The human ear is a unique organ, quite complex in its structure. But at the same time, the method of its work is very simple. The organ of hearing receives sound signals, amplifies them and converts them from ordinary mechanical vibrations into electrical nerve impulses. The anatomy of the ear is represented by many complex constituent elements, the study of which is divided into a whole science.
Everyone knows that the ears are a pair of organs located in the temporal part of the human skull. But a person cannot see the structure of the ear in full, since the auditory canal is located quite deep. Only the ears are visible. The human ear is capable of perceiving sound waves up to 20 meters in length or 20,000 mechanical vibrations per unit time.
The hearing organ is responsible for the ability to hear in the human body. In order for this task to be completed in accordance with its original purpose, the following anatomical components exist:
Human ear
- , presented in the form auricle and ear canal;
- , consisting of the eardrum, a small cavity of the middle ear, a system of auditory ossicles, and the Eustachian tube;
- Inner ear, formed from a transducer of mechanical sounds and electrical nerve impulses - the cochlea, as well as a system of labyrinths (regulators of balance and position of the human body in space).
Also, the anatomy of the ear is represented by the following structural elements of the auricle: helix, antihelix, tragus, antitragus, earlobe. The clinical one is physiologically attached to the temple by special muscles called vestigial muscles.
This structure of the hearing organ is susceptible to the influence of external negative factors, as well as the formation of otohematomas, inflammatory processes etc. Ear pathologies include congenital diseases, which are characterized by underdevelopment of the auricle (microtia).
Outer ear
The clinical form of the ear consists of the outer and middle sections, as well as the inner part. All these anatomical components of the ear are aimed at performing vital functions.
The human outer ear is formed by the pinna and the outer ear canal. The auricle is presented in the form of elastic, dense cartilage, covered with skin on top. Below you can see the earlobe - a single fold of skin and fatty tissue. The clinical form of the auricle is quite unstable and extremely sensitive to any mechanical damage. It is not surprising that professional athletes experience acute form deformation of the auricle.
The auricle serves as a kind of receiver for mechanical signals. sound waves and frequencies that surround a person everywhere. It is she who is the repeater of signals from outside world into the ear canal. If in animals the auricle is very mobile and plays the role of a barometer of dangers, then in humans everything is different.
The concha of the hearing organ is lined with folds that are designed to receive and process distortions of sound frequencies. This is necessary so that the brain can perceive the information necessary for navigation. The auricle acts as a kind of navigator. Also, this anatomical element of the ear has the function of creating surround stereo sound in the ear canal.
The auricle is capable of detecting sounds that travel at a distance of 20 meters from a person. This is achieved due to the fact that it is directly connected to the ear canal. Next, the cartilage of the passage is converted into bone tissue. 
The ear canal contains cerumen glands, which are responsible for the production of earwax, which is necessary to protect against the influence of pathogenic microorganisms. Sound waves that are perceived by the auricle penetrate the ear canal and hit the eardrum.
To avoid rupture of the eardrum during air travel, explosions, higher level noise, etc. Doctors recommend opening your mouth to push the sound wave away from the membrane.
All vibrations of noise and sound come from the auricle to the middle ear.
Structure of the middle ear
The clinical form of the middle ear is presented in the form of a tympanic cavity. This vacuum space is localized near the temporal bone. This is where they are located auditory ossicles, called as malleus, incus, stirrup. All these anatomical elements are aimed at converting noise in the direction of their outer ear into the inner ear.
Structure of the middle ear
If we examine in detail the structure of the auditory ossicles, we can see that they are visually presented in the form of a series-connected chain that transmits sound vibrations. The clinical manubrium of the sensory organ is closely attached to the tympanic membrane. Further, the head of the malleus is attached to the incus, and that to the stirrup. Disruption of any physiological element leads to functional disorder organ of hearing.
The middle ear is anatomically connected to the upper respiratory tract, namely with the nasopharynx. The connecting link here is the Eustachian tube, which regulates the pressure of air supplied from outside. If the ambient pressure sharply increases or decreases, then a person’s ears naturally become blocked. This is the logical explanation for the painful sensations a person experiences when the weather changes.
Strong headache, bordering on migraine, suggests that the ears at this time are actively protecting the brain from damage.
