Everyone knows that the human ear has a complex structure: outer, middle and inner ear. The middle ear plays an important role in the entire auditory process, as it performs a sound-conducting function. Diseases occurring in the middle ear pose a direct threat to human life. Therefore, studying the structure, functions and methods of protecting the middle ear from infections is a very urgent task.
Organ structure
The middle ear is located deep in the temporal bone and is represented by the following organs:
- tympanic cavity;
The middle ear is structured as a collection of air cavities. Its central part is the tympanic cavity - the area between the i. It has a mucous surface and resembles a prism or tambourine. The tympanic cavity is separated from the skull by an upper wall.
The anatomy of the middle ear provides for its separation by a bony wall from the inner ear. There are 2 holes in this wall: round and oval. Each opening, or window, is protected by an elastic membrane.
The middle ear cavity contains and, which transmit sound vibrations. These bones include the malleus, incus and stirrup. The names of the bones arose in connection with the peculiarities of their structure. The mechanism of interaction of the auditory ossicles resembles a system of levers. The malleus, incus and stirrup are connected by joints and ligaments. In the center of the eardrum is the handle of the malleus, its head is connected to the incus, and it is connected with a long process to the head of the stapes. The stapes enters the foramen ovale, behind which is the vestibule - the part of the inner ear filled with fluid. All bones are covered with a mucous membrane.
An important element of the middle ear is the auditory tube. It connects the tympanic cavity with the external environment. The mouth of the tube is located at the level of the hard palate and opens into the nasopharynx. The opening of the auditory tube is closed when there are no sucking or swallowing movements. There is one feature of the structure of the tube in newborns: it is wider and shorter than in an adult. This fact makes it easier for viruses to penetrate.
The mastoid process is a process of the temporal bone that is located behind it. The structure of the appendage is cavitary, since it contains cavities filled with air. The cavities communicate with each other through narrow slits, which allows the middle ear to improve its acoustic properties.
The structure of the middle ear also suggests the presence of muscles. The tensor tympani muscle and the stapedius muscle are the smallest muscles in the entire body. With their help, the auditory ossicles are supported and adjusted. In addition, the muscles of the middle ear provide accommodation of the organ to sounds of varying heights and strengths.
Purpose and functions
The functioning of the hearing organ is impossible without this element. The middle ear contains the most important components, which together perform the function of sound conduction. Without the middle ear, this function could not be realized and the person would not be able to hear.
The auditory ossicles provide bone conduction of sound and mechanical transmission of vibrations to the oval window of the vestibule. 2 small muscles perform a number of important tasks for hearing:
- maintain the tone of the eardrum and the mechanism of the auditory ossicles;
- protect the inner ear from strong sound irritations;
- provide accommodation of the sound-conducting apparatus to sounds of varying strength and height.
Based on the functions performed by the middle ear with all its components, we can conclude that without it, the auditory function would be unfamiliar to a person.
Middle ear diseases
Ear diseases are one of the most unpleasant ailments for humans. They pose a great danger not only to health, but also to human life. The middle ear, as the most important part of the auditory organ, is susceptible to various diseases. Leaving middle ear disease untreated, a person risks becoming hard of hearing and significantly reducing the quality of his life.
It ends with the tympanic membrane, blindly closing the auditory canal, bordering:
- with the joint of the lower jaw, when chewing, the movement is transmitted to the cartilaginous part of the passage;
- with cells of the mastoid process, facial nerve;
- with the salivary gland.
The membrane between the outer ear and the middle ear is an oval translucent fibrous plate, measuring 10 mm in length, 8-9 mm in width, 0.1 mm in thickness. The membrane area is about 60 mm 2.
The plane of the membrane is located obliquely to the axis of the ear canal at an angle, drawn funnel-shaped into the cavity. The maximum tension of the membrane is in the center. Behind the eardrum is the middle ear cavity.
