Anatomically, what three parts is the ear divided into? The structure of the hearing organ. Sections of the peripheral part of the auditory analyzer

The middle ear is a component of the ear. Occupies the space between the external auditory organ and the eardrum. Its structure involves numerous elements that have certain features and functions.

Structural features

The middle ear consists of several important elements. Each of these components has structural features.

Tympanic cavity

This is the middle part of the ear, very vulnerable, often subject to inflammatory diseases. It is located behind the eardrum, not reaching the inner ear. Its surface is covered with a thin mucous membrane. It has the shape of a prism with four irregular faces and is filled with air inside. Consists of several walls:

• The outer wall with a membranous structure is formed by the inner part of the eardrum as well as the bone of the ear canal.
• The inner wall at the top has a recess in which the window of the vestibule is located. It is a small oval hole, which is covered by the lower surface of the stapes. Below it there is a cape along which a furrow runs. Behind it is a funnel-shaped dimple in which the cochlear window is placed. From above it is limited by a bone ridge. Above the window of the cochlea there is a tympanic sinus, which is a small depression.
• The upper wall, which is called the tegmental wall, as it is formed by hard bone substance and protects it. The deepest part of the cavity is called the dome. This wall is necessary to separate the tympanic cavity from the walls of the skull.
• The lower wall is jugular, as it participates in the creation of the jugular fossa. It has an uneven surface because it contains drum cells necessary for air circulation.
• The posterior mastoid wall contains an opening that leads into the mastoid cave.
• The anterior wall has a bone structure and is formed by substance from the carotid artery canal. Therefore, this wall is called the carotid wall.

Conventionally, the tympanic cavity is divided into 3 sections. The lower one is formed by the lower wall of the tympanic cavity. The middle is the larger part, the space between the upper and lower borders. The upper section is the part of the cavity corresponding to its upper border.

Auditory ossicles

They are located in the area of ​​the tympanic cavity and are important, since without them sound perception would be impossible. These are the hammer, anvil and stirrup.

Their name comes from the corresponding shape. They are very small in size and are lined on the outside with mucous membrane.

These elements connect to each other to form real joints. They have limited mobility, but allow you to change the position of the elements. They are connected to each other as follows:

• The hammer has a rounded head connected to the handle.
• The anvil has a rather massive body, as well as 2 processes. One of them is short, rests against the hole, and the second is long, directed towards the handle of the hammer, thickened at the end.
• The stirrup includes a small head, covered on top with articular cartilage, which serves to articulate the incus and 2 legs - one straight and the other more curved. These legs are attached to the oval plate contained in the fenestra vestibule.

The main function of these elements is the transmission of sound impulses from the membrane to the oval window of the vestibule. In addition, these vibrations are amplified, which makes it possible to transmit them directly to the perilymph of the inner ear. This occurs due to the fact that the auditory ossicles are articulated in a lever manner. In addition, the size of the stapes is many times smaller than the eardrum. Therefore, even small sound waves make it possible to perceive sounds.

Muscles

The middle ear also has 2 muscles - they are the smallest in the human body. The muscle bellies are located in the secondary cavities. One serves to tension the eardrum and is attached to the handle of the hammer. The second is called the stirrup and is attached to the head of the stapes.

These muscles are necessary to maintain the position of the auditory ossicles and regulate their movements. This provides the ability to perceive sounds of varying strengths.

Eustachian tube

The middle ear connects to the nasal cavity through the Eustachian tube. It is a small canal, about 3-4 cm long. On the inside it is covered with a mucous membrane, on the surface of which there is ciliated epithelium. The movement of its cilia is directed towards the nasopharynx.

Conventionally divided into 2 parts. The one that is adjacent to the ear cavity has walls with a bone structure. And the part adjacent to the nasopharynx has cartilaginous walls. In the normal state, the walls are adjacent to each other, but when the jaw moves, they diverge in different directions. Thanks to this, air flows freely from the nasopharynx into the hearing organ, ensuring equal pressure within the organ.

Due to its close proximity to the nasopharynx, the Eustachian tube is susceptible to inflammatory processes, since infection can easily enter it from the nose. Its patency may be impaired due to colds.

In this case, the person will experience congestion, which brings some discomfort. To deal with it, you can do the following:

• Examine the ear. An unpleasant symptom may be caused by an ear plug. You can remove it yourself. To do this, drop a few drops of peroxide into the ear canal. After 10-15 minutes, the sulfur will soften, so it can be easily removed.
• Move your lower jaw. This method helps with mild congestion. It is necessary to push the lower jaw forward and move it from side to side.
• Apply the Valsalva technique. Suitable in cases where ear congestion does not go away for a long time. It is necessary to close your ears and nostrils and take a deep breath. You should try to exhale it with your nose closed. The procedure should be carried out very carefully, as during it the blood pressure may change and the heartbeat may accelerate.
• Use Toynbee's method. You need to fill your mouth with water, close your ears and nostrils, and take a sip.

