Diseases of the external ear anatomy and physiology. Anatomy of the human ear. The outer wall of the tympanic cavity and the mastoid cave.

Performs a function that is of great importance for the full functioning of a person. Therefore, it makes sense to study its structure in more detail.

Anatomy of the ears

The anatomical structure of the ears, as well as their component parts, has a significant impact on the quality of hearing. A person’s speech directly depends on the full functioning of this function. Therefore, the healthier the ear, the easier it is for a person to carry out the process of life. It is these features that determine the fact that the correct anatomy of the ear is of great importance.

Initially, it is worth starting to consider the structure of the hearing organ with the auricle, which is the first thing that catches the eye of those who are not experienced in the topic of human anatomy. It is located between the mastoid process on the back side and the temporal mandibular joint in front. It is thanks to the auricle that a person’s perception of sounds is optimal. In addition, this particular part of the ear is of no small cosmetic importance.

The basis of the auricle can be defined as a plate of cartilage, the thickness of which does not exceed 1 mm. On both sides it is covered with skin and perichondrium. The anatomy of the ear also points to the fact that the only part of the shell that lacks a cartilaginous skeleton is the lobe. It consists of skin-covered fatty tissue. The auricle has a convex inner part and a concave outer part, the skin of which is tightly fused with the perichondrium. Speaking about the inside of the shell, it is worth noting that in this area the connective tissue is much more developed.

It is worth noting the fact that two-thirds of the length of the external auditory canal is occupied by the membranous-cartilaginous section. As for the bone department, it gets only a third part. The basis of the membranous-cartilaginous section is the continuation of the cartilage of the auricle, which looks like a groove open at the back. Its cartilaginous framework is interrupted by vertically running Santorini fissures. They are covered with fibrous tissue. The border of the ear canal is located exactly in the place where these gaps are located. It is this fact that explains the possibility of developing a disease that appears in the outer ear, in the area of ​​the parotid gland. It is worth understanding that this disease can spread in reverse order.

Those for whom information on the topic “anatomy of the ears” is relevant should also pay attention to the fact that the membranous cartilaginous section is connected to the bony part of the external auditory canal through fibrous tissue. The narrowest part can be found in the middle of this section. It is called the isthmus.

Within the membranous-cartilaginous section, the skin contains sulfur and sebaceous glands, as well as hair. It is from the secretion of these glands, as well as the scales of the epidermis that have been rejected, that earwax is formed.

Walls of the external auditory canal

The anatomy of the ears includes information about the various walls that are located in the external meatus:

• Upper bone wall. If a fracture occurs in this part of the skull, it may result in liquorrhea and bleeding from the ear canal.
• Front wall. It is located on the border with the temporomandibular joint. The movements of the jaw itself are transmitted to the membranous-cartilaginous part of the external passage. Sharp painful sensations can accompany the chewing process if inflammatory processes are present in the area of ​​the anterior wall.

• The anatomy of the human ear concerns the study of the posterior wall of the external auditory canal, which separates the latter from the mastoid cells. The facial nerve passes through the base of this wall.
• Bottom wall. This part of the external meatus separates it from the salivary parotid gland. Compared to the top one, it is 4-5 mm longer.

Innervation and blood supply to the hearing organs

It is imperative that those who study the structure of the human ear pay attention to these functions. The anatomy of the organ of hearing includes detailed information about its innervation, which is carried out through the trigeminal nerve, the auricular branch of the vagus nerve, and also. It is the posterior auricular nerve that supplies the rudimentary muscles of the auricle with nerves, although their functional role can be defined as quite low.

Regarding the topic of blood supply, it is worth noting that the blood supply is provided from the external carotid artery system.

The blood supply directly to the auricle itself is carried out using the superficial temporal and posterior auricular arteries. It is this group of vessels, together with the branches of the maxillary and posterior auricular arteries, that provide blood flow in the deep parts of the ear and the eardrum in particular.

Cartilage receives nutrition from vessels located in the perichondrium.

