Auditory sensory system structure and functions table. Location and structure of receptor cells of the spiral organ

Sensor system (analyzer)- called the part of the nervous system consisting of perceptive elements - sensory receptors, nerve pathways that transmit information from the receptors to the brain and parts of the brain that process and analyze this information

The sensor system includes 3 parts

1. Receptors - sense organs

2. Conductor section connecting receptors to the brain

3. Section of the cerebral cortex, which perceives and processes information.

Receptors- a peripheral link designed to perceive stimuli from the external or internal environment.

Sensory systems have a general structure plan and sensory systems are characterized by

Multi-layering- presence of several layers nerve cells, the first of which is associated with receptors, and the latter with neurons of the motor areas of the cerebral cortex. Neurons are specialized for processing different types sensory information.

Multichannel- the presence of multiple parallel channels for processing and transmitting information, which ensures detailed signal analysis and greater reliability.

Different number of elements in adjacent layers, which forms the so-called “sensory funnels” (narrowing or expanding) They can ensure the elimination of redundancy of information or, conversely, a fractional and complex analysis of signal features

Differentiation sensory system vertically and horizontally. Vertical differentiation means the formation of sections of the sensory system, consisting of several neural layers (olfactory bulbs, cochlear nuclei, geniculate bodies).

Horizontal differentiation represents the presence of receptors and neurons with different properties within the same layer. For example, rods and cones in the retina process information differently.

The main task of the sensory system is the perception and analysis of the properties of stimuli, on the basis of which sensations, perceptions, and ideas arise. This constitutes the forms of a sensory, subjective reflection of the external world

Functions of touch systems

1. Signal detection. Each sensory system in the process of evolution has adapted to the perception of adequate stimuli inherent to a given system. The sensory system, for example the eye, can receive different - adequate and inadequate irritations (light or a blow to the eye). Sensory systems perceive force - the eye perceives 1 light photon (10 V -18 W). Eye shock(10V -4W). Electric current(10V -11W)
2. Signal discrimination.
3. Signal transmission or conversion. Any sensory system works as a transducer. It converts one form of energy from an active stimulus into energy nervous irritation. The sensory system should not distort the stimulus signal.

• May be spatial in nature
• Temporary transformations
• limitation of information redundancy (inclusion of inhibitory elements that inhibit neighboring receptors)
• Identification of essential signal features

1. Information coding - in the form of nerve impulses
2. Signal detection, etc. e. identifying signs of a stimulus that has behavioral significance
3. Provide image recognition
4. Adapt to stimuli
5. Interaction of sensory systems, which form the scheme of the surrounding world and at the same time allow us to relate ourselves to this scheme, for our adaptation. All living organisms cannot exist without receiving information from environment. The more accurately an organism receives such information, the higher its chances will be in the struggle for existence.

Sensory systems are capable of responding to inappropriate stimuli. If you try the battery terminals, it causes taste sensation- sour, this is the effect of electric current. This reaction of the sensory system to adequate and inadequate stimuli has raised the question for physiology - how much we can trust our senses.

Johann Müller formulated in 1840 the law of specific energy of the sense organs.

The quality of sensations does not depend on the nature of the stimulus, but is determined entirely by the specific energy inherent in the sensitive system, which is released when the stimulus acts.

With this approach, we can only know what is inherent in ourselves, and not what is in the world around us. Subsequent studies showed that excitations in any sensory system arise on the basis of one energy source - ATP.

Muller's student Helmholtz created symbol theory, according to which he considered sensations as symbols and objects of the surrounding world. The theory of symbols denied the possibility of knowing the world around us.

These 2 directions were called physiological idealism. What is a sensation? A sensation is a subjective image of the objective world. Sensations are images of the external world. They exist in us and are generated by the action of things on our senses. For each of us, this image will be subjective, i.e. it depends on the degree of our development, experience, and each person perceives surrounding objects and phenomena in his own way. They will be objective, i.e. this means that they exist, regardless of our consciousness. Since there is subjectivity of perception, then how to decide who perceives most correctly? Where will the truth be? The criterion of truth is Practical activities. Consistent learning is taking place. At each stage it turns out new information. The child tastes the toys and takes them apart into parts. It is from these deep experiences that we gain deeper knowledge about the world.

Classification of receptors.

1. Primary and secondary. Primary receptors represent a receptor ending that is formed by the very first sensory neuron (Pacinian corpuscle, Meissner's corpuscle, Merkel's disk, Ruffini's corpuscle). This neuron lies in spinal ganglion. Secondary receptors perceive information. Due to specialized nerve cells, which then transmit excitation to the nerve fiber. Sensitive cells of the organs of taste, hearing, balance.
2. Remote and contact. Some receptors perceive excitation through direct contact - contact, while others can perceive irritation at some distance - distant
3. Exteroceptors, interoreceptors. Exteroceptors- perceive irritation from external environment- vision, taste, etc. and they provide adaptation to the environment. Interoreceptors- receptors of internal organs. They reflect the state of the internal organs and internal environment of the body.
4. Somatic - superficial and deep. Superficial - skin, mucous membranes. Deep - receptors of muscles, tendons, joints
5. Visceral
6. CNS receptors
7. Receptors of special senses - visual, auditory, vestibular, olfactory, gustatory

By the nature of information perception

1. Mechanoreceptors (skin, muscles, tendons, joints, internal organs)
2. Thermoreceptors (skin, hypothalamus)
3. Chemoreceptors (aortic arch, carotid sinus, medulla oblongata, tongue, nose, hypothalamus)
4. Photoreceptors (eye)
5. Pain (nociceptive) receptors (skin, internal organs, mucous membranes)

Mechanisms of receptor excitation

In the case of primary receptors, the action of the stimulus is perceived by the ending of the sensory neuron. An active stimulus can cause hyperpolarization or depolarization of the surface membrane receptors, mainly due to changes in sodium permeability. An increase in permeability to sodium ions leads to depolarization of the membrane and a receptor potential arises on the receptor membrane. It exists as long as the stimulus is in effect.

Receptor potential does not obey the “All or nothing” law; its amplitude depends on the strength of the stimulus. It has no refractory period. This allows the receptor potentials to be summed up during the action of subsequent stimuli. It spreads melenno, with extinction. When the receptor potential reaches a critical threshold, it causes an action potential to appear at the nearest node of Ranvier. At the node of Ranvier, an action potential arises, which obeys the “All or Nothing” law. This potential will be spreading.

