increase or increase in sound pressure level due to the outer ear can be hypothetically demonstrated by experiment.

Using two miniature microphones, with one located at the auricle and the other at the eardrum, this effect can be determined. Upon presentation of pure tones of various frequencies with an intensity equal to 70 dB SPL (when measured by a microphone located at the auricle), levels will be determined at the level of the eardrum.

So, at frequencies below 1400 Hz, the ultrasound, equal to 73 dB, is determined at the eardrum. This value is only 3 dB above the level measured at the auricle. With increasing frequency, the amplification effect increases significantly and reaches a maximum value of 17 dB at a frequency of 2500 Hz. The function reflects the role of the outer ear as a resonator or amplifier of high-frequency sounds.

Estimated changes in sound pressure generated by a source located in a free sound field at the measurement location: auricle, external auditory meatus, eardrum (resulting curve) (according to Shaw, 1974)

The resonance of the outer ear was determined by the location of the sound source directly in front of the subject at eye level. When raising the sound source above your head, the blockage at a frequency of 10 kHz shifts toward higher frequencies, and the peak of the resonance curve expands and covers a larger frequency range. In addition, each line displays a different angle of displacement of the sound source. Thus, the outer ear provides "coding" of the displacement of the object in the vertical plane, expressed in the amplitude of the sound spectrum and, especially, at frequencies above 3000 Hz.

In addition, it has been clearly demonstrated that the frequency-dependent increase in SPL when measured in a free sound field and in the tympanic membrane is mainly due to the effects of the auricle and the external auditory canal.

And finally, the outer ear also performs a localization function. The location of the auricle provides the most effective perception of sounds from sources located in front of the subject. The attenuation of the intensity of sounds emanating from a source located behind the subject is the basis of localization. And, above all, this applies to high frequency sounds having short wavelengths.

Thus, the main functions of the outer ear include:
   1. protective;
   2. amplification of high-frequency sounds;
   3. determination of the displacement of the sound source in the vertical plane;
   4. localization of the sound source.

Middle ear

The middle ear consists of a tympanic cavity, cells of the mastoid process, tympanic membrane, auditory ossicles, and auditory tube. In humans, the eardrum has a conical shape with elliptical contours and an area of \u200b\u200babout 85 mm2 (only 55 mm2 of which are susceptible to sound waves). Most of the tympanic membrane, pars tensa, consists of radial and circular collagen fibers. In this case, the central fibrous layer is the most important structurally.

Using the method of holography, it was found that the eardrum does not oscillate as a whole. Its vibrations are unevenly distributed over its area. In particular, between the frequencies of 600 and 1500 Hz, there are two distinct sections of the maximum displacement (maximum amplitude) of the oscillations. The functional value of the uneven distribution of vibrations over the surface of the tympanic membrane continues to be studied.

According to the data obtained by the holographic method, the amplitude of vibrations of the eardrum at the maximum sound intensity is 2x105 cm, while at the threshold intensity of the stimulus it is 104 cm (J. Bekesi measurements). The oscillatory movements of the eardrum are quite complex and heterogeneous. Thus, the largest amplitude of oscillations during stimulation by a tone with a frequency of 2 kHz takes place below umbo. When stimulated by low-frequency sounds, the point of maximum displacement corresponds to the posterior upper part of the eardrum. The nature of vibrational movements is complicated by an increase in the frequency and intensity of sound.

Between the eardrum and the inner ear are three bones: a malleus, an anvil and a stirrup. The handle of the malleus is connected directly to the membrane, while its head is in contact with the anvil. The long process of the anvil, namely, its lenticular process, is connected to the head of the stapes. The stirrup, the smallest bone in humans, consists of a head, two legs and a base plate located in the vestibule window and fixed in it with the help of an annular ligament.

Thus, the direct connection of the eardrum with the inner ear is through a chain of three auditory ossicles. The middle ear also includes two muscles located in the tympanic cavity: the muscle that stretches the eardrum (tensor tympani) and has a length of up to 25 mm, and the stirrup muscle (t.stapedius), whose length does not exceed 6 mm. The tendon of the stirrup muscle attaches to the head of the stapes.

Note that an acoustic stimulus that reaches the eardrum can be transmitted through the middle ear to the inner ear in three ways: (1) through bone sound conduction through the bones of the skull directly to the inner ear, bypassing the middle ear; (2) through the airspace of the middle ear; and (3) through the chain of auditory ossicles. As will be demonstrated below, the third way of sound conduction is most effective. However, a prerequisite for this is the equalization of pressure in the tympanic cavity with atmospheric pressure, which is what is done with the normal functioning of the middle ear through the auditory tube.

In adults, the auditory tube is directed downward, which ensures the evacuation of fluids from the middle ear into the nasopharynx. Thus, the auditory tube performs two main functions: firstly, through it the air pressure is equalized on both sides of the eardrum, which is a prerequisite for vibration of the eardrum, and secondly, the auditory tube provides a drainage function.

It was indicated above that sound energy is transmitted from the eardrum through the chain of the auditory ossicles (the foot plate of the stapes) to the inner ear. However, if we assume that sound is transmitted directly through the air to the fluids of the inner ear, it is necessary to recall the greater resistance of the fluids of the inner ear compared to air. What is the meaning of the seeds?

