Structural and functional characteristics auditory analyzer
The auditory sensory system is the second most important distant analyzer in humans; it plays an important role in humans in connection with the emergence of articulate speech.
Hearing analyzer function: energy conversion sound waves into the energy of nervous excitement and auditory sensation.
Like any analyzer, the auditory analyzer consists of a peripheral, conductive and cortical section.
Peripheral department: converts the energy of sound waves into the energy of nervous excitation - receptor potential (RP). This department includes:
a) inner ear (sound-receiving apparatus),
b) middle ear (sound-conducting apparatus),
c) inner ear (sound hearing apparatus)
The components of this department are combined into the concept - organ of hearing.
Outer ear: a) collecting sound (auricle) and directing the sound wave into the external auditory canal,
b) conducting a sound wave through the ear canal to the eardrum,
c) mechanical protection and protection from environmental temperature influences of all other parts of the hearing organ.
Middle ear (sound-conducting section) is the tympanic cavity with 3 auditory ossicles: the malleus, the incus and the stapes.
Eardrum separates the external auditory canal from the tympanic cavity. Hammer handle woven into the eardrum, his other horse is articulated with an anvil, which in turn is articulated with stirrup. The stirrup is adjacent to oval window membrane. The pressure in the tympanic cavity is equal to atmospheric pressure, which is very important for adequate perception of sounds. This function is performed Eustachian tube, which connects the middle ear cavity to the pharynx. When swallowing, the tube opens, resulting in ventilation of the tympanic cavity and equalization of the pressure in it with atmospheric pressure. If external pressure changes rapidly (rapid rise to altitude), and swallowing does not occur, then the pressure difference between atmospheric air and air in the tympanic cavity leads to tension of the eardrum and the appearance of discomfort(“blocked ears”), decreased perception of sounds.
The area of the eardrum (70 mm2) is significantly more area oval window (3.2 mm 2), due to which it occurs increased pressure sound waves on the membrane of the oval window 25 times . Lever mechanism seeds reduces the amplitude of sound waves is 2 times, so the same amplification of sound waves occurs at the oval window of the tympanic cavity. Hence, the middle ear amplifies sound by about 60-70 times, and if we take into account the amplifying effect of the outer ear, then this value increases by 180-200 times .
In this regard, with strong sound vibrations, to prevent the destructive effect of sound on the receptor apparatus of the inner ear, the middle ear reflexively turns on « defense mechanism» . It is as follows. There are 2 muscles in the middle ear: one of them stretches the eardrum, the other fixes the stapes. Under strong sound impacts, these muscles contract, thereby limiting the amplitude of vibration of the eardrum and fixing the stapes. This “quenches” the sound wave and prevents overexcitation and destruction of the phonoreceptors of the organ of Corti.
Inner ear. It is represented by the cochlea - a spirally twisted bone canal (2.5 turns in humans). This canal is divided along its entire length into three narrow parts (scalenes) by two membranes: the main and vestibular membrane (Reisner).
On the main membrane there is a spiral organ - the organ of Corti (organ of Corti) - this is the actual sound-receiving apparatus with receptor cells. This is the peripheral section of the auditory analyzer.
The helicotrema (orifice) connects the superior and inferior canals at the apex of the cochlea. The middle channel is separate.
Above the organ of Corti is a tectorial membrane, one end of which is fixed and the other remains free. The hairs of the outer and inner hair cells of the organ of Corti come into contact with the tectorial membrane, which is accompanied by their excitation, i.e. the energy of sound vibrations is transformed into the energy of the excitation process.
The transformation process begins with sound waves entering the outer ear; they move the eardrum. Vibrations of the tympanic membrane through the system of auditory ossicles of the middle ear are transmitted to the membrane of the oval window, which causes vibrations of the perilymph of the scala vestibule. These vibrations are transmitted through the helicotrema to the perilymph of the scala tympani and reach the round window, protruding it towards the middle ear. This prevents the sound wave from dying out as it passes through the vestibular and tympanic canals of the cochlea. Vibrations of the perilymph are transmitted to the endolymph, which causes vibrations of the main membrane. The fibers of the basilar membrane begin to vibrate together with the receptor cells (outer and inner hair cells) of the organ of Corti. In this case, the phonoreceptor hairs come into contact with the tectorial membrane. The cilia of the hair cells are deformed, which causes the formation of a receptor potential, and on its basis - an action potential (nerve impulse), which is then conducted along the auditory nerve to the next section of the auditory analyzer.