In the secondary receptor, the action of the stimulus is perceived by the receptor cell. A receptor potential arises in this cell, the consequence of which will be the release of the transmitter from the cell into the synapse, which acts on the postsynaptic membrane of the sensitive fiber and the interaction of the transmitter with the receptors leads to the formation of another, local potential, which is called generator. Its properties are identical to receptor ones. Its amplitude is determined by the amount of released mediator. Mediators - acetylcholine, glutamate.

Action potentials occur periodically because They are characterized by a refractory period, when the membrane loses its excitability. Action potentials arise discretely and the receptor in the sensory system works like an analog-to-discrete converter. An adaptation is observed in the receptors - adaptation to the action of stimuli. There are those who adapt quickly and those who adapt slowly. During adaptation, the amplitude of the receptor potential and the number of nerve impulses that travel along the sensitive fiber decrease. Receptors encode information. It is possible by the frequency of potentials, by the grouping of impulses into separate volleys and the intervals between volleys. Coding is possible based on the number of activated receptors in the receptive field.

Threshold of irritation and threshold of entertainment.

Threshold of irritation- the minimum strength of the stimulus that causes a sensation.

Threshold of entertainment- the minimum force of change in the stimulus at which a new sensation arises.

Hair cells are excited when the hairs are displaced by 10 to -11 meters - 0.1 amstrom.

In 1934, Weber formulated a law establishing a relationship between the initial strength of stimulation and the intensity of sensation. He showed that the change in the strength of the stimulus is a constant value

∆I / Io = K Io=50 ∆I=52.11 Io=100 ∆I=104.2

Fechner determined that sensation is directly proportional to the logarithm of irritation

S=a*logR+b S-sensation R-irritation

S=KI in A Degree I - strength of irritation, K and A - constants

For tactile receptors S=9.4*I d 0.52

In sensory systems there are receptors for self-regulation of receptor sensitivity.

Influence of the sympathetic system - sympathetic system increases the sensitivity of receptors to the action of stimuli. This is useful in a situation of danger. Increases the excitability of receptors - reticular formation. Efferent fibers have been found in the sensory nerves, which can change the sensitivity of the receptors. Such nerve fibers are found in the auditory organ.

Sensory hearing system

For most people living in a modern shutdown, their hearing is progressively declining. This happens with age. This is facilitated by pollution from environmental sounds - vehicles, discotheques, etc. Changes in the hearing aid become irreversible. The human ears contain 2 sensory organs. Hearing and balance. Sound waves propagate in the form of compression and discharge in elastic media, and the propagation of sounds in dense media is better than in gases. Sound has 3 important properties- pitch or frequency, power, or intensity and timbre. The pitch of sound depends on the vibration frequency and the human ear perceives frequencies from 16 to 20,000 Hz. With maximum sensitivity from 1000 to 4000 Hz.

The main frequency of the sound of a man's larynx is 100 Hz. Women - 150 Hz. When talking, additional high-frequency sounds appear in the form of hissing and whistling, which disappear when talking on the phone and this makes speech more understandable.

The power of sound is determined by the amplitude of vibrations. Sound power is expressed in dB. Power is a logarithmic relationship. Whispering speech - 30 dB, normal speech - 60-70 dB. The sound of transport is 80, the noise of an airplane engine is 160. A sound power of 120 dB causes discomfort, and 140 leads to painful sensations.

Timbre is determined by secondary vibrations on sound waves. Ordered vibrations create musical sounds. And random vibrations simply cause noise. The same note sounds differently different instruments due to various additional fluctuations.

The human ear has 3 components - the outer, middle and inner ear. The outer ear is represented by the auricle, which acts as a sound-collecting funnel. The human ear picks up sounds less perfectly than the rabbit, and horses, which can control their ears. The auricle is based on cartilage, with the exception of the earlobe. Cartilage tissue gives elasticity and shape to the ear. If cartilage is damaged, it is restored by growing. Outer ear canal S-shaped - inward, forward and downward, length 2.5 cm. The ear canal is covered with skin with low sensitivity of the outer part and high sensitivity of the inner part. The outer part of the ear canal contains hair that prevents particles from entering the ear canal. The glands of the ear canal produce a yellow lubricant, which also protects the ear canal. At the end of the passage is the eardrum, which consists of fibrous fibers covered on the outside with skin and on the inside with mucous membrane. The eardrum separates the middle ear from the outer ear. It vibrates with the frequency of the perceived sound.

The middle ear is represented by the tympanic cavity, the volume of which is approximately 5-6 drops of water and tympanic cavity filled with water, lined with mucous membrane and contains 3 auditory ossicles: malleus, incus and stapes. The middle ear communicates with the nasopharynx via the Eustachian tube. At rest, the lumen of the Eustachian tube is closed, which equalizes the pressure. Inflammatory processes, leading to inflammation of this tube, causing a feeling of congestion. The middle ear is separated from the inner ear by an oval and round opening. Vibrations of the eardrum through a system of levers are transmitted by the stapes to oval window, and the outer ear transmits sounds by air.

There is a difference in the area of ​​the tympanic membrane and the oval window (the area of ​​the tympanic membrane is 70 mm per sq. and that of the oval window is 3.2 mm per sq.). When vibrations are transferred from the membrane to the oval window, the amplitude decreases and the strength of vibrations increases by 20-22 times. At frequencies up to 3000 Hz, 60% of E is transmitted to inner ear. In the middle ear there are 2 muscles that change vibrations: the tensor tympani muscle (attached to the central part of the eardrum and to the handle of the malleus) - as the force of contraction increases, the amplitude decreases; stapes muscle - its contractions limit the vibrations of the stapes. These muscles prevent injury to the eardrum. In addition to airborne sound transmission, there is also bone transfer, but this sound force is not able to cause vibrations in the bones of the skull.