The Eustachian tube is very important because it maintains normal pressure in the ear. And when it is blocked for various reasons, this pressure is disrupted, the patient complains of tinnitus.

If after carrying out the above manipulations the symptom does not go away, you should consult a doctor. Otherwise, complications may develop.

Mastoid

This is a small bone formation, convex above the surface and shaped like a papilla. Located behind the ear. It is filled with numerous cavities - cells connected to each other by narrow slits. The mastoid process is necessary to improve the acoustic properties of the ear.

Main functions

The following functions of the middle ear can be distinguished:

1. Sound conduction. With its help, sound is sent to the middle ear. The outer part picks up sound vibrations, then they pass through the auditory canal, reaching the membrane. This leads to its vibration, which affects the auditory ossicles. Through them, vibrations are transmitted to the inner ear through a special membrane.
2. Even distribution of pressure in the ear. When the atmospheric pressure is very different from that in the middle ear, it is equalized through the Eustachian tube. Therefore, when flying or when immersed in water, the ears temporarily become blocked, as they adapt to new pressure conditions.
3. Safety function. The middle part of the ear is equipped with special muscles that protect the organ from injury. With very strong sounds, these muscles reduce the mobility of the auditory ossicles to a minimum level. Therefore, the membranes do not rupture. However, if the strong sounds are very sharp and sudden, the muscles may not have time to perform their functions. Therefore, it is important to protect yourself from such situations, otherwise you may partially or completely lose your hearing.

Thus, the middle ear performs very important functions and is an integral part of the auditory organ. But it is very sensitive, so it should be protected from negative influences. Otherwise, various diseases may appear that lead to hearing impairment.

There are quite a lot of diseases that signal their development with ear pain. To determine what specific disease has affected the organ of hearing, you need to understand how the human ear works.

Diagram of the auditory organ

First of all, let's understand what an ear is. This is an auditory-vestibular paired organ that performs only 2 functions: the perception of sound impulses and responsibility for the position of the human body in space, as well as for maintaining balance. If you look at the human ear from the inside, its structure suggests the presence of 3 parts:

• external (external);
• average;
• internal.

Each of them has its own no less intricate device. When connected, they form a long pipe that penetrates into the depths of the head. Let's look at the structure and functions of the ear in more detail (they are best demonstrated by a diagram of the human ear).

What is the outer ear

The structure of the human ear (its external part) is represented by 2 components:

• auricle;
• external ear canal.

The shell is an elastic cartilage that is completely covered by skin. It has a complex shape. In its lower segment there is a lobe - this is a small fold of skin filled inside with a fatty layer. By the way, it is the outer part that has the highest sensitivity to various types of injuries. For example, among fighters in the ring it often has a form that is very far from its original form.

The auricle serves as a kind of receiver for sound waves, which, entering it, penetrate deep into the organ of hearing. Since it has a folded structure, the sound enters the passage with minor distortion. The degree of error depends, in particular, on the location from which the sound originates. Its location can be horizontal or vertical.

It turns out that more accurate information about where the sound source is located enters the brain. So, it can be argued that the main function of the shell is to catch sounds that should enter the human ear.

If you look a little deeper, you can see that the concha is extended by the cartilage of the external ear canal. Its length is 25-30 mm. Next, the cartilage zone is replaced by bone. The outer ear is completely lined with skin, which contains 2 types of glands:

• sulfuric;
• greasy

The outer ear, the structure of which we have already described, is separated from the middle part of the hearing organ by means of a membrane (also called the eardrum).

How does the middle ear work?

If we consider the middle ear, its anatomy consists of:

• tympanic cavity;
• eustachian tube;
• mastoid process.

They are all interconnected. The tympanic cavity is a space outlined by the membrane and the area of ​​the inner ear. Its location is the temporal bone. The structure of the ear here looks like this: in the anterior part there is a union of the tympanic cavity with the nasopharynx (the function of the connector is performed by the Eustachian tube), and in the posterior part - with the mastoid process through the entrance to its cavity. There is air in the tympanic cavity, which enters through the Eustachian tube.

The anatomy of the human ear (child) under 3 years old has a significant difference from how the adult ear works. Babies do not have a bone passage, and the mastoid process has not yet grown. The children's middle ear is represented by only one bony ring. Its inner edge has the shape of a groove. This is where the drum membrane is located. In the upper zones of the middle ear (where this ring is not present), the membrane connects to the lower edge of the squama of the temporal bone.

When the baby reaches 3 years of age, the formation of his ear canal is completed - the structure of the ear becomes the same as in adults.

Anatomical features of the internal section

The inner ear is its most difficult part. The anatomy in this part is very complex, so it was given a second name - “membranous labyrinth of the ear.” It is located in the rocky zone of the temporal bone. The middle ear is joined by windows - round and oval. Comprises:

• vestibule;
• cochlea with organ of Corti;
• semicircular canals (filled with fluid).