There are:
- middle ear cavity (tympanum);
- auditory tube (Eustachian tube);
- auditory ossicles.
Tympanic cavity
The cavity is located in the temporal bone, its volume is 1 cm 3. It houses the auditory ossicles, articulated with the eardrum.
The mastoid process, consisting of air cells, is located above the cavity. It houses a cave - an air cell that serves in the anatomy of the human ear as the most characteristic landmark when performing any operations on the ear.
Eustachian tube
The formation is 3.5 cm long, with a lumen diameter of up to 2 mm. Its upper mouth is located in the tympanic cavity, the lower pharyngeal mouth opens in the nasopharynx at the level of the hard palate.
The auditory tube consists of two sections, separated by its narrowest point - the isthmus. A bony part extends from the tympanic cavity, and below the isthmus there is a membranous-cartilaginous part.
The walls of the tube in the cartilaginous section are normally closed, opening slightly during chewing, swallowing, and yawning. The expansion of the lumen of the tube is provided by two muscles associated with the velum palatine. The mucous membrane is lined with epithelium, the cilia of which move towards the pharyngeal mouth, providing the drainage function of the pipe.
The smallest bones in human anatomy, the auditory ossicles of the ear, are intended to conduct sound vibrations. In the middle ear there is a chain: malleus, stirrup, incus.
The malleus is attached to the tympanic membrane, its head articulates with the incus. The incus process is connected to the stapes, which is attached at its base to the window of the vestibule, located on the labyrinthine wall between the middle and inner ear.
The structure is a labyrinth consisting of a bone capsule and a membranous formation that follows the shape of the capsule.
In the bone labyrinth there are:
- vestibule;
- snail;
- 3 semicircular canals.
Snail
The bone formation is a three-dimensional spiral of 2.5 turns around the bone rod. The width of the base of the cochlear cone is 9 mm, the height is 5 mm, the length of the bone spiral is 32 mm. A spiral plate extends from the bone rod into the labyrinth, which divides the bone labyrinth into two channels.
At the base of the spiral lamina are the auditory neurons of the spiral ganglion. The bony labyrinth contains perilymph and a membranous labyrinth filled with endolymph. The membranous labyrinth is suspended in the bony labyrinth using cords.
Perilymph and endolymph are functionally connected.
- Perilymph – its ionic composition is close to blood plasma;
- endolymph - similar to intracellular fluid.
Violation of this balance leads to increased pressure in the labyrinth.
The cochlea is an organ in which physical vibrations of the perilymph fluid are converted into electrical impulses from the nerve endings of the cranial centers, which are transmitted to the auditory nerve and the brain. At the top of the cochlea there is an auditory analyzer - the organ of Corti.
vestibule
The most ancient anatomically middle part of the inner ear is the cavity bordering the scala cochlea through a spherical sac and semicircular canals. On the wall of the vestibule leading into the tympanic cavity, there are two windows - an oval window, covered by the stapes, and a round window, which represents the secondary eardrum.
Features of the structure of the semicircular canals
All three mutually perpendicular bony semicircular canals have a similar structure: they consist of an expanded and simple pedicle. Inside the bones there are membranous canals that repeat their shape. The semicircular canals and vestibular sacs make up the vestibular apparatus and are responsible for balance, coordination, and determining the position of the body in space.
In a newborn, the organ is not formed and differs from an adult in a number of structural features.
Auricle
- The shell is soft;
- the lobe and curl are weakly expressed and are formed by the age of 4 years.
auditory canal
- The bone part is not developed;
- the walls of the passage are located almost closely;
- The drum membrane lies almost horizontally.
- Almost adult size;
- In children, the eardrum is thicker than in adults;
- covered with mucous membrane.
Tympanic cavity
In the upper part of the cavity there is an open gap, through which, in acute otitis media, the infection can penetrate into the brain, causing the phenomenon of meningism. In an adult, this gap closes.