A change in external pressure reflexively causes a reaction in a person in the form of yawning. To get rid of it, doctors advise swallowing saliva several times or blowing sharply into a pinched nose.
The inner ear is the most complex in its structure, which is why in otolaryngology it is called the labyrinth. This organ human ear consists of the vestibule of the labyrinth, cochlea, and semicircular tubules. Further, the division follows the anatomical forms of the labyrinth of the inner ear.
Inner ear model
The vestibule or membranous labyrinth consists of the cochlea, utricle and sac, connected to form the endolymphatic duct. There is also a clinical form of receptor fields here. Next, we can consider the structure of organs such as the semicircular canals (lateral, posterior and anterior). Anatomically, each of these canals has a pedicle and an ampullary end.
The inner ear is presented in the form of a cochlea, the structural elements of which are the scala vestibule, cochlear duct, scala tympani, and organ of Corti. It is in the spiral or organ of Corti that pillar cells are localized.
Physiological features
The organ of hearing has two main purposes in the body, namely maintaining and forming the balance of the body, as well as accepting and transforming surrounding noise and vibrations into sound forms.
In order for a person to be in balance both at rest and during movement, the vestibular apparatus functions 24 hours a day. But not everyone knows that the clinical form of the inner ear is responsible for the ability to walk on two limbs, following a straight line. This mechanism is based on the principle of communicating vessels, which are represented in the form of hearing organs.
The ear contains the semicircular canals, which maintain fluid pressure in the body. If a person changes the position of the body (state of rest, movement), then clinical structure The ear “adjusts” to these physiological conditions by regulating intracranial pressure.
The body is at rest due to such organs of the inner ear as the uterus and saccule. Due to the constantly moving fluid in them, nerve impulses are transmitted to the brain.
Clinical support for the body's reflexes is also provided by muscle impulses supplied by the middle ear. Another complex of ear organs is responsible for concentrating attention on a specific object, that is, it takes part in performing the visual function.
Based on this, we can say that the ear is an irreplaceable, priceless organ. human body. Therefore, it is so important to monitor his condition and promptly contact specialists if there are any hearing pathologies.
The ear performs two main functions: the organ of hearing and the organ of balance. The organ of hearing is the main information system that takes part in the formation speech function, therefore, human mental activity. There are external, middle, and inner ears.
External ear - auricle, external auditory canal
Middle ear – tympanic cavity, auditory tube, mastoid process
Inner ear (labyrinth) - cochlea, vestibule and semicircular canals.
The outer and middle ear provide sound conduction, and inner ear receptors of both the auditory and vestibular analyzers are located.
Outer ear. The auricle is a curved plate of elastic cartilage, covered on both sides by perichondrium and skin. The auricle is a funnel that provides optimal perception of sounds in a certain direction of sound signals. It also has significant cosmetic value. Such anomalies of the auricle are known as macro- and microotia, aplasia, protrusion, etc. Disfigurement of the auricle is possible with perichondritis (trauma, frostbite, etc.). Its lower part - the lobe - is devoid of cartilage and contains fatty tissue. In the auricle there are distinguished helix (helix), antihelix (anthelix), tragus (tragus), antitragus (antitragus). The helix is part of the external auditory canal. The external auditory canal in an adult consists of two sections: the external - membranous-cartilaginous, equipped with hairs, sebaceous glands and their modifications - earwax glands (1/3); internal – bone, not containing hair and glands (2/3).
The topographic-anatomical relationships of the parts of the auditory canal have clinical significance. Front wall – borders on the articular capsule of the lower jaw (important for external otitis and injuries). From below – The parotid gland is adjacent to the cartilaginous part. The anterior and lower walls are pierced by vertical slits (Santorini slits) in an amount from 2 to 4, through which suppuration can pass from the parotid gland to the auditory canal, as well as in the opposite direction. Rear – borders the mastoid process. The descending part of the facial nerve passes deep into this wall (radical surgery). Upper – borders on the middle cranial fossa. Superior posterior – is the anterior wall of the antrum. Its omission indicates purulent inflammation cells of the mastoid process.