As part of a topic such as “Anatomy and Physiology of the Ear,” it is worth considering the process of venous outflow in this part of the body and the movement of lymph. Venous blood leaves the ear through the posterior auricular and posterior mandibular veins.

As for lymph, its outflow from the external ear is carried out through nodes that are located in the mastoid process in front of the tragus, as well as under the lower wall of the external auditory canal.

Eardrum

This part of the hearing organ serves as the separation of the outer and middle ear. In essence, we are talking about a translucent fibrous plate that is quite strong and resembles an oval shape.

Without this plate, the ear will not be able to fully function. The anatomy of the structure of the eardrum reveals in sufficient detail: its size is approximately 10 mm, its width is 8-9 mm. An interesting fact is that in children this part of the hearing organ is almost the same as in adults. The only difference comes down to its shape - at an early age it is round and noticeably thicker. If we take the axis of the external auditory canal as a guide, then in relation to it the eardrum is located obliquely, at an acute angle (approximately 30°).

It is worth noting that this plate is located in the groove of the fibrocartilaginous tympanic ring. Under the influence of sound waves, the eardrum begins to tremble and transmits vibrations to the middle ear.

Tympanic cavity

Clinical anatomy of the middle ear includes information about its structure and function. This part of the hearing organ also includes the auditory tube with a system of air cells. The cavity itself is a slit-like space in which 6 walls can be distinguished.

Moreover, in the middle ear there are three ear bones - the incus, malleus and stirrup. They are connected using small joints. In this case, the hammer is in close proximity to the eardrum. It is he who is responsible for the perception of sound waves transmitted by the membrane, under the influence of which the hammer begins to tremble. Subsequently, the vibration is transmitted to the incus and stapes, and then the inner ear reacts to it. This is the anatomy of the human ears in their middle part.

How does the inner ear work?

This part of the hearing organ is located in the area of ​​the temporal bone and looks like a labyrinth. In this part, the resulting sound vibrations are converted into electrical impulses that are sent to the brain. Only after this process is completely completed is a person able to respond to sound.

It is also important to pay attention to the fact that the human inner ear contains semicircular canals. This is relevant information for those who study the structure of the human ear. The anatomy of this part of the hearing organ looks like three tubes that are bent in the shape of an arc. They are located in three planes. Due to the pathology of this part of the ear, disturbances in the functioning of the vestibular apparatus are possible.

Anatomy of sound production

When sound energy enters the inner ear, it is converted into impulses. Moreover, due to the structure of the ear, the sound wave travels very quickly. The consequence of this process is the appearance of a shear-promoting cover plate. As a result, the stereocilia of hair cells are deformed, which, having entered a state of excitation, transmit information using sensory neurons.

Conclusion

It is easy to see that the structure of the human ear is quite complex. For this reason, it is important to ensure that the hearing organ remains healthy and prevent the development of diseases found in this area. Otherwise, you may encounter a problem such as impaired sound perception. To do this, at the first symptoms, even if they are minor, it is recommended to visit a highly qualified doctor.

Middle ear (a), upper and inner walls of the tympanic cavity (b)a
b

Outer wall of the tympanic cavity and mastoid cave

2
1
10
3
4
9
7
8
6
5
1 - supratympanic
recess;
2 - mastoid cave;
3 - mastoid process;
4 - descending knee
facial nerve;
5 - sigmoid sinus;
6 - inner bulb
jugular vein;
7 - internal sleepy
artery;
8 - auditory tube;
9 - eardrum;
10 - head of the hammer

Sections of the tympanic cavity

Tympanum:
1 - external auditory
passage;
2 - cave;
3 - epitympanum;
4 - facial nerve;
5 - labyrinth;
6 - mesotympanum;
7, 8 - auditory tube;
9 - jugular vein

Connection of the middle ear with the nasal cavity and nasopharynx

Eardrum and ossicular chain

2
5
6
3
1
4
1-
2-
3-
5-
7
stretched part of the eardrum;
the loose part of the eardrum;
hammer handle; 4 - light cone;
hammer; 6 - anvil; 7 - stirrup