The mastoid process in children is not developed; it is a cavity (atrium). The development of the appendage begins at the age of 2 years and ends by 6 years.
Eustachian tube
In children, the auditory tube is wider, shorter than in adults, and located horizontally.
The complex paired organ receives sound vibrations of 16 Hz - 20,000 Hz. Injuries and infectious diseases reduce the sensitivity threshold and lead to gradual hearing loss. Advances in medicine in the treatment of ear diseases and hearing aids make it possible to restore hearing in the most difficult cases of hearing loss.
Video about the structure of the auditory analyzer
The middle ear (auris media) consists of several interconnected air cavities: the tympanic cavity (cavum tympani), the auditory tube (tuba auditiva), the entrance to the cave (aditus ad antrum), the cave (antrum) and the associated air cells of the mastoid process (cellulae mastoidea). Through the auditory tube, the middle ear communicates with the nasopharynx; under normal conditions, this is the only communication between all cavities of the middle ear and the external environment.
1 - horizontal semicircular canal; 2 - canal of the facial nerve; 3 - roof of the tympanic cavity; 4 - window of the vestibule; 5 - muscle semi-channel; 6 - tympanic opening of the auditory tube; 7 - canal of the carotid artery; 8 - promontorium; 9 - tympanic nerve; 10 - jugular fossa; 11 - cochlear window; 12 - drum string; 13 - pyramidal process; 14 - entrance to the cave.
Drum cavity (Fig. 4.4). The tympanic cavity can be compared to an irregularly shaped cube with a volume of up to 1 cm3. It has six walls: upper, lower, anterior, posterior, outer and inner.
The upper wall, or roof, of the tympanic cavity (tegmen tympani) is represented by a bone plate 1-6 mm thick. It separates the tympanic cavity from the middle cranial fossa. There are small holes in the roof through which vessels pass that carry blood from the dura mater to the mucous membrane of the middle ear. Sometimes dehiscences form in the upper wall; in these cases, the mucous membrane of the tympanic cavity is directly adjacent to the dura mater.
In newborns and children of the first years of life, on the border between the pyramid and the scales of the temporal bone there is an unclosed fissure (fissura petrosquamosa), which causes the occurrence of brain symptoms in them during acute inflammation of the middle ear. Subsequently, a suture (sutura petrosquamosa) is formed at this place and the connection with the cranial cavity in this place is eliminated.
The lower (jugular) wall, or the bottom of the tympanic cavity (paries jugularis), borders on the underlying jugular fossa (fossa jugularis), in which the bulb of the jugular vein (bulbus) is located venae jugularis). The more the fossa protrudes into the tympanic cavity, the thinner the bone wall. The lower wall may be very thin or have dehiscences, through which the vein bulb sometimes protrudes into the tympanic cavity. This makes it possible for the jugular vein bulb to be injured, accompanied by severe bleeding, during paracentesis or careless scraping of granulations from the bottom of the tympanic cavity.
The anterior wall, tubular or carotid (paries tubaria, s.caroticus), of the tympanic cavity is formed by a thin bone plate, outside of which the internal carotid artery is located. There are two openings in the anterior wall, the upper of which, narrow, leads into the semicanal for the muscle that stretches the tympanic membrane (semicanalis m.tensoris tympani), and the lower, wide, leads into the tympanic opening of the auditory tube (ostium tympanicum tybae auditivae). In addition, the anterior wall is pierced by thin canaliculi (canaliculi caroticotympanici), through which vessels and nerves pass into the tympanic cavity; in some cases it has dehiscence.
The posterior (mastoid) wall of the tympanic cavity (paries mastoideus) borders the mastoid process. In the upper part of this wall there is a wide passage (aditus adantrum), connecting the supratympanic recess - the attic (attic) with the permanent cell of the mastoid process - the cave (antrum mastoideum). Below this passage there is a bony protrusion - a pyramidal process, from which the stapedius muscle (m.stapedius) begins. On the outer surface of the pyramidal process there is a tympanic foramen (apertura tympanica canaliculi chordae), through which the tympanic chord (chorda tympani), extending from the facial nerve, enters the tympanic cavity. The descending limb of the facial nerve canal passes through the thickness of the lower part of the posterior wall.