The organ of hearing and balance, the vestibulocochlear organ in humans, has a complex structure, perceives vibrations of sound waves and determines the orientation of the body’s position in space. The vestibular-cochlear organ is divided into three parts: external, middle and inner ear. These parts are closely related anatomically and functionally. The outer and middle ear conduct sound vibrations to the inner ear, and are thus a sound-conducting apparatus. The inner ear, in which the bony and membranous labyrinths are distinguished, forms the organ of hearing and balance. Outer ear includes the auricle, external auditory canal and eardrum, which are designed to capture and conduct sound vibrations.
The auricle consists of elastic cartilage and has a complex configuration; the outside is covered with skin. There is no cartilage in the lower part, the so-called lobule or lobe. The free edge of the shell is rolled up and is called a helix, and the ridge running parallel to it is called an antihelix. At the anterior edge of the auricle there is a protrusion - the tragus, and behind it is the antitragus. The auricle is attached to the temporal bone by ligaments and has rudimentary muscles that are well expressed in animals. The auricle is designed to concentrate sound vibrations as much as possible and direct them into the external auditory opening.
External auditory canal It is an S-shaped tube that opens from the outside with the auditory opening and ends blindly in the depths and is separated from the middle ear cavity by the eardrum. The length of the ear canal in an adult is about 36 mm, the diameter at the beginning reaches 9 mm, and at the narrow place 6 mm. The cartilaginous part, which is a continuation of the cartilage of the auricle, makes up 1/3 of its length, the remaining 2/3 is formed by the bone canal of the temporal bone. At the junction of one part to another, the external auditory canal is narrowed and curved. It is lined with skin and is rich in fatty glands that produce earwax.
Eardrum- a thin translucent oval plate measuring 11x9 mm, which is located on the border of the outer and middle ear. It is located obliquely, forming an acute angle with the lower wall of the ear canal. The eardrum consists of two parts: a large lower part, the tense part, and a smaller upper part, the loose part. On the outside it is covered with skin, its base is formed by connective tissue, and on the inside it is lined with mucous membrane. In the center of the eardrum there is a depression - the navel, which corresponds to the attachment with inside hammer handle.
Middle ear includes a mucous membrane-lined and air-filled tympanic cavity (volume about 1 cm3) and an auditory (Eustachian) tube. The middle ear cavity connects with the mastoid cave and, through it, with the mastoid cells of the mastoid process.
Tympanic cavity located in the thickness of the pyramid of the temporal bone, between the tympanic membrane laterally and the bony labyrinth medially. It has six walls: 1) the upper tegmental wall - separates it from the cranial cavity and is located on the upper surface of the pyramid of the temporal bone; 2) inferior jugular - the wall separates the tympanic cavity from the outer base of the skull, is located on the lower surface of the pyramid of the temporal bone and corresponds to the area of the jugular fossa; 3) medial labyrinth - separates the tympanic cavity from the bony labyrinth of the inner ear.
On this wall there is an oval opening - the window of the vestibule, closed by the base of the stapes; slightly higher on this wall there is a protrusion of the facial canal, and below is the window of the cochlea, closed by the secondary tympanic membrane, which separates the tympanic cavity from the scala tympani; 4) posterior mastoid - separates the tympanic cavity from the mastoid process and has an opening that leads to the mastoid cave, the latter in turn connects with the mastoid cells; 5) anterior carotid - borders the carotid canal. Here is the tympanic opening of the auditory tube, through which the tympanic cavity is connected to the nasopharynx; 6) lateral membranous - formed by the tympanic membrane and the surrounding parts of the temporal bone. In the tympanic cavity there are three auditory ossicles covered with mucous membrane, as well as ligaments and muscles. The auditory ossicles are small. Connecting with each other, they form a chain that stretches from the eardrum to the oval opening. All bones are connected to each other using joints and are covered with a mucous membrane. The hammer is fused with the handle to the eardrum, and the head, through a joint, is connected to the anvil, which in turn is movably connected to the stirrup.