Auditory ossicles

Inner ear: vestibular receptors are located in the ampoules of the semicircular canals and vestibular sacs

4
9
5
8
3
1
6
10
2
7
1 - snail;
2 - vestibule;
3, 4, 5 - horizontal,
frontal and
sagittal semicircular
channels;
6 - window of the vestibule;
7 - cochlear window;
8, 9, 10 - ampoules
horizontal,
frontal and
sagittal semicircular
channels

Inner ear (ear labyrinth)

Frontal section of the cochlea (a) and spiral organ (b) a b

Diagram of the movement of perilymph and the location of receptors in the cochlea

The structure of the otolith receptor of the vestibular apparatus

Hairs
sensitive
cells along with
otoliths and
jelly-like
mass form
otolith
membrane

Sound wave conduction diagram

Basic properties of the auditory analyzer.

The hearing analyzer allows
differentiate sounds:
By
altitude (frequency) - range
perception from 16 to 20,000 Hz.
by volume (intensity) of sound - from
1 to 140 dB.
by timbre (individual coloring)
sound.

Sound volume

Volume
sound reflects its intensity,
i.e. the energy transferred by the sound wave to
surface unit (W/cm2). Range between
threshold of perception and maximum
tolerable pressure is 1014 and
measured in billions.
The unit of measurement for loudness level is
calculate the bel - decimal logarithm of the ratio
intensity of a given sound to its threshold
level.
Decibel - 0.1 decimal logarithm.
Then the range of auditory perception is from 0 to
130 dB.

Additional properties of the hearing analyzer:

Adaptation
- physiological
adaptation of the hearing organ to the strength of sound
irritant. Under the influence of strong sounds
ear sensitivity decreases, and in silence,
on the contrary, it is getting worse. Adaptation follows
distinguish fatigue of the auditory analyzer.
Ototopics
- ability to determine
direction of the sound source. Ototopics
possible only with binaural hearing.

The hearing analyzer consists of the following main parts:

peripheral
department -
outer, middle and inner ear
(to the spiral organ);
conducting pathways;
central (cortical) department
analyzer.

Sound conducting and sound receiving systems:

5
3
1
4
2
6
7
1 - outer ear; 2 - middle ear; 3 - internal
ear;
4 - pathways; 5 - cortical center;
6 - sound-conducting apparatus;
7 - sound-receiving apparatus

The concept of sensorineural and conductive hearing loss

Main functions of the hearing analyzer:
Sound conduction - delivery of sound energy to
snail receptors.
Sound perception - transformation of physical
energy of sound vibrations into nerve impulses,
carrying them to centers in the cerebral cortex,
analysis and comprehension of sounds.
Accordingly, a distinction is made between sound-conducting and
sound-receiving sections of the analyzer, and when
their pathologies - conductive (sound-conducting) and
sensorineural (impaired sound perception)
hearing loss.

Study of the functions of the auditory analyzer

Subjective methods:
Sound reactotest
Study of the perception of whispered and
colloquial speech
Tuning fork research
Audiometry (tone threshold and
suprathreshold, speech, noise)
Objective methods
(electrophysiological methods
registration of reaction to sound):
Registration of otoacoustic emissions
Recording auditory evoked potentials
Impedancemetry

Hearing passport (tuning fork test results) of a patient with right-sided conductive hearing loss

Right ear (AD)
Tests
Left ear (AS)
+
SSH
1m
ShR
6m
5m
RR
6m
35 s
S128 (V=90 s)
90 s
52 s
S128 (K=50 s)
50 s
23 s
From 2048 (40 s)
37 s
-- (neg.)
Rinne Experience (R)
+
Weber experiment (W)
-- (neg.)
Jelle's Experience (G)
+
Conclusion: there is hearing loss on the right according to the type
sound conduction disturbances.