Inner ear

The inner ear is a labyrinth of interconnected tubes and extensions. The organ of balance is located in the inner ear. The labyrinth has bone base, and inside there is a membranous labyrinth and there is endolymph. The auditory part includes the cochlea; it forms 2.5 revolutions around the central axis and is divided into 3 scalae: vestibular, tympanic and membranous. The vestibular canal begins with the membrane of the oval window and ends with the round window. At the apex of the cochlea, these 2 channels communicate using helicocream. And both of these channels are filled with perilymph. In the middle membranous canal there is a sound-receiving apparatus - the organ of Corti. The main membrane is built from elastic fibers that start at the base (0.04mm) and up to the apex (0.5mm). Toward the top, the fiber density decreases 500 times. The organ of Corti is located on the basilar membrane. It is built from 20-25 thousand special hair cells located on supporting cells. Hair cells lie in 3-4 rows (outer row) and in one row (inner). At the top of the hair cells there are stereocilia or kinocilia, the largest stereocilia. Sensory fibers approach hair cells 8 FCN pairs from the spiral ganglion. In this case, 90% of the isolated sensory fibers end up on the inner hair cells. Up to 10 fibers converge on one inner hair cell. And in the composition nerve fibers There are also efferent ones (olivo-cochlear bundle). They form inhibitory synapses on sensory fibers from the spiral ganglion and innervate the outer hair cells. Irritation of the organ of Corti is associated with the transmission of ossicular vibrations to the oval window. Low-frequency vibrations propagate from the oval window to the apex of the cochlea (the entire main membrane is involved). At low frequencies, excitation of the hair cells lying at the apex of the cochlea is observed. Bekashi studied the propagation of waves in the cochlea. He found that as the frequency increases, a smaller column of liquid is involved. High-frequency sounds cannot involve the entire column of fluid, so the higher the frequency, the less the perilymph vibrates. Vibrations of the main membrane can occur when sounds are transmitted through the membranous canal. When the main membrane oscillates, the hair cells shift upward, which causes depolarization, and if downward, the hairs deviate inward, which leads to hyperpolarization of the cells. When hair cells depolarize, Ca channels open and Ca promotes an action potential that carries information about sound. The external auditory cells have efferent innervation and the transmission of excitation occurs with the help of Ach on the external hair cells. These cells can change their length: they shorten with hyperpolarization and lengthen with polarization. Changing the length of the outer hair cells affects the oscillatory process, which improves the perception of sound by the inner hair cells. The change in hair cell potential is associated with the ionic composition of the endo- and perilymph. Perilymph resembles cerebrospinal fluid, while endolymph has high concentration K(150 mmol). Therefore, the endolymph acquires a positive charge to the perilymph (+80mV). Hair cells contain a lot of K; they have membrane potential and negatively charged inside and positive outside (MP = -70 mV), and the potential difference makes it possible for K to penetrate from the endolymph into the hair cells. Changing the position of one hair opens 200-300 K channels and depolarization occurs. Closure is accompanied by hyperpolarization. In Corti organ goes frequency coding due to excitation of different parts of the main membrane. At the same time, it was shown that low-frequency sounds can be encoded by the same number of nerve impulses as sound. Such encoding is possible when perceiving sound up to 500Hz. Encoding of sound information is achieved by increasing the number of fibers firing at a more intense sound and due to the number of activated nerve fibers. The sensory fibers of the spiral ganglion end in the dorsal and ventral nuclei of the cochlea of ​​the medulla oblongata. From these nuclei, the signal enters the olive nuclei of both its own and the opposite side. From her neurons come ascending paths as part of the lateral loop that approaches the lower tubercles of the quadrigeminal and the medial geniculate body of the optic tubercle. From the latter, the signal goes to the superior temporal gyrus (Heschl’s gyrus). This corresponds to fields 41 and 42 (primary zone) and field 22 (secondary zone). In the central nervous system there is a topotonic organization of neurons, that is, sounds are perceived with different frequencies and different intensities. Cortical center has implications for perception, sound sequencing, and spatial localization. If field 22 is damaged, the definition of words is impaired (receptive opposition).

The nuclei of the superior olive are divided into medial and lateral parts. And the lateral nuclei determine the unequal intensity of sounds coming to both ears. The medial nucleus of the superior olive detects temporal differences in input sound signals. It was discovered that signals from both ears enter different dendritic systems of the same perceptive neuron. Violation auditory perception may manifest as ringing in the ears when irritated inner ear or auditory nerve and two types of deafness: conductive and nervous. The first is associated with lesions of the outer and middle ear (cerumen plug). The second is associated with defects of the inner ear and lesions of the auditory nerve. Older people lose the ability to perceive high-frequency voices. Thanks to two ears, it is possible to determine the spatial localization of sound. This is possible if the sound deviates from the middle position by 3 degrees. When perceiving sounds, adaptation may develop due to the reticular formation and efferent fibers (by influencing the outer hair cells.

Visual system.

Vision is a multi-link process that begins with the projection of an image onto the retina of the eye, then there is excitation of photoreceptors, transmission and transformation in the neural layers visual system and ends with the adoption by the higher cortical parts of the decision about the visual image.

Structure and functions of the optical apparatus of the eye. The eye has a spherical shape, which is important for turning the eye. Light passes through several transparent media - the cornea, lens and vitreous body, which have certain refractive powers, expressed in diopters. Diopter is equal to the refractive power of a lens with a focal length of 100 cm. The refractive power of the eye when viewing distant objects is 59D, close objects are 70.5D. A smaller, inverted image is formed on the retina.

Accommodation- adaptation of the eye to clearly seeing objects at different distances. The lens plays a major role in accommodation. When viewing close objects, the ciliary muscles contract, the ligament of Zinn relaxes, and the lens becomes more convex due to its elasticity. When looking at the distant ones, the muscles are relaxed, the ligaments are tense and stretch the lens, making it more flattened. The ciliary muscles are innervated by parasympathetic fibers of the oculomotor nerve. Normally, the farthest point of clear vision is at infinity, the closest is 10 cm from the eye. The lens loses its elasticity with age, so the closest point of clear vision moves away and senile farsightedness develops.

Refractive errors of the eye.

Myopia (myopia). If the longitudinal axis of the eye is too long or the refractive power of the lens increases, the image is focused in front of the retina. The person has trouble seeing into the distance. Glasses with concave lenses are prescribed.

Farsightedness (hypermetropia). It develops when the refractive media of the eye decreases or when the longitudinal axis of the eye shortens. As a result, the image is focused behind the retina and the person has difficulty seeing nearby objects. Glasses with convex lenses are prescribed.

Astigmatism is unequal refraction of rays in different directions, due to the not strictly spherical surface of the cornea. They are compensated by glasses with a surface approaching cylindrical.