If you imagine two people trying to communicate when one is in the water and the other is on the shore, it should be borne in mind that about 99.9% of the sound energy will be lost. This means that about 99.9% of the energy will be affected and only 0.1% of the sound energy will reach the liquid medium. The observed loss corresponds to a decrease in sound energy of approximately 30 dB. Possible losses are compensated by the middle ear through the following two mechanisms.

As noted above, the surface of the eardrum with an area of \u200b\u200b55 mm2 is effective in terms of the transmission of sound energy. The area of \u200b\u200bthe foot plate of the stapes, which is in direct contact with the inner ear, is about 3.2 mm2. Pressure can be defined as the force applied to a unit area. And, if the force applied to the tympanic membrane is equal to the force reaching the foot plate of the stapes, then the pressure at the foot plate of the stapes will be greater than the sound pressure measured at the eardrum.

This means that the difference in the areas of the tympanic membrane to the stapes foot plate provides a 17-fold increase in pressure (measured at the foot plate) (55 / 3.2), which corresponds to 24.6 dB in decibels. Thus, if about 30 dB is lost during direct transfer from air to liquid, then due to differences in the surface areas of the tympanic membrane and the footbase of the stapes, the noted loss is compensated by 25 dB.

The transfer function of the middle ear, showing an increase in pressure in the fluids of the inner ear, compared with the pressure on the eardrum, at different frequencies, expressed in dB (according to von Nedzelnitsky, 1980)

The transfer of energy from the eardrum to the foot plate of the stapes depends on the functioning of the auditory ossicles. The bones act like a lever system, which is primarily determined by the fact that the length of the head and neck of the malleus is greater than the length of the long appendix of the anvil. The effect of the lever system of seeds corresponds to 1.3. An additional increase in the energy supplied to the foot plate of the stapes is determined by the conical shape of the eardrum, which, when vibrated, is accompanied by an increase in the force applied to the hammer by a factor of 2.

All of the above indicates that the energy applied to the eardrum, when reaching the foot plate of the stapes, is amplified 17x1.3x2 \u003d 44.2 times, which corresponds to 33 dB. However, of course, the gain between the tympanic membrane and the base plate depends on the frequency of stimulation. So, it follows that at a frequency of 2500 Hz the increase in pressure corresponds to 30 dB or more. Above this frequency, the gain decreases. In addition, it should be emphasized that the resonance range of the conch and the external auditory meatus noted above leads to significant amplification in a wide frequency range, which is very important for the perception of sounds like speech.

An integral part of the lever system of the middle ear (the chain of the auditory ossicles) are the muscles of the middle ear, which are usually in a state of tension. However, upon presentation of sound with an intensity of 80 dB in relation to the threshold of auditory sensitivity (IF), reflex contraction of the stirrup muscle occurs. In this case, the sound energy transmitted through the chain of auditory ossicles is attenuated. The magnitude of this attenuation is 0.6-0.7 dB for each decibel of the increase in stimulus intensity above the threshold of the acoustic reflex (about 80 dB IF).

Attenuation is from 10 to 30 dB for loud sounds and is more pronounced at frequencies below 2 kHz, i.e. has a frequency dependence. The time of reflex contraction (latent period of the reflex) ranges from the minimum values \u200b\u200bof 10 ms when high-intensity sounds are presented, to 150 ms when stimulated by relatively low-intensity sounds.

Another function of the muscles of the middle ear is to limit distortion (non-linearities). This is ensured both by the presence of elastic ligaments of the auditory ossicles and by direct muscle contraction. From anatomical positions, it is interesting to note that the muscles are located in narrow bony channels. This prevents muscle vibration during stimulation. Otherwise, there would be harmonic distortions that would be transmitted to the inner ear.

The movements of the auditory ossicles are not identical at different frequencies and levels of stimulation intensity. Due to the size of the head of the malleus and the body of the anvil, their mass is evenly distributed along the axis passing through the two large ligaments of the malleus and the short process of the anvil. At medium levels of intensity, the chain of auditory ossicles moves in such a way that the foot plate of the stapes oscillates around an axis mentally drawn vertically through the back leg of the stapes, like doors. The front of the base plate enters and leaves the cochlea like a percussion cap.

Such movements are possible due to the asymmetric length of the annular ligament of the stapes. At very low frequencies (below 150 Hz) and at very high intensities, the nature of rotational movements changes dramatically. So the new axis of rotation becomes perpendicular to the vertical axis marked above.

Stirrup movements acquire a rocking character: it oscillates like a children's swing. This is expressed by the fact that when one half of the base plate is immersed in the cochlea, the other moves in the opposite direction. As a result, the movements of the fluids of the inner ear are suppressed. At very high levels of stimulation intensity and frequencies exceeding 150 Hz, the stirrup foot plate simultaneously rotates around both axes.

