The pathway of the auditory analyzer connects the organ of Corti with the overlying parts of the central nervous system. The first neuron is located in a spiral node located at the base of the hollow cochlear node and passes through the channels of the bony spiral plate to the spiral organ and ends at the outer hair cells. The axons of the spiral node make up the auditory nerve, which enters the cerebellopontine angle into the brainstem, where they end in synapses with the cells of the dorsal and ventral nuclei.
The axons of the second neurons from the cells of the dorsal nucleus form cerebral strips located in the rhomboid fossa on the border of the pons and the medulla oblongata. Most of the cerebral strip passes to the opposite side and near the midline passes into the brain substance, connecting to the lateral loop of its side. The axons of the second neurons from the cells of the ventral nucleus are involved in the formation of the trapezius body. Most of the axons go to the opposite side, switching in the upper olive and the nuclei of the trapezius body. A smaller part of the fibers ends on their side.
Axons of the nuclei of the superior olive and trapezoidal body (III neuron) participate in the formation of a lateral loop with fibers of II and III neurons. Some of the fibers of the second neuron are interrupted in the nucleus of the lateral loop or switch to the third neuron in the medial geniculate body. These fibers of the third neuron of the lateral loop, passing by the medial geniculate body, end in the lower colliculus of the midbrain, where tr.tectospinalis is formed. Those fibers of the lateral loop belonging to the neurons of the superior olive, from the bridge penetrate into the superior pedicles of the cerebellum and then reach its nuclei, and the other part of the axons of the superior olive goes to the motor neurons of the spinal cord. Axons of the third neuron, located in the medial geniculate body, form the auditory radiance, ending in the Heschl transverse gyrus of the temporal lobe.
Central office of the auditory analyzer.
In humans, the cortical auditory center is the transverse gyrus of Heschl, including, in accordance with the cytoarchitectonic division of Brodmann, the fields 22, 41, 42, 44, 52 of the cortex cerebral hemispheres.
In conclusion, it should be said that, as in other cortical representations of other analyzers, in the auditory system there is a relationship between the zones of the auditory cortex. So each of the zones of the auditory cortex is associated with other zones organized tonotopically. In addition, there is a homotopic organization of connections between analogous zones of the auditory cortex of two hemispheres (there are both intracortical and interhemispheric connections). At the same time, the main part of the bonds (94%) homotopically terminate in the cells of layers III and IV, and only an insignificant part - in the V and VI layers.
94. Vestibular peripheral analyzer. On the eve of the labyrinth, there are two membranous sacs with an otolith apparatus located in them. On the inner surface of the sacs there are elevations (spots) lined with neuroepithelium, consisting of supporting and hair cells. The hairs of sensitive cells form a network that is covered with a jelly-like substance containing microscopic crystals - otoliths. With rectilinear body movements, the otoliths are displaced and mechanical pressure, which causes irritation of the neuroepithelial cells. The impulse is transmitted to the vestibular node, and then along the vestibular nerve (VIII pair) to the medulla oblongata.
On the inner surface of the ampullae of the membranous ducts there is a protrusion - an ampullar ridge, consisting of sensitive neuroepithelial cells and supporting cells. Sensitive hairs sticking together are presented in the form of a brush (cupula). Irritation of the neuroepithelium occurs as a result of movement of the endolymph when the body is displaced at an angle (angular acceleration). The impulse is transmitted by the fibers of the vestibular branch of the vestibular cochlear nerve, which ends in the nuclei of the medulla oblongata. This vestibular area is associated with the cerebellum, spinal cord, nuclei of the oculomotor centers, cerebral cortex.
In accordance with the associative connections of the vestibular analyzer, vestibular reactions are distinguished: vestibulosensory, vestibulo-vegetative, vestibulosomatic (animal), vestibulocerebellar, vestibulospinal, vestibulo-ocular motor.
95. Pathway of the vestibular (statokinetic) analyzer ensures the conduction of nerve impulses from the hairy sensory cells of the ampullar crests (ampullae of the semicircular ducts) and spots (elliptical and spherical sacs) to the cortical centers of the cerebral hemispheres.