The outer ear is supplied with blood from the external carotid artery due to the superficial temporal (a. temporalis superficialis), occipital (a. occipitalis), posterior auricular and deep auricular arteries (a. auricularis posterior et profunda). Venous outflow is carried out into the superficial temporal (v. temporalis superficialis), external jugular (v. jugularis ext.) and jaw (v. maxillaris) veins. Lymph is drained to the lymph nodes located on the mastoid process and anterior to the auricle. Innervation is carried out by branches of the trigeminal and vagus nerves, as well as from the auricular nerve from the upper cervical plexus. Due to the vagal reflex with sulfur plugs and foreign bodies, cardialgic phenomena and cough are possible.
The boundary between the outer and middle ear is the eardrum. The diameter of the eardrum (Fig. 1) is approximately 9 mm, thickness 0.1 mm. The eardrum serves as one of the walls of the middle ear, tilted forward and downward. In an adult it is oval in shape. B/p consists of three layers:
external - epidermal, is a continuation of the skin of the external auditory canal,
internal - mucous membrane lining the tympanic cavity,
the fibrous layer itself, located between the mucous membrane and the epidermis and consisting of two layers of fibrous fibers - radial and circular.
The fibrous layer is poor in elastic fibers, so the eardrum is low-elastic and can rupture under sudden pressure fluctuations or very strong sounds. Usually, after such injuries, a scar subsequently forms due to the regeneration of the skin and mucous membrane; the fibrous layer does not regenerate.
In the b/p there are two parts: tense (pars tensa) and loose (pars flaccida). The tense part is inserted into the bone tympanic ring and has a middle fibrous layer. Loose or relaxed, it is attached to a small notch of the lower edge of the squama of the temporal bone; this part does not have a fibrous layer.
On otoscopic examination, the color of the b/p is pearlescent or pearl-gray with a slight sheen. For the convenience of clinical otoscopy, the b/p is mentally divided into four segments (anterosuperior, anterioinferior, posterosuperior, posteroinferior) by two lines: one is a continuation of the handle of the hammer to the lower edge of the b/p, and the second runs perpendicular to the first through the navel of the b/p.
Middle ear. The tympanic cavity is a prismatic space in the thickness of the base of the pyramid of the temporal bone with a volume of 1-2 cm³. It is lined with a mucous membrane that covers all six walls and from behind passes into the mucous membrane of the mastoid cells, and in front into the mucous membrane of the auditory tube. It is represented by single-layer squamous epithelium, with the exception of the mouth of the auditory tube and the bottom of the tympanic cavity, where it is covered with ciliated columnar epithelium, the movement of the cilia is directed towards the nasopharynx.
External (membranous) The wall of the tympanic cavity over a larger extent is formed by the inner surface of the ear canal, and above it - by the upper wall of the bony part of the auditory canal.
Internal (labyrinth) the wall is also the outer wall of the inner ear. In its upper section there is a window of the vestibule, closed by the base of the stapes. Above the window of the vestibule there is a protrusion of the facial canal, below the window of the vestibule there is a round-shaped elevation called the promontory (promontorium), corresponding to the protrusion of the first curl of the cochlea. Below and posterior to the promontory there is a fenestra cochlea, closed by a secondary b/p.
Upper (tire) the wall is a rather thin bone plate. This wall separates the middle cranial fossa from the tympanic cavity. Dehiscences are often found in this wall.
Lower (jugular) wall - formed by the petrous part of the temporal bone and is located 2–4.5 mm below the b/p. It borders on the bulb of the jugular vein. Often in the jugular wall there are numerous small cells that separate the bulb of the jugular vein from the tympanic cavity; sometimes dehiscence is observed in this wall, which facilitates the penetration of infection.
Anterior (sleepy) the wall in the upper half is occupied by the tympanic orifice of the auditory tube. Its lower part borders the canal of the internal carotid artery. Above the auditory tube is the hemicanal of the tensor tympani muscle (m. tensoris tympani). The bone plate separating the internal carotid artery from the mucous membrane of the tympanic cavity is penetrated by thin tubules and often has dehiscence.
Posterior (mastoid) the wall borders the mastoid process. In the upper section of its back wall there is an entrance to the cave. The canal of the facial nerve passes deep into the posterior wall; the stapedius muscle begins from this wall.