Pupil and pupillary reflex. The pupil is the hole in the center of the iris through which light rays pass into the eye. The pupil improves the clarity of the image on the retina, increasing the depth of field of the eye and by eliminating spherical aberration. If you cover your eye from light and then open it, the pupil quickly constricts - the pupillary reflex. In bright light the size is 1.8 mm, in medium light - 2.4, in the dark - 7.5. Enlargement results in poor image quality but increases sensitivity. The reflex has adaptive significance. The pupil is dilated by the sympathetic, and constricted by the parasympathetic. U healthy sizes both pupils are the same.

Structure and functions of the retina. The retina is the inner light-sensitive layer of the eye. Layers:

Pigmented - a series of branched epithelial cells of black color. Functions: screening (prevents the scattering and reflection of light, increasing clarity), regeneration of visual pigment, phagocytosis of fragments of rods and cones, nutrition of photoreceptors. The contact between the receptors and the pigment layer is weak, so this is where retinal detachment occurs.

Photoreceptors. Flasks are responsible for color vision, there are 6-7 million of them. Sticks for twilight, there are 110-123 million of them. They are located unevenly. IN fovea- only flasks, here - the greatest visual acuity. Sticks are more sensitive than flasks.

The structure of the photoreceptor. Consists of the outer receptive part - the outer segment, with visual pigment; connecting leg; nuclear part with presynaptic ending. The outer part consists of disks - a double-membrane structure. The outer segments are constantly updated. The presynaptic terminal contains glutamate.

Visual pigments. The sticks contain rhodopsin with absorption in the region of 500 nm. In the flasks - iodopsin with absorptions of 420 nm (blue), 531 nm (green), 558 (red). The molecule consists of the opsin protein and the chromophore part - retinal. Only the cis isomer perceives light.

Physiology of photoreception. When a quantum of light is absorbed, cis-retinal transforms into trans-retinal. This causes spatial changes in the protein part of the pigment. The pigment becomes discolored and becomes metarhodopsin II, which is able to interact with the near-membrane protein transducin. Transducin is activated and binds to GTP, activating phosphodiesterase. PDE breaks down cGMP. As a result, the concentration of cGMP falls, which leads to the closure of ion channels, while the sodium concentration decreases, leading to hyperpolarization and the emergence of a receptor potential that spreads throughout the cell to the presynaptic terminal and causes a decrease in the release of glutamate.

Restoration of the original dark state of the receptor. When metarhodopsin loses its ability to interact with transducin, guanylate cyclase, which synthesizes cGMP, is activated. Guanylate cyclase is activated by a drop in the concentration of calcium released from the cell by the exchange protein. As a result, the concentration of cGMP increases and it again binds to the ion channel, opening it. When opened, sodium and calcium enter the cell, depolarizing the receptor membrane, transferring it to a dark state, which again accelerates the release of the transmitter.

Retinal neurons.

Photoreceptors synapse with bipolar neurons. When light acts on the transmitter, the release of the transmitter decreases, which leads to hyperpolarization of the bipolar neuron. From the bipolar, the signal is transmitted to the ganglion. Impulses from many photoreceptors converge on a single ganglion neuron. The interaction of neighboring retinal neurons is ensured by horizontal and amacrine cells, the signals of which change synaptic transmission between receptors and bipolar (horizontal) and between bipolar and ganglion (amacrine). Amacrine cells exert lateral inhibition between adjacent ganglion cells. The system also contains efferent fibers that act on the synapses between bipolar and ganglion cells, regulating the excitation between them.

Nerve pathways.

The 1st neuron is bipolar.

2nd - ganglionic. Their processes are part of optic nerve, make a partial decussation (necessary to provide each hemisphere with information from each eye) and go to the brain as part of the optic tract, ending up in the lateral geniculate body of the thalamus (3rd neuron). From the thalamus - to the projection zone of the cortex, field 17. Here is the 4th neuron.

Visual functions.

Absolute sensitivity. For a visual sensation to occur, the light stimulus must have a minimum (threshold) energy. The stick can be excited by one quantum of light. Sticks and flasks differ little in excitability, but the number of receptors sending signals to one ganglion cell is different in the center and at the periphery.

Visual alaptation.

Adaptation of the visual sensory system to bright lighting conditions - light adaptation. The opposite phenomenon is dark adaptation. The increase in sensitivity in the dark is gradual, due to the dark restoration of visual pigments. First, the iodopsin of the flasks is restored. This has little effect on sensitivity. Then rod rhodopsin is restored, which greatly increases sensitivity. For adaptation, the processes of changing connections between retinal elements are also important: weakening of horizontal inhibition, leading to an increase in the number of cells, sending signals to the ganglion neuron. The influence of the central nervous system also plays a role. When one eye is illuminated, it reduces the sensitivity of the other.

Differential visual sensitivity. According to Weber's law, a person will distinguish a difference in lighting if it is 1-1.5% stronger.

Luminance Contrast occurs due to mutual lateral inhibition of visual neurons. A gray stripe on a light background appears darker than gray on a dark background, since cells excited by a light background inhibit cells excited by a gray stripe.

Blinding brightness of light. Too bright light causes unpleasant feeling blindness. Upper limit glare depends on the adaptation of the eye. The longer the dark adaptation, the less brightness causes blinding.

Inertia of vision. The visual sensation does not appear and disappear immediately. From irritation to perception it takes 0.03-0.1 s. Irritations that quickly follow one after another merge into one sensation. Minimum frequency of light stimuli at which fusion occurs individual sensations, is called the critical flicker fusion frequency. This is what the movie is based on. Sensations that continue after the cessation of irritation - successive images (the image of a lamp in the dark after it is turned off).

Color vision.

The entire visible spectrum from violet (400nm) to red (700nm).

Theories. Helmholtz's three-component theory. Color sensation provided by three types of bulbs, sensitive to one part of the spectrum (red, green or blue).

Hering's theory. The flasks contain substances sensitive to white-black, red-green and yellow-blue radiation.

Consistent color images. If you look at a painted object and then at White background, then the background will acquire an additional color. The reason is color adaptation.

Color blindness. Color blindness is a disorder in which it is impossible to distinguish between colors. Protanopia does not distinguish the color red. With deuteranopia - green. For tritanopia - blue. Diagnosed using polychromatic tables.

A complete loss of color perception is achromasia, in which everything is seen in shades of gray.