In addition, the inner ear, the structure of which provides for the presence of a vestibular system (apparatus), is responsible for constantly keeping a person’s body in a state of balance, as well as for the possibility of acceleration in space. The vibrations that occur in the oval window are transmitted to the fluid that fills the semicircular canals. The latter serves as an irritant for the receptors located in the cochlea, and this already causes the triggering of nerve impulses.

It should be noted that the vestibular apparatus has receptors in the form of hairs (stereocilia and kinocilia), which are located on special elevations - the macula. These hairs are located one opposite the other. By shifting, stereocilia provoke excitation, and kinocilia help inhibit.

Let's sum it up

In order to more accurately imagine the structure of the human ear, a diagram of the hearing organ should be before your eyes. It usually depicts a detailed structure of the human ear.

It is obvious that the human ear is a rather complex system, consisting of many different formations, and each of them performs a number of important and truly irreplaceable functions. The diagram of the ear demonstrates this clearly.

Regarding the structure of the outer part of the ear, it should be noted that each person has individual characteristics determined by genetics that in no way affect the main function of the hearing organ.

Ears require regular hygienic care. If you neglect this need, you can partially or completely lose your hearing. Also, lack of hygiene can lead to the development of diseases affecting all parts of the ear.

Hearing is a type of sensitivity that determines the perception of sound vibrations. Its importance is invaluable in the mental development of a full-fledged personality. Thanks to hearing, the sound part of the surrounding reality is known, the sounds of nature are known. Without sound, audible speech communication between people, people and animals, between people and nature is impossible; without it, musical works could not appear.

People's hearing acuity varies. In some it is reduced or normal, in others it is increased. There are people with absolute pitch. They are able to recognize the pitch of a given tone from memory. An ear for music allows you to accurately determine the intervals between sounds of different pitches and recognize melodies. Individuals with an ear for music when performing musical works have a sense of rhythm and are able to accurately repeat a given tone or musical phrase.

Using hearing, people are able to determine the direction of sound and its source. This property allows you to navigate in space, on the ground, to distinguish the speaker among several others. Hearing, together with other types of sensitivity (vision), warns of dangers that arise during work, being outdoors, among nature. In general, hearing, like vision, makes a person’s life spiritually rich.

A person perceives sound waves with the help of hearing with an oscillation frequency of 16 to 20,000 hertz. As we age, our perception of high frequencies decreases. Auditory perception also decreases when exposed to sounds of great strength, high and especially low frequencies.

One of the parts of the inner ear - the vestibular - determines the sense of the body’s position in space, maintains the balance of the body, and ensures a person’s upright posture.

How does the human ear work?

Outer, middle and inner - the main parts of the ear

The human temporal bone is the bony seat of the hearing organ. It consists of three main sections: external, middle and internal. The first two serve to conduct sounds, the third contains a sound-sensitive apparatus and a balance apparatus.

Structure of the outer ear

The outer ear is represented by the auricle, external auditory canal, and eardrum. The auricle catches and directs sound waves into the ear canal, but in humans it has almost lost its main purpose.

The external auditory canal conducts sounds to the eardrum. In its walls there are sebaceous glands that secrete so-called earwax. The eardrum is located on the border between the outer and middle ear. This is a round plate measuring 9*11mm. It receives sound vibrations.

Structure of the middle ear

The middle ear is located between the external auditory canal and the inner ear. It consists of the tympanic cavity, which is located directly behind the eardrum, into which it communicates with the nasopharynx through the Eustachian tube. The tympanic cavity has a volume of about 1 cubic cm.

It contains three auditory ossicles connected to each other:

• Hammer;
• anvil;
• stapes.

These ossicles transmit sound vibrations from the eardrum to the oval window of the inner ear. They reduce the amplitude and increase the strength of the sound.

Structure of the inner ear

The inner ear, or labyrinth, is a system of cavities and canals filled with fluid. The hearing function here is performed only by the cochlea - a spirally twisted canal (2.5 turns). The remaining parts of the inner ear ensure that the body maintains balance in space.

Sound vibrations from the eardrum are transmitted through the auditory ossicle system through the foramen ovale to the fluid that fills the inner ear. Vibrating, the liquid irritates the receptors located in the spiral (corti) organ of the cochlea.

spiral organ- This is a sound-receiving apparatus located in the cochlea. It consists of a main membrane (plate) with supporting and receptor cells, as well as a covering membrane hanging over them. Receptor (perceiving) cells have an elongated shape. One end of them is fixed on the main membrane, and the opposite end contains 30-120 hairs of different lengths. These hairs are washed by fluid (endolymph) and come into contact with the integumentary plate hanging over them.

Sound vibrations from the eardrum and auditory ossicles are transmitted to the fluid that fills the cochlear canals. These vibrations cause vibrations of the main membrane along with the hair receptors of the spiral organ.