The base of the stapes closes the window of the vestibule. There are two muscles in the tympanic cavity: one goes from the canal of the same name to the handle of the malleus, and the other, the stapedius muscle, goes from the back wall to the back leg of the stapes. When the stapedius muscle contracts, the pressure of the base on the perilymph changes. Eustachian tube has an average length of 35 mm, a width of 2 mm, serves to allow air to flow from the pharynx into the tympanic cavity and maintains pressure in the cavity equal to the external one, which is very important for the normal operation of the sound-conducting apparatus. The auditory tube has cartilaginous and bony parts and is lined with ciliated epithelium.
The cartilaginous part of the auditory tube begins with the pharyngeal opening on the side wall of the nasopharynx, goes down and laterally, then narrows and forms an isthmus. The bony part is smaller than the cartilaginous part, lies in the hemicanal of the pyramid of the temporal bone of the same name and opens into the tympanic cavity through the opening of the auditory tube. Inner ear located in the thickness of the pyramid of the temporal bone, separated from the tympanic cavity by its labyrinthine wall. It consists of a bone labyrinth and a membranous labyrinth inserted into it. The bony labyrinth consists of the cochlea, vestibule and semicircular canals. The vestibule is a cavity of small size and irregular shape. There are two openings on the lateral wall: the window of the vestibule and the window of the cochlea. On the medial wall of the vestibule there is a crest of the vestibule, which divides the cavity of the vestibule into two recesses - the anterior spherical and posterior elliptical. Through an opening on the posterior wall, the cavity of the vestibule is connected to the bony semicircular canals, and through an opening on the anterior wall, the spherical recess of the vestibule is connected to the bony spiral canal of the cochlea.
Snail- the anterior part of the bony labyrinth, it is a convoluted spiral canal of the cochlea, which forms 2.5 turns around the axis of the cochlea. The base of the cochlea is directed medially towards the internal auditory canal; the top of the cochlea's dome is towards the tympanic cavity. The axis of the cochlea lies horizontally and is called the bony cochlear shaft. A bone spiral plate wraps around the rod, which partially blocks the spiral canal of the cochlea. At the base of this plate is the spiral canal of the rod, where the spiral ganglion of the cochlea lies.
Bone semicircular canals They are three arcuately bent thin tubes that lie in three mutually perpendicular planes. On a transverse section, the width of each bony semicircular canal is about 2 mm. The anterior (sagittal, superior) semicircular canal lies above the other canals, and its upper point on the anterior wall of the pyramid forms an arcuate eminence. The posterior (frontal) semicircular canal is located parallel to the posterior surface of the pyramid of the temporal bone. The lateral (horizontal) semicircular canal projects slightly into the tympanic cavity. Each semicircular canal has two ends - bony pedicles. One of them is a simple bone stalk, the other is an ampullary bone stalk. The semicircular canals open with five openings into the cavity of the vestibule, and the adjacent legs of the anterior and posterior valves form a common bony pedicle, which opens with one opening.
Membranous labyrinth in its shape and structure it coincides with the shape of the bone labyrinth and differs only in size, since it is located inside the bone labyrinth. The space between the bony and membranous labyrinths is filled with perilymph, and the cavity of the membranous labyrinth is filled with endolymph.
The walls of the membranous labyrinth are formed by a connective tissue layer, a basic membrane and an epithelial layer. The membranous vestibule consists of two depressions: an elliptical one, called the utricle, and a spherical one, the sac. The sac passes into the endolymphatic duct, which ends in the endolymphatic sac. Both recesses, together with the membranous semicircular ducts with which the uterus is connected, form the vestibular apparatus and are an organ of balance. They contain the peripheral apparatus of the vestibule nerve. The membranous semicircular ducts have a common membranous pedicle and are connected to the bony semicircular canals in which they lie through connective tissue cords.