Perception of space.

Visual acuity- the maximum ability of the eye to distinguish individual details of objects. A normal eye distinguishes two points visible at an angle of 1 minute. Maximum sharpness in the macula area. Determined by special tables.

Sound waves- these are mechanical vibrations of the medium different frequencies and amplitudes. We perceive these vibrations as sounds that differ in pitch and volume.

Our hearing analyzer is capable of perceiving sound vibrations in the frequency range from 16 Hz to 20,000 Hz. Sample low sound(125 Hz) is the hum of a refrigerator, and the high sound (5000 Hz) is the squeak of a mosquito. Frequencies below 16 Hz (infrasound) and above 20,000 Hz (ultrasound) do not cause us to experience sound sensations. However, both infrasound and ultrasound affect our body. We perceive the intensity of sound waves as the loudness of sounds. Their unit of measurement is bel (decibel): the volume of a quiet whisper is 10 decibels, a loud scream is 80 - 90 decibels, and a sound of 130 decibels causes severe pain in the ears.

The air cavity is located on the eardrum - middle ear. It is connected using eustachian tube with the pharynx, and through it - with the oral cavity. These canals connect the external environment to the middle ear and act as a safety net that protects it from injury. Usually the entrance to the Eustachian tube is closed; it opens only when swallowing. If the middle ear experiences excessive pressure due to the action of sound waves, just open your mouth and take a sip: the pressure in the middle ear will be equal to atmospheric pressure.

The middle ear is an amplifier that can change the amplitude of sound waves that are transmitted from the eardrum to the inner ear. How does this happen? From the eardrum stretches a chain of small bones, movably connected to each other: the hammer, the anvil and the stirrup. The handle of the malleus is attached to the eardrum, and the stirrup rests on another membrane. This membrane of the opening, called the oval window, is the border between the middle and inner ear.

Eardrum vibrations cause movement auditory ossicles, which push the membrane of the oval window, and it begins to vibrate. This membrane is much smaller in area than the eardrum, and therefore it vibrates with a greater amplitude. Increased vibrations of the oval window membrane are transmitted to the inner ear.

The inner ear is located deep in temporal bone skulls It is here, in a special device called the cochlea, that the receptor apparatus of the auditory analyzer is located. The cochlea is a bony canal containing two longitudinal membranes. The lower (basal) membrane is formed by dense connective tissue, and the upper one is formed by thin single-layer tissue. Membranes divide the cochlear canal into three parts - the upper, middle and lower canals. The lower and upper channels at the top of the curls are combined with each other, and the middle one is a closed cavity. The channels are filled with fluids: the lower and upper ones are filled with perilymph, and the middle one is filled with endolymph, which is viscous to the perilymph. The upper canal starts from the oval window, and the lower one ends with a rounded window, which is located under the oval window. Vibrations of the membrane of the oval window are transmitted to the perilymph, and waves arise in it. They spread through the upper and lower channels, reaching the membrane of the rounded window.

The structure of the receptor apparatus of the auditory analyzer

What are the consequences of wave movements in the perilymph? To find out this, let us consider the structure of the receptor apparatus of the auditory analyzer. On the basement membrane of the middle canal along its entire length there is a so-called cortoi organ - an apparatus containing receptors and supporting cells. Each receptor cell contains up to 70 outgrowths - hairs. A covering membrane is located above the hair cells and is in contact with the hairs. The organ of Corti is divided into sections, each of which is responsible for the perception of waves of a certain frequency.

The fluid contained in the volute channels is a transmission link that carries the energy of sound vibrations into the integumentary membrane of the organ of corti. When the wave moves by the perilymph in the upper canal, the thin membrane between it and the middle canal bends, acts on the endolymph, and presses the integumentary membrane into the hair cells. In response to mechanical action - pressing on the hairs - signals are formed in the receptors, which they transmit to the dendrites of sensory neurons. Nerve impulses arise in these neurons, which are sent along axons united into the auditory nerve to the central department sound analyzer. The pitch of the sound we perceive is determined by which part of the organ of Corti the signal came from.

Central section of the auditory analyzer

Nerve impulses sensory neurons auditory nerves enter numerous nuclei of the brain stem, where primary processing signals, then to the thalamus, and from it to the temporal region of the cortex (auditory zone). Here, with the participation of associative zones of the cortex, recognition of auditory stimuli occurs, and we experience sound sensations. At all levels of signal processing there are leading pathways through which there is a constant exchange of information between symmetrically located nuclei, which belong to the central structures of the left and right ears.

Hearing is important in human life, which is primarily associated with the perception of speech. A person does not hear all sound signals, but only those that have biological and social significance for him. Since sound is propagating waves, the main characteristics of which are frequency and amplitude, hearing is characterized by the same parameters. Frequency is subjectively perceived as the tonality of a sound, and amplitude as its intensity and volume. The human ear is capable of perceiving sounds with a frequency from 20 Hz to 20,000 Hz and an intensity of up to 140 dB (pain threshold). The most sensitive hearing lies in the range of 1–2 thousand Hz, i.e. in the field of speech signals.

The peripheral section of the auditory analyzer - the organ of hearing, consists of the outer, middle and inner ear (Fig. 4).

Rice. 4. Human ear: 1 – auricle; 2 – external auditory canal; 3 – eardrum; 4 – Eustachian tube; 5 – hammer; 6 – anvil; 7 – stirrup; 8 – oval window; 9 – snail.

Outer ear includes the auricle and external auditory canal. These structures act as a horn and concentrate sound vibrations in a certain direction. The auricle is also involved in determining the localization of sound.

Middle ear includes the eardrum and auditory ossicles.

The eardrum, which separates the outer ear from the middle ear, is a 0.1 mm thick septum woven from fibers running in different directions. In its shape, it resembles a funnel directed inward. The eardrum begins to vibrate when sound vibrations pass through the external auditory canal. The vibrations of the eardrum depend on the parameters of the sound wave: the higher the frequency and volume of the sound, the higher the frequency and greater the amplitude of the vibrations of the eardrum.