The bodies of the first neurons of the statokinetic analyzer lie in the vestibule node located at the bottom of the internal auditory canal. The peripheral processes of the pseudo-unipolar cells of the vestibular node end on the hairy sensory cells of the ampullary crests and spots.
The central processes of pseudo-unipolar cells in the form of the vestibular part of the vestibular cochlear nerve, together with the cochlear part through the internal auditory opening, enter the cranial cavity, and then into the brain to the vestibular nuclei lying in the region of the vestibular field, area vesribularis of the rhomboid fossa
The ascending part of the fibers ends on the cells of the upper vestibular nucleus (ankylosing spondylitis *) The fibers that make up the descending part, end in the medial (Schwalbe **), lateral (Deiters ***) and lower Roller ****) vestibular nuclei
Axons of cells of vestibular nuclei (II neurons) form a series of bundles that go to the cerebellum, to the nuclei of the nerves of the eye muscles, the nuclei vegetative centers, cerebral cortex, to the spinal cord
Part of cell axons lateral and superior vestibular nucleus in the form of a vestibular spinal pathway, it is directed to the dorsal mine, located along the periphery at the border of the anterior and lateral cords and ends segment by segment on the motor animal cells of the anterior horns, carrying out vestibular impulses to the muscles of the neck of the trunk and extremities, ensuring the maintenance of body balance
Part of the axons of neurons lateral vestibular nucleus is directed to the medial longitudinal bundle of its own and the opposite side, providing a connection between the balance organ through the lateral nucleus with the nuclei of the cranial nerves (III, IV, VI bunk), which innervate the muscles of the eyeball, which allows you to maintain the direction of gaze, despite changes in the position of the head. Maintaining body balance relies heavily on coordinated movements eyeballs and heads
Cell axons of vestibular nuclei form connections with neurons of the reticular formation of the brain stem and with the nuclei of the midbrain tegmental
The emergence of autonomic reactions(decrease in heart rate, drop blood pressure, nausea, vomiting, blanching of the face, increased motility of the gastrointestinal tract, etc.) in response to excessive irritation of the vestibular apparatus can be explained by the presence of connections of the vestibular nuclei through the reticular formation with the nuclei of the vagus and glossopharyngeal nerves
Conscious determination of the position of the head is achieved by the presence of connections vestibular nuclei with the cerebral cortex In this case, the axons of the cells of the vestibular nuclei pass to the opposite side and are directed as part of the medial loop to the lateral nucleus of the thalamus, where they switch to neurons III
Axons of III neurons pass through the back of the posterior leg of the inner capsule and reach cortical nucleus stato-kinetic analyzer, which is scattered in the cortex of the superior temporal and postcentral gyri, as well as in the superior parietal lobe of the cerebral hemispheres
96. Foreign bodies in the external auditory canal are most often found in children when, while playing, they push various small objects (buttons, balls, pebbles, peas, beans, paper, etc.) into their ear. However, in adults, foreign bodies are often found in the external auditory canal. They can be fragments of matches, pieces of cotton wool stuck in the ear canal at the time of cleaning the ear from wax, water, insects, etc.
Clinical picture depends on the size and nature of foreign bodies in the outer ear. So, foreign bodies with a smooth surface usually do not injure the skin of the external auditory canal and may not cause discomfort for a long time. All other objects quite often lead to reactive inflammation of the skin of the external auditory canal with the formation of a wound or ulcerative surface. Foreign bodies (cotton wool, pea, beans, etc.) swollen from moisture, covered with earwax, can lead to blockage of the ear canal. It should be borne in mind that one of the symptoms of a foreign body of the ear is hearing loss as a sound conduction disorder. It occurs as a result of a complete blockage of the ear canal. A number of foreign bodies (peas, seeds) are capable of swelling in conditions of moisture and heat, so they are removed after the infusion of substances that contribute to their shrinkage. Insects caught in the ear, at the moment of movement, cause unpleasant, sometimes painful sensations.