Clinically, the tympanic cavity is conventionally divided into three sections: lower (hypotympanum), middle (mesotympanum), upper or attic (epitympanum).
The auditory ossicles, which are involved in sound conduction, are located in the tympanic cavity. The auditory ossicles - malleus, incus, stapes - are a closely connected chain located between the tympanic membrane and the window of the vestibule. And through the window of the vestibule, the auditory ossicles transmit sound waves to the fluid of the inner ear.
Hammer – it distinguishes between a head, a neck, a short process and a handle. The handle of the malleus is fused with the anvil, a short process protrudes outward from the upper portion of the anvil, and the head articulates with the body of the incus.
Anvil – it has a body and two legs: short and long. The short leg is placed at the entrance to the cave. The long leg connects to the stirrup.
Stirrup – it distinguishes head, front and rear legs, connected to each other by a plate (base). The base covers the window of the vestibule and is strengthened with the window using an annular ligament, due to which the stapes is movable. And this ensures the constant transmission of sound waves into the fluid of the inner ear.
Middle ear muscles. Tensor tympani muscle (m. tensor tympani), innervated trigeminal nerve. The stapes muscle (m. stapedius) is innervated by a branch of the facial nerve (n. stapedius). The muscles of the middle ear are completely hidden in the bone canals; only their tendons pass into the tympanic cavity. They are antagonists and contract reflexively, protecting the inner ear from excessive amplitude of sound vibrations. Sensitive innervation of the tympanic cavity is provided by the tympanic plexus.
The auditory or pharyngotympanic tube connects the tympanic cavity with the nasopharynx. The auditory tube consists of bone and membranous-cartilaginous sections, opening into the tympanic cavity and nasopharynx, respectively. The tympanic opening of the auditory tube opens in the upper part of the anterior wall of the tympanic cavity. The pharyngeal opening is located on the lateral wall of the nasopharynx at the level of the posterior end of the inferior turbinate, 1 cm posterior to it. The hole lies in a fossa bounded above and behind by a protrusion of the tubal cartilage, behind which there is a depression - the Rosenmüllerian fossa. The mucous membrane of the tube is covered with multinucleated ciliated epithelium (the movement of the cilia is directed from the tympanic cavity to the nasopharynx).
The mastoid process is a bone formation, the type of structure of which is distinguished: pneumatic, diploetic (consists of spongy tissue and small cells), sclerotic. The mastoid process, through the entrance to the cave (aditus ad antrum), communicates with the upper part of the tympanic cavity - the epitympanum (attic). In the pneumatic type of structure, the following groups of cells are distinguished: threshold, perianthral, angular, zygomatic, perisinous, perifacial, apical, perilabyrinthine, retrolabyrinthine. At the border of the posterior cranial fossa and mastoid cells there is an S-shaped depression to accommodate the sigmoid sinus, which drains venous blood from the brain to the jugular vein bulb. Sometimes the sigmoid sinus is located close to the ear canal or superficially, in this case they speak of sinus previa. This must be kept in mind when performing surgery on the mastoid process.
The blood supply to the middle ear is carried out by branches of the external and internal carotid arteries. Venous blood flows into the pharyngeal plexus, the bulb of the jugular vein and the middle cerebral vein. Lymphatic vessels carry lymph to the retropharyngeal lymph nodes and deep nodes. The innervation of the middle ear comes from the glossopharyngeal, facial and trigeminal nerves.
Due to topographic-anatomical proximity facial nerve Let us trace its course to the formations of the temporal bone. The trunk of the facial nerve is formed in the region of the cerebellopontine triangle and is directed together with the VIII cranial nerve into the internal auditory canal. In the thickness of the petrous part of the temporal bone, near the labyrinth, its petrous ganglion is located. In this area, the greater petrosal nerve branches off from the trunk of the facial nerve, containing parasympathetic fibers for the lacrimal gland. Next, the main trunk of the facial nerve passes through the thickness of the bone and reaches the medial wall of the tympanic cavity, where it turns posteriorly at a right angle (the first genu). The bony (fallopian) nerve canal (canalis facialis) is located above the window of the vestibule, where the nerve trunk can be damaged during surgical interventions. At the level of the entrance to the cave, the nerve in its bone canal is directed steeply downward (second genu) and exits the temporal bone through the stylomastoid foramen (foramen stylomastoideum), breaking up in a fan shape into separate branches, the so-called crow's foot (pes anserinus), innervating the facial muscles. At the level of the second genu, the stapedius departs from the facial nerve, and more caudally, almost at the exit of the main trunk from the stylomastoid foramen, the chorda tympani. The latter passes in a separate tubule, penetrates the tympanic cavity, moving anteriorly between the long leg of the incus and the handle of the malleus, and leaves the tympanic cavity through the petrotympanic (Glaserian) fissure (fissura petrotympanical).
