Abstract: Human sensory systems

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- the presence of several layers of nerve cells, the first of which is associated with receptors, and the last with neurons of the motor areas of the cerebral cortex. Neurons are specialized for processing different types of 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 of the 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 the energy of nervous stimulation. 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 the 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 a 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 activity. Consistent learning is taking place. At each stage new information is obtained. 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 the 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 the 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 - the 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 - height 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 on different instruments due to different additional vibrations.

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. The external auditory canal is S-shaped - inward, forward and downward, length 2.5 cm. The auditory 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 a tympanic cavity, the volume of which is approximately 5-6 drops of water and the tympanic cavity is filled with water, lined with a mucous membrane and contains 3 auditory ossicles: the malleus, the incus and the stirrup. 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 cause 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 the 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 the 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 the air transmission of sounds, there is also bone transmission, 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 a 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. Sensitive fibers of the 8th pair of cranial nerves from the spiral ganglion approach the hair cells. 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 the nerve fibers also contain efferent ones (olivo-cochlear fascicle). 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, and endolymph has a high concentration of K (150 mmol). Therefore, the endolymph acquires a positive charge to the perilymph (+80mV). Hair cells contain a lot of K; they have a membrane potential that is 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 the organ of Corti, frequency encoding occurs due to the 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 its neurons there are ascending pathways as part of the lateral lemniscus, which approach the inferior colliculi and the medial geniculate body of the optic thalamus. 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 with different frequencies and different intensities are perceived. The cortical center is important 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 the arrival of sound signals. It was discovered that signals from both ears enter different dendritic systems of the same perceptive neuron. Impairment of auditory perception can manifest itself as ringing in the ears due to irritation of the inner ear or auditory nerve and two types of deafness: conductive and nerve. 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 of the visual system, and ends with the decision by the higher cortical parts of 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. In healthy people, the sizes of 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. The flasks are responsible for color vision, there are 6-7 million of them. The sticks are for twilight vision, there are 110-123 million of them. They are located unevenly. In the central fovea there are only bulbs; here is 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 go as part of the 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. Increased 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. Light that is too bright causes an unpleasant feeling of being blinded. The upper limit of 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. The minimum frequency of repetition of light stimuli at which the fusion of individual sensations occurs is called the critical frequency of flicker fusion. 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 a white background, the background will take on a complementary 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.

Properties of the conductor section of analyzers

This section of the analyzers is represented by afferent pathways and subcortical centers. The main functions of the conduction department are: analysis and transmission of information, implementation of reflexes and inter-analyzer interaction. These functions are provided by the properties of the conductor section of the analyzers, which are expressed as follows.

1. From each specialized formation (receptor), there is a strictly localized specific sensory path. These pathways typically transmit signals from the same type of receptor.

2. From each specific sensory pathway, collaterals extend to the reticular formation, as a result of which it is a structure of convergence of various specific pathways and the formation of multimodal or nonspecific pathways, in addition, the reticular formation is the site of inter-analyzer interaction.

3. There is a multichannel conduction of excitation from receptors to the cortex (specific and nonspecific paths), which ensures the reliability of information transfer.

4. During the transfer of excitation, multiple switching of excitation occurs at different levels of the central nervous system. There are three main switching levels:

• spinal or stem (medulla oblongata);
• thalamus;
• the corresponding projection zone of the cerebral cortex.

At the same time, within the sensory pathways there are afferent channels for urgent transmission of information (without switching) to higher brain centers. It is believed that through these channels the pre-superstructure of higher brain centers for the perception of subsequent information is carried out. The presence of such pathways is a sign of improved brain design and increased reliability of sensory systems.

5. In addition to specific and nonspecific pathways, there are so-called associative thalamo-cortical pathways associated with associative areas of the cerebral cortex. It has been shown that the activity of thalamo-cortical associative systems is associated with an intersensory assessment of the biological significance of a stimulus, etc. Thus, the sensory function is carried out on the basis of the interconnected activity of specific, nonspecific and associative brain formations, which ensure the formation of adequate adaptive behavior of the body.