Diagnostics. Recognition of foreign bodies is usually not difficult. Large foreign bodies are retained in the cartilaginous part of the ear canal, while small ones can penetrate deep into the bony section. They are clearly visible during otoscopy. Thus, the diagnosis of a foreign body of the external auditory canal should and can be made during otoscopy. In cases where, with unsuccessful or inept attempts to remove a foreign body, undertaken earlier, inflammation with infiltration of the walls of the external auditory canal has occurred, the diagnosis becomes difficult. In such cases, if a foreign body is suspected, short-term anesthesia is indicated, during which both otoscopy and removal of the foreign body are possible. Radiography is used to detect metallic foreign bodies.
Treatment. After determining the size, shape and nature of the foreign body, the presence or absence of any complication, the method of its removal is selected. The safest method of removing uncomplicated foreign bodies is to wash them out with warm water from a Janet-type syringe with a capacity of 100-150 ml, which is performed in the same way as removing a sulfur plug. When trying to remove with tweezers or forceps, a foreign body can slip out and penetrate from the cartilaginous section into the bony section of the ear canal, and sometimes even through the eardrum into the middle ear. In these cases, the removal of a foreign body becomes more difficult and requires great care and good fixation of the patient's head, short-term anesthesia is required. The hook of the probe must be held under the control of vision by the foreign body and pulled out. A complication of instrumental removal of a foreign body can be a rupture of the tympanic membrane, dislocation of the auditory ossicles, etc. Swollen foreign bodies (peas, beans, beans, etc.) must be previously dehydrated by infusing 70% alcohol into the ear canal for 2-3 days, as a result of which they shrink and are removed without much difficulty by washing. Insects, if they enter the ear, are killed by pouring a few drops of pure alcohol or heated liquid oil into the ear canal, and then removed by washing. In cases where a foreign body wedged into the bone region and led to a sharp inflammation of the tissues of the ear canal or led to an injury to the tympanic membrane, they resort to surgery under anesthesia. An incision is made in the soft tissues behind the auricle, the back wall of the cutaneous ear canal is exposed and cut, and the foreign body is removed. Sometimes it is necessary to surgically expand the lumen of the bone section by removing part of its posterior wall.
1. Peripheral department -it is a receptor apparatus with intercalated formations.
2. Conducting department:from receptors nerve impulses are transmitted to 1st neuron - a spiral ganglion that lies in the basement membrane. The axons of these cells are part of the precochlear nerve (YIII pair) and end with synapses on the cells 2nd neuron, which lies in the medulla oblongata (the bottom of the 4th ventricle of the brain is the rhomboid fossa). From the medulla oblongata, the axons of 2 neurons go to midbrain (lower tubercles of the quadruple) and the medial geniculate body. Before the geniculate body, a part of the fibers crosses. Some of the information does not go further, but closes in on the motor path unconditioned reflexes auditory system (motor reactions to auditory stimuli).
3rd neuronis located in the thalamus (the simplest reflexes are closed, the main thing is highlighted, information is grouped).
3. Cortical section of the auditory analyzer -the cortex of the temporal lobe of the cerebral hemispheres. The received nerve impulses are transformed in the form of sound sensations.
BONE AND AIR CONDUCTIVITY OF SOUNDS. AUDIOMETRY
Air and bone conduction
The eardrum is included in sound vibrations and transfers their energy along the chain of the bones of the middle ear to the perilymph of the vestibular ladder. The sound transmitted along this path propagates in the air - this is air conduction.
The sensation of sound also occurs when a vibrating object, such as a tuning fork, is placed directly on the skull; in this case, the main part of the energy is transmitted through the bones of the skull - this is bone conduction. For excitement inner ear movement of the inner ear fluid is necessary. The sound transmitted through the bones causes this movement in two ways:
1. Areas of compression and rarefaction passing along the bones of the skull move fluid from the voluminous vestibular labyrinth to the cochlea and back ("compression theory").
2. The bones of the middle ear have a certain mass, and therefore the vibrations of the bones due to inertia are delayed in comparison with the vibrations of the bones of the skull.
Hearing impairment testing
The most important clinical test is threshold audiometry (Fig. 32).