Audiogram with normal hearing

Curves
air and
bone
conductivity
coincide and
located
near the 0–10 line
dB

Audiogram for conductive hearing loss

Promotion
thresholds
sound perception
by air
conductivity;
auditory thresholds
along the bone
no conductivity
changed
There is a bone-air gap
- “snail reserve”

Audiogram for sensorineural hearing loss

Air and
bone
conductivity
violated in
the same
degrees;
bone-air
gap
absent.
Violated
perception
mainly
high tones -
descending
curve

Audiogram for mixed hearing loss

Along with the increase
bone thresholds
available
bone-air
break - loss
hearing with air
conductivity
exceeds the loss
with bone
carrying out

Diagram of an acoustic impedance meter and tympanogram

Different classes of auditory evoked potentials (AEPs)

Vestibular reactions

Vestibulosensory
Vestibulocorticalis).
(tr.
Vestibulosomatic
(via tractus
vestibulospinalis, tr. vestibulocerebellaris,
tr. Vestibulolongitudinalis).
Vestibulovegetative
(tr. Vestibuloreticularis).

Nystagmus is involuntary movements of the eyeballs. Vestibular (labyrinthine) nystagmus - involuntary rhythmic movements of the eyeballs

Nystagmus is involuntary movements of the eyes
apples
Vestibular (labyrinthine) nystagmus
- involuntary rhythmic movements
eyeballs, in which fast
and slow components.
Arrival of the slow component
associated with the activity of receptors or
vestibular nuclei, fast - with
functioning of cortical or
subcortical structures of the brain.

Adequate stimuli of the vestibular analyzer:

For
ampullary receptors: angular
acceleration, Coriolis acceleration.
For otolith receptors:
linear acceleration, gravity,
Coriolis acceleration.

Vestibular nystagmus is classified as spontaneous or induced by nature.

Nystagmus is visually assessed:
in direction: right, left, up,
down;
- on the plane: horizontal,
vertical, rotary;

- by amplitude: small-, medium- or
large-scale;
- by dynamics: damped or constant;
- by rhythm: rhythmic, non-rhythmic;

(endogenous) and induced (rotational,
caloric, galvanic, pressor,
optokinetic)
-

Characteristics of vestibular nystagmus

- in direction: right or left.
- on the plane: horizontal-rotary;
- by strength: nystagmus I, II, III degrees;
- in amplitude: small-, or
medium-wide;
- dynamics: damped;
- by rhythm: rhythmic;
- origin: spontaneous
(endogenous) and induced
(rotational, caloric,
galvanic, pressor)

Functional study of the vestibular analyzer:

Subjective feelings.
Spontaneous nystagmus (SpNy).
Performing index tests (finger-finger, finger-nose).
Spontaneous hand deviation reaction
(Fisher-Wodak).
Romberg pose.
Adiadochokinesis.
Walk with open eyes.
Flanking gait.
Pressor test.

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

Outer ear

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

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 different frequencies are presented at an intensity equal to 70 dB SPL (measured with a microphone located 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)

Resonance of the outer ear was determined by placing the sound source directly in front of the subject at eye level. When the sound source is raised overhead, the 10 kHz rolloff shifts toward higher frequencies, and the peak of the resonance curve expands and covers a larger frequency range. In this case, each line displays different displacement angles of the sound source. Thus, the outer ear provides “coding” of the displacement of an object in the vertical plane, expressed in the amplitude of the sound spectrum and, especially, at frequencies above 3000 Hz.

In addition, it is clearly demonstrated that the frequency-dependent increase in SPL measured in the free sound field and at the tympanic membrane is mainly due to the effects of the pinna and 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 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

The middle ear consists of the tympanic cavity, mastoid cells, tympanic membrane, auditory ossicles, and auditory tube. In humans, the eardrum has a conical shape with elliptical contours and an area of ​​about 85 mm2 (only 55 mm2 of which is exposed to the sound wave). 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 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 2x105 cm, while at threshold stimulus intensity it is 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)

The transfer of energy from the eardrum to the footplate of the stapes depends on the functioning of the auditory ossicles. The ossicles 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 process of the incus. The effect of the lever system of bones 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 it vibrates, is accompanied by a 2-fold increase in the forces applied to the malleus.