The outer (membranous) wall of the tympanic cavity (paries membranaceus) is formed by the tympanic membrane and partially in the attic area by a bone plate that extends from the upper bone walls of the external auditory canal.
Internal (labyrinthine, medial, promotorial ) the wall of the tympanic cavity (paries labyrinthicus) is the outer wall of the labyrinth and separates it from the cavity of the middle ear. In the middle part of this wall there is an oval-shaped elevation - a promontory (promontorium), formed by the protrusion of the main curl of the cochlea.
Posterior and superior to the promontory there is a niche for the window of the vestibule (oval window according to the old nomenclature; fenestra vestibuli), closed by the base of the stapes (basis stapedis). The latter is attached to the edges of the window by means of an annular ligament (lig. annulare). In the direction posterior and downward from the promontory there is another niche, at the bottom of which there is a cochlear window (round window according to the old nomenclature; fenestra cochleae), leading into the cochlea and closed by a secondary tympanic membrane (membrana ympany secundaria), which consists of three layers: outer - mucous, middle - connective tissue and internal - endothelial.
How does sound perception occur?
The sound waves reach the outer concha and are transmitted to the outer ear, where they cause the eardrum to move. These vibrations are amplified through the auditory ossicles and transmitted to the membrane of the middle window. In the inner ear, vibrations provoke the movement of perilymph.
If the vibrations are quite strong, then they reach the endolymph, and it, in turn, provokes irritation of the hair cells (receptors) of the organ of Corti. Sounds of different pitches move fluid in different directions, which is detected by nerve cells. They convert mechanical vibrations into a nerve impulse, which reaches the temporal lobe of the cortex through the auditory nerve.
A sound wave entering the ear is converted into a nerve impulse
The physiology of sound perception is difficult to study, since sound causes a slight displacement of the membrane, fluid vibrations are very small, and the anatomical region itself is small and located in the capsule of the labyrinth.
The anatomy of the human ear allows it to detect waves from 16 to 20 thousand vibrations per second. This is not much compared to other animals. For example, a cat perceives ultrasound and is able to detect up to 70 thousand vibrations per second. With age, a person's sound perception deteriorates.
Thus, a thirty-five-year-old person can perceive sound no higher than 14 thousand Hz, and those over 60 years old can only perceive up to 1 thousand vibrations per second.
Ear diseases
The pathological process occurring in the ears can be inflammatory, non-inflammatory, traumatic or fungal. Non-inflammatory diseases include otosclerosis, vestibular neuritis, Meniere's disease.
Otosclerosis develops as a result of pathological tissue proliferation, due to which the auditory ossicles lose mobility and deafness occurs. Most often, the disease begins during puberty and by the age of 30 a person has severe symptoms.
Meniere's disease develops due to the accumulation of fluid in a person's inner ear. Signs of pathology: nausea, vomiting, tinnitus, dizziness, difficulties with coordination. Vestibular neuritis may develop.
This pathology, if it occurs in isolation, does not cause hearing impairment, however, it can provoke nausea, dizziness, vomiting, tremor, headache, and convulsions. The most common ear diseases are inflammatory in nature.
Depending on the location of the inflammation, there are:
- otitis externa;
- otitis media;
- internal otitis;
- labyrinthitis.
Occur as a result of the development of infection.
If otitis media is ignored, the auditory nerve is affected, which can lead to irreversible deafness
Hearing decreases as a result of the formation of plugs in the outer ear. Normally, sulfur is excreted on its own, but if its production is increased or its viscosity changes, it can accumulate and block the movement of the eardrum.