1. The test subject is presented with different tones through one telephone earpiece. The doctor, starting with a certain intensity of sound, which is defined as subthreshold, gradually increases the sound pressure until the subject reports that he hears a sound. This sound pressure is plotted on a graph. On audiographic forms, the normal hearing threshold is shown with a bold line and marked "O dB". In contrast to the graph in fig. 31 more high values the auditory threshold is applied below the zero line (which characterizes the degree of hearing loss); thus, it demonstrates how much the threshold level for a given patient (in dB) differs from the normal one. Note that in this case we are not talking about the sound pressure level, which is measured in decibels of SPL. When it is determined by how many dB the patient's hearing threshold is below normal, they say that hearing loss is so many dB. For example, if you plug both ears with your fingers, the hearing loss will be approximately 20 dB (when doing this experiment, you should avoid making noise with your fingers if possible). Using telephone headphones, the sound perception is tested when air conduction. Bone conduction is tested in a similar way, but instead of headphones, a tuning fork is used, which is placed on the mastoid process of the temporal bone from the side to be tested, so that the vibrations propagate through the bones of the skull. By comparing the cutoff curves for bone and air conduction, deafness associated with injury to the middle ear can be distinguished from that caused by damage to the inner ear.
RINNE AND WEBER'S EXPERIENCES
2. Using tuning forks (with a frequency of 256 Hz), conduction disturbances can be very easily distinguished from damage to the inner ear or from retrocochlear damage if it is known which ear is damaged.
AND. Weber's experience.
The stem of the sounding tuning fork is placed along the midline of the skull; in this case, the patient with a lesion of the inner ear reports that he hears the tone with a healthy ear; in a patient with a lesion of the middle ear, the sensation of tone shifts to the damaged side.
There is a simple explanation:
In case of injury to the inner ear:damaged receptors cause weaker stimulation in the auditory nerve, so the tone appears louder in the healthy ear.
If the middle ear is affected:first, the affected ear undergoes changes due to inflammation, and the weight of the ossicles increases. This improves the conditions for arousal of the inner ear due to bone conduction. Secondly, because in case of violations of the less sounds reach the inner ear and it adapts to a lower noise level, the receptors become more sensitive than on the healthy side.
B. Rinne test.
Allows you to compare air and bone conduction in the same ear. The sounding tuning fork is placed on the mastoid process (bone conduction) and held there until the patient stops hearing the sound, after which the tuning fork is transferred directly to the outer ear (air conduction). People with normal hearing and those with impaired perception. The tone is heard again (Rinne test is positive), and those with impaired conduction do not hear (Rinne test is negative).
46. \u200b\u200bPATHOLOGICAL HEARING DISORDERS AND THEIR DEFINITION Deafness is a common pathology. Hearing impairment reasons:
1. Violation of sound conduction.Damage to the middle ear - the sound conduction apparatus. For example, when inflammation occurs, the auditory ossicles do not transmit the normal amount of sound energy to the inner ear.
2. Impaired sound perception (sensorineural hearing loss). In this case, the hair receptors of the organ of Corti are damaged. As a result, the transfer of information from the cochlea to the central nervous system is disrupted. Such damage can occur with sound trauma under the action of high-intensity sound (more than 130 dB) or under the action of ototoxic substances (the ionic apparatus of the inner ear is damaged) - these are antibiotics, some diuretics.
3. Retrocochlear damage.In this case, the inner and middle ear are not damaged. Either the central part of the primary afferent auditory fibers or other components of the auditory tract are affected (for example, in a brain tumor).
Organ of hearing - in humans, it is paired - it allows you to perceive and analyze all the variety of sounds of the external world. Thanks to hearing, a person not only distinguishes sounds, recognizes their character, location, but also masters the ability to speak.
Distinguish between the outer, middle and inner human ear:
Outer ear - the sound-conducting part of the organ of hearing - consists of the auricle, which catches sound vibrations, and the external auditory canal, along which sound waves are directed to the eardrum.
Auricle is a cartilaginous plate covered by the perichondrium and skin; its lower part - the lobe - is devoid of cartilage and contains fatty tissue. The auricle is richly innervated: the branches of the large ear, ear-temporal and vagus nerve... These nerve communications connect it to the deep structures of the brain that regulate activity. internal organs... Muscles are also suitable for the auricle: lifting, moving forward, pulling back, but they are all rudimentary, and a person, as a rule, cannot actively move the auricle, capturing sound vibrations, as, for example, animals do. the sound wave hits external auditory canal 2 centimeters long and about a centimeter in diameter. All over it is covered with skin. In its thickness lie sebaceous glands, as well as sulfur, emitting earwax.