These vibrations are transmitted to the auditory ossicles - the malleus, incus and stapes. The surface of the stapes is adjacent to the membrane of the oval window. The auditory ossicles form a system of levers between themselves, which amplifies the vibrations transmitted from the eardrum. The ratio of the surface of the stapes to the tympanic membrane is 1:22, which increases the pressure of sound waves on the oval window membrane by the same amount. This circumstance is of great importance, since even weak sound waves acting on the eardrum are able to overcome the resistance of the oval window membrane and set in motion a column of fluid in the cochlea. Thus, the vibrational energy transmitted to the inner ear increases approximately 20 times. However, with very loud sounds, the same system of bones, with the help of special muscles, weakens the transmission of vibrations.

In the wall separating the middle ear from the inner ear, in addition to the oval one, there is also a round window, also covered with a membrane. Fluid oscillations in the cochlea, which arose at the oval window and passed along the cochlea's passages, reach the round window without damping. If this window with a membrane did not exist, due to the incompressibility of the liquid, its vibrations would be impossible.

The middle ear cavity communicates with the external environment through eustachian tube, which ensures the maintenance of constant pressure in the cavity, close to atmospheric, which creates the most favorable conditions for vibration of the eardrum.

Inner ear(labyrinth) includes the auditory and vestibular receptor apparatus. The auditory part of the inner ear - the cochlea - is a spirally twisted, gradually expanding bone canal (in humans, 2.5 turns, stroke length about 35 mm) (Fig. 5).

Along its entire length, the bone canal is divided by two membranes: a thinner vestibular (Reissner) membrane and a more dense and elastic main (basilar, basal) membrane. At the top of the cochlea, both of these membranes are connected and there is an opening in them - the helicotrema. The vestibular and basilar membranes divide the bony canal into three fluid-filled passages or stairs.

The upper canal of the cochlea, or scala vestibular, originates from the oval window and continues to the apex of the cochlea, where it communicates through the helicotrema with the lower canal of the cochlea, the scala tympani, which begins in the area of ​​the round window. The upper and lower canals are filled with perilymph, which resembles cerebrospinal fluid in composition. The middle - membranous canal (scala cochlea) does not communicate with the cavity of other canals and is filled with endolymph. On the basilar (main) membrane in the scala cochlea the receptor apparatus of the cochlea is located - Corti organ consisting of hair cells. Above the hair cells is a tectorial membrane. When sound vibrations are transmitted through the system of auditory ossicles to the cochlea, the latter vibrates the fluid and, accordingly, the membrane on which the hair cells are located. The hairs touch the tectorial membrane and become deformed, which is the direct cause of the excitation of receptors and the generation of receptor potential. The receptor potential causes the release of a mediator, acetylcholine, at the synapse, which in turn leads to the generation of action potentials in the auditory nerve fibers. This excitation is then transmitted to the nerve cells of the spiral ganglion of the cochlea, and from there to the auditory center of the medulla oblongata - the cochlear nuclei. After switching on the neurons of the cochlear nuclei, the impulses arrive to the next cell cluster - the nuclei of the superior olivary pontine complex. All afferent pathways from the cochlear nuclei and nuclei of the superior olive complex end in the posterior colliculus, or inferior colliculus, the auditory center of the midbrain. From here, nerve impulses enter the geniculate body of the thalamus, the cell processes of which are directed to the auditory cortex. The auditory cortex is located in the upper part of the temporal lobe and includes areas 41 and 42 (according to Brodmann).

In addition to the ascending (afferent) auditory pathway, there is also a descending centrifugal, or efferent, pathway designed to regulate sensory flow

.Principles of processing auditory information and basics of psychoacoustics

The main parameters of sound are its intensity (or sound pressure level), frequency, duration and spatial localization of the sound source. What mechanisms underlie the perception of each of these parameters?

Sound intensity at the receptor level it is encoded by the amplitude of the receptor potential: the louder the sound, the greater the amplitude. But here, as in the visual system, there is not a linear, but a logarithmic dependence. Unlike the visual system, the auditory system also uses another method - coding by the number of excited receptors (due to different threshold levels in different hair cells).

In the central parts of the auditory system, with increasing intensity, as a rule, the frequency of nerve impulses increases. However, for central neurons, the most significant is not the absolute level of intensity, but the nature of its change over time (amplitude-temporal modulation).

Frequency of sound vibrations. The receptors on the basement membrane are located in a strictly defined order: on the part located closer to the oval window of the cochlea, the receptors respond to high frequencies, and those located on the membrane closer to the apex of the cochlea respond to low frequencies. Thus, the frequency of sound is encoded by the location of the receptor on the basement membrane. This coding method is also preserved in the overlying structures, since they are a kind of “map” of the basement membrane and the relative position of the nerve elements here exactly corresponds to that on the basement membrane. This principle is called topical. At the same time, it should be noted that at high levels of the sensory system, neurons no longer respond to a pure tone (frequency), but to its change in time, i.e. to more complex signals, which, as a rule, have one or another biological significance.

Sound duration is encoded by the duration of the discharge of tonic neurons, which are capable of being excited during the entire duration of the stimulus.

Spatial sound localization is achieved primarily through two different mechanisms. Their activation depends on the frequency of the sound or its wavelength. With low-frequency signals (up to approximately 1.5 kHz), the wavelength is less than the interear distance, which is on average 21 cm in humans. In this case, the source is localized due to the different time of arrival of the sound wave at each ear depending on the azimuth. At frequencies greater than 3 kHz, the wavelength is obviously less than the inter-ear distance. Such waves cannot go around the head; they are repeatedly reflected from surrounding objects and the head, losing the energy of sound vibrations. In this case, localization is carried out mainly due to interaural differences in intensity. In the frequency range from 1.5 Hz to 3 kHz, the temporary localization mechanism changes to the intensity estimation mechanism, and the transition region turns out to be unfavorable for determining the location of the sound source.

When determining the location of a sound source, it is important to assess its distance. Signal intensity plays a significant role in solving this problem: the greater the distance from the observer, the lower the perceived intensity. At large distances (more than 15 m), we take into account the spectral composition of the sound that has reached us: high-frequency sounds decay faster, i.e. “run” a shorter distance; low-frequency sounds, on the contrary, attenuate more slowly and spread further. This is why sounds made by a distant source seem lower to us. One of the factors that significantly facilitates the assessment of distance is the reverberation of the sound signal from reflective surfaces, i.e. perception of reflected sound.

The auditory system is capable of determining not only the location of a stationary, but also a moving sound source. The physiological basis for assessing the localization of a sound source is the activity of the so-called motion detector neurons located in the superior olivary complex, dorsal colliculus, internal geniculate body and auditory cortex. But the leading role here belongs to the upper olive trees and the rear hills.