Thanks to such complex rotational movements, a further increase in the level of stimulation is accompanied by only minor movements of the fluids of the inner ear. It is these complex stapes movements that protect the inner ear from excessive stimulation. However, in experiments on cats, it was demonstrated that the stirrup makes piston-like movements when stimulated with low frequencies, even at an intensity of 130 dB SPL. At 150 dB SPL, rotational movements are added. However, given the fact that today we are dealing with hearing loss due to exposure to industrial noise, we can conclude that the human ear does not have truly adequate protective mechanisms.

When describing the main properties of acoustic signals, the acoustic impedance was considered as their essential characteristic. The physical properties of acoustic impedance or impedance is fully manifested in the functioning of the middle ear. The impedance or acoustic resistance of the middle ear is made up of components caused by fluids, bones, muscles and ligaments of the middle ear. Its components are resistance (true acoustic impedance) and reactivity (or reactive acoustic impedance). The main resistive component of the middle ear is the resistance exerted by the fluids of the inner ear to the foot plate of the stapes.

The resistance arising from the displacement of the moving parts should also be taken into account, but its magnitude is much smaller. It should be remembered that the resistive component of the impedance does not depend on the frequency of stimulation, in contrast to the reactive component. Reactivity is determined by two components. The first is the mass of middle ear structures. It affects primarily high frequencies, which is expressed in an increase in impedance due to the reactivity of the mass with increasing frequency of stimulation. The second component is the properties of contraction and stretching of muscles and ligaments of the middle ear.

When we say that the spring is easily stretched, we mean that it is malleable. If the spring is stretched with difficulty, we talk about its rigidity. These characteristics make the greatest contribution at low stimulation frequencies (below 1 kHz). At medium frequencies (1-2 kHz), both reactive components suppress each other, and the resistive component prevails in the impedance of the middle ear.

One way to measure the impedance of the middle ear is to use an electro-acoustic bridge. If the middle ear system is stiff enough, the pressure in the cavity will be higher than with high supple structures (when sound is absorbed by the eardrum). Thus, sound pressure measured with a microphone can be used to study the properties of the middle ear. Often the impedance of the middle ear, measured with an electro-acoustic bridge, is expressed in terms of compliance. This is because impedance is usually measured at low frequencies (220 Hz), and in most cases only the properties of contraction and extension of muscles and ligaments of the middle ear are measured. So, the higher the compliance, the lower the impedance and the easier the system works.

With contraction of the muscles of the middle ear, the entire system becomes less malleable (i.e., more rigid). From an evolutionary point of view, there is nothing strange in the fact that when leaving the water for land to level differences in the resistance of fluids and structures of the inner ear and air cavities of the middle ear, evolution provided a transmission link, namely a chain of auditory ossicles. However, in what ways is sound energy transmitted to the inner ear in the absence of auditory ossicles?

First of all, the inner ear is directly stimulated by air vibrations in the middle ear cavity. And again, due to large differences in the impedance of the fluids and the structures of the inner ear and air, the fluids move only slightly. In addition, with direct stimulation of the inner ear through changes in sound pressure in the middle ear, there is an additional weakening of the transmitted energy due to the fact that both inputs to the inner ear (the vestibule window and the cochlear window) are simultaneously activated, and at some frequencies the sound pressure is also transmitted and in phase.

Considering that the cochlear window and the vestibule window are located on opposite sides of the main membrane, the positive pressure applied to the membrane of the cochlea window will be accompanied by the deflection of the main membrane in one direction, and the pressure applied to the foot plate of the stapes by the deflection of the main membrane in the opposite direction . When the same pressure is applied to both windows at the same time, the main membrane will not move, which in itself eliminates the perception of sounds.

A hearing loss of 60 dB is often determined in patients who have no auditory ossicles. Thus, the next function of the middle ear is to provide the transmission path of the stimulus to the oval window of the vestibule, which, in turn, provides displacements of the membrane of the cochlear window corresponding to pressure fluctuations in the inner ear.

Another way to stimulate the inner ear is through bone sound, in which changes in acoustic pressure cause vibrations of the bones of the skull (especially the temporal bone), and these vibrations are transmitted directly to the fluids of the inner ear. Due to the colossal differences in bone and air impedance, stimulation of the inner ear due to bone conduction cannot be considered as an important component of normal auditory perception. However, if a source of vibration is applied directly to the skull, the inner ear is stimulated by passing sounds through the bones of the skull.

The differences in the impedance of the bones and fluids of the inner ear are very slight, which contributes to the partial transmission of sound. Measurement of auditory perception during bone conduction of sounds is of great practical importance in the pathology of the middle ear.

Inner ear

Progress in the study of the anatomy of the inner ear was determined by the development of microscopy methods and, in particular, transmission and scanning electron microscopy.

The inner ear of mammals consists of a number of membranous sacs and ducts (forming a membranous labyrinth) enclosed in a bone capsule (bone labyrinth), located, in turn, in the solid temporal bone. The bone labyrinth is divided into three main parts: semicircular canals, vestibule and cochlea. The peripheral part of the vestibular analyzer is located in the first two formations, while the peripheral part of the auditory analyzer is located in the cochlea.

The human snail has 2 3/4 curls. The largest curl is the main curl, the smallest is the apical curl. The structures of the inner ear also include an oval window, in which there is a foot plate of the stapes, and a round window. The snail blindly ends in the third curl. Its central axis is called modiolus.