Inner ear lies in the thickness of the pyramid of the temporal bone, two parts are distinguished in it: the bony and membranous labyrinth. The bony labyrinth includes the vestibule, cochlea, and three bony semicircular canals. The bony labyrinth is filled with fluid - perilymph. The membranous labyrinth contains endolymph.
The vestibule is located between the tympanic cavity and the internal auditory canal and is represented by an oval-shaped cavity. The outer wall of the vestibule is the inner wall of the tympanic cavity. The inner wall of the vestibule forms the floor of the internal auditory canal. There are two depressions on it - spherical and elliptical, separated from each other by a vertically running ridge of the vestibule (crista vestibule).
The bony semicircular canals are located in the posteroinferior part of the bone labyrinth in three mutually perpendicular planes. There are lateral, anterior and posterior semicircular canals. These are arched curved tubes in each of which there are two ends or bone legs: expanded or ampullary and unexpanded or simple. The simple bony pedicles of the anterior and posterior semicircular canals join to form a common bony pedicle. The canals are also filled with perilymph.
The bony cochlea begins in the anterioinferior section of the vestibule with a canal that bends spirally and forms 2.5 turns, as a result of which it is called the spiral canal of the cochlea. There is a base and apex of the cochlea. The spiral channel winds around a cone-shaped bone shaft and ends blindly at the apex of the pyramid. The bone plate does not reach the opposite outer wall of the bony cochlea. The continuation of the spiral bone plate is the tympanic plate of the cochlear duct (main membrane), which reaches the opposite wall of the bone canal. The width of the spiral bone plate gradually narrows towards the apex, and the width of the tympanic wall of the cochlear duct increases accordingly. Thus, the shortest fibers of the tympanic wall of the cochlear duct are located at the base of the cochlea, and the longest at the apex.
The spiral bone plate and its continuation, the tympanic wall of the cochlear duct, divide the cochlear canal into two floors: the upper one, the scala vestibule, and the lower one, the scala tympani. Both scalae contain perilymph and communicate with each other through an opening at the apex of the cochlea (helicotrema). The scala vestibule borders the window of the vestibule, closed by the base of the stapes; the scala tympani borders the window of the cochlea, closed by the secondary tympanic membrane. The perilymph of the inner ear communicates with the subarachnoid space through the perilymphatic duct (cochlear aqueduct). In this regard, suppuration of the labyrinth can cause inflammation of the soft meninges.
The membranous labyrinth is suspended in the perilymph, filling the bony labyrinth. In the membranous labyrinth, two apparatuses are distinguished: vestibular and auditory.
The hearing aid is located in the membranous cochlea. The membranous labyrinth contains endolymph and is a closed system.
The membranous cochlea is a spirally wrapped canal - the cochlear duct, which, like the cochlea, makes 2½ turns. In cross section, the membranous cochlea has a triangular shape. It is located in top floor bony cochlea. The wall of the membranous cochlea, bordering the scala tympani, is a continuation of the spiral bone plate - the tympanic wall of the cochlear duct. The wall of the cochlear duct, bordering the scala vestibule - the vestibular plate of the cochlear duct, also extends from the free edge of the bony plate at an angle of 45º. The outer wall of the cochlear duct is part of the outer bony wall of the cochlear canal. On the spiral ligament adjacent to this wall there is a vascular striatum. The tympanic wall of the cochlear duct consists of radial fibers arranged in the form of strings. Their number reaches 15,000 - 25,000, their length at the base of the cochlea is 80 microns, at the apex - 500 microns.