During oscillations, the hair cells touch the integumentary membrane. As a result of this, an electrical potential difference arises in them, leading to the excitation of auditory nerve fibers that extend from the receptors. It turns out a kind of microphone effect, in which the mechanical energy of endolymph vibrations is converted into electrical nervous excitation. The nature of the excitations depends on the properties of sound waves. High tones are picked up by a narrow part of the main membrane, at the base of the cochlea. Low tones are recorded by the wide part of the main membrane, at the apex of the cochlea.

From the receptors of the organ of Corti, excitation spreads along the fibers of the auditory nerve to the subcortical and cortical (in the temporal lobe) hearing centers. The entire system, including the sound-conducting parts of the middle and inner ear, receptors, nerve fibers, hearing centers in the brain, makes up the auditory analyzer.

Vestibular apparatus and orientation in space

As already mentioned, the inner ear plays a dual role: the perception of sounds (the cochlea with the organ of Corti), as well as the regulation of body position in space, balance. The latter function is provided by the vestibular apparatus, which consists of two sacs - round and oval - and three semicircular canals. They are interconnected and filled with liquid. On the inner surface of the sacs and extensions of the semicircular canals there are sensitive hair cells. Nerve fibers extend from them.

Angular accelerations are perceived mainly by receptors located in the semicircular canals. The receptors are excited by the pressure of the channel fluid. Straight-line accelerations are recorded by the receptors of the vestibule sacs, where the otolith apparatus. It consists of sensory hairs of nerve cells embedded in a gelatinous substance. Together they form a membrane. The upper part of the membrane contains inclusions of calcium bicarbonate crystals - otoliths. Under the influence of linear accelerations, these crystals force the membrane to bend by the force of their gravity. In this case, deformations of the hairs occur and excitation occurs in them, which is transmitted along the corresponding nerve to the central nervous system.

The function of the vestibular apparatus as a whole can be represented as follows. The movement of the fluid contained in the vestibular apparatus, caused by movement of the body, shaking, pitching, causes irritation of the sensitive hairs of the receptors. Excitations are transmitted along the cranial nerves to the medulla oblongata and the pons. From here they go to the cerebellum, as well as the spinal cord. This connection with the spinal cord causes reflex (involuntary) movements of the muscles of the neck, torso, and limbs, which aligns the position of the head and torso and prevents falls.

When consciously determining the position of the head, excitation comes from the medulla oblongata and the pons through the visual thalamus to the cerebral cortex. It is believed that the cortical centers for controlling balance and body position in space are located in the parietal and temporal lobes of the brain. Thanks to the cortical ends of the analyzer, conscious control of balance and body position is possible, and upright posture is ensured.

Hearing hygiene

• Physical;
• chemical
• microorganisms.

Physical hazards

Physical factors should be understood as traumatic effects during bruises, when picking various objects in the external auditory canal, as well as constant noise and especially sound vibrations of ultra-high and especially infra-low frequencies. Injuries are accidents and cannot always be prevented, but eardrum injuries during ear cleaning can be completely avoided.

How to properly clean a person's ears? To remove wax, it is enough to wash your ears daily and there will be no need to clean it with rough objects.

A person encounters ultrasounds and infrasounds only in production conditions. To prevent their harmful effects on the hearing organs, safety regulations must be followed.

Constant noise in large cities and in enterprises has a harmful effect on the hearing organ. However, the health service is fighting these phenomena, and engineering and technical thought is aimed at developing production technology to reduce noise levels.

The situation is worse for those who like to play musical instruments loudly. The effect of headphones on a person’s hearing is especially negative when listening to loud music. In such individuals, the level of perception of sounds decreases. There is only one recommendation - to accustom yourself to moderate volume.

Chemical hazards

Hearing diseases as a result of the action of chemicals occur mainly due to violations of safety precautions in handling them. Therefore, you must follow the rules for working with chemicals. If you do not know the properties of a substance, then you should not use it.

Microorganisms as a harmful factor

Damage to the organ of hearing by pathogenic microorganisms can be prevented by timely healing of the nasopharynx, from which pathogens penetrate into the middle ear through the Eustachian canal and initially cause inflammation, and if treatment is delayed, decrease and even loss of hearing.

To preserve hearing, general strengthening measures are important: organizing a healthy lifestyle, observing a work and rest schedule, physical training, and reasonable hardening.

For people suffering from weakness of the vestibular apparatus, manifested in intolerance to travel in transport, special training and exercises are desirable. These exercises are aimed at reducing the excitability of the balance apparatus. They are done on rotating chairs and special simulators. The most accessible training can be done on a swing, gradually increasing its time. In addition, gymnastic exercises are used: rotational movements of the head, body, jumping, somersaults. Of course, vestibular apparatus training is carried out under medical supervision.

All analyzed analyzers determine the harmonious development of the individual only with close interaction.

22741 0

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

Outer ear

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

By using two miniature microphones, one placed at the pinna of the ear and the other at the eardrum, this effect can be detected. When pure tones of varying frequencies are presented at an intensity equal to 70 dB SPL (measured with a microphone placed at the auricle), levels will be determined at the level of the eardrum.