A cross section of the cochlea, from which it follows that the cochlea is divided into three sections: the vestibule ladder, as well as the tympanic and median ladders. The spiral channel of the cochlea has a length of 35 mm and is partially divided along the entire length with a thin bony spiral plate extending from the modiolus (osseus spiralis lamina). Continues it, the main membrane (membrana basilaris) connecting with the outer bone wall of the cochlea at the spiral ligament, thereby completing the separation of the canal (with the exception of a small hole at the top of the cochlea called helicotrema).

The vestibule staircase extends from the oval window located on the vestibule to helicotrema. A drum ladder extends from a round window and also to helicotrema. The spiral ligament, as a connecting link between the main membrane and the bone wall of the cochlea, supports at the same time the vascular strip. Most of the spiral ligament consists of rare fibrous compounds, blood vessels, and connective tissue cells (fibrocytes). Zones located near the spiral ligament and spiral protrusion include more cellular structures, as well as large mitochondria. The spiral protrusion is separated from the endolymphatic space by a layer of epithelial cells.

A thin Reissner membrane, attached to the outer wall of the cochlea slightly higher than the main membrane, departs from the bone spiral plate upward in the diagonal direction. It extends along the entire snail htinnik and connects to the main membrane of helicotrema. Thus, a cochlear duct (ductus cochlearis) is formed, or a median staircase bounded above by a Reissner membrane, below by a main membrane, and outside by a vascular strip.

The vascular strip is the main vascular zone of the cochlea. It has three main layers: the marginal layer of dark cells (chromophiles), the middle layer of light cells (chromophobes), and the main layer. Within these layers passes a network of arterioles. The surface layer of the strip is formed exclusively from large marginal cells that contain many mitochondria and whose nuclei are located close to the endolymphatic surface.

Marginal cells make up the bulk of the vascular strip. They have finger-shaped processes that provide a close connection with similar processes of cells of the middle layer. The basal cells attach to the spiral ligament have a flat shape and long processes penetrating the marginal and middle layers. The cytoplasm of basal cells is similar to the cytoplasm of helical fibrocytes.

Blood supply to the vascular strip is carried out by a spiral modiolar artery through the vessels passing through the staircase of the vestibule to the lateral wall of the cochlea. The collecting venules located in the wall of the tympanic ladder direct blood into the spiral modiolar vein. The vascular strip carries out the main metabolic control of the cochlea.

The drum ladder and the vestibule ladder contain a fluid called the perilymph, while the median ladder contains the endolymph. The ionic composition of the endolymph corresponds to the composition determined within the cell and is characterized by a high potassium content and low sodium concentration. For example, in humans, the concentration of Na is 16 mM; K - 144.2 mm; Cl -114 meq / l. Perilymph, on the contrary, contains high concentrations of sodium and low concentrations of potassium (in humans, Na is 138 mM, K is 10.7 mM, Cl is 118.5 meq / l), which in composition corresponds to extracellular or cerebrospinal fluids. Maintenance of the noted differences in the ionic composition of the endo- and perilymphs is ensured by the presence of epithelial layers in the membranous labyrinth with many dense, hermetic joints.

Most of the main membrane consists of radial fibers with a diameter of 18-25 microns, forming a compact homogeneous layer, enclosed in a homogeneous basic substance. The structure of the main membrane is significantly different from the base of the cochlea to the apex. At the base - the fibers and the integumentary layer (from the side of the tympanic ladder) are located more often compared to the apex. In addition, while the bone capsule of the cochlea decreases towards the apex, the main membrane expands.

So at the base of the cochlea, the main membrane has a width of 0.16 mm, while at helicotrema its width reaches 0.52 mm. The noted structural factor underlies the stiffness gradient along the cochlear length, which determines the propagation of the traveling wave and promotes passive mechanical tuning of the main membrane.

Cross sections of the Corti organ at the base (a) and the apex (b) indicate differences in the width and thickness of the main membrane, (c) and (d) scanning electron microphotograms of the main membrane (view from the side of the tympanic ladder) at the base and apex of the cochlea ( e). The total physical characteristics of the main human membrane

Measurement of various characteristics of the main membrane formed the basis of the membrane model proposed by Bekesi, who described in his hypothesis of auditory perception a complex pattern of its movements. From his hypothesis it follows that the main human membrane is a thick layer of densely spaced fibers about 34 mm long, directed from the base to helicotrema. The main membrane at the apex is wider, softer and without any tension. Its basal end is already, more rigid than apical, may be in a state of some tension. The listed facts are of certain interest when considering the vibratory characteristics of the membrane in response to acoustic stimulation.

VVK - internal hair cells; NVC - external hair cells; NSC, VSC - external and internal pillar cells; TK - Corti Tunnel; OS - the main membrane; TS - tympanal layer of cells below the main membrane; D, G - supporting cells of Deiters and Hensen; PM - integumentary membrane; PG - Hensen strip; KBB - cells of the internal groove; PBT radial nerve fiber tunnel

Thus, the stiffness gradient of the main membrane is due to differences in its width, which increases toward the apex, a thickness that decreases toward the apex, and the anatomical structure of the membrane. On the right is the basal part of the membrane, on the left is the apical. Scanning electron micrograms demonstrate the structure of the main membrane from the side of the tympanic ladder. The differences in thickness and frequency of radial fibers between the base and the top are clearly defined.