Central, or cortical, division of the sensory system , according to I.P. Pavlov, it consists of two parts: central part, i.e. “nucleus”, represented by specific neurons that process afferent impulses from receptors, and peripheral part, i.e. “scattered elements” - neurons dispersed throughout the cerebral cortex. The cortical ends of the analyzers are also called “sensory zones”, which are not strictly limited areas; they overlap each other. Currently, in accordance with cytoarchitectonic and neurophysiological data, projection (primary and secondary) and associative tertiary zones of the cortex are distinguished. Excitation from the corresponding receptors to the primary zones is directed along fast-conducting specific pathways, while activation of the secondary and tertiary (associative) zones occurs along polysynaptic nonspecific pathways. In addition, the cortical zones are interconnected by numerous associative fibers.

CLASSIFICATION OF RECEPTORS

The classification of receptors is based primarily on on the nature of sensations that arise in humans when they are irritated. Distinguish visual, auditory, olfactory, gustatory, tactile receptors, thermoreceptors, proprioceptors and vestibuloreceptors (receptors for the position of the body and its parts in space). The question of the existence of special pain receptors .

Receptors by location divided into external , or exteroceptors, And internal , or interoreceptors. Exteroceptors include auditory, visual, olfactory, taste and tactile receptors. Interoreceptors include vestibuloreceptors and proprioceptors (receptors of the musculoskeletal system), as well as interoreceptors that signal the state of internal organs.

By the nature of contact with the external environment receptors are divided into distant receiving information at a distance from the source of stimulation (visual, auditory and olfactory), and contact – excited by direct contact with a stimulus (gustatory and tactile).

Depending on the nature of the type of perceived stimulus , to which they are optimally tuned, there are five types of receptors.

· Mechanoreceptors are excited by their mechanical deformation; located in the skin, blood vessels, internal organs, musculoskeletal system, auditory and vestibular systems.

· Chemoreceptors perceive chemical changes in the external and internal environment of the body. These include taste and olfactory receptors, as well as receptors that respond to changes in the composition of blood, lymph, intercellular and cerebrospinal fluid (changes in O 2 and CO 2 tension, osmolarity and pH, glucose levels and other substances). Such receptors are found in the mucous membrane of the tongue and nose, carotid and aortic bodies, hypothalamus and medulla oblongata.

· Thermoreceptors react to temperature changes. They are divided into heat and cold receptors and are found in the skin, mucous membranes, blood vessels, internal organs, hypothalamus, midbrain, medulla oblongata and spinal cord.

· Photoreceptors The retina of the eye perceives light (electromagnetic) energy.

· Nociceptors , the excitation of which is accompanied by painful sensations (pain receptors). The irritants of these receptors are mechanical, thermal and chemical (histamine, bradykinin, K + , H +, etc.) factors. Painful stimuli are perceived by free nerve endings, which are found in the skin, muscles, internal organs, dentin, and blood vessels. From a psychophysiological point of view, receptors are divided according to the sense organs and the sensations generated into visual, auditory, gustatory, olfactory And tactile.

Depending on the structure of the receptors they are divided into primary , or primary sensory, which are specialized endings of a sensory neuron, and secondary , or secondary sensory cells, which are cells of epithelial origin capable of forming a receptor potential in response to an adequate stimulus.

Primary sensory receptors can themselves generate action potentials in response to stimulation by an adequate stimulus if the magnitude of their receptor potential reaches a threshold value. These include olfactory receptors, most skin mechanoreceptors, thermoreceptors, pain receptors or nociceptors, proprioceptors and most interoreceptors of internal organs. The neuron body is located in the spinal ganglion or cranial nerve ganglion. In the primary receptor, the stimulus acts directly on the endings of the sensory neuron. Primary receptors are phylogenetically more ancient structures; they include olfactory, tactile, temperature, pain receptors and proprioceptors.