The spiral organ (Corti) is located on the tympanic wall of the cochlear duct and consists of highly differentiated hair cells, supporting columnar cells and supporting Deiters cells.
The upper ends of the inner and outer rows of columnar cells are inclined towards each other, forming a tunnel. The outer hair cell is equipped with 100 - 120 hairs - stereocilia, which have a thin fibrillar structure. The plexuses of nerve fibers around the hair cells are directed through tunnels to the spiral ganglion at the base of the spiral bone plate. There are up to 30,000 ganglion cells in total. The axons of these ganglion cells connect in the internal auditory canal in cochlear nerve. Above the spiral organ is a covering membrane, which begins near the origin of the vestibular wall of the cochlear duct and covers the entire spiral organ in the form of a canopy. Stereocilia of hair cells penetrate the integumentary membrane, which plays a special role in the process of sound reception.
The internal auditory canal begins with the internal auditory opening, located on the posterior edge of the pyramid, and ends with the bottom of the internal auditory canal. It contains the periocochlear nerve (VIII), consisting of the superior vestibular root and the inferior cochlear root. Located above it facial nerve and next to it is the intermediate nerve.
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 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 The eardrum, 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 largest 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. Character oscillatory movements becomes more complex as the frequency and intensity of sound increases.
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, prerequisite in this case, the pressure in the tympanic cavity is equalized with atmospheric pressure, which is carried out when normal functioning 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 eardrum to the footplate of the stapes provides an increase in pressure measured at the footplate 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 air to liquid, 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 over 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. Very high levels stimulation intensity and frequencies exceeding 150 Hz, the footplate of the stapes simultaneously rotates 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 stapes 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 manifested in to the fullest 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 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 cochlear window and the vestibule window are located on opposite sides of the main membrane, positive pressure applied to the cochlear window membrane 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 at bone conduction sounds has a lot practical significance with pathology of the middle ear.
Inner ear
Progress in the study of the anatomy of the inner ear was determined by the development of microscopy methods and, in particular, transmission and scanning electron microscopy.
The 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 oval window, located in the vestibule, to 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 compounds, blood vessels and cells connective tissue(fibrocytes). The zones located close to the spiral ligament and the spiral protrusion include more cellular structures, as well as large 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. Basal cells are attached to the spiral ligament and have flat shape and long processes penetrating 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 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 fluid. 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). Total physical characteristics 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 main 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 some 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 there 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 (PF) ( support system external third row of the NVK (NVKZ)). 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 top ends 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 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 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 rows of V- or W-shape 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 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 large number 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 NVCs.
PS - cross connections; KP - cuticular plate; C - connection within a row; K - root; SC - stereocilium; PM - cover 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 human hearing organ is designed to receive sound signals from outside, convert them into nerve impulses and transmit them to the brain. The structure of the ear and its functions are quite complex, despite the apparent simplicity of the basic principle of operation of all structures. Everyone knows that ears are paired organ, their inner part is in temporal bones on both sides of the skull. With the naked eye you can only see the outer parts of the ear - the well-known auricles, located outside and blocking the view of the complex internal structure human ear.
The structure of the ears
The anatomy of the human ear is studied in biology lessons, so every schoolchild knows that the auditory organ is capable of distinguishing between different vibrations and noises. This is ensured by the structural features of the organ:
- (concha and beginning of the auditory canal);
- human middle ear (tympanic membrane, cavity, Eustachian tube);
- internal (the cochlea, which converts mechanical sounds into impulses understandable to the brain, which serves to maintain the balance of the human body in space).
External, visible part The auditory organ is the pinna. It consists of elastic cartilage tissue, which is closed by a small fold of fat and skin.
It is easily deformed and damaged, often because of this the original structure of the hearing organ is disrupted.
The outer part of the auditory organ is designed to receive and transmit sound waves coming from the surrounding space to the brain. Unlike similar organs in animals, these parts of the hearing organ in humans are practically motionless and do not play any role. additional roles. To carry out the transmission of sounds and create surround sound in the auditory canal, the inside of the shell is completely covered with folds, which help to process any external sound frequencies and noises, which are then transmitted to the brain. The human ear is visually depicted below.