In the middle staircase on the main membrane is the organ of Corti. The outer and inner pillar cells form the inner Corti tunnel, filled with a fluid called cortilympha. Inward from the inner pillars is one row of inner hair cells (IVC), and outward from the outer pillars are three rows of smaller cells, called outer hair cells (NEC), and supporting cells.

,
illustrating the supporting structure of the Corti organ, consisting of Deiters cells (e) and their phalangeal processes (FO) (supporting system of the outer third row of the NEC (NEC)). Phalangeal processes extending from the apex of the Deuteron cells form part of the reticular plate at the apex of the hair cells. Stereocilia (SC) are located above the reticular plate (according to I.Hunter-Duvar)

Deiters and Hensen cells support NEC on the side; a similar function, but with respect to the IHC, is performed by the border cells of the inner groove. The second type of fixation of hair cells is carried out by the reticular plate, which holds the upper ends of the hair cells, ensuring their orientation. Finally, the third type is also carried out by Deiters cells, but located below the hair cells: one Deiters cell per one hair cell.

The upper end of the cylindrical Deuters cell has a cup-shaped surface on which the hair cell is located. A thin process departs from the same surface to the surface of the Corti organ, forming the phalangeal process and part of the reticular plate. These Deiters cells and phalangeal processes form the main vertical support mechanism for hair cells.

A. Transmission electron microphotogram VVK. Stereocilia (SC) VVK are projected into the median ladder (SL), and their base is immersed in the cuticular plate (CP). H - the core of the IHC, VSP - the nerve fibers of the internal spiral node; VSK, NSC - internal and external pillar cells of the Corti tunnel (TC); BUT - nerve endings; OM - main membrane
B. Transmission electron microphotogram of NEC. A clear distinction is determined in the form of NEC and IAC. NEC is located on the deepened surface of the Deiters cell (D). At the base of the NIAC, efferent nerve fibers (E) are determined. The space between the NEC is called the Nuele space (NP). Within it, the phalangeal processes (FO) are determined

The form of NEC and IAC is significantly different. The upper surface of each VVC is covered with a cuticular membrane into which stereocilia are immersed. Each VVC has about 40 hairs arranged in two or more rows of a U-shape.

Only a small part of the cell surface remains where the basal body or altered kinocilia remains free of the cuticular plate. The basal body is located at the outer edge of the IHC, away from the modiolus.

The upper surface of the NEC contains about 150 stereocilia located in three or more rows of a V- or W-shaped on each NEC.

One row of the IAC and three rows of the IAC are clearly defined. Between the NIAC and the VVC, the heads of the internal pillar cells (VSC) are visible. Between the tops of the NEC rows, the tops of the phalangeal processes (FO) are determined. The supporting cells of Deiters (D) and Hensen (G) are located at the outer edge. The W-shaped orientation of the cilia of the NEC is inclined with respect to the VVC. Moreover, the slope is different for each row of NEC (according to I.Hunter-Duvar)

The tops of the longest hairs of the NEC (in a row remote from the modiolus) are in contact with the gel-like integumentary membrane, which can be described as a cell-free matrix consisting of colophones, fibrils and a homogeneous substance. It extends from the spiral protrusion to the outer edge of the reticular lamina. The thickness of the integumentary membrane increases from the base of the cochlea to the apex.

The main part of the membrane consists of fibers with a diameter of 10-13 nm, emanating from the inner zone and extending at an angle of 30 ° to the apical curl of the cochlea. Toward the outer edges of the integumentary membrane, the fibers propagate in the longitudinal direction. The average length of stereocilia depends on the position of the NEC along the snail length. So, at the apex their length reaches 8 microns, while at the base it does not exceed 2 microns.

The number of stereocilia decreases in the direction from the base to the apex. Each stereocilia has a club shape that expands from the base (at the cuticular plate 130 nm) to the apex (320 nm). Between stereocilia there is a powerful network of crosses, so a large number of horizontal connections connect stereocilia located both in the same and in different rows of NEC (laterally and below the apex). In addition, a thin process departs from the apex of the shorter stereocilia of the NEC, connecting to the longer stereocilia of the next row of the NEC.

PS - cross connections; KP - cuticular plate; C is a compound within a row; K is the root; SC - stereocilia; PM - integument membrane

Each stereocilia is covered with a thin plasma membrane, under which there is a cylindrical cone containing long fibers directed along the length of the hair. These fibers are composed of actin and other structural proteins that are in a crystalline state and give rigidity to stereocilia.

Ya.A. Altman, G. A. Tavartkiladze

The auditory sensory system of a person perceives and distinguishes a huge range of sounds. Their diversity and wealth serves us as a source of information about current events of the surrounding reality, and as an important factor affecting the emotional and mental state of our body. In this article we will consider the anatomy of the human ear, as well as the features of the functioning of the peripheral part of the auditory analyzer.