The sac communicates with the cavity of the cochlear canal. The membranous cochlea, also called the cochlear duct, includes the peripheral apparatus of the cochlear nerve. On the basilar plate of the cochlear duct, which is a continuation of the bony spiral plate, there is a protrusion of the neuroepithelium, called the spiral or organ of Corti. It consists of supporting and epithelial cells located on the main membrane. Nerve fibers - processes - approach them nerve cells main ganglion. It is the organ of Corti that is responsible for the perception of sound stimuli, since the nerve processes are receptors of the cochlear part of the vestibulocochlear nerve. Above the spiral organ is a covering membrane.
TICKET 29 (STRUCTURE AND FUNCTIONS OF THE VESTIBULAR SENSOR SYSTEM)
The human auditory sensory system perceives and distinguishes a huge range of sounds. Their diversity and richness serves for us both as a source of information about current events in the surrounding reality, and as an important factor influencing the emotional and mental condition our body. In this article we will look at the anatomy of the human ear, as well as the features of the functioning of the peripheral part of the auditory analyzer.
Mechanism for distinguishing sound vibrations
Scientists have found that the perception of sound, which is essentially air vibrations in the auditory analyzer, is transformed into the process of excitation. Responsible for the sensation of sound stimuli in the auditory analyzer is its peripheral part, which contains receptors and is part of the ear. It perceives vibration amplitude, called sound pressure, in the range from 16 Hz to 20 kHz. In our body, the auditory analyzer also plays such an important role as participation in the work of the system responsible for the development of articulate speech and the entire psycho-emotional sphere. First let's get acquainted with general plan structure of the hearing organ.
Sections of the peripheral part of the auditory analyzer
The anatomy of the ear distinguishes three structures called the outer, middle and inner ear. Each of them performs specific functions, not only interconnected, but also collectively carrying out the processes of receiving sound signals and converting them into nerve impulses. They are transmitted along the auditory nerves to the temporal lobe of the cerebral cortex, where sound waves are transformed into the form of various sounds: music, birdsong, the sound of the sea surf. In the process of phylogenesis of the biological species “Homo sapiens,” the organ of hearing played a vital role, as it ensured the manifestation of such a phenomenon as human speech. The sections of the hearing organ were formed during human embryonic development from the outer germ layer - the ectoderm.
Outer ear
This part of the peripheral section captures and directs air vibrations to the eardrum. The anatomy of the external ear is represented by the cartilaginous concha and the external auditory canal. What does it look like? The external shape of the auricle has characteristic curves - curls, and is very different in different people. One of them may contain Darwin's tubercle. It is considered a vestigial organ, and is homologous in origin to the pointed upper edge of the ear of mammals, especially primates. The lower part is called the lobe and is connective tissue covered with skin.
The auditory canal is the structure of the outer ear
Further. The auditory canal is a tube consisting of cartilage and partly bone tissue. It is covered with epithelium containing modified sweat glands, releasing sulfur, which moisturizes and disinfects the passage cavity. The muscles of the auricle in most people are atrophied, unlike mammals, whose ears actively respond to external sound stimuli. Pathologies of violations of the anatomy of the ear structure are recorded in early period development of the branchial arches of the human embryo and can take the form of splitting of the lobe, narrowing of the external auditory canal, or agenesis - the complete absence of the auricle.
Middle ear cavity
The auditory canal ends with an elastic film that separates the outer ear from its middle part. This is the eardrum. It receives sound waves and begins to vibrate, which causes similar movements of the auditory ossicles - the hammer, incus and stapes, located in the middle ear, deep in the temporal bone. The hammer is attached to the eardrum with its handle, and its head is connected to the incus. It, in turn, with its long end closes with the stapes, and it is attached to the window of the vestibule, behind which the inner ear is located. Everything is very simple. The anatomy of the ears has revealed that a muscle is attached to the long process of the malleus, which reduces the tension of the eardrum. And the so-called “antagonist” is attached to the short part of this auditory ossicle. A special muscle.