Diseases of a traumatic nature include damage to the auricle due to bruises, the presence of foreign bodies in the auditory canal, deformation of the eardrum, burns, acoustic injuries, and vibration injuries.
There are many reasons why hearing loss can occur. It may occur as a result of a violation of sound perception or sound transmission. In most cases, medicine can restore hearing. Drug therapy, physiotherapy, and surgical treatment are carried out.
Doctors are able to replace the auditory ossicles or eardrum with synthetic ones, and install an electrode in the human inner ear that will transmit vibrations to the brain. But if hair cells are damaged as a result of pathology, then hearing cannot be restored.
The structure of the human ear is complex and the appearance of a negative factor can impair hearing or lead to complete deafness. Therefore, a person must maintain hearing hygiene and prevent the development of infectious diseases.
Table of contents of the topic "Anatomy of the ear":1. Vestibulocochlear organ, organum vestibulocochleare. The structure of the balance organ (pre-cochlear organ).
2. Embryogenesis of the organ of hearing and gravity (balance) in humans.
3. External ear, auris externa. Auricle, auricula. External auditory canal, meatus acusticus externus.
4. Eardrum, membrana tympani. Vessels and nerves of the external ear. Blood supply to the external ear.
5. Middle ear, auris media. Tympanic cavity, cavitas tympanica. Walls of the tympanic cavity.
6.
7. Muscle tensor tympani, m. tensor tympani. Stapedius muscle, m. stapedius Functions of the muscles of the middle ear.
8. Auditory tube, or Eustachian tube, tuba auditiva. Vessels and nerves of the middle ear. Blood supply to the middle ear.
9. Inner ear, labyrinth. Bone labyrinth, labyrinthus osseus. vestibule, vestibulum.
10. Bone semicircular canals, canales semicirculares ossei. Snail, cochlea.
11. Membranous labyrinth, labyrinthus membranaceus.
12. Structure of the auditory analyzer. Spiral organ, organon spirale. Helmholtz's theory.
13. Vessels of the inner ear (labyrinth). Blood supply to the inner ear (labyrinth).
Auditory ossicles: Hammer, malleus; Anvil, incus; Stirrup, stapes. Functions of the bones.
Located in tympanic cavity three small auditory ossicles Based on their appearance, they are called the malleus, incus and stirrup.
1. malleus, malleus, equipped with a rounded head, caput mallei, which through cervix, collum mallei, connects with handle, manubrium mallei.
2. Anvil, incus, has a body, corpus incudis, and two diverging processes, one of which is more short, crus breve, directed backwards and rests on the hole, and the other - long shoot, crus longum, runs parallel to the handle of the malleus medially and posteriorly from it and at its end has a small oval thickening, processus lenticularis, articulated with the stirrup.
3. Stirrup, stapes, in its form justifies its name and consists of small head, caput stapedis, bearing the articular surface for processus lenticularis anvil and two legs: anterior, more straight, crus anterius, and back, more curved, crus posterius, which connect with oval plate, basis stapedis, inserted into the window of the vestibule.
At the junctions of the auditory ossicles, two true joints with limited mobility: articulatio incudomallearis and articulatio incudostapedia. The stirrup plate is connected to the edges fenestra vestibuli through connective tissue, syndesmosis tympano-stapedia.
Auditory ossicles strengthened, in addition, by several more separate ligaments. Generally all three auditory ossicles represent a more or less mobile chain running across the tympanic cavity from the eardrum to the labyrinth. Ossicular mobility gradually decreases in the direction from the malleus to the stapes, which protects the spiral organ located in the inner ear from excessive shocks and sharp sounds.
The chain of ossicles performs two functions:
1) bone conduction of sound and
2) mechanical transmission of sound vibrations to the oval window of the vestibule, fenestra vestibuli.
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 orifice 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 middle ear consists of the tympanic cavity and the auditory tube, which communicates with the nasopharynx.