Questions and tasks for self-control

1. Consider the structure of the hearing organ. Describe the functions of the external ear.

2. What is the role middle ear in the transmission of sound vibrations?

3. Consider the structure of the cochlea and the organ of Corti.

4. What are auditory receptors and what is the immediate cause of their excitation?

5. How is sound vibrations converted into nerve impulses?

6. Describe the central sections of the auditory analyzer.

7. Describe the mechanisms for encoding sound intensity on different levels auditory system?

8. How is sound frequency encoded?

9. What mechanisms of spatial localization of sound do you know?

10. In what frequency range does the human ear perceive sounds? Why do the lowest intensity thresholds in humans lie in the region of 1–2 kHz?

Sound signals (sound radiation) from the external environment (mainly air vibrations with different frequencies and strengths), including speech signals. This feature is implemented using - essential component, which has gone through a difficult path of evolution.

The auditory sensory system consists of the following sections:

• the peripheral section, which is a complex specialized organ consisting of the outer, middle and inner ear;
• conduction section - the first neuron of the conduction section, located in the spiral ganglion of the cochlea, receives from the receptors of the inner ear, from here information flows along its fibers, i.e., along the auditory nerve (included in 8 pairs of cranial nerves) to the second neuron in the medulla oblongata and after crossing, part of the fibers goes to the third neuron in the posterior colliculus, and part to the nuclei - the internal geniculate body;
• cortical section - represented by the fourth neuron, which is located in the primary (projective) auditory field and the cortical area and ensures the occurrence of sensation, and more complex processing of sound information occurs in the nearby secondary auditory field, which is responsible for the formation of perception and recognition of information. The information received enters the tertiary field of the lower parietal zone, where it is integrated with other forms of information

Hearing is a human sensory organ that is capable of perceiving and distinguishing sound waves consisting of alternating compactions and rarefaction of air with a frequency of 16 to 20,000 Hz. A frequency of 1 Hz (hertz) is equal to 1 oscillation in 1 second). The human hearing organ is not capable of perceiving infrasounds (frequency less than 20 Hz) and ultrasounds (frequency more than 20,000 Hz).

The human auditory analyzer consists of three parts:

The receptor apparatus contained in the inner ear;

Nerve pathways (eighth pair of cranial nerves);

The hearing center, which is located in the temporal lobes of the cerebral cortex.

The auditory receptors (phonoreceptors, or organ of Corti) are contained in the cochlea of ​​the inner ear, which is located in the pyramid of the temporal bone. Sound vibrations, before reaching the auditory receptors, pass through a system of sound-conducting and sound-amplifying devices of the hearing organ, which is the ear.

The ear, in turn, consists of 3 parts: external, .

The outer ear serves to catch sounds and consists of the pinna and the external auditory canal. The auricle is formed by elastic cartilage, the outside is covered with skin, and at the bottom it is complemented by a fold that is filled with fatty tissue and is called the lobe.

The external auditory canal is up to 2.5 cm long, lined with skin with fine hair and modified sweat glands, which produce earwax, which consists of fat cells and performs the function of protecting the ear cavity from dust and water. The external auditory canal ends with the eardrum, which is capable of receiving sound waves.

consists of the tympanic cavity and the auditory (Eustachian) tube. At the border between the outer and middle ear is the eardrum, which is covered on the outside with epithelium and on the inside with mucous membrane. Sound vibrations approaching the eardrum cause it to vibrate at the same frequency. WITH inside The eardrum contains the tympanic cavity, inside which there are interconnected auditory ossicles: the hammer (attaches to the eardrum), the incus and the stapes (closes the oval window of the vestibule of the inner ear). Vibrations from the eardrum are transmitted through the ossicular system to the inner ear. The auditory ossicles are placed so that they form levers that reduce the range of sound vibrations, but contribute to their amplification.

Paired Eustachian tubes connect the cavities of the inner left and right ears with the nasopharynx, which helps balance atmospheric and sound (with open mouth) pressure outside and inside the eardrum.

The inner ear is located in the cavity of the pyramid of the temporal bone and is divided into the bony and membranous labyrinth. The first is a bony cavity and consists of the vestibule, three semicircular canals (the location of the vestibular apparatus of the balance organ, which will be discussed later) and the helix of the inner ear. The membranous labyrinth is formed by connective tissue and is a complex system of tubules contained in the cavities of the bony labyrinths. All cavities of the inner ear are filled with fluid, which in the middle of the membranous labyrinth is called endolymph, and outside it is called perilymph. In the vestibule there are two membranous bodies: a round and an oval sac. From the oval sac (pistil), with five openings, the membranous labyrinths of the three semicircular canals begin, forming the vestibular apparatus, and the membranous cochlear duct is associated with the round sac.

The helix of the inner ear is the interosseous labyrinth of the cochlea, up to 35 mm long, which is divided by the longitudinal basal and synchronous (Reisner) membranes into the vestibular or vestibular scala (starting from the oval window of the vestibule), scala tympani (ending with the round window, or the secondary tympanic membrane, which makes it possible vibrations of the perilymph) and the middle steps or membranous cochlear duct from connective tissue. The cavities of the vestibular and tympanic scalae at the top of the cochlea (which are 2.5 turns around its axis) are connected to each other by a thin canal (gechikotrema) and are filled, as indicated, with perilymph, and the cavity of the membranous cochlear duct is filled with endolymph. In the middle of the membranous cochlear duct, there is a sound-receiving apparatus called the spiral, or organ of Corti (organ of Corti). This organ has a main (basal) membrane consisting of approximately 24 thousand fibrous fibers. On the main membrane (Plate), along it there are a number of supporting and 4 rows of hair (sensitive) cells, which are auditory receptors. The second structural part of the organ of Corti is the covering, or fibrous plate, hanging over the hair cells and which is supported by pillar cells, or rods of Corti. Specific feature hair cells is the presence at the top of each of them up to 150 hairs (micro-villi). There are one row (3.5 thousand) of internal and 3 rows (up to 20 thousand) of external hair cells, which differ in the level of sensitivity (for excitation internal cells require more energy, since their hairs have almost no contact with the integumentary plate). The hairs of the outer hair cells are washed by the endolymph and are directly in contact with and partially immersed in the substance of the integumentary plate. The bases of the hair cells are covered by the nerve processes of the helical branch of the auditory nerve. The medulla oblongata (in the zone of the nucleus of the VIII pair of cranial nerves) contains the second neuron of the auditory tract. Next, this path goes to the lower tubercles of the chotirigorbi body (roof) of the midbrain and, partially crossing at the level of the medial geniculate bodies of the thalamus, goes to the centers of the primary auditory cortex (primary auditory fields), contained in the area of ​​the Sylvian fissure of the upper part of the left and right temporal lobes cerebral cortex. Associative auditory fields, distinguish tonality, timbre, intonation and other shades of sounds, and also compare current information with what is in a person’s memory (provide a “mention” of sound images) are adjacent to the primary ones and cover a significant area.