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 window of the cochlea and the window of the 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 be accompanied by a 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 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 membrane of the cochlear window 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

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 mammalian inner ear consists of a series of membranous sacs and ducts (forming the membranous labyrinth) enclosed in a bony capsule (osseous labyrinth), located in turn in the dura temporal bone. The bony labyrinth is divided into three main parts: the semicircular canals, the vestibule and the 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 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 vestibule, 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.

A thin Reissner's membrane extends upward from the bony spiral plate in a diagonal direction and is attached to the outer wall of the cochlea slightly above the main membrane. It extends along the entire body of the cochlea and is connected to the main membrane of the helicotrema. Thus, the cochlear duct (ductus cochlearis) or the median scala is formed, bounded above by the Reissner membrane, below by the main membrane, and outside by the stria vascularis.

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 vestibule 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.

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 main substance. The structure of the main membrane differs significantly from the base of the cochlea to the apex. At the base, the fibers and the covering layer (from the side of the scala tympani) are located more often than at the apex. In addition, while the bony capsule of the cochlea decreases towards the apex, the main membrane expands.

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

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

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

Thus, the gradient of the stiffness of the main membrane is due to differences in its width, which increases towards the apex, thickness, which decreases towards 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 part. Scanning electron micrograms demonstrate the structure of the main membrane from the side of the scala tympani. Differences in the thickness and frequency of radial fibers between the base and apex are clearly identified.

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.

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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)

Deiters and Hensen cells support the NVC laterally; a similar function, but in relation to the IVC, is performed by the border cells of the internal 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 hair cell.

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 medianum (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 the 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.

The shape of the NVK and VVC is significantly different. The upper surface of each IVC is covered with a cuticular membrane into which stereocilia are embedded. Each VVC has about 40 hairs, arranged in two or more rows in a U-shape.

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 IVC. In this case, the slope is different for each row of the NVC (according to I. Hunter-Duvar)

The apices of the longest hairs of the NVC (in the row distant from the modiolus) are in contact with a gel-like integumentary membrane, which can be described as an acellular matrix consisting of zolocones, fibrils and a homogeneous substance. It extends from the spiral projection to the outer edge of the reticular plate. 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 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 IVC (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 NVCs.

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

Each stereocilium 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 the stereocilia.

Ya.A. Altman, G. A. Tavartkiladze

The peripheral section of the auditory analyzer performs two main functions:

• sound conduction, i.e. delivery of sound energy to the receptor apparatus of the cochlea;
• sound perception is the transformation of the physical energy of sound vibrations into nervous excitement. According to these functions, a distinction is made between sound-conducting and sound-receiving devices.

Sound transmission is carried out with the participation auricle, external auditory canal, eardrum, chains auditory ossicles, fluids of the inner ear, membrane of the cochlear window, as well as Reissner's, basilar and integumentary membranes.

The main route of sound delivery to the receptor is airborne. Sound vibrations enter external auditory canal, reach eardrum and cause it to fluctuate. In the phase of increased pressure, the eardrum, together with the handle of the malleus, moves inward. In this case, the body of the incus, connected to the head of the malleus, thanks to the suspensory ligaments, is displaced outward, and the long process of the incus is displaced inward, thus displacing the stapes inwardly. By pressing into the window of the vestibule, the stapes jerkily leads to a displacement of the perilymph of the vestibule.

Further propagation of the sound wave occurs along the perilymph of the scala vestibule, through the helicotrema it is transmitted to the scala tympani and ultimately causes a displacement of the membrane of the cochlear window towards the tympanic cavity. Vibrations of the perilymph through Reissner's vestibular membrane are transmitted to the endolymph and basilar membrane, on which the spiral organ with sensitive hair cells is located. The propagation of a sound wave in the perilymph is possible due to the presence of an elastic membrane of the cochlear window, and in the endolymph - due to the elastic endolymphatic sac communicating with the endolymphatic space of the labyrinth through the endolymphatic duct.