Tympanic cavity, cavum tympani(see Fig. 356, 359), is located at the base of the pyramid of the temporal bone between the external auditory canal and the labyrinth (inner ear). It contains a chain of three small bones that transmit sound vibrations from the eardrum to the labyrinth. The tympanic cavity has a very small size (volume about 1 cm3) and resembles a tambourine placed on its edge, strongly inclined towards the external auditory canal. There are six walls in the tympanic cavity:
1. Lateral wall of the tympanic cavity, paries membranaceus, formed by the eardrum and the bony plate of the external auditory canal. The upper dome-shaped expanded part of the tympanic cavity, recessus epitympdnicus, contains two auditory ossicles: the head of the malleus and the incus. In case of disease, pathological changes in the middle ear are most pronounced in the recessus epitympanicus.
2. The medial wall of the tympanic cavity is adjacent to the labyrinth, and therefore is called labyrinthine, paries labyrinthicus. It has two windows: round, snail window- fenestra cochleae, leading to the cochlea and extended membrana tympani secundaria, and oval, vestibule window- fenestra vestibuli, opening into the vestibulum labyrinthii. The base of the third auditory ossicle, the stapes, is inserted into the last hole.
3. Posterior wall of the tympanic cavity, paries mastofdeus, carries an elevation, eminentia pyramidalis, for placing m. stapedius Recessus epitympanicus continues posteriorly into the cave of the mastoid process, antrum mastoideum, where the air cells of the latter open, cellulae mastoideae. Antrum mastoideum is a small cavity protruding towards the mastoid process, from the outer surface of which it is separated by a layer of bone bordering the posterior wall of the auditory canal immediately behind the spina suprameatum, where the cave is usually opened during suppuration in the mastoid process.
4. The anterior wall of the tympanic cavity is called paries caroticus, since the internal carotid artery is close to it. In the upper part of this wall there is an internal opening of the auditory tube, ostium tympanicum tubae auditivae, which gapes widely in newborns and young children, which explains the frequent penetration of infection from the nasopharynx into the middle ear cavity and further into the skull.
5. The upper wall of the tympanic cavity, paries tegmentalis, corresponds to the tegmen tympani on the anterior surface of the pyramid and separates the tympanic cavity from the cranial cavity.
6. The lower wall, or bottom, of the tympanic cavity, paries jugularis, facing the base of the skull adjacent to the fossa jugularis.
Located in the tympanic cavity are three small auditory ossicles(Fig. 358) are named after their appearance as malleus, incus and stirrup. 1. Hammer, malleus, equipped with a rounded head, caput mallei, which, through a neck, collum mallei, is connected to the handle, manubrium mallei. 2. Anvil, incus, has a body, corpus incudis, and two diverging processes, of which one shorter one, crus breve, is directed backward and rests on the fossa, and the other long process, crus longum, runs parallel to the handle of the malleus medially and posteriorly from it and at its end has a small oval thickening, processus lenticutdris, articulated with the stirrup. 3. Stirrup, stages, in its shape justifies its name and consists of a small head, caput stapedis, bearing the articular surface for the processus lenticuldris of the incus and two legs: the anterior, more straight, crus anterius, and the posterior, more curved, crus posterius, which connect to the oval plate, basis stapedis, inserted into the window of the vestibule.
At the junctions of the auditory ossicles, two real joints with limited mobility are formed: art. incudomalledris and art. incudostapedia. The stapes plate is connected to the edges of the fenestra vestibuli through connective tissue, syndesmosis tympanosiapedia. The auditory ossicles are also strengthened by several separate ligaments. In general, all three auditory ossicles represent a more or less mobile chain running across the tympanic cavity from the eardrum to the labyrinth. The mobility of the ossicles gradually decreases in the direction from the malleus to the stapes, which protects the organ of Corti, located in the inner ear, from excessive shocks and sharp sounds.
