Clinical anatomy of the middle ear. Functions of the middle ear and possible diseases Structure of the middle ear cavity
The anatomy of the human middle ear is represented by the eardrum and the auditory tube, which connects the hearing organ to the nasopharynx. The cavity of the middle ear is located in the temporal zone between the outer and inner ear. The sound enters the ear canal, is reflected from the membrane and then goes to the labyrinth.
The size of the eardrum and the cavity in which it is located is only one cubic centimeter. Visually, this section resembles a drum, which is slightly tilted in the direction of the ear canal. The ear consists of six walls of the tympanic cavity, in particular:
Hammer and anvil
- The lateral wall, which is located between the eardrum and the bone of the hearing organ. The anatomy of the middle ear is represented by two auditory ossicles, the malleus and the incus. It is in this part of the ear that various inflammatory processes most often occur.
- The medial wall located directly next to the labyrinth. It consists of two windows - round and closed. Both of these openings lead towards the cochlea.
- The posterior wall, covering the tympanic cavity and having a certain elevation. In this section, suppuration usually accumulates, which is the result of an inflammatory process.
- The anterior wall of the eardrum, located in close proximity to the carotid artery, and having a number of internal openings for the passage of the auditory tube. Due to the fact that the anterior wall of the eardrum in children and newborns is anatomically completely open, this increases the risk of infection from the nasal sinuses into the ear of a small person. The danger is that the infectious process can quickly spread to the brain.
- The upper wall of the eardrum, designed to separate the skull and ear.
- The lower wall covering the skull and the middle ear itself.
Nerves, muscles and vessels of the hearing organ
But the structure of the middle ear does not end there. It also contains 3 small auditory ossicles, which are called the malleus, incus and stapes. Where the ear connects to the joints that ensure its mobility is the stapes plate. This place is completely lined with connective tissue, damage to which leads to disruption of the conductivity of the sound signal and subsequently causes hearing loss.
The principle of operation of the middle ear is the complete sound conduction of external noise directly from the eardrum to the so-called window of the vestibule of the ear.
The human middle ear consists of a series of arteries, lymphatic vessels, and nerve clots. The arteries are located in close proximity to the eardrum and its branches. Lymphatic vessels penetrate the human throat and penetrate the ear.
Vessel branches can be observed behind the auricle. Penetration of infection into the nasopharynx in most cases is accompanied by inflammation of the postauricular lymph nodes. The nerve roots, in turn, arise from the carotid artery and penetrate the tympanic plexus.
Pathologies of the hearing organ
Middle ear diseases are the most common among a number of pathologies in otolaryngology. They are extremely difficult due to the fact that the middle ear is located in close proximity to the cranial fossa, nasopharynx and upper respiratory tract. This means that an infection that enters these organs quickly spreads throughout these organs.
All pathological processes affecting the ear affect the brain, nose and throat.
That is why doctors recommend contacting a medical facility as soon as you feel any discomfort in the upper respiratory tract. The same applies to symptoms such as headache, runny nose, noise (ringing) in the ears, etc.
The middle ear reacts very sensitively to any changes in both external and internal pressure. The reaction to such changes may be accompanied by rupture of the eardrum, disorders of the vascular system, and the occurrence of aerootitis.
Classification of inflammatory processes
Absolutely all inflammatory processes of the middle ear can be classified according to the form of their occurrence into acute and chronic, occurring with or without complications, hematogenous and tubogenic, as well as specific and not.
The most common pathologies of the middle ear are the following:
- Catarrh of the ear, occurring in an acute form;
- Chronic catarrh;
- Inflammatory process of the middle ear;
- Catarrhal inflammation occurring in a non-perforative form;
- An allergic reaction expressed as otitis media;
- Mastoiditis;
- Mechanical damage to the ear;
- Concussion processes;
- Injuries of various natures affecting the temporal region;
- Mesotympanitis;
- Flu;
- Syphilis and tuberculosis of the middle ear.
Symptoms of inflammatory processes in the hearing organ
Diseases of the middle ear occur mainly in the form of catarrhal and purulent otitis media. The cause of catarrhal otitis lies in dysfunction of the auditory tube. As a result of this process, the ear begins to fill with purulent discharge. This pathology occurs in a relatively mild form and does not cause severe complications. If the disease is not identified in time, it develops into a chronic form called exudative otitis media.
Purulent otitis, characterized by a serious inflammatory process, is almost always characterized by a complication. In this case, correct and accurate diagnosis, as well as subsequent treatment, lead to a complete recovery. Timely therapy allows you to eliminate the general symptoms of the pathology and close the cavity of the eardrum. As a rule, hearing is restored in 95% of clinical cases.
Acute purulent otitis may develop in a different way. If exudate in the form of pus begins to accumulate in the ear canal, this leads to the formation of adhesions. This disease is aggravated by an imaginary recovery, during which the person begins to feel much lighter. As a rule, if the symptoms disappear, this does not mean that the pathology has receded.
The condition of the tympanic cavity may return to normal for some time, but the perforation does not close completely and does not even scar. The course of the disease must be monitored throughout the year, as the main symptoms may appear after a few months.
If acute purulent otitis media resumes after some time, then this pathology is called recurrent otitis media. This form of the disease is extremely dangerous, because in addition to hearing loss, a person may experience scarring of the eardrum and its subsequent perforation.
If you experience discomfort in the ear area, headaches, increased pressure in the temporal region, as well as previous traumatic brain injuries and other inflammatory processes, you must urgently make an appointment with an otolaryngologist. Diagnosis should be aimed not only at examining the middle ear, but also at examining the degree of sound perception. Be sure to insist on an audiogram, which will identify hearing loss at an early stage.
The human ear has a very complex anatomical structure that allows it to capture sound waves, determine the direction of the sound source and correctly identify it. It consists of three main sections: the outer, middle and inner ear. Each of which has strictly defined functions and a special structure. The human middle ear primarily performs the conversion of sound waves into nerve impulses. This is its main, but not the only function.
General structure and operating principle
The middle ear begins just behind the eardrum, which is located at the end of the ear canal and separates it from the outer ear. The middle ear consists of three main elements:
- tympanic cavity;
- mastoid processes;
- auditory tube
The eardrum is a small piece of thin connective tissue that is directly involved in converting sound waves received by the outer ear.
The tympanic cavity of the middle ear is located in the recess of the temporal bone. Inside it, in close proximity, are the three smallest bones of the human skeleton: the malleus, stirrup and incus. Acoustic waves cause the eardrum to vibrate, and these vibrations are transmitted to the bones. And the stirrup sends a signal through the oval window to the fluid that fills the inner ear - perilymph.
Interestingly, the design of the auditory ossicles allows not only transmission, but also significantly amplification of sound. The surface of the stapes is an order of magnitude smaller than the area of the eardrum, which means it hits the oval window much stronger, giving a person the opportunity to hear even very quiet sounds.
Protective functions of the middle ear
The functions of the middle ear are not limited to sound conduction. It is also a reliable protective barrier that protects the delicate inner ear from:
- ingress of moisture, dust and dirt particles;
- penetration and reproduction of pathogenic microorganisms;
- too intense exposure to sound waves;
- sudden changes in atmospheric pressure;
- mechanical impact.
The middle ear cavity is filled with air and connects to the nasopharynx via the Eustachian tube. Under normal conditions, there is equal air pressure on both sides of the eardrum. But if the atmospheric pressure changes sharply in any direction, then this stretches the eardrum and can lead to its rupture.
This phenomenon is called barotrauma. The same thing happens when you suddenly dive to great depths. To prevent barotrauma, the dive should be done slowly. And when taking off or landing a plane, open your mouth slightly or make frequent swallowing movements.
The anatomy of the middle ear allows for partial compensation of loud sounds. It houses two very small muscles, one of which controls the tension of the eardrum, and the other controls the amplitude of oscillation of the stapes. The protective mechanism inherent in nature ensures a reflex contraction of these muscles when sounds are too loud. The movement of the stapes is limited and ear sensitivity is temporarily reduced. It takes about 10 ms to trigger. Therefore, during explosions, gunshots and other rapid sounds, it does not have time to compensate for the noise.
Middle ear diseases
The structure of the middle ear is such that when it is diseased, the normal conductivity of sound is primarily affected and the threshold of hearing sensitivity is sharply reduced. Inner ear diseases are most often caused by injury, hypothermia, or exposure to pathogenic microorganisms.
Moreover, viruses and bacteria can enter the ear not only through the external auditory canal, but also from the mouth or nose through the Eustachian tube. This is why ARVI, influenza, rubella, and sore throat are often complicated by otitis media.
Among the most common diseases of the middle ear, doctors note:
- acute and chronic otitis;
- barotrauma;
- mechanical injuries;
- congenital pathologies;
- hearing loss 1-4 degrees.
Especially dangerous is purulent otitis media, which, if not properly treated, can lead to inflammation of the meninges (meningitis) and even general blood poisoning (sepsis). Pus accumulates behind the eardrum and presses on it, causing severe pain. Sometimes it is partially perforated, and in some cases it is completely ruptured, which can lead to partial or complete hearing loss.
Unfortunately, the structure of the middle ear is such that diseases appear already at the stage when the inflammatory process has developed. The main symptoms of disease of this organ are: sharp shooting pain, increased body temperature, often redness of the tragus, headache, and periodic dizziness.
With otitis media, pus or yellowish exudate with an unpleasant odor may be released from the ear. If these symptoms appear, you should immediately consult a doctor. Delay and improper treatment can have very serious consequences.
The middle ear consists of cavities and canals communicating with each other: the tympanic cavity, the auditory (Eustachian) tube, the passage to the antrum, the antrum and the cells of the mastoid process (Fig.). The boundary between the outer and middle ear is the eardrum (see).
Rice. 1. Lateral wall of the tympanic cavity. Rice. 2. Medial wall of the tympanic cavity. Rice. 3. Section of the head, carried out along the axis of the auditory tube (lower part of the cut): 1 - ostium tympanicum tubae audltivae; 2 - tegmen tympani; 3 - membrane tympani; 4 - manubrium mallei; 5 - recessus epitympanicus; 6 -caput mallei; 7 -incus; 8 - cellulae mastoldeae; 9 - chorda tympani; 10 - n. facialis; 11 - a. carotis int.; 12 - canalis caroticus; 13 - tuba auditiva (pars ossea); 14 - prominentia canalis semicircularis lat.; 15 - prominentia canalis facialis; 16 - a. petrosus major; 17 - m. tensor tympani; 18 - promontorium; 19 - plexus tympanicus; 20 - steps; 21- fossula fenestrae cochleae; 22 - eminentia pyramidalis; 23 - sinus sigmoides; 24 - cavum tympani; 25 - entrance to meatus acustlcus ext.; 26 - auricula; 27 - meatus acustlcus ext.; 28 - a. et v. temporales superficiales; 29 - glandula parotis; 30 - articulatio temporomandibularis; 31 - ostium pharyngeum tubae auditivae; 32 - pharynx; 33 - cartilago tubae auditivae; 34 - pars cartilaginea tubae auditivae; 35 - n. mandibularis; 36 - a. meningea media; 37 - m. pterygoideus lat.; 38 - in. temporalis.
The middle ear consists of the tympanic cavity, the eustachian tube and the mastoid air cells.
Between the outer and inner ear is the tympanic cavity. Its volume is about 2 cm3. It is lined with mucous membrane, filled with air and contains a number of important elements. Inside the tympanic cavity there are three auditory ossicles: the malleus, the incus and the stirrup, so named for their resemblance to the indicated objects (Fig. 3). The auditory ossicles are connected to each other by movable joints. The hammer is the beginning of this chain; it is woven into the eardrum. The anvil occupies a middle position and is located between the malleus and stapes. The stapes is the final link in the chain of auditory ossicles. On the inside of the tympanic cavity there are two windows: one is round, leading into the cochlea, covered by a secondary membrane (unlike the already described tympanic membrane), the other is oval, into which a stirrup is inserted, as if in a frame. The average weight of the malleus is 30 mg, the incus is 27 mg, and the stapes is 2.5 mg. The malleus has a head, a neck, a short process and a handle. The handle of the hammer is woven into the eardrum. The head of the malleus is connected to the incus joint. Both of these bones are suspended by ligaments from the walls of the tympanic cavity and can move in response to vibrations of the eardrum. When examining the tympanic membrane, a short process and the handle of the malleus are visible through it.
Rice. 3. Auditory ossicles.
1 - anvil body; 2 - short process of the incus; 3 - long process of the anvil; 4 - rear leg of the stirrup; 5 - foot plate of the stirrup; 6 - hammer handle; 7 - anterior process; 8 - neck of the malleus; 9 - head of the hammer; 10 - malleus-incus joint.
The anvil has a body, short and long processes. With the help of the latter, it is connected to the stirrup. The stirrup has a head, a neck, two legs and a main plate. The handle of the malleus is woven into the eardrum, and the footplate of the stapes is inserted into the oval window, thereby forming a chain of auditory ossicles. Sound vibrations travel from the eardrum to the chain of auditory ossicles, which form a lever mechanism.
There are six walls in the tympanic cavity; The outer wall of the tympanic cavity is mainly the eardrum. But since the tympanic cavity extends upward and downward beyond the tympanic membrane, bone elements, in addition to the tympanic membrane, also participate in the formation of its outer wall.
The upper wall - the roof of the tympanic cavity (tegmen tympani) - separates the middle ear from the cranial cavity (middle cranial fossa) and is a thin bone plate. The inferior wall, or floor of the tympanic cavity, is located slightly below the edge of the eardrum. Below it is the bulb of the jugular vein (bulbus venae jugularis).
The posterior wall borders the pneumatic system of the mastoid process (antrum and cells of the mastoid process). The descending part of the facial nerve passes through the posterior wall of the tympanic cavity, from which the auricular chord (chorda tympani) arises here.
The anterior wall in its upper part is occupied by the mouth of the Eustachian tube, connecting the tympanic cavity with the nasopharynx (see Fig. 1). The lower section of this wall is a thin bone plate that separates the tympanic cavity from the ascending segment of the internal carotid artery.
The inner wall of the tympanic cavity simultaneously forms the outer wall of the inner ear. Between the oval and round windows there is a protrusion on it - a promontory (promontorium), corresponding to the main curl of the cochlea. On this wall of the tympanic cavity above the oval window there are two elevations: one corresponds to the facial nerve canal passing here directly above the oval window, and the second corresponds to the protrusion of the horizontal semicircular canal, which lies above the facial nerve canal.
There are two muscles in the tympanic cavity: the stapedius muscle and the tensor tympani muscle. The first is attached to the head of the stapes and is innervated by the facial nerve, the second is attached to the handle of the malleus and is innervated by a branch of the trigeminal nerve.
The Eustachian tube connects the tympanic cavity with the nasopharynx cavity. In the unified International Anatomical Nomenclature, approved in 1960 at the VII International Congress of Anatomists, the name “Eustachian tube” was replaced by the term “auditory tube” (tuba anditiva). The eustachian tube has bony and cartilaginous parts. It is covered with a mucous membrane lined with ciliated columnar epithelium. The cilia of the epithelium move towards the nasopharynx. The length of the pipe is about 3.5 cm. In children, the pipe is shorter and wider than in adults. In a calm state, the tube is closed, since its walls in the narrowest place (at the place where the bone part of the tube transitions into the cartilaginous part) are adjacent to each other. When swallowing movements, the tube opens and air enters the tympanic cavity.
The mastoid process of the temporal bone is located behind the auricle and external auditory canal.
The outer surface of the mastoid process consists of compact bone tissue and ends at the bottom with an apex. The mastoid process consists of a large number of air (pneumatic) cells separated from each other by bony septa. Often there are mastoid processes, the so-called diploetic ones, when their basis is spongy bone, and the number of air cells is insignificant. In some people, especially those suffering from chronic suppurative disease of the middle ear, the mastoid process consists of dense bone and does not contain air cells. These are the so-called sclerotic mastoid processes.
The central part of the mastoid process is a cave - the antrum. It is a large air cell that communicates with the tympanic cavity and with other air cells of the mastoid process. The upper wall, or roof of the cave, separates it from the middle cranial fossa. In newborns, the mastoid process is absent (not yet developed). It usually develops in the 2nd year of life. However, the antrum is also present in newborns; it is located above the ear canal, very superficially (at a depth of 2-4 mm) and subsequently moves posteriorly and downward.
The upper border of the mastoid process is the temporal line - a protrusion in the form of a roller, which is like a continuation of the zygomatic process. In most cases, the floor of the middle cranial fossa is located at the level of this line. On the inner surface of the mastoid process, which faces the posterior cranial fossa, there is a grooved depression in which the sigmoid sinus is located, which drains venous blood from the brain to the bulb of the jugular vein.
The middle ear is supplied with arterial blood mainly from the external and to a lesser extent from the internal carotid arteries. The innervation of the middle ear is carried out by the branches of the glossopharyngeal, facial and sympathetic nerves.
The human ear is a unique organ that functions on a pair basis, which is located in the very depths of the temporal bone. The anatomy of its structure allows it to capture mechanical vibrations in the air, as well as transmit them through internal environments, then convert sound and transmit it to the brain centers.
According to the anatomical structure, the human ears can be divided into three parts, namely the outer, middle and inner.
Elements of the middle ear
Studying the structure of the middle part of the ear, you can see that it is divided into several components: the tympanic cavity, the ear tube and the auditory ossicles. The latter include the anvil, malleus and stirrup.
Hammer of the middle ear
This part of the auditory ossicles includes elements such as the neck and manubrium. The head of the malleus is connected through the malleus joint to the structure of the body of the incus. And the handle of this hammer is connected to the eardrum by fusion with it. A special muscle is attached to the neck of the malleus, which stretches the eardrum of the ear.
Anvil
This element of the ear has at its disposal a length of six to seven millimeters, which consists of a special body and two legs with short and long sizes. The one that is short has a lenticular process that fuses with the incus stapes joint and with the head of the stapes itself.
What else does the auditory ossicle of the middle ear include?
Stirrup
The stirrup has a head, as well as front and rear legs with part of the base. The stapedius muscle is attached to its posterior leg. The base of the stapes itself is built into the oval-shaped window of the vestibule of the labyrinth. The annular ligament in the form of a membrane, which is located between the supporting base of the stapes and the edge of the oval window, helps ensure the mobility of this auditory element, which is ensured by the action of air waves directly on the eardrum.
Anatomical description of the muscles attached to the bones
Two transverse striated muscles are attached to the auditory ossicles, which perform certain functions for transmitting sound vibrations.
One of them stretches the eardrum and originates from the walls of the muscular and tubal canals related to the temporal bone, and then it is attached to the neck of the malleus itself. The function of this tissue is to pull the hammer handle inward. Tension occurs to the side. In this case, the eardrum is tensed and therefore it is, as it were, stretched and concave in the region of the middle ear.
Another muscle of the stapes originates in the thickness of the pyramidal increase in the mastoid wall of the tympanic region and is attached to the leg of the stapes, located posteriorly. Its function is to contract and remove the base of the stapes itself from the hole. During powerful vibrations of the auditory ossicles, along with the previous muscle, the auditory ossicles are held, which significantly reduces their displacement.
The auditory ossicles, which are connected by joints, and, in addition, the muscles related to the middle ear, completely regulate the movement of air flows at different levels of intensity.
Tympanic cavity of the middle ear
In addition to the ossicles, the structure of the middle ear also includes a certain cavity, which is commonly called the tympanum. The cavity is located in the temporal part of the bone, and its volume is one cubic centimeter. The auditory ossicles with the eardrum nearby are located in this area.
Above the cavity is placed which consists of cells carrying air currents. It also contains a certain cave, that is, a cell through which air molecules move. In the anatomy of the human ear, this area serves as the most characteristic landmark when performing any surgical interventions. How the auditory ossicles are connected is of interest to many.
Eustachian tube in the anatomy of the human middle ear structure
This area is a formation that can reach a length of three and a half centimeters, and the diameter of its lumen can be up to two millimeters. Its upper origin is located in the tympanic region, and the lower pharyngeal opening opens in the nasopharynx approximately at the level of the hard palate.
The auditory tube consists of two sections, which are separated by the narrowest point in its area, the so-called isthmus. A bony part extends from the tympanic region, which extends below the isthmus; it is usually called membranous-cartilaginous.
The walls of the tube, located in the cartilaginous section, are usually closed when at rest, but when chewing they can open slightly, this can also happen during swallowing or yawning. The increase in the lumen of the tube occurs through two muscles that are associated with the palatine curtain. The shell of the ear is covered with epithelium and has a mucous surface, and its cilia move towards the pharyngeal mouth, which allows the drainage function of the pipe to be performed.
Other facts about the auditory ossicle in the ear and the structure of the middle ear
The middle ear is directly connected to the nasopharynx through the Eustachian tube, whose immediate function is to regulate pressure that does not come from the air. A sharp popping of human ears can signal a transient decrease or increase in environmental pressure.
Long and prolonged pain in the temples most likely indicates that the ears are currently trying to actively fight the infection that has arisen and thus protect the brain from all sorts of disruptions to its performance.
Internal auditory ossicle
Fascinating facts of pressure also include reflex yawning, which signals that there have been sharp changes in the environment around a person, and therefore a reaction in the form of yawning has been caused. You should also know that the human middle ear contains a mucous membrane in its structure.
We should not forget that unexpected, even sharp sounds can provoke muscle contraction on a reflex basis and harm both the structure and functioning of hearing. The functions of the auditory ossicles are unique.
All of these structures carry within them the functionality of the auditory ossicles, such as the transmission of perceived noise, as well as its transfer from the outer region of the ear to the inner. Any disruption or failure of the functioning of at least one of the buildings can lead to complete destruction of the hearing organs.
Inflammation of the middle ear
The middle ear is a small cavity between the inner ear and the middle ear, which transforms air vibrations into fluid vibrations, which are registered by auditory receptors in the inner ear. This occurs with the help of special bones (hammer, incus, stirrup) due to sound vibration from the eardrum to the auditory receptors. To equalize the pressure between the cavity and the environment, the middle ear communicates with the nose through the Eustachian tube. The infectious agent penetrates this anatomical structure and provokes inflammation - otitis media.
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 development of speech function, and 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 ears provide sound conduction, and the inner ear contains receptors for both the auditory and vestibular analyzers.
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 are of clinical importance. 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 descent indicates purulent inflammation of the mastoid cells.
The external ear is supplied with blood from the external carotid artery system through 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 in the back 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. A 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. The tensor tympani muscle is innervated by the 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 to 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 anteroinferior section of the vestibule with a canal that bends spirally and forms 2.5 turns, which is why 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 the upper floor of the 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 strip. 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 to the 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. Above it is the facial nerve and next to it is the intermediate nerve.