The mechanism for distinguishing sound vibrations

Scientists have found that the perception of sound, which, in essence, is the vibration of the air in the auditory analyzer, is transformed into an excitation process. The peripheral part containing receptors and part of the ear is responsible for the sensation of sound stimuli in the auditory analyzer. She perceives the amplitude of oscillations, called sound pressure, in the range from 16 Hz to 20 kHz. In our body, the auditory analyzer also plays such a crucial role as participation in the work of the system responsible for the development of articulate speech and the entire psycho-emotional sphere. First, get acquainted with the general plan of the structure of the organ of hearing.

Departments of the peripheral part of the auditory analyzer

The anatomy of the ear distinguishes three structures called the outer, middle and inner ear. Each of them performs specific functions, not only interconnected, but all together carrying out the processes of receiving sound signals, their conversion into nerve impulses. According to the auditory nerves, they are transmitted to the temporal lobe of the cerebral cortex, where the transformation of sound waves into the form of various sounds takes place: music, birdsong, the sound of the sea surf. In the process of phylogenesis of the biological species “Homo sapiens”, the hearing organ played a crucial role, as it ensured the manifestation of such a phenomenon as human speech. Departments of the organ of hearing were formed during the embryonic development of a person from the external germinal leaf, the ectoderm.

Outer ear

This part of the peripheral section picks up and directs air vibrations to the eardrum. The anatomy of the outer ear is represented by the cartilaginous concha and the external auditory canal. What does it look like? The external shape of the auricle has characteristic bends - curls, and is very different in different people. On one of them there may be a Darwin hillock. It is considered a vestigial organ, and is homologous in origin to the pointed upper edge of the ear of mammals, especially primates. The lower part is called the lobe and is a connective tissue covered with skin.

The auditory meatus is the structure of the outer ear

Further. The auditory meatus is a tube made up of cartilage and partly bone. It is covered with an epithelium containing modified sweat glands that secrete sulfur, which moisturizes and disinfects the passage cavity. The auricle muscles in most people are atrophied, unlike mammals, whose ears actively respond to external sound stimuli. Pathologies of violations of the anatomy of the structure of the ear are recorded in the early period of development of the gill arches of the human embryo and may take the form of splitting of the lobe, narrowing of the external auditory canal or agenesis - the complete absence of the auricle.

Middle ear cavity

The auditory meatus ends with an elastic film separating the outer ear from its middle part. This is the eardrum. She receives sound waves and begins to oscillate, which causes similar movements of the auditory ossicles - a malleus, anvil and stapes, located in the middle ear, in the depth of the temporal bone. The hammer with its handle is attached to the eardrum, and the head is connected to the anvil. She, in turn, closes with a long end with a stepladder, and it attaches to the vestibule window, behind which is the inner ear. Everything is very simple. Anatomy of the ears revealed that a muscle is attached to the long process of the malleus, which reduces the tension of the eardrum. And the so-called "antagonist" is attached to the short part of this auditory ossicle. Special muscle.

Eustachian tube

The middle ear is connected to the pharynx through a canal named after the scientist who described its structure, Bartolomeo Eustahio. The tube serves as a device that equalizes the pressure of the atmospheric air on the eardrum from two sides: from the external auditory canal and the middle ear cavity. This is necessary so that the vibrations of the eardrum without distortion are transmitted to the fluid of the membranous labyrinth of the inner ear. The Eustachian tube is heterogeneous in its histological structure. Anatomy of the ears revealed that it contains not only the bone part. Also cartilage. Sinking down from the middle ear cavity, the tube ends with a pharyngeal opening located on the lateral surface of the nasopharynx. During swallowing, muscle fibrils attached to the cartilage of the tube contract, its lumen expands, and a portion of the air enters the tympanic cavity. The pressure on the membrane at this moment becomes the same on both sides. Around the pharyngeal opening is a section of lymphoid tissue that forms nodes. It is called Gerlach's amygdala and is part of the immune system.

Features of the anatomy of the inner ear

This part of the peripheral part of the auditory sensory system is located deep in the temporal bone. It consists of semicircular canals related to the organ of equilibrium and the bone labyrinth. The latter structure contains a cochlea, inside which is located the organ of Corti, which is a sound-receiving system. Along the spiral, the cochlea is divided by a thin vestibular plate and a denser main membrane. Both membranes divide the cochlea into canals: lower, middle and upper. At its wide base, the upper channel begins with an oval window, and the lower is closed by a round window. Both of them are filled with liquid contents - perilymph. It is considered a modified cerebrospinal fluid - a substance that fills the spinal canal. Endolymph is another fluid that fills the channels of the cochlea and accumulates in the cavity where the nerve endings of the equilibrium organ are located. We will continue to study the anatomy of the ears and consider those parts of the auditory analyzer that are responsible for transcoding sound vibrations into the excitation process.

The meaning of the organ of Corti

Inside the cochlea there is a membranous wall called the main membrane, on which there is a cluster of cells of two types. Some perform the function of support, others are sensory - hairy. They perceive the oscillations of the perilymph, convert them into nerve impulses and transmit further to the sensitive fibers of the vestibular cochlear (auditory) nerve. Further, the excitation reaches the cortical center of hearing located in the temporal lobe of the brain. It distinguishes sound signals. The clinical anatomy of the ear is confirmed by the fact that what we hear with two ears is important in determining the direction of sound. If sound vibrations reach them at the same time, a person perceives sound in front and behind. And if the waves come in one ear earlier than the other, then perception occurs on the right or left.