The maximum possible measured distance in meters (m), from where the human hearing organs distinguish and pick up noises, sounds and vibrations, is on average 25-30 m. The auricle helps to do this by direct connection with the ear canal, the cartilage of which at the end turns into bone tissue and goes deep into the skull. The ear canal also contains sulfur glands: the sulfur they produce protects the ear space from pathogenic bacteria and their destructive influence. Periodically, the glands cleanse themselves, but sometimes this process fails. In this case, sulfur plugs are formed. Removing them requires qualified assistance.
“Caught” in the cavity of the auricle sound vibrations move inward along the folds and enter the auditory canal, then collide with the eardrum. That is why when flying by air or traveling in a deep subway, as well as any sound overload, it is better to open your mouth slightly. This will help protect the delicate tissues of the membrane from rupture, pushing the sound entering the hearing organ back with force.
Structure of the middle and inner ear
The middle part of the ear (the diagram below reflects the structure of the hearing organ), located inside the bones of the skull, serves to convert and further send a sound signal or vibration to the inner ear. If you look at the section, you will clearly see that its main parts are a small cavity and auditory ossicles. Each such bone has its own special name, associated with the functions it performs: stapes, malleus and incus.
The structure in this part is special: the auditory ossicles form a single mechanism tuned to the subtle and consistent transmission of sounds. The malleus is connected by its lower part to the eardrum, and its upper part is connected to the incus, connected directly to the stapes. Such a sequential structure of the human ear is fraught with disruption of the entire organ of hearing if even just one element of the chain fails.
The middle part of the ear is connected to the organs of the nose and throat through the Eustachian tubes, which control the air coming from outside and the pressure it exerts. It is these parts of the hearing organ that sensitively detect any pressure changes. An increase or decrease in pressure is felt by a person in the form of stuffy ears. Due to the peculiarities of the anatomy, fluctuations in external atmospheric pressure can provoke reflex yawning. Periodic swallowing can help quickly get rid of this reaction.
This part is located the deepest and is considered the most complex in its anatomy. The inner ear includes the labyrinth and the cochlea. The labyrinth itself is very complex in its structure: it consists of a cochlea, receptor fields, a utricle and a sac, connected together into one duct. Behind them are located semicircular canals of 3 types: lateral, anterior, and posterior. Each such channel includes an ampullary end and a small stalk. The cochlea is a complex of various structures. Here the organ of hearing has the scala vestibule and the scala tympani, and a spiral organ, inside of which the so-called pillar cells are located.
Connection of elements of the auditory organ
Knowing how the ear works, you can understand the essence of its purpose. Hearing organ must perform its functions constantly and uninterruptedly, ensuring adequate retransmission of external noise into sound nerve impulses understandable to the brain and allowing the human body to remain in balance regardless of general position in space. To maintain this function, the vestibular apparatus never stops working, remaining active both day and night. The ability to maintain upright posture is ensured by the anatomical structure of the inner part of each ear, where the internal components embody communicating vessels that operate according to the same principle.
Fluid pressure is maintained by semicircular tubules, which adapt to any change in body position in the surrounding world - be it movement or, conversely, rest. During any movement in space, they regulate intracranial pressure.
The rest of the body is ensured by the utricle and the sac, in which fluid constantly moves, thanks to which nerve impulses enter directly into the brain.
These same impulses support the general reflexes of the human body and the concentration of attention on a specific object, that is, they not only perform the direct functions of the organ of hearing, but also support visual mechanisms.
Ears are one of the most important organs of the human body. Any disruption of its functionality entails severe consequences, affecting the quality of human life. It is important not to forget to monitor the condition of this organ and in case of any unpleasant or unusual sensations, consult with medical workers specializing in this area of medicine. People should always take responsibility for their health.
The functionality of the hearing organs is determined by their rather complex “design”. The work of all structures of the ears, the structure of their departments ensure the reception of sound, its transformation and transmission of processed information to the brain.
To understand how sound from outside is transmitted to the brain, you need to study how the human ear works.
Structure of the outer ear
The structure and functions of the ear should be studied from its visible part. Main task outer ear - sound reception. This part of the organ consists of two elements: the auricle and the ear canal, and ends with the eardrum.