Middle ear separated from the external tympanic membrane, formed by the connective tissue. Eardrum serves as an outer wall (and there are six walls in total) narrow vertical chamber - the tympanic cavity. This cavity is the main part of the human middle ear; it contains a chain of three miniature auditory ossicles, movably interconnected by joints. The chain is maintained in a state of some tension by two very small muscles.
The first of the three bones is the hammer - fused with the tympanic membrane. Vibrations of the membrane caused by sound wavestransmitted to the hammer, from him the second bone is the anvil, and then the third is the stirrup... The base of the stirrup is movably inserted into an oval-shaped window, "cut out" on the inner wall of the tympanic cavity. This wall (it is called labyrinthine) separates the tympanic cavity from the inner ear. In addition to the window, covered by the base of the stirrup, there is another round hole in the wall - snail windowclosed with a thin membrane. The facial nerve passes through the thickness of the labyrinth wall.
The middle ear also includes auditory, or eustachian, tubeconnecting the tympanic cavity with the nasopharynx. Through this pipe 3.5 - 4.5 centimeters long, the air pressure in the tympanic cavity is balanced with atmospheric pressure.
Inner ear as part of the organ of hearing, it is represented by the vestibule and the cochlea.
The vestibule - a miniature bone chamber - in front of it passes into the cochlea - a thin-walled bone tube, twisted into a spiral. This tube makes two and a half curls around the bony axial shaft, gradually tapering towards the apex. In shape, it is very similar to a grape snail (hence the name).
Height from base snails to its top is 4 - 5 millimeters. The cochlear cavity is divided into three independent channels by a spiral bone protrusion and a connective tissue membrane. Upper channel, communicating with the vestibule, is called the staircase of the vestibule , lower channel, or drum ladder reaches the wall of the tympanic cavity and rests directly on the round window, closed by the membrane. These two channels communicate with each other through a narrow opening in the apex of the cochlea.They are filled with a specific liquid - perilymph, which vibrates under the influence of sound. First, from the jolts of the stirrup, the perilymph begins to vibrate, filling the staircase of the vestibule, and then through the hole in the region of the top, the wave of vibrations is transmitted to the perilymph of the tympanic staircase.
The third, membranous canal, formed by the connective tissue membrane, is inserted into the bone labyrinth of the cochlea and repeats it in shape. It is also filled with liquid - endolymph. The soft walls of the membranous canal are very sensitive to vibrations of the perilymph and transmit them to the endolymph. And already under its influence, collagen fibers of the main membrane, protruding into the lumen of the membranous canal, begin to vibrate. On this membrane is located the actual receptor apparatus of the auditory analyzer - the auditory, or Corti's organ. In the receptor hair cells of the apparatus, physical energy sound vibrations converted into nerve impulses.
The sensory endings of the auditory nerve approach the hair cells, which perceive information about sound and transmit it along nerve fibers to the auditory centers of the brain. The Higher Hearing Center is located in temporal lobe cerebral cortex: analysis and synthesis of sound signals is carried out here.
39. The organ of balance: the general plan of the structure. Pathway of the vestibular analyzer.
Predoor-cochlear organ in the process of evolution in animals it emerged as a complex organ of balance (vestibule ), perceiving the position of the body (heads) when it moves in space, and the organ of hearing. The first of them in the form of a primitive structure (static bubble) appears also in invertebrates. In fish due to the complication of their motor functions first one, and then the second semicircular canal is formed. In terrestrial vertebrates with their complex movements, an apparatus was formed, which in humans is represented by a vestibule and three semicircular canals located in three mutually perpendicular planes and perceiving not only the position of the body in space and its movement along a straight line, but also movements (turns of the body, head in any plane). Vestibular pathway (statokinetic) analyzerensures the conduction of nerve impulses from the hairy sensory cells of the ampullary scallops(ampullae of semicircular ducts) and stains(elliptical and spherical sacs) in the cortical centers of the cerebral hemispheres. The bodies of the first neurons statokinetic analyzer lie in the vestibule node located at the bottom of the internal auditory canal. Peripheral processes The pseudo-unipolar cells of the vestibular node end on the hairy sensory cells of the ampullar crests and spots. Central processes pseudo-unipolar cells in the form of the vestibular part of the vestibular cochlear nerve together with the cochlear part through the internal auditory opening enter the cranial cavity, and then into the brain to the vestibular nuclei lying in the region of the vestibular field,area vesribularis diamond-shaped fossa. The ascending part of the fibers ends on the cells of the upper vestibular nucleus(Bekhtereva). The fibers that make up the descending part end in the medial (Schwalbe), lateral (Deiters) and lower Roller) vestibular nuclei.