Eustachian tube
The middle ear is connected to the pharynx through a canal named after the scientist who described its structure, Bartolomeo Eustachio. The pipe serves as a pressure equalizing device atmospheric air on the eardrum on both sides: from the external auditory canal and the middle ear cavity. This is necessary so that vibrations of the eardrum are transmitted without distortion to the fluid of the membranous labyrinth of the inner ear. The Eustachian tube is heterogeneous in its histological structure. The anatomy of the ears has revealed that it contains more than just a bone part. Also cartilaginous. Descending down from the middle ear cavity, the tube ends with the pharyngeal opening, located on the lateral surface of the nasopharynx. During swallowing, the muscle fibrils attached to the cartilaginous part of the tube contract, its lumen expands, and a portion of air enters the tympanic cavity. The pressure on the membrane at this moment becomes equal on both sides. Around the pharyngeal opening there is an area of lymphoid tissue that forms nodes. It is called Gerlach's tonsil and is part of the immune system.
Features of the anatomy of the inner ear
This part of the peripheral auditory sensory system is located deep in the temporal bone. It consists of semicircular canals related to the organ of balance and the bony labyrinth. The last structure contains the cochlea, inside which is the organ of Corti, which is a sound-receiving system. Along the spiral, the cochlea is divided by a thin vestibular plate and a denser basilar membrane. Both membranes divide the cochlea into canals: lower, middle and upper. At its wide base, the upper canal begins with an oval window, and the lower one is closed by a round window. Both of them are filled with liquid contents - perilymph. It is considered a modified cerebrospinal fluid - a substance that fills the spinal canal. Endolymph is another fluid that fills the canals of the cochlea and accumulates in the cavity where the nerve endings of the organ of balance are located. Let's continue to study the anatomy of the ears and consider those parts of the auditory analyzer that are responsible for transcoding sound vibrations into the process of excitation.
Significance of the organ of Corti
Inside the cochlea there is a membranous wall called the basilar membrane, on which there is a collection of two types of cells. Some perform the function of support, others are sensory - hair-like. They perceive vibrations of the perilymph, convert them into nerve impulses and transmit them further to the sensory fibers of the vestibulocochlear (auditory) nerve. Next, the excitation reaches the cortical hearing center, located in temporal lobe brain. It distinguishes sound signals. Clinical anatomy ear confirms the fact that to determine the direction of sound, what we hear with both ears is important. If sound vibrations reach them simultaneously, a person perceives sound from front and back. And if the waves arrive in one ear earlier than in the other, then perception occurs on the right or left.
Theories of sound perception
At the moment, there is no consensus on how exactly the system functions, analyzing sound vibrations and translating them into the form of sound images. The anatomy of the human ear structure highlights the following scientific concepts. For example, Helmholtz's resonance theory states that the main membrane of the cochlea functions as a resonator and is capable of decomposing complex vibrations into simpler components because its width is unequal at the apex and base. Therefore, when sounds appear, resonance occurs, as in a string instrument - a harp or a piano.
Another theory explains the process of sound appearance by the fact that a traveling wave appears in the cochlear fluid as a response to vibrations of the endolymph. The vibrating fibers of the main membrane resonate with a specific vibration frequency, and nerve impulses arise in the hair cells. They travel along the auditory nerves to temporal part the cerebral cortex, where the final analysis of sounds occurs. Everything is extremely simple. Both of these theories of sound perception are based on knowledge of the anatomy of the human ear.
The ear is a complex organ that performs two functions: listening, through which we perceive sounds and interpret them, thus communicating with environment; and maintaining body balance.
Auricle- captures and directs sound waves into the internal auditory canal;
Back labyrinth, or semicircular canals - directs movements to the head and brain to regulate the balance of the body;
Front labyrinth, or cochlea - contains sensory cells that, capturing vibrations of sound waves, transform mechanical impulses into nerve impulses;
Auditory nerve- directs general nerve impulses to the brain;
Middle ear bones: hammer, incus, stirrup - receive vibrations from auditory waves, amplify them and transmit them to the inner ear;
External auditory canal- captures sound waves coming from outside and directs them to the middle ear;
Eardrum- a membrane that vibrates when sound waves hit it and transmits vibrations along the chain of bones in the middle ear;
Eustachian tube- a canal that connects the eardrum to the pharynx and allows for support
in balance the pressure created in the middle ear with the pressure of the environment.
The ear is divided into three sections, the functions of which are different.