Secondary sensory receptors respond to the action of a stimulus only by the appearance of a receptor potential, the magnitude of which determines the amount of mediator released by these cells. With its help, secondary receptors act on the nerve endings of sensitive neurons, generating action potentials depending on the amount of mediator released from the secondary receptors. In secondary receptors there is a special cell synaptically connected to the end of the dendrite of the sensory neuron. This is a cell, such as a photoreceptor, of epithelial nature or neuroectodermal origin. Secondary receptors are represented by taste, auditory and vestibular receptors, as well as chemosensitive cells of the carotid glomerulus. Retinal photoreceptors, which have a common origin with nerve cells, are often classified as primary receptors, but their lack of ability to generate action potentials indicates their similarity to secondary receptors.

By speed of adaptation receptors are divided into three groups: quickly adaptable (phase), slow to adapt (tonic) and mixed (phasotonic), adapting at an average speed. An example of rapidly adapting receptors are the vibration (Pacini corpuscles) and touch (Meissner corpuscles) receptors on the skin. Slowly adapting receptors include proprioceptors, lung stretch receptors, and pain receptors. Retinal photoreceptors and skin thermoreceptors adapt at an average speed.

Most receptors are excited in response to stimuli of only one physical nature and therefore belong to monomodal . They can also be excited by some inappropriate stimuli, for example, photoreceptors - by strong pressure on the eyeball, and taste buds - by touching the tongue to the contacts of a galvanic battery, but it is impossible to obtain qualitatively distinguishable sensations in such cases.

Along with monomodal there are multimodal receptors, the adequate stimuli of which can be irritants of different nature. This type of receptor includes some pain receptors, or nociceptors (Latin nocens - harmful), which can be excited by mechanical, thermal and chemical stimuli. Thermoreceptors have polymodality, reacting to an increase in potassium concentration in the extracellular space in the same way as to an increase in temperature.

Visual perception begins with the projection of an image onto the retina and excitation of photoreceptors, then the information is sequentially processed in the subcortical and cortical visual centers, resulting in a visual image that, thanks to the interaction of the visual analyzer with other analyzers, quite correctly reflects objective reality. Visual sensory system - a sensory system that provides: - coding of visual stimuli; and hand-eye coordination. Through the visual sensory system, animals perceive objects and objects of the external world, the degree of illumination and the length of daylight hours.

The visual sensory system, like any other, consists of three sections:

1. Peripheral section - the eyeball, in particular - the retina (receives light stimulation)

2. Conducting section - axons of ganglion cells - optic nerve - optic chiasm - optic tract - diencephalon (geniculate bodies) - midbrain (quadrigeminal) - thalamus

3. Central section - occipital lobe: area of ​​the calcarine sulcus and adjacent gyri.

Optic tract consist of several neurons. Three of them - photoreceptors (rods and cones), bipolar cells and ganglion cells - are located in the retina.

After the chiasm, the optic fibers form optic tracts, which, at the base of the brain, go around the gray tubercle, pass along the lower surface of the cerebral peduncles and end in the external geniculate body, the cushion of the optic tubercle (thalamus opticus) and the anterior quadrigemale. Of these, only the first is a continuation of the visual pathway and the primary visual center.

The ganglion cells of the external geniculate body end with the fibers of the optic tract and begin with the fibers of the central neuron, which pass through the posterior knee of the internal capsule and then, as part of the Graziole bundle, are directed to the occipital lobe cortex, the cortical visual centers, in the area of ​​the calcarine sulcus.

So, the neural pathway of the visual analyzer begins in the layer of retinal ganglion cells and ends in the occipital cortex of the brain and has peripheral and central neurons. The first consists of the optic nerve, chiasm and visual pathways with the primary visual center in the lateral geniculate body. The central neuron begins here and ends in the occipital lobe of the brain.

The physiological significance of the visual pathway is determined by its function in conducting visual perception. The anatomical relationships of the central nervous system and the visual pathway determine its frequent involvement in the pathological process with early ophthalmological symptoms, which are of great importance in the diagnosis of diseases of the central nervous system and in the dynamics of monitoring the patient.