Thus, at frequencies below 1400 Hz, an SPL of 73 dB is determined at the eardrum. This value is only 3 dB higher than the level measured at the auricle. As the frequency increases, the gain 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.

Calculated changes in sound pressure produced by a source located in a free sound field at the measurement site: auricle, external auditory canal, eardrum (resulting curve) (after Shaw, 1974)

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 weakening 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 that have 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

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

The amplitude of vibration of the eardrum at maximum sound intensity according to data obtained by the holographic method is equal to 2x105 cm, while at threshold stimulus intensity it is equal to 104 cm (measurements by J. Bekesy). The oscillatory movements of the eardrum are quite complex and heterogeneous. Thus, the greatest amplitude of oscillations during stimulation with a tone with a frequency of 2 kHz occurs below umbo. When stimulated with low-frequency sounds, the point of maximum displacement corresponds to the posterior superior part of the tympanic membrane. The nature of oscillatory movements becomes more complex with increasing frequency and intensity of sound.

Between the eardrum and the inner ear are three bones: the malleus, the incus and the stirrup. The handle of the hammer is connected directly to the membrane, while its head is in contact with the anvil. The long process of the incus, namely its lenticular process, connects to the head of the stapes. The stapes, the smallest bone in humans, consists of a head, two legs and a foot plate, located in the window of the vestibule and fixed in it using the 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 stapedius muscle (tensor tympani), the length of which does not exceed 6 mm. The stapedius tendon 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) by bone conduction through the bones of the skull directly to the inner ear, bypassing the middle ear; (2) through the air space of the middle ear and (3) through the chain of auditory ossicles. As will be demonstrated below, the third path of sound conduction is the most effective. However, a prerequisite for this is the equalization of pressure in the tympanic cavity with atmospheric pressure, which is accomplished during 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 on both sides of the eardrum is equalized, which is a prerequisite for vibration of the eardrum, and, secondly, the auditory tube provides a drainage function.

It was stated above that sound energy is transmitted from the eardrum through the chain of auditory ossicles (the footplate 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, one in the water and the other on the shore, then you should keep 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 reduction 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 ​​55 mm2 is effective in terms of transmitting sound energy. The area of ​​the 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 per unit area. And, if the force applied to the eardrum is equal to the force reaching the footplate of the stapes, then the pressure at the footplate 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 foot plate of the stapes provides an increase in pressure measured at the foot plate by 17 times (55/3.2), which in decibels corresponds to 24.6 dB. Thus, if about 30 dB are lost during direct transmission from the air to the liquid medium, then due to differences in the surface areas of the eardrum and the foot plate of the stapes, the noted loss is compensated by 25 dB.

Transfer function of the middle ear, showing the increase in pressure in the fluids of the inner ear, compared to the pressure on the eardrum, at various frequencies, expressed in dB (after von Nedzelnitsky, 1980)

All of the above indicates that the energy applied to the eardrum, upon reaching the foot plate of the stapes, is amplified by 17x1.3x2=44.2 times, which corresponds to 33 dB. However, of course, the enhancement that occurs between the eardrum and the footplate depends on the frequency of stimulation. Thus, it follows that at a frequency of 2500 Hz the increase in pressure corresponds to 30 dB and higher. Above this frequency the gain decreases. In addition, it should be emphasized that the above-mentioned resonant range of the concha and external auditory canal determines reliable amplification in a wide frequency range, which is very important for the perception of sounds like speech.

An integral part of the middle ear's lever system (chain of ossicles) are the middle ear muscles, which are usually in a state of tension. However, when a sound is presented with an intensity of 80 dB relative to the threshold of auditory sensitivity (AS), a reflex contraction of the stapedius muscle occurs. In this case, the sound energy transmitted through the chain of auditory ossicles is weakened. The magnitude of this attenuation is 0.6-0.7 dB for every decibel increase in stimulus intensity above the acoustic reflex threshold (about 80 dB IF).

The attenuation ranges 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 a minimum value of 10 ms when high-intensity sounds are presented, to 150 ms when stimulated by sounds of relatively low intensity.

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

The movements of the auditory ossicles are not the same at different frequencies and intensity levels of stimulation. Due to the size of the head of the malleus and the body of the incus, their mass is evenly distributed along an axis passing through the two large ligaments of the malleus and the short process of the incus. At moderate levels of intensity, the chain of auditory ossicles moves in such a way that the footplate of the stapes oscillates around an axis mentally drawn vertically through the posterior leg of the stapes, like doors. The front part of the footplate enters and exits the cochlea like a piston.

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

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

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

When presenting the basic properties of acoustic signals, acoustic impedance was considered as an essential characteristic. The physical properties of acoustic resistance or impedance are fully reflected in the functioning of the middle ear. The impedance or acoustic resistance of the middle ear is made up of components caused by the 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 against the footplate of the stapes.