The chain of bones performs two functions: 1) bone conduction of sound and 2) mechanical transmission of sound vibrations to the oval window.
The latter function is carried out thanks to two small muscles associated with the auditory ossicles and located in the tympanic cavity, which regulate the movements of the chain of ossicles. One of them, m. tensor tympani, embedded in semicanalis m. tensoris tympani, which makes up the upper part of the canalis musculotubarius of the temporal bone; its tendon is attached to the handle of the malleus near the neck. This muscle, pulling the handle of the malleus inward, strains the eardrum. In this case, the entire ossicular system is displaced inward and the stapes is pressed into the oval window. The muscle is innervated from the third branch of the trigeminal nerve through the n branch. tensoris tympani. Another muscle m. stapedius, is placed in the eminentia pyramidalis and is attached to the posterior leg of the stapes at the head. In function, this muscle is an antagonist of the previous one and produces a reverse movement of the bones in the middle ear, in the direction from the oval window. The muscle receives its innervation from n. facialis, which, passing through the neighborhood, produces a small branch, n. stapedius
In general, the function of the muscles of the middle ear is diverse: 1) maintaining the normal tone of the eardrum and the chain of auditory ossicles; 2) protection of the inner ear from excessive sound stimulation and 3) accommodation of the sound-conducting apparatus to sounds of varying strength and height. The basic principle of operation of the middle ear as a whole is sound conduction from the eardrum to the oval window.
Auditory, or Eustachian, tube, tuba auditiva(Eustachii; hence the name for inflammation of the tube - eustachitis), serves to access air from the pharynx into the tympanic cavity, thereby maintaining a balance between the pressure in this cavity and external atmospheric pressure, which is necessary for the correct conduction of oscillations of the tympanic membrane to the labyrinth. The auditory tube consists of bone and cartilage parts that are connected to each other. At the place of their connection (isthmus tubae), the tube channel is the narrowest. The bony part of the tube, starting in the tympanic cavity with a hole, ostium tympanicum tubae auditivae, occupies the lower larger section of the muscular-tubal canal (semicanalis tubae auditivae) of the temporal bone. The cartilaginous part, which forms a continuation of the bone part, is formed by elastic cartilage (Fig. 359).
Downwards, the tube ends on the lateral wall of the nasopharynx with the pharyngeal mouth, ostium pharyngeum tubae auditivae, and the edge of the cartilage, protruding into the pharynx, forms the torus tubarius. The mucous membrane lining the auditory tube is covered with ciliated epithelium and contains mucous glands, gldndulae tubdriae mucosae, and lymphatic follicles, which accumulate in large numbers at the pharyngeal mouth (tubal tonsil). Fibers m originate from the cartilaginous part of the tube. tensor veli palatini, as a result of which, when this muscle contracts during swallowing, the lumen of the tube can expand, which facilitates the entry of air into the tympanic cavity.
Vessels and nerves of the middle ear. Arteries originate mainly from a. carotis externa. Numerous vessels penetrate the tympanic cavity from its branches: from a. auricularis posterior, from a. maxillaris, from a. pharyngea ascendens, as well as from the trunk of a. carotis interna as it passes through its canal. The veins accompany the arteries and flow into the plexus pharyngeus, vv. meningeae mediae et v. auricularis profunda. The lymphatic vessels of the middle ear go partly to the nodes on the side wall of the pharynx, partly to the lymph nodes behind the auricle.
Nerves: the mucous membrane of the tympanic cavity and auditory tube is supplied by sensory branches from n. tympanicus, arising from the ganglion inferius of the glossopharyngeal nerve. Together with the branches of the sympathetic plexus of the internal carotid artery, they form the tympanic plexus, plexus tympanicus. Its upper continuation is n. petrosus minor, going to the ganglion oticum. The motor nerves of the small muscles of the bar" of the bath cavity were indicated in their description.
The three tiny bones of the middle ear - the malleus, the incus and the stapes - have long attracted the attention of paleontologists, because the formation of this structure is associated with the evolution of the most ancient mammals.