Axons of cells of vestibular nuclei (II neurons) form a series of bundles that go to the cerebellum, to the nuclei of the nerves of the eye muscles, the nuclei of the autonomic centers, the cerebral cortex and to the spinal cord.
Part of the axons of the cells of the lateral and superior vestibular nucleus in the form of the vestibular spinal pathway, it is directed to the dorsal mine, located along the periphery at the border of the anterior and lateral cords and ends segment by segment on the motor animal cells of the anterior horns, carrying out vestibular impulses to the muscles of the neck of the trunk and extremities, ensuring the maintenance of body balance.
Part of axons of neurons of the lateral vestibular nucleus directed into the medial longitudinal bundle of its own and the opposite side, providing a connection between the balance organ through the lateral nucleus with the nuclei cranial nerves (III, IV, VI bunk), innervating the muscles of the eyeball, which allows you to maintain the direction of gaze, despite changes in the position of the head. Maintaining the balance of the body depends to a large extent on coordinated movements of the eyeballs and the head.
Cell axons of the vestibular nuclei form connections with the neurons of the reticular formation of the brain stem and with the nuclei of the tegmental midbrain. The appearance of autonomic reactions (decrease in pulse rate, drop in blood pressure, nausea, vomiting, pale face, increased peristalsis gastrointestinal tract etc.) in response to excessive irritation of the vestibular apparatus can be explained by the presence of connections of the vestibular nuclei through the reticular formation with the nuclei of the vagus and glossopharyngeal nerves.
Conscious determination of the position of the head is achieved by the presence of connections of the vestibular nuclei with the cerebral cortex.In this case, the axons of the cells of the vestibular nuclei pass to the opposite side and are directed as part of the medial loop to the lateral nucleus of the thalamus, where they switch to neurons III.
Axons of III neurons pass through the posterior part of the posterior leg of the internal capsule and reach the cortical nucleus of the statokinetic analyzer, which is scattered in the cortex of the superior temporal and postcentral gyri, as well as in the superior parietal lobe of the cerebral hemispheres.
The auditory analyzer includes three main parts: the organ of hearing, the auditory nerves, the subcortical and cortical centers of the brain. Not many people know how the auditory analyzer works, but today we will try to figure it out together.
A person recognizes the world around him and adapts in society thanks to the senses. One of the most important are the organs of hearing, which pick up sound vibrations and provide a person with information about what is happening around him. The collection of systems and organs that provide the sense of hearing is called the auditory analyzer. Let's take a look at the structure of the organ of hearing and balance.
The structure of the auditory analyzer
The functions of the auditory analyzer, as mentioned above, are to perceive sound and give information to a person, but for all, at first glance, simplicity, this is a rather complex procedure. In order to better understand how the departments of the auditory analyzer in the human body work, you need to thoroughly understand what is it internal anatomy auditory analyzer.
The auditory analyzer includes:
- the receptor (peripheral) apparatus is, and;
- conductive (middle) apparatus - the auditory nerve;
- central (cortical) apparatus - auditory centers in the temporal lobes of the cerebral hemispheres.
The hearing organs in children and adults are identical, they include three types of hearing aid receptors:
- receptors that perceive fluctuations in air waves;
- receptors that give a person an idea of \u200b\u200bthe location of the body;
- receptor centers that allow you to perceive the speed of movement and its direction.