The resistance that occurs when moving parts are displaced should also be taken into account, but its magnitude is much less. It should be remembered that the resistive component of the impedance does not depend on the stimulation frequency, unlike the reactive component. Reactivity is determined by two components. The first is the mass of structures in the middle ear. 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 the muscles and ligaments of the middle ear.

When we say that a spring stretches easily, we mean that it is flexible. If the spring stretches with difficulty, we talk about its stiffness. These characteristics make the greatest contribution at low stimulation frequencies (below 1 kHz). At mid-frequencies (1-2 kHz), both reactive components cancel each other out and the resistive component dominates the middle ear impedance.

One way to measure middle ear impedance is to use an electroacoustic bridge. If the middle ear system is sufficiently rigid, the pressure in the cavity will be higher than if the structures are highly compliant (when sound is absorbed by the eardrum). Thus, sound pressure measured using a microphone can be used to study the properties of the middle ear. Often, middle ear impedance measured using an electroacoustic bridge is expressed in compliance units. This is because impedance is typically measured at low frequencies (220 Hz), and in most cases only the contraction and elongation properties of the muscles and ligaments of the middle ear are measured. So, the higher the compliance, the lower the impedance and the easier the system operates.

As the muscles of the middle ear contract, the entire system becomes less pliable (i.e., more rigid). From an evolutionary point of view, there is nothing strange in the fact that when leaving the water on land, to level out differences in the resistance of the fluids and structures of the inner ear and the air cavities of the middle ear, evolution provided a transmission link, namely the 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 stimulated directly by vibrations of the air in the middle ear cavity. Again, due to the large differences in impedance between the fluids and structures of the inner ear and air, the fluids move only slightly. In addition, when directly stimulating the inner ear through changes in sound pressure in the middle ear, there is an additional attenuation of the transmitted energy due to the fact that both inputs to the inner ear (the window of the vestibule and the window of the cochlea) are simultaneously activated, and at some frequencies the sound pressure is also transmitted and in phase.

Considering that the fenestra cochlea and the fenestra vestibule are located on opposite sides of the main membrane, positive pressure applied to the membrane of the cochlear window will be accompanied by a deflection of the main membrane in one direction, and pressure applied to the foot plate of the stapes will deflect 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 detected in patients who lack auditory ossicles. Thus, the next function of the middle ear is to provide a path for transmitting stimuli to the oval window of the vestibule, which, in turn, provides displacements of the cochlear window membrane corresponding to pressure fluctuations in the inner ear.

Another way to stimulate the inner ear is bone conduction, in which changes in acoustic pressure cause vibrations in the bones of the skull (primarily the temporal bone), and these vibrations are transmitted directly to the fluids of the inner ear. Because of the enormous differences in impedance between bone and air, stimulation of the inner ear by bone conduction cannot be considered an important part of normal auditory perception. However, if a source of vibration is applied directly to the skull, the inner ear is stimulated by conducting sounds through the bones of the skull.

Differences in impedance between the bones and fluids of the inner ear are quite small, allowing partial transmission of sound. Measuring auditory perception during bone conduction of sounds is of great practical importance in middle ear pathology.

Inner ear

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

A transverse section of the cochlea, from which it follows that the cochlea is divided into three sections: the scala vestibuli, as well as the scala tympani and median scala. The spiral canal of the cochlea has a length of 35 mm and is partially divided along the entire length by a thin bony spiral plate extending from the modiolus (osseus spiralis lamina). It continues with the main membrane (membrana basilaris) connecting to the outer bony wall of the cochlea at the spiral ligament, thereby completing the division of the canal (with the exception of a small hole at the apex of the cochlea, called helicotrema).

The scala vestibule extends from the oval window, located in the vestibule, to the helicotrema. The scala tympani extends from the round window and also to the helicotrema. The spiral ligament, being the connecting link between the main membrane and the bony wall of the cochlea, also supports the stria vascularis. Most of the spiral ligament consists of sparse fibrous joints, blood vessels, and connective tissue cells (fibrocytes). The areas located close to the spiral ligament and the spiral protrusion include more cellular structures, as well as larger mitochondria. The spiral projection is separated from the endolymphatic space by a layer of epithelial cells.

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

Marginal cells make up the bulk of the stria vascularis. They have finger-like processes that provide a close connection with similar processes of the cells of the middle layer. The basal cells attached to the spiral ligament have a flat shape and long processes penetrating into the marginal and medial layers. The cytoplasm of basal cells is similar to the cytoplasm of fibrocytes of the spiral ligament.

The blood supply to the stria vascularis is carried out by the spiral modiolar artery through vessels passing through the scala vestibuli to the lateral wall of the cochlea. Collecting venules located in the wall of the scala tympani direct blood to the spiral modiolar vein. The stria vascularis exerts the main metabolic control of the cochlea.