To see an object clearly, it is necessary that the rays of each point of it be focused on the retina. If you look into the distance, then close objects are seen unclearly, blurry, since the rays from nearby points are focused behind the retina. It is impossible to see objects at different distances from the eye with equal clarity at the same time.

Refraction(ray refraction) reflects the ability of the optical system of the eye to focus the image of an object on the retina. The peculiarities of the refractive properties of any eye include the phenomenon spherical aberration . It lies in the fact that rays passing through the peripheral parts of the lens are refracted more strongly than rays passing through its central parts (Fig. 65). Therefore, the central and peripheral rays do not converge at one point. However, this feature of refraction does not interfere with the clear vision of the object, since the iris does not transmit rays and thereby eliminates those that pass through the periphery of the lens. The unequal refraction of rays of different wavelengths is called chromatic aberration .

The refractive power of the optical system (refraction), i.e. the ability of the eye to refract, is measured in conventional units - diopters. Diopter is the refractive power of a lens in which parallel rays, after refraction, converge at a focus at a distance of 1 m.

We see the world around us clearly when all parts of the visual analyzer “work” harmoniously and without interference. In order for the image to be sharp, the retina obviously must be in the back focus of the eye's optical system. Various disturbances in the refraction of light rays in the optical system of the eye, leading to defocusing of the image on the retina, are called refractive errors (ametropia). These include myopia, farsightedness, age-related farsightedness and astigmatism (Fig. 5).

Fig.5. Ray path for various types of clinical refraction of the eye

a - emetropia (normal);

b - myopia (myopia);

c - hypermetropia (farsightedness);

D - astigmatism.

With normal vision, which is called emmetropic, visual acuity, i.e. The maximum ability of the eye to distinguish individual details of objects usually reaches one conventional unit. This means that a person is able to consider two separate points visible at an angle of 1 minute.

With refractive error, visual acuity is always below 1. There are three main types of refractive error - astigmatism, myopia (myopia) and farsightedness (hyperopia).

Refractive errors result in nearsightedness or farsightedness. The refraction of the eye changes with age: it is less than normal in newborns, and in old age it can decrease again (the so-called senile farsightedness or presbyopia).

Astigmatism due to the fact that, due to its innate characteristics, the optical system of the eye (cornea and lens) refracts rays unequally in different directions (along the horizontal or vertical meridian). In other words, the phenomenon of spherical aberration in these people is much more pronounced than usual (and it is not compensated by pupil constriction). Thus, if the curvature of the corneal surface in the vertical section is greater than in the horizontal section, the image on the retina will not be clear, regardless of the distance to the object.

The cornea will have, as it were, two main focuses: one for the vertical section, the other for the horizontal section. Therefore, light rays passing through an astigmatic eye will be focused in different planes: if the horizontal lines of an object are focused on the retina, then the vertical lines will be in front of it. Wearing cylindrical lenses, selected taking into account the actual defect of the optical system, to a certain extent compensates for this refractive error.

Myopia and farsightedness caused by changes in the length of the eyeball. With normal refraction, the distance between the cornea and the fovea (macula) is 24.4 mm. With myopia (myopia), the longitudinal axis of the eye is greater than 24.4 mm, so rays from a distant object are focused not on the retina, but in front of it, in the vitreous body. To see clearly into the distance, it is necessary to place concave glasses in front of myopic eyes, which will push the focused image onto the retina. In the farsighted eye, the longitudinal axis of the eye is shortened, i.e. less than 24.4 mm. Therefore, rays from a distant object are focused not on the retina, but behind it. This lack of refraction can be compensated by accommodative effort, i.e. an increase in the convexity of the lens. Therefore, a farsighted person strains the accommodative muscle, examining not only close, but also distant objects. When viewing close objects, the accommodative efforts of farsighted people are insufficient. Therefore, to read, farsighted people must wear glasses with biconvex lenses that enhance the refraction of light.

Refractive errors, in particular myopia and farsightedness, are also common among animals, for example, horses; Myopia is very often observed in sheep, especially cultivated breeds.