The organ of hearing of each person consists of 3 parts, considering each of them in more detail, you can understand how a person perceives sounds. So, this is the complex and the auditory canal. The shell is a cavity of elastic cartilage that is covered with a thin layer of skin. The outer ear is a kind of amplifier for converting sound vibrations. Auricles located on both sides human head and do not play a role, since they simply collect sound waves. immobile, and even if their external part is absent, then the structure of the human auditory analyzer will not receive much harm.
Considering the structure and functions of the external auditory canal, we can say that it is a small canal 2.5 cm long, which is lined with skin with fine hairs. The canal contains apocrine glands capable of producing earwax, which, together with hairs, helps protect the following ear sections from dust, pollution and foreign particles. The outer part of the ear only helps to collect sounds and conduct them in central department auditory analyzer.
Eardrum and middle ear
It looks like a small oval with a diameter of 10 mm, a sound wave passes through it into the inner ear, where it creates some vibrations in the liquid, which fills this section of the human auditory analyzer. For the transmission of air vibrations in the human ear, there is a system, it is their movements that activate the fluid vibration.
It is located between the outer part of the organ of hearing and the inner section. This part of the ear looks like a small cavity, with a capacity of no more than 75 ml. This cavity is associated with the pharynx, cells mastoid and the auditory tube, which is a kind of fuse that equalizes the pressure inside the ear and outside. I would like to note that the eardrum is always subjected to the same atmospheric pressure both outside and inside, this allows the hearing organ to function normally. If there is a difference between the pressures inside and outside, then hearing loss will appear. 
The structure of the inner ear
The most complicated part of the auditory analyzer is, it is also called the "labyrinth". The main receptor apparatus that picks up sounds is the hair cells of the inner ear, or, as they say, "cochlea".
The conduction section of the auditory analyzer consists of 17,000 nerve fibers, which resemble the structure of a telephone cable with separately insulated wires, each of which transmits certain information to neurons. It is the hairy cells that respond to fluctuations in the fluid inside the ear and transmit nerve impulses in the form of acoustic information to the peripheral part of the brain. And the peripheral part of the brain is responsible for the senses.
The pathways of the auditory analyzer provide fast transmission of nerve impulses. Simply put, the pathways of the auditory analyzer connect the hearing organ with the central nervous system person. The stimulation of the auditory nerve activates the motor pathways, which are responsible, for example, for twitching the eye due to a strong sound. The cortical section of the auditory analyzer connects the peripheral receptors of both sides, and when capturing sound waves, this section compares sounds from two ears at once.
The mechanism of transmission of sounds at different ages
The anatomical characteristics of the auditory analyzer does not change at all with age, but I would like to note that there are some age-related features.
The hearing organs begin to form in the embryo at 12 weeks of development. The ear begins its functionality immediately after birth, but at initial stages a person's auditory activity is more like reflexes. Sounds of different frequency and intensity cause different reflexes in children, it can be closing the eyes, flinching, opening the mouth or rapid breathing. If the newborn reacts in this way to distinct sounds, then it is clear that the auditory analyzer is developed normally. In the absence of these reflexes, additional research is required. Sometimes the child's reaction is impeded by the fact that initially the middle ear of the newborn is filled with a certain fluid that interferes with the movement of the auditory ossicles, over time, the specialized fluid completely dries up and instead of it the middle ear fills up with air.
The baby begins to differentiate dissimilar sounds from 3 months, and at 6 months of life begins to distinguish tones. At 9 months of age, a child can recognize the voices of parents, the sound of a car, a bird's song and other sounds. Children begin to identify a familiar and someone else's voice, recognize it and begin to haunt, rejoice, or even look for the source of their native sound with their eyes if it is not nearby. The development of the auditory analyzer lasts up to 6 years, after which the child's hearing threshold decreases, but the hearing acuity increases. This continues for up to 15 years, then works in the opposite direction.
In the period from 6 to 15 years old, you can notice that the level of hearing development is different, some children pick up sounds better and are able to repeat them without difficulty, they manage to sing and copy sounds well. Other children do it worse, but at the same time they hear perfectly, sometimes they say to such children "the bear frowned in his ear." Communication between children and adults is of great importance, it is this that forms the speech and musical perception of the child.
Concerning anatomical features, then in newborns the auditory tube is much shorter than in adults and wider, because of this infection from respiratory tract so often affects their hearing organs.