For the organ of hearing, sound waves emanating from the vibration of elastic bodies are an adequate stimulus. Sound vibrations in air, water and other media are divided into periodic (which are called tones and are high and low) and non-periodic (noise). The main characteristic of each sound tone is the length of the sound wave, which corresponds to a certain frequency (number) of vibrations per 1 second. The length of the sound wave is determined by dividing the path traveled by the sound in I second by the number of complete oscillations carried out by the body that sounds in the same time. As stated, human ear capable of perceiving sound vibrations within the range of 16-20000 Hz, the strength of which is expressed in decibels (dB). The strength of sound depends on the range (amplitude) of vibrations of air particles and is characterized by timbre (color). The ear is most excitable to sounds with a frequency of oscillations from 1000 to 4000 Hz. Below and above this indicator, the excitability of the ear decreases.

In modern physiology, the resonance theory of hearing is accepted, which was once proposed by K. L. Helmholtz (1863). Airborne sound waves entering the external auditory canal cause vibrations of the eardrum, which are then transmitted to the system of auditory ossicles, which mechanically amplify these sound vibrations of the eardrum 35-40 times and through the stapes and oval window of the vestibule transmit them to the perilymph contained in the vestibular cavity and the tympanic steps of the helix. Fluctuations in the perilymph, in turn, cause synchronous fluctuations in the endolymph contained in the cavity of the cochlear duct. This causes a corresponding vibration of the basal (main) membrane, the fibers of which have different lengths, are tuned to different tones and are actually a set of resonators vibrating in unison with different sound vibrations. The shortest waves are perceived at the base of the main membrane, and the longest at the apex.

During the vibration of the corresponding resonating sections of the main membrane, the basal and sensitive hair cells located on it also vibrate. The terminal microvilli of the hair cells are deformed from the integumentary plate, which leads to the excitation of the auditory sensation in these cells and the further conduction of nerve impulses along the fibers of the cochlear nerve to the central nervous system. nervous system. Since there is no complete isolation of the fibrous fibers of the main membrane, the hairs of neighboring cells begin to vibrate at the same time, which creates overtones (sound sensations caused by the number of vibrations that are 2, 4, 8, etc. times greater than the number of vibrations of the main tone). This effect determines the volume and polyphony of sound sensations.

With prolonged exposure to strong sounds, the excitability of the sound analyzer decreases, and with prolonged exposure to silence, it increases, which reflects the adaptation of hearing. The greatest adaptation is observed in the zone of higher sounds.

Excessive and prolonged noise not only leads to hearing loss, but can also cause mental disorders in people. There are specific and nonspecific effects of noise on the human body. Specific effect manifests itself in hearing impairment varying degrees, and nonspecific - in various disorders of autonomic reactivity, functional state cardiovascular system and digestive tract, endocrine disorders etc. In young and middle-aged people, at a noise level of 90 dB, which continues for an hour, the excitability of the cells of the cerebral cortex decreases, coordination of movements, visual acuity, stability of clear vision are impaired, the latent period of visual and auditory-motor functions is prolonged. reactions. For the same duration of operation under conditions of noise exposure at a level of 95-96 dB, even more sudden violations brain traffic jam dynamics, extreme inhibition develops, disorders of autonomic functions intensify, and indicators of muscle performance (endurance, fatigue) and performance indicators significantly deteriorate. Prolonged stay in conditions of exposure to noise, the level of which reaches 120 dB, in addition to the above, causes disturbances in the form of neurasthenic manifestations: irritability, headaches, insomnia, disorders appear endocrine system. Under such conditions, significant changes also occur in the state of the cardiovascular system: vascular tone and heart rate are disrupted, and blood pressure increases.

Noise has a particularly negative impact on children and adolescents. A deterioration in the functional state of the auditory and other analyzers is observed in children already under the influence of “school” noise, the intensity level of which in the main premises of the school ranges from 40 to 50 dB. In the classroom, the noise intensity level is on average 50-80 dB, and during breaks and gyms and workshops can reach 95-100 dB. Important in reducing “school” noise has hygienic correct location classrooms in the school building, as well as the use of soundproofing materials when finishing rooms where significant noise is generated.

The cochlear organ functions from the day the child is born, but newborns experience relative deafness associated with the structural features of their ears: the tympanum is thicker than in adults and is located almost horizontally. The middle ear cavity in newborns is filled with amniotic fluid, which makes it difficult for the auditory ossicles to vibrate. During the first 1.5-2 months of the child’s life, this fluid gradually resolves, and instead of it, air penetrates from the nasopharynx through the auditory (Eustachys) tubes. Eustachian tube in children it is wider and shorter (2-2.5 cm) than in adults (3.5-4 cm), which creates favorable conditions for germs, mucus and liquid to enter the middle ear cavity during regurgitation, vomiting, runny nose, which may cause inflammation of the middle ear (otitis media).

Becomes at the end of the 2nd at the beginning of the 3rd month. In the second month of life, the child already becomes able to differentiate different tones of sounds, at 3-4 months he begins to distinguish the pitch of sounds ranging from 1 to 4 octaves, and at 4-5 months sounds become conditioned reflex stimuli. Children of 5-6 months acquire the ability to respond more actively to the sounds of their native language, while responses to non-specific sounds gradually disappear. At the age of 1-2 years, children are able to differentiate almost all sounds.

For an adult, the sensitivity threshold is 10-12 dB, for children 6-9 years old it is 17-24 dB, for children 10-12 years old it is 14-19 dB. The greatest hearing acuity is achieved in middle and older children school age. Children perceive low tones better.