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

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

Cross sections of the organ of Corti at the base (a) and apex (b) indicate differences in the width and thickness of the main membrane, (c) and (d) - scanning electron microphotographs of the main membrane (view from the side of the scala tympani) at the base and apex of the cochlea ( d). Summary physical characteristics of the human main membrane

IHC - inner hair cells; OHC - outer hair cells; NSC, VSC - external and internal pillar cells; TK - Corti tunnel; OS - main membrane; TC - tympanic layer of cells below the main membrane; D, G - supporting cells of Deiters and Hensen; PM - cover membrane; PG - Hensen's strip; ICB - internal groove cells; RVT-radial nerve fiber tunnel

The organ of Corti is located in the median scala on the basilar membrane. The outer and inner columnar cells form the internal tunnel of Corti, filled with a fluid called cortilymph. Inward from the inner pillars is one row of inner hair cells (IHC), and outward from the outer pillars are three rows of smaller cells called outer hair cells (OHC) and supporting cells.

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

The upper end of the cylindrical Deiters cell has a cup-shaped surface on which the hair cell is located. From the same surface, a thin process extends to the surface of the organ of Corti, 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 of VVC. Stereocilia (SC) of the VVC are projected into the scala mediana (SL), and their base is immersed in the cuticular plate (CP). N - core of the IVC, VSP - nerve fibers of the internal spiral ganglion; VSC, NSC - internal and external columnar cells of the tunnel of Corti (TC); BUT - nerve endings; OM - main membrane
B. Transmission electron microphotogram of NVC. There is a clear difference in the form of NVK and VVC. The NVC is located on the recessed surface of the Deiters cell (D). At the base of the NVK, efferent nerve fibers (E) are identified. The space between the NVC is called the Nuel space (NP). Within it, the phalangeal processes (PF) are determined.

Only a small area of ​​the cell surface remains free from the cuticular plate, where the basal body or modified kinocilium is located. The basal body is located at the outer edge of the VVC, away from the modiolus.

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

One row of VVC and three rows of NVK are clearly defined. Between the IVC and the IVC, the heads of the internal pillar cells (ISC) are visible. Between the tops of the rows of the NVK, the tops of the phalangeal processes (PF) are determined. The supporting cells of Deiters (D) and Hensen (G) are located at the outer edge. The W-shaped orientation of the NVC cilia is tilted relative to the IHC. In this case, the slope is different for each row of the NVC (according to I. Hunter-Duvar)

The main part of the membrane consists of fibers with a diameter of 10-13 nm, emanating from the inner zone and running at an angle of 30° to the apical helix of the cochlea. Towards the outer edges of the covering membrane, the fibers spread in the longitudinal direction. The average length of stereocilia depends on the position of the NVK along the length of the cochlea. Thus, at the top 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 stereocilium has the shape of a club, which expands from the base (at the cuticular plate - 130 nm) to the apex (320 nm). There is a powerful network of crossovers between the stereocilia; thus, a large number of horizontal connections are connected by stereocilia located both in the same and in different rows of the NVC (laterally and below the apex). In addition, a thin process extends from the apex of the shorter stereocilium of the NVC, connecting to the longer stereocilium of the next row of NVC.

PS - cross connections; KP - cuticular plate; C - connection within a row; K - root; SC - stereocilium; PM - covering membrane

Ya.A. Altman, G. A. Tavartkiladze

A person receives most of the information about the world around him through vision and hearing. Moreover, the structure of the ear is very complex. Any disturbances in the middle ear or other parts of the hearing system can lead not only to hearing loss, but also to the creation of a situation where a person’s life is in danger. Let's figure out what the functions and structure of the middle ear are, what diseases affect this part of the hearing system and how to prevent their occurrence.

The middle ear is located between the inner and outer ears. The main purpose of this part of the hearing aid is to conduct sounds. The middle ear consists of the following parts:

1. Auditory ossicles. They are the stirrup, hammer and anvil. It is these details that help transmit sounds, and distinguish them by strength and height. The peculiarities of the auditory ossicles help protect the hearing aid from sharp and loud sounds.
2. Eustachian tube. This is the passage connecting the nasopharynx with the tympanic cavity. Its mouth is closed when a person swallows or sucks something. In newly born children, for some time the auditory tube is wider and shorter than in adulthood.
3. Tympanic cavity. It is this part of the middle ear that contains the auditory ossicles described above. The location of the tympanic cavity is the area between the outer ear and the temporal bone.
4. Mastoid. This is the convex part of the temporal bone. It contains cavities that are filled with air and communicate with each other through narrow holes.

The middle ear is a device that conducts sound vibrations, consisting of air cavities and complex anatomical formations. The tympanic cavity is lined with mucous membrane and is separated from the rest of the skull by an upper wall. All auditory ossicles are also covered with mucous membrane. The middle and inner ear are separated by a bony wall. They are connected to each other only by two holes:

• round window;
• oval window in the ear.