;the outer ear consists of the pinna and the external auditory canal, its purpose is to capture sounds;
; the middle ear is located in the temporal bone, separated from the inner ear by a movable membrane - the eardrum - and contains three articular bones: the malleus, the incus and the stapes, which take part in the transmission of sounds to the cochlea;
;the inner ear, also called the labyrinth, is formed of two sections that perform various functions: the anterior labyrinth, or cochlea, where the organ of Corti is located, is responsible for hearing, and the posterior labyrinth, or semicircular canals, in which impulses are generated that take part in maintaining the balance of the body (article “Balance and Hearing”)
The inner ear, or labyrinth, consists of a very strong bony skeleton, the ear capsule, or bony labyrinth, within which is a membranous mechanism with a structure similar to that of bone, but consisting of membranous tissue. The inner ear is hollow, but filled with fluid: between the bony labyrinth and the membrane there is perilymph, while the labyrinth itself is filled with endolymph. The anterior labyrinth, a bony form called the cochlea, contains structures that generate auditory impulses. The posterior labyrinth, which takes part in regulating the balance of the body, has a bony skeleton consisting of a cubic part, a vestibule and three arc-shaped canals - semicircular, each of which includes a space with a flat plane.
The cochlea, so named because of its spiral shape, contains a membrane consisting of fluid-filled canals: a central triangular canal and a helix containing endolymph, which is located between the scala vestibuli and the scala tympani. These two scalae are partially separated, they pass into the large canals of the cochlea, covered with thin membranes that separate the inner ear from the middle ear: the scala tympani begins with the oval window, while the scala vestibule reaches the rounded window. The cochlea, which has a triangular shape, consists of three faces: the upper, which is separated from the scala vestibule by the Reissner membrane, the lower, separated from the scala tympani by the main membrane, and the lateral, which is attached to the shell and is a vascular groove that produces endolymph. Inside the cochlea there is a special auditory organ - the Corti organ (the mechanism of sound perception is described in detail in the article "
The hearing organs allow us to perceive a variety of sounds from the outside world, recognize their nature and location. Thanks to the ability to hear, a person gains the ability to speak. The organ of hearing is a complex, finely tuned system of three sections sequentially interconnected.
Outer ear
The first section is the auricle - a complex cartilaginous plate covered on both sides with skin, and the external auditory canal.
The main function of the auricle is to receive acoustic vibrations of the air. From the hole in auricle the external auditory canal begins - a tube 27 - 35 mm long, extending deep into the temporal bone of the skull. The skin lining the ear canal contains sulfur glands, the secretion of which prevents infection from penetrating into the hearing organ. The eardrum, a thin but strong membrane, separates the outer ear from the second part of the hearing organ, the middle ear.
Middle ear
The recess contains the main part of the auditory (Eustachian) tube - the connecting link between the middle ear and the nasopharynx. When swallowing, it opens and allows air to enter the middle ear, which balances the pressure in the tympanum and external auditory canal.
In the middle ear there are miniature movably connected to each other - a complex mechanism for transmitting acoustic vibrations coming from the external auditory canal to the auditory cells of the inner ear. The first bone is a hammer, attached to the long end; the second is an anvil, connected to the third miniature bone, a stirrup. The stapes is adjacent to the oval window, from which the inner ear begins. The bones that contain the hearing organ are very small. For example, the mass of the stapes is only 2.5 mg.
Inner ear
The third section of the hearing organ is represented by the vestibule (a miniature bone chamber), semicircular canals and a special formation - a thin-walled bone tube twisted into a spiral.
This part, shaped like a snail, is called the auditory cochlea.
The hearing organ has important anatomical structures that allow you to maintain balance and assess the position of the body in space. These are the vestibule and semicircular canals, filled with fluid and lined from the inside with very sensitive cells. When a person changes body position, fluid shifts in the channels. Receptors detect fluid displacement and send a signal about this event to the brain. This is how the organ of hearing and balance allows the brain to learn about the movements of our body.
The membrane located inside the cochlea consists of approximately 25 thousand tiny fibers of various lengths, each of which responds to sounds of a certain frequency and excites the endings auditory nerve. Nervous excitation is first transmitted to the brain and then reaches the cerebral cortex. IN hearing centers brain irritations are analyzed and systematized, as a result of which we hear sounds that fill the world.