Sound perception
For the auditory analyzer, sound is an adequate stimulus. The main characteristics of each sound tone are the frequency and amplitude of the sound wave.
The higher the frequency, the higher the pitch. The strength of the sound, expressed by its loudness, is proportional to the amplitude and is measured in decibels (dB). The human ear is able to perceive sound in the range from 20 Hz to 20,000 Hz (children - up to 32,000 Hz). The ear has the greatest excitability to sounds with a frequency of 1000 to 4000 Hz. Below 1000 and above 4000 Hz, the excitability of the ear is greatly reduced.
A sound with a strength of up to 30 dB is very weak, from 30 to 50 dB corresponds to a person's whisper, from 50 to 65 dB - ordinary speech, from 65 to 100 dB - loud noise, 120 dB - "pain threshold", and 140 dB - causes damage to the middle (ruptured tympanic membrane) and inner (destruction of Corti's organ) ear.
The threshold of speech hearing in children 6-9 years old is 17-24 dBA, in adults - 7-10 dBA. With the loss of the ability to perceive sounds from 30 to 70 dB, difficulties are observed when speaking, below 30 dB - almost complete deafness is stated.
With prolonged exposure to the ear of strong sounds (2-3 minutes), hearing acuity decreases, and in silence - is restored; 10-15 seconds are enough for this (auditory adaptation).
Lifetime Hearing Aid Changes
The age characteristics of the auditory analyzer change slightly throughout a person's life.
In newborns, the perception of the pitch and loudness of sound is reduced, but by 6-7 months, the sound perception reaches the adult's norm, although the functional development of the auditory analyzer, associated with the development of fine differentiations to auditory stimuli, lasts up to 6-7 years. The greatest hearing acuity is characteristic of adolescents and young men (14-19 years old), then gradually decreases.
In old age auditory perception changes its frequency. So, in childhood, the threshold of sensitivity is much higher, it is 3200 Hz. From 14 to 40 years old we are at a frequency of 3000 Hz, and at 40-49 years old at 2000 Hz. After 50 years only at 1000 Hz, it is from this age that the upper limit of hearing begins to decrease, which explains the deafness in old age.
Elderly people often have blurred perception or choppy speech, that is, they hear with some interference. They can hear part of the speech well, and skip a few words. In order for a person to hear normally, he needs both ears, one of which perceives sound, and the other maintains balance. With age, the structure of the eardrum will change in a person, it can become denser under the influence of certain factors, which will disturb the balance. When it comes to gender sensitivity to sounds, men lose hearing much faster than women.
I would like to note that with special training, even in old age, an increase in the hearing threshold can be achieved. Likewise, exposure to loud noise in a constant mode can adversely affect the hearing system even at a young age. In order to avoid negative consequences from constant exposure loud sound on the human body, you need to monitor. This is a set of measures aimed at creating normal conditions for the functioning of the auditory organ. In young people, the critical noise limit is 60 dB, and in children school age critical threshold 60 dB. It is enough to stay in a room with such a noise level for an hour and negative consequences will not keep you waiting.
Another age-related change in the hearing aid is the fact that earwax hardens over time, which prevents the air waves from vibrating normally. If a person has a tendency to cardiovascular disease... It is likely that the blood in the damaged vessels will circulate faster, and with age, a person will distinguish extraneous noises in the ears.
Modern medicine has long figured out how the auditory analyzer works and is very successfully working on hearing aids that allow people to return hearing after 60 years of age and enable children with developmental defects of the auditory organ to live a full life.
The physiology and operation of the auditory analyzer is very complex, and it is very difficult for people without the appropriate skills to understand it, but in any case, every person should be theoretically familiar.
Now you know how the receptors and parts of the auditory analyzer work.
Bibliography:
- A. A. Drozdov "ENT diseases: lecture notes", ISBN: 978-5-699-23334-2;
- Palchun V.T. " Short course otorhinolaryngology: a guide for physicians. " ISBN: 978-5-9704-3814-5;
- Shvetsov A.G. Anatomy, physiology and pathology of the organs of hearing, vision and speech: Tutorial... Veliky Novgorod, 2006
Prepared under the editorship of A.I. Reznikov, doctor of the first category