Each of them is protected by a flexible and elastic membrane. The stapes, one of the auditory ossicles, enters the oval window, located in front of the water-filled inner ear.

Important! Also, muscles play a huge role in the operation of this part of the hearing aid. There is a muscle that affects the eardrum, and a group of muscles that controls the auditory ossicles.

Functions of the middle ear

Air cavities and other anatomical formations located in the middle ear provide sound passage. The main functions of the middle ear are:

• maintaining the functionality of the eardrum;
• transmission of sound vibrations;
• protection of the inner ear from sharp and too loud sounds;
• ensuring the sensitivity of sounds of a wide variety of strength, pitch and volume.

Important! The main function of the middle ear is to conduct sounds. And any disease or injury that affects this part of the hearing aid can lead to irreversible complete or partial hearing loss.

Middle ear diseases

Experts call the following signs and conditions of a person the main symptoms of problems in the middle ear area:

• pain in the ear area of ​​varying intensity (mostly very severe);
• feeling of stuffiness;
• decreased or complete loss of hearing;
• discharge of fluid or pus from the ear canal;
• increased body temperature;
• decreased appetite and poor sleep;
• change in color of the eardrum to a redder color.

Among the most common diseases of the middle ear are the following:

1. Purulent otitis media of the middle ear. This is an inflammation in which purulent and purulent-bloody discharge from the ear canal is observed, the person complains of unbearable pain, and hearing deteriorates significantly. The disease affects the middle ear cavity and eardrum, and can spread to other parts of the hearing system.
2. Cicatricial otitis. In this case, the inflammatory process led to the formation of scars and decreased mobility of the auditory ossicles. Because of this, severe hearing loss is observed.
3. Mesotympanitis. The disease is similar in symptoms to purulent otitis. In this case, the eardrum is affected, and the person notices decreased hearing and purulent discharge.
4. Epitempanitis. During this disease, inflammation of the epitympanic space of the middle ear occurs; a protracted course of the inflammatory process can disrupt the structure of the middle and inner ear, which will entail a decrease and a sharp deterioration in hearing.
5. Mastoiditis. Most often, this is a consequence of purulent otitis not treated correctly and in a timely manner, which affects not only the middle ear, but also the mastoid process.
6. Qatar of the middle ear. The disease usually precedes purulent otitis and affects the auditory tube.
7. Bullous otitis media. The disease occurs against the background of influenza and has symptoms similar to other otitis media. The focus of the inflammatory process is located in the supratympanic air cavity.

Important! Often, problems with the middle ear can arise against the background of various infectious diseases, for example, sore throat, sinusitis, rhinitis, laryngitis, and influenza. Also common causes are improper care of the ears and nose, injuries, water getting into the ear canal, hypothermia and drafts.

Prevention of middle ear diseases

Wear a hat during the winter season

To prevent the development of middle ear diseases, experts recommend that children and adults adhere to the following rules:

1. Treat diseases of the upper respiratory tract, nose and ears in a timely manner. If treatment is incorrectly selected or absent, the infection quickly spreads from the nasopharynx or outer ear further and disrupts the functioning of the hearing aid. Always follow the recommendations of doctors during the treatment of diseases of the ENT organs. Do not stop therapy, even if you feel great, do not change the dosage and treatment regimen of drugs, do not extend the period of their use.
2. If a person has congenital abnormalities of the ear structure, then they should be resolved with the help of a specialist, if possible. Sometimes it is necessary to undergo surgery, and in some cases it is enough to take certain medications.
3. Maintaining hygiene. Accumulation of wax, dirt or water entering the ear canal can lead to inflammation. Therefore, try to clean your ears and your children’s ears with cotton wool pads in a timely manner. When swimming or bathing, use special caps and earplugs, and avoid direct water jets entering the ear canal.
4. Make sure your ears are not injured. The entry of a foreign body, the use of sharp and hard objects when cleaning the ears, as well as some other reasons can cause inflammation and provoke infection in the middle ear.
5. In winter, wear a hat. Protect yourself from drafts and hypothermia, sudden changes in temperature and humidity. It is best for young children to wear special thin caps, even if the room temperature is comfortable.
6. In childhood, as a preventive measure for frequently occurring otitis media and other inflammatory processes due to overgrown or greatly enlarged adenoids, their removal is sometimes recommended.

Important! The best prevention of middle ear diseases is strengthening the immune system. A balanced diet, moderate physical activity, hardening - all this will increase the body's endurance and resistance to infections and significantly reduce the risk of developing diseases.

Remember, middle ear diseases are very dangerous for a person’s hearing and life. If you have any disturbing symptoms, you should immediately consult a doctor. Self-medication for otitis media and other inflammatory processes is prohibited either in childhood or in adulthood. This can lead to serious complications, including the spread of infection beyond the middle ear, penetration into the brain, as well as reduction and complete loss of hearing. The sooner you see a doctor and start treatment, the lower the risk of complications and the higher the chance of eliminating the disease as soon as possible without any consequences.