Theories of Sound Perception

At present, there is no consensus on exactly how the system functions that analyzes sound vibrations and translates them into the form of sound images. The anatomy of the structure of the human ear highlights the following scientific ideas. For example, the Helmholtz resonance theory claims that the cochlear's main membrane functions as a resonator and is capable of decomposing complex vibrations into simpler components, since its width is not the same at the top and bottom. Therefore, when sounds appear, resonance occurs, as in a stringed instrument - a harp or piano.

Another theory explains the process of the appearance of sounds by the fact that a traveling wave appears in the fluid of the cochlea as a response to oscillations of the endolymph. Vibrating fibers of the main membrane resonate with a specific frequency of vibration; nerve impulses appear in the hair cells. They enter the auditory nerves into the temporal part of the cerebral cortex, where the final analysis of sounds takes place. Everything is extremely simple. Both of these theories of sound perception are based on knowledge of the anatomy of the human ear.

The ear is a complex vestibular-auditory organ that has the ability to perceive sound impulses. Also, this body is responsible for the balance of the body, the ability to hold it in a certain position. The organ is paired, located on the temporal parts of the skull. Outside it is limited only to the auricles, which is caused by the process of evolution.

The organ of hearing itself appeared in the ancient ancestors of vertebrates from certain, special skin folds that served as sense organs. They are called lateral organs. The ear of a modern person can perceive sound vibrations from 20 m to 1.6 cm, namely 16 - 20 000 Hz.

The structure of the human ear is heterogeneous. The organ of hearing consists of the External, middle and inner ear, that is, only three parts. The process of capturing sounds begins with air vibrations. They are caught by the outer ear. It represents the auricle and the external auditory meatus.

The structure of the outer ear

The auricle picks up the sound itself and its direction. The cartilage of the external auditory canal, which is approximately 2.5 cm in length, continues. The cartilaginous part of the passage gradually passes into the bone. All skin, which is lined with a passage, is penetrated by sebaceous, sulfur glands. They are modified sweat glands.

The canal inside ends with an elastic eardrum. It is necessary, inter alia, to separate the outer ear from the middle. Sound waves captured by the auricle hit the membrane, causing it to vibrate. These vibrations are transmitted further into the middle ear.

The structure of the middle ear

The middle ear is a cavity, approximately 1 cubic centimeter. It contains small auditory ossicles, namely: malleus (malleus), incus (anvil) and stapes (stapes). Auditory waves, reflected from the eardrum, pass to the hammer, then the anvil and stapes. After that - they fall into the inner ear.

In its cavity is the Eustachian, or auditory, tube that connects to the nasopharynx. From it, air penetrates into the tympanic cavity, as a result of which the pressure on the tympanic membrane from the tympanic cavity is equalized. In the event that the pressure is not equalized and it is unusual on both sides of the membrane, it can simply burst.

Inside the tympanic cavity, which separates the middle ear from the inner ear, there are two holes, the so-called window (round and oval), which are tightened with a leather membrane.

The main purpose of the middle ear is to conduct sound vibrations from the eardrum, bypassing the auditory ossicles directly to the oval opening leading to the inner ear.

The structure of the inner ear

The inner ear is located in the temporal bone. It consists of two labyrinths - temporal and bone. Moreover, the temporal is located inside the bone, and between them there is a small space that is filled with fluid (endolymph). In the maze is the organ of hearing - the snail. There is also an organ of equilibrium - the vestibular apparatus.

The cochlea is a spiral bone channel, which in humans is 2.5 turns. It is divided into two parts by the main membrane - the membranous septum. It, in turn, is also divided into two parts - the upper and lower stairs, which are connected at the top of the cochlea.

On the main membrane is a sound pickup device called a Corti's organ. The membrane consists of 24 thousand fibers of different lengths, which are stretched like strings, each of which reacts to its own specific sound. The organ of Corti itself consists of cells, among which there are especially sensitive auditory cells with hairs (hair cells). They are the receptors of sound vibrations.

Drawing a conclusion from the foregoing, it should be noted that according to its functional purpose, the ear is divided into two main parts: the sound-conducting apparatus, namely the outer and middle ear and the sound-receiving apparatus - the inner ear.

How is the perception of sounds?

Sound vibrations, which are captured by the auricle, pass further into the ear canal, and then fall on the eardrum, which catches them and produces vibrations. They pass through the auditory ossicles to the second membrane of the oval opening (window), which leads to the cavity of the inner ear. Fluctuations of this membrane affect the spiral snail. All vibrations in this confined space occur due to the membrane of a round hole (window).

Bypassing the perilymph, sound waves fall on the endolymph, which, in turn, causes unrest in the main membrane. They stir up the hair cells located in the organ of Corti. And already these cells transform sound waves, creating a process of nervous excitement. It is projected through the auditory nerve into the temporal zone of the cerebral cortex, processed there as information on what kind of sound a person is currently hearing.