Skin receptors

• Pain receptors.
• Pacinian corpuscles are encapsulated pressure receptors in a round multilayered capsule. Located in subcutaneous fat. They are quickly adapting (they react only at the moment the impact begins), that is, they register the force of pressure. They have large receptive fields, that is, they represent gross sensitivity.
• Meissner's corpuscles are pressure receptors located in the dermis. They are a layered structure with a nerve ending running between the layers. They are quickly adaptable. They have small receptive fields, that is, they represent subtle sensitivity.
• Merkel discs are unencapsulated pressure receptors. They are slowly adapting (react throughout the entire duration of exposure), that is, they record the duration of pressure. They have small receptive fields.
• Hair follicle receptors - respond to hair deviation.
• Ruffini endings are stretch receptors. They are slow to adapt and have large receptive fields.

Basic functions of the skin: The protective function of the skin is the protection of the skin from mechanical external influences: pressure, bruises, ruptures, stretching, radiation exposure, chemical irritants; Immune function of the skin. T lymphocytes present in the skin recognize exogenous and endogenous antigens; Largehans cells deliver antigens to the lymph nodes, where they are neutralized; Receptor function of the skin - the ability of the skin to perceive pain, tactile and temperature stimulation; The thermoregulatory function of the skin lies in its ability to absorb and release heat; The metabolic function of the skin combines a group of private functions: secretory, excretory, resorption and respiratory activity. Resorption function - the ability of the skin to absorb various substances, including medications; The secretory function is carried out by the sebaceous and sweat glands of the skin, secreting sebum and sweat, which, when mixed, form a thin film of water-fat emulsion on the surface of the skin; Respiratory function is the ability of the skin to absorb oxygen and release carbon dioxide, which increases with increasing ambient temperature, during physical work, during digestion, and the development of inflammatory processes in the skin.

Skin structure

Causes of pain. Pain occurs when, firstly, the integrity of the protective covering membranes of the body (skin, mucous membranes) and internal cavities of the body (meninges, pleura, peritoneum, etc.) is violated and, secondly, the oxygen regime of organs and tissues to a level that causes structural and functional damage.

Classification of pain. There are two types of pain:

1. Somatic, which occurs when the skin and musculoskeletal system are damaged. Somatic pain is divided into superficial and deep. Superficial pain is called pain of skin origin, and if its source is localized in the muscles, bones and joints, it is called deep pain. Superficial pain manifests itself in tingling and pinching. Deep pain, as a rule, is dull, poorly localized, tends to radiate into surrounding structures, and is accompanied by unpleasant sensations, nausea, severe sweating, and a drop in blood pressure.

2.Visceral, which occurs when internal organs are damaged and has a similar picture with deep pain.

Projection and referred pain. There are special types of pain - projection and reflected.

As an example projection pain A sharp blow to the ulnar nerve can be given. Such a blow causes an unpleasant, difficult to describe sensation that spreads to those parts of the arm that are innervated by this nerve. Their occurrence is based on the law of pain projection: no matter what part of the afferent pathway is irritated, pain is felt in the area of ​​the receptors of this sensory pathway. One of the common causes of projection pain is compression of the spinal nerves at their entry into the spinal cord as a result of damage to the intervertebral cartilaginous discs. Afferent impulses in nociceptive fibers in this pathology cause pain sensations that are projected to the area associated with the injured spinal nerve. Projection (phantom) pain also includes pain that patients feel in the area of ​​the removed part of the limb.

Referred pain Pain sensations are called not in the internal organs from which pain signals come, but in certain parts of the skin surface (Zakharyin-Ged zone). So, with angina pectoris, in addition to pain in the heart area, pain is felt in the left arm and shoulder blade. Referred pain differs from projection pain in that it is caused not by direct stimulation of nerve fibers, but by irritation of some receptive endings. The occurrence of these pains is due to the fact that the neurons conducting pain impulses from the receptors of the affected organ and the receptors of the corresponding area of ​​the skin converge on the same neuron of the spinothalamic tract. Irritation of this neuron from the receptors of the affected organ in accordance with the law of pain projection leads to the fact that pain is also felt in the area of ​​skin receptors.