- The auricle is cartilage tissue special shape, covered with a skin-fat layer;
- part of the auricle - the lobe - is devoid of a cartilaginous base and consists entirely of skin and fatty tissue;
- unlike animal ears, human ear practically motionless;
- the shape of the ears allows you to capture sound waves of different frequencies from different distances;
- the shape of the auricle in each person is unique, like fingerprints, but has common parts: the tragus and antitragus, the helix, the legs of the helix, the antihelix;
- passing and reflecting from the labyrinths of curls of the auricle, sound waves emanating from different directions are successfully captured by the auditory organ;
- the ear device serves to amplify received sound waves - their quality is improved in the internal part of the outer part of the organ by special folds covering the ear canal;
- The inside of the ear canal is lined with glands that produce earwax, a substance that protects the organ from the penetration of bacteria;
- to prevent drying of the skin surface inside the ear canal, the sebaceous glands produce a lubricating secretion;
- The ear canal is closed by the eardrum, dividing the external and middle section auditory organ.
The structure of the human ear in this section helps the hearing organ perform its sound-conducting functions. His “job” here is:
- In the collection of sound waves by the ears.
- Transport and amplification of sound in the ear canal.
- The influence of sound waves on the eardrum, which transmits vibrations to the middle ear.
Under bone tissue The middle ear area is located on the skull. Its device allows you to convert sound vibrations received from the eardrum and send them further - to the internal section.
Immediately behind the eardrum, a small cavity opens (no more than 1 sq. cm), in which the auditory ossicles are located, forming a single mechanism: the stapes, the malleus and the incus. They transmit sounds from the eardrum very sensitively and subtly.
The lower part of the malleus is attached to the eardrum, and the upper part is attached to the incus. When sound passes through the outer ear and enters the middle ear, its vibrations are transmitted to the hammer. He, in turn, reacts to them with his movement and hits the anvil with his head.
The anvil amplifies the incoming sound vibrations and transmits them to the stapes associated with it. The latter closes the passage to the inner ear, and with its vibration transmits the received information further.
The structure of the ear and its functionality in this department is not limited only to sound transmission. The Eustachian tube, which connects the nasopharynx to the ear, comes here. Its main function is to equalize pressure in the ENT system.
The anatomy of the human ear becomes much more complicated towards the internal part. It continues the process of amplifying sound vibrations. Here the processing of the received information by nerve receptors begins, which then transmit it to the brain.
The most complex part of the human ears in terms of structure and functionality is the inner part, located deep under the temporal bone. It consists of:
- A labyrinth characterized by the complexity of its construction. This element is divided into two sections - temporal and bone. The labyrinth, thanks to its winding passages, continues to amplify the vibrations entering the organ, increasing their intensity.
- Semicircular tubules, which are presented in three types - lateral, anterior and posterior. They are filled with special lymphatic fluids that absorb the vibrations that the labyrinth transmits to them.
- A snail, also consisting of several components. The scala vestibule, scala tympani, duct and spiral organ serve to amplify the resulting vibrations, and the receptors located on the surface of this element transmit information about the occurring sound vibrations to the brain.
Some researchers believe that the brain, in turn, is able to influence the functioning of receptors located in the cochlea. When we need to concentrate on something and not be distracted by the noise around us, we can nerve fibers an “order” is received that temporarily stops their work.
In normal operating mode, the vibrations transmitted by the stapes through the oval window pass through the labyrinth and are reflected in the lymphatic fluid. Its movements are detected by receptors lining the surface of the cochlea. These fibers are of many types and each of them responds to a certain sound. These receptors convert the received sound vibrations into nerve impulses and transmit them directly to the brain, the processing scheme for what is heard is completed at this stage.
Once in a person’s ears, the structure of which requires high-quality amplification, even the quietest sound becomes available for analysis by the brain - that’s why we perceive whispers and rustles. Thanks to the variety of receptors lining the cochlea, we can hear loud speech against a background of noise and enjoy music, recognizing in it the playing of all instruments at the same time.
The inner ear contains the vestibular apparatus, which is responsible for balance. He carries out his functions around the clock and it works even when we sleep. Components of this important body act as communicating vessels, controlling our position in space.