Studying the complexity of various mechanical and electromechanical processes occurring in this organ, it becomes clear that for a good, high-quality hearing, all its parts are necessary. And for the ear to properly and efficiently perform its functions, it is necessary that each of its components is in perfect order. This is also extremely important for the work of the entire vestibular apparatus of a person.

Svetlana, www.site

When making this or that diagnosis, otolaryngologists, first of all, have to find out in which part of the ear the focus of the disease arose. Often, patients complaining of pain cannot determine exactly where the inflammation occurs. And all because they know little about the anatomy of the ear - a rather complex organ of hearing, consisting of three parts.

Below you can familiarize yourself with the structure of the human ear and learn about the features of each of its components.

There are a lot of diseases leading to the appearance of pain in the ears. To understand them, you need to know the anatomy of the structure of the ear. It includes three parts: the outer, middle and inner ear. The outer ear consists of the auricle, the external auditory canal and the eardrum, which is the boundary between the outer and middle ear. The middle ear is located in the temporal. It includes the tympanic cavity, the auditory (Eustachian) tube and the mastoid process. The inner ear is a labyrinth consisting of semicircular canals, which are responsible for the sense of balance, and the cochlea, which is responsible for turning sound vibrations into an impulse recognized by the cortex of the cerebral hemispheres.

Above the photo shows a diagram of the structure of the human ear: internal, secondary and external.

Anatomy and structure of the outer ear

Let's start with the anatomy of the outer ear: it is supplied by the branches of the external carotid artery. In the innervation, in addition to the branches of the trigeminal nerve, the ear branch of the vagus nerve, which branches in the posterior wall of the ear canal, takes part. Mechanical irritation of this wall often contributes to the appearance of the so-called reflex cough.

The structure of the outer ear is such that the outflow of lymph from the walls of the ear canal gets into the nearest lymph nodes located in front of the auricle, on the mastoid process and under the lower wall of the ear canal. Inflammatory processes that occur in the external auditory canal are often accompanied by a significant increase and the appearance of pain in the data area.

If you look at the eardrum from the ear canal, you can see a funnel-like concavity in its center. The deepest place of this concavity in the structure of the human ear is called the navel. Starting from it anteriorly and upward, there is a handle of a malleus fused with a fibrous-like layer of the tympanic membrane. At the top, this handle ends with a small, pin-sized, elevation, which is a short process. From it anterior and posterior folds anterior and posterior. They delimit the relaxed part of the eardrum from the stretched one.

The structure and anatomy of the middle ear of a person

The anatomy of the middle ear includes the tympanic cavity, the mastoid process and the Eustachian tube, which are interconnected. The tympanic cavity is a small space located inside the temporal bone between the inner ear and the eardrum. The structure of the middle ear has the following peculiarity: in front, the tympanic cavity communicates with the nasopharynx through the Eustachian tube, and behind - through the entrance to the cave with the cave itself, as well as with the cells of the mastoid process. In the tympanic cavity is air entering it through the Eustachian tube.

The anatomy of the structure of the human ear of the first to three years of age differs from the anatomy of the adult ear: in newborns there is no bone auditory meatus, as well as the mastoid process. They have only one bone ring, along the inner edge of which there is a so-called bone groove. The eardrum is inserted into it. In the upper sections, where there is no bone ring, the eardrum attaches directly to the lower edge of the temporal bone scales, which is called the rivine notch. When the child is three years old, his external auditory canal is fully formed.

Scheme of the structure and anatomy of the inner ear of a person

The structure of the inner ear includes bone and membranous labyrinths. Bone surrounds from all sides the membranous labyrinth, having the appearance of a case. The endolymph is located in the membranous labyrinth, and the free space remaining between the membranous and the bone labyrinth is filled with perilymph, or cerebrospinal fluid.

The bony labyrinth includes the vestibule, the cochlea and three semicircular canals. The vestibule is the central part of the bone labyrinth. On its outer wall there is an oval window, and on the inside there are two impressions necessary for the vestibule sacs, which look like membranes. The anterior sac communicates with the membranous cochlea located anterior to the vestibule, and the posterior sac with membranous semicircular canals located posteriorly and upward from the vestibule itself. The anatomy of the inner ear is such that otolith apparatuses, or terminal apparatuses of statokinetic reception, are in interconnected vestibule sacs. They consist of a specific nerve epithelium, which is covered by a membrane from above. It contains otoliths, which are crystals of phosphate and carbonate lime.

Semicircular canals are in three mutually perpendicular planes. The external channel is horizontal, the posterior is sagittal, and the upper is frontal. Each of the semicircular canals has one expanded and one simple, or smooth, leg. The sagittal and frontal channels have one common smooth leg.

In the ampoule of each of the membranous canals there is a scallop. It is a receptor and is a terminal nerve apparatus composed of highly differentiated nerve epithelium. The free surface of the epithelial cells is covered with hairs that perceive any displacement or pressure of the endolymph.

The vestibule and semicircular canal receptors are represented by the peripheral ends of the nerve fibers of the vestibular analyzer.

The cochlea is a bone canal that forms two curls around a bone shaft. Outward resemblance to an ordinary garden snail gave the name to this organ.

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