Antipain (antinociceptive) system. In the second half of the twentieth century, evidence was obtained of the existence of a physiological system that limits the conduction and perception of pain sensitivity. Its important component is the “gate control” of the spinal cord. It is carried out in the posterior columns by inhibitory neurons, which, through presynaptic inhibition, limit the transmission of pain impulses along the spinothalamic pathway.

A number of brain structures have a descending activating effect on inhibitory neurons of the spinal cord. These include the central gray matter, raphe nuclei, locus coeruleus, lateral reticular nucleus, paraventricular and preoptic nuclei of the hypothalamus. The somatosensory area of ​​the cortex unites and controls the activity of the structures of the analgesic system. Impairment of this function can cause unbearable pain.

The most important role in the mechanisms of the analgesic function of the central nervous system is played by the endogenous opiate system (opiate receptors and endogenous stimulants).

Endogenous stimulants of opiate receptors are enkephalins and endorphins. Some hormones, for example corticoliberin, can stimulate their formation. Endorphins act primarily through morphine receptors, which are especially numerous in the brain: in the central gray matter, raphe nuclei, and middle thalamus. Enkephalins act through receptors located primarily in the spinal cord.

Theories of pain. There are three theories of pain:

1.Intensity theory . According to this theory, pain is not a specific feeling and does not have its own special receptors, but occurs when super-strong stimuli act on the receptors of the five senses. Convergence and summation of impulses in the spinal cord and brain are involved in the formation of pain.

2.Specificity theory . According to this theory, pain is a specific (sixth) sense that has its own receptor apparatus, afferent pathways and brain structures that process pain information.

3.Modern theory pain is based primarily on the theory of specificity. The existence of specific pain receptors has been proven.

At the same time, the modern theory of pain uses the position about the role of central summation and convergence in the mechanisms of pain. The most important achievement in the development of modern pain theory is the study of the mechanisms of central pain perception and the body's anti-pain system.

Functions of proprioceptors

Proprioceptors include muscle spindles, tendon organs (or Golgi organs) and joint receptors (receptors of the joint capsule and articular ligaments). All these receptors are mechanoreceptors, the specific stimulus of which is their stretching.

Muscle spindles human, are oblong formations several millimeters long, tenths of a millimeter wide, which are located in the thickness of the muscle. In different skeletal muscles, the number of spindles per 1 g of tissue varies from several units to hundreds.

Thus, muscle spindles, as sensors of the state of muscle strength and the speed of its stretching, respond to two influences: peripheral - a change in muscle length, and central - a change in the level of activation of gamma motor neurons. Therefore, the reactions of spindles under conditions of natural muscle activity are quite complex. When a passive muscle is stretched, spindle receptors are activated; it causes the myotatic reflex, or stretch reflex. During active muscle contraction, a decrease in its length has a deactivating effect on the spindle receptors, and the excitation of gamma motor neurons, accompanying the excitation of alpha motor neurons, leads to reactivation of the receptors. As a result, impulses from spindle receptors during movement depend on the length of the muscle, the speed of its shortening and the force of contraction.

Golgi tendon organs (receptors) in humans are located in the area of ​​connection between the muscle fibers and the tendon, sequentially relative to the muscle fibers.

The tendon organs are an elongated fusiform or cylindrical structure, the length of which in humans can reach 1 mm. This is the primary sensory receptor. Under resting conditions, i.e. when the muscle is not contracted, background impulses come from the tendon organ. Under conditions of muscle contraction, the frequency of impulses increases in direct proportion to the magnitude of the muscle contraction, which allows us to consider the tendon organ as a source of information about the force developed by the muscle. At the same time, the tendon organ reacts poorly to muscle stretching.

As a result of the sequential attachment of tendon organs to muscle fibers (and in some cases to muscle spindles), stretching of tendon mechanoreceptors occurs when muscles are tense. Thus, unlike muscle spindles, tendon receptors inform the nerve centers about the degree of tension in the mouse, and the rate