The air route for delivering sound waves to the inner ear is the main one. However, there is another way of conducting sounds to the organ of Corti - bone-tissue, when sound vibrations hit the bones of the skull, spread through them and reach the cochlea.

There are inertial and compression types of bone conduction. When exposed to low sounds, the skull vibrates as a whole, and due to the inertia of the chain auditory ossicles the result is a relative movement of the labyrinth capsule relative to the stapes, which causes a displacement of the fluid column in the cochlea and excitation of the spiral organ. This is an inertial type of bone conduction of sounds. The compression type occurs during the transmission of high-pitched sounds, when the energy of the sound wave causes periodic compression of the labyrinth capsule by the wave, which leads to protrusion of the membrane of the cochlear window and, to a lesser extent, the base of the stapes. Just like air conduction, the inertial path of sound wave transmission requires normal mobility of the membranes of both windows. With the compression type of bone conduction, the mobility of one of the membranes is sufficient.

Vibration of the skull bones can be caused by touching it with a sounding tuning fork or bone telephone of an audiometer. The bone transmission route becomes particularly important when the transmission of sounds through the air is disrupted.

Let's consider the role of individual elements organ of hearing in conducting sound waves.

Auricle plays the role of a kind of collector, directing high-frequency sound vibrations to the entrance to external auditory canal. The auricles also have a certain significance in vertical ototopics. When the position of the auricles changes, the vertical ototopy is distorted, and when they are turned off by introducing hollow tubes into the external auditory canals, it completely disappears. However, this does not impair the ability to localize sound sources horizontally.

External auditory canal is a conductor of sound waves to the eardrum. The width and shape of the external auditory canal do not play a special role in sound transmission. However, complete closure of the lumen of the external auditory canal or its obstruction prevents the propagation of sound waves and leads to a noticeable deterioration in hearing.

In the ear canal close eardrum a constant level of temperature and humidity is maintained regardless of fluctuations in temperature and humidity in the external environment, and this ensures the stability of the elastic properties of the eardrum. In addition, in the external auditory canal there is a selective amplification of 10-12 dB of sound waves with a frequency of about 3 kHz. From a physical point of view, this is explained by the resonant properties of the ear canal, which has a length of about 2.7 cm, which is!/4 wavelengths of the resonant frequency.

In his practice, an otorhinolaryngologist - head and neck surgeon quite often encounters infectious diseases of the outer ear. They can be classified based on location, cause and duration (acute, subacute chronic). Before discussing individual diseases, it is worth recalling the normal anatomy and physiology of the outer ear.

Outer ear represented by the auricle and external auditory canal (EA). They consist of elastic cartilage derived from the mesoderm and a small amount of subcutaneous tissue covered by skin with appendages. The lobe contains fatty tissue, but no cartilage. The auricle develops from six embryonic tubercles, three each from the first and second branchial arches. During normal fetal development, these tubercles fuse to form the auricle. As the lower jaw develops, the auricle moves from the corner of the mouth to the temporal region. The tragus and antitragus form a protective barrier that prevents large foreign bodies from entering the external auditory canal.

External auditory canal originates from the first ectodermal branchial groove located between the mandibular (1) and hyoid (2) arches. The epithelium lining this groove contacts the endoderm of the first pharyngeal pouch, forming the tympanic membrane, which represents the medial border of the external auditory canal. Connective tissue of mesodermal origin, which is located between the ectoderm and endoderm, forms the fibrous layer of the tympanic membrane. The external auditory canal, including the lateral surface of the tympanic membrane, is derived from the ectoderm and is lined by squamous epithelium.

External auditory trip is formed by the 12th week of gestation, at which time it is still filled with epithelial tissue. Recanalization occurs around 28 weeks.

a - Six preauricular tubercles are formed from the first and second gill arches, from which the auricle will then develop.
b - Development of six preauricular tubercles into the cartilaginous skeleton of the auricle.
c - Derivatives of six tubercles. Normal ear.

Outer 40% front and bottom external auditory canal consist of cartilage tissue; here between the cartilage and the skin there is a thin layer of subcutaneous fat. The medial 60% of the external auditory canal is represented by bone tissue, the main mass is represented by the tympanic ring; the amount of soft tissue between the skin and periosteum in this area is minimal. The average length of the external auditory canal of an adult is 2.5 cm. Since the eardrum is located obliquely, the posterior superior part of the auditory canal is approximately 6 mm shorter than the anterior inferior part.

The bottleneck ear canal is located at the junction of its bone and cartilaginous parts, which is called the isthmus.

In transverse direction of the ear canal makes a slight bend up and back in the shape of the letter “S”. Protection of the external auditory canal and tympanic membrane is provided by three anatomical factors: the presence of the tragus and antitragus, the skin of the auditory canal and the sulfur glands contained in it, as well as the isthmus of the external auditory canal.

In the skin cartilaginous part of the external auditory canal there are many sebaceous and apocrine glands (). Hair also grows here. These structures also perform a protective function; together they are called the apocrine-sebaceous complex. The secretions of the glands, mixing with the deflated epithelium, form sulfur masses with an acidic pH, which serve as the main barrier against infection.

Intussusception epidermis forms the outer wall of the hair follicle, and the hair shaft forms the inner wall. Between them is the follicular canal. The alveoli of the sebaceous and apocrine glands secrete their products into short, straight efferent ducts, which open into the follicular canal. Blockage in any of these areas predisposes to the development of infection.

Normal external auditory canal has the properties of self-defense and self-purification. The wax slowly moves from the isthmus to the lateral part of the external auditory canal and then leaves it. Manipulation in the ear canal and overly active hygiene procedures disrupt these normal protective mechanisms and contribute to the development of infection. Individual anatomical factors may contribute to the accumulation of wax in the ear canal.

External auditory canal along its entire length (except for the lateral surface) it borders on other anatomical formations. On the medial side it is limited by the eardrum, which, provided it is intact, is a reliable barrier against infection. A horseshoe-shaped tympanic ring separates the auditory meatus from the middle cranial fossa. The posterior wall of the external auditory canal borders the mastoid process.

Through external auditory canal there are several blood vessels (primarily in the area of ​​the tympanomastoid suture), which can contribute to the spread of infection from the external auditory canal to the mastoid process. Posterior to the cartilaginous part of the external auditory canal, its dense connective tissue extends to the mastoid process, which can cause secondary infection.

Above external auditory canal borders on the middle cranial fossa, and below - on the infratemporal fossa and the base of the skull. The infectious process can spread to these structures. Anterior to the external auditory canal lie the temporomandibular joint and the parotid salivary gland.

Lymphatic vessels of the outer ear are also a channel for the spread of infection. From the upper and anterior part of the external auditory canal, lymph drainage goes to the preauricular lymph nodes of the parotid salivary gland and to the upper deep cervical lymph nodes. From the lower part of the auditory canal, lymph flows into the infraauricular lymph nodes located near the angle of the lower jaw. Posteriorly, the lymph flow goes to the postauricular and upper deep cervical lymph nodes.

The external auditory canal and pinna receive blood supply from the superficial temporal and posterior auricular branches of the external carotid artery. Venous outflow goes through the veins of the same name. The superficial temporal vein drains into the mandibular vein, which then usually divides and joins both jugular veins. The posterior auricular vein in most cases flows into the external jugular vein, but sometimes blood from it flows into the sigmoid sinus through the emissary mastoid vein.

Sensory innervation external auditory canal and auricle is provided by cutaneous and cranial nerves. The auriculotemporal branches of the trigeminal nerve (V), facial nerve (VII), glossopharyngeal nerve (IX), vagus nerve (X), and the greater auricular cervical plexus nerve (C2-C3) are involved. The vestigial muscles of the auricle - anterior, superior and posterior - are innervated by the facial nerve (VII).