And now, the authors of a new article on the PNAS journal website report yet another remarkable discovery. The first is three completely preserved right auditory ossicles (extracted from the fragmentary skull SKW 18, Swartkrans, age 1.8 million years). The uniqueness of the find can be appreciated if we consider that until now only two cases of preservation of all three bones were known for fossil hominids - and both times this (child La Ferrassie and teenager Le Moustier 2...). It is interesting that, as stated in the appendix to the article, the left stapes from this skull is also present, the bone can be seen in the cavity of the middle ear, but it is walled up there, and no attempts have been made to remove it yet.
Comment from the Scientific Editor of ANTHROPOGENES.RU: In fact, these bones are well preserved; they are also protected by the temporal bone. Only usually they are lost when the skull is cleaned from the ground. Apparently, they decided to clean it carefully once. For the first time not with a screwdriver! They invented a super-brush made from Mexican jerboa wool to clean the ears of australopithecines!
The second find is the left malleus and part of the right stapes (fragment of the skull Stw 255 from Sterkfontein, 2.0-2.5 million years ago).
What are the results? (for those who are not fans of anatomical details - that is, all normal people :) - you can skip this part of the text and go straight to the conclusions).
Hammer
The main feature of the malleus of the middle ear of modern humans, in comparison with great apes, is the shortening and thickening of the “handle” and the accompanying lengthening of the body (head). This change in shape in the process of evolution was combined with a decrease in the size of the eardrum.
The authors of the article describe in detail the morphology of this bone in two early hominids, point out some differences between them (the shape of the handle and head, the presence of an anterior process in Africanus and its absence in Robustus, etc.), but make the main conclusion: in all major dimensions, both malleus of early hominids are extremely similar to humans. At the same time, Africanus is more human, and the robustus hammer still has some specific features. Logical!
Anvil
A distinctive feature of the anvil of modern humans is the larger size of the long process and the larger angle between the long and short processes, in comparison with other anthropoids.
Unfortunately, the anvil of Africanus was not found, so the researchers are only considering Paranthropus. The authors draw attention to the fact that even in the existing two finds, variations in morphology are visible - for example, a depression along the lower edge of the short process is present in SKW 18, but is absent in SK 848. And here there is a certain specialization of the paranthropus - the articular facet is oriented differently than in humans and in apes (although there are variations here too), the body of the anvil has a peculiar “swollen” shape. In general, in terms of its metric characteristics, the anvil of Paranthropus is primitive, and is closest to the chimpanzee.
Stapes
Unlike the malleus and incus, the stapes of apes and humans differ little in structure. The difference between them is only in size: in humans the stirrup is larger.
Small stirrup sizesP. robustus AndA. africanus bring them closer to apes.
Conclusions:
- Despite some differences, in general the auditory ossicles of the two hominids are similar to each other.
- Hammer P. robustus And A. africanus similar to human. Probably, it was already such in the common ancestor of the hominids in question. How long ago did the hammer take on a human form? To find out, you need some kind of auditory ossicles.
- On the contrary, in the structure of the anvil of Paranthropus we see features characteristic of apes. Unfortunately, nothing can be said about Africanus...
- Stapes P. robustus And A. africanus small, like a monkey's.
In modern primates, the length of the malleus and incus, as well as the area of the oval plate of the stapes, are important characteristics that influence the sensitivity of hearing. Apparently, thanks to the combination of a “human” hammer and a “monkey” anvil, Paranthropus’s hearing had some intermediate, “ape-human” features.
In conclusion, the authors point out that in most primates (except humans!) there is some loss of sensitivity to sounds at medium frequencies, and this feature of hearing is associated with the functional length of the incus. According to this characteristic, Paranthropus's hearing apparently differed from that of humans. The authors leave the conversation about other intricacies of Australopithecus hearing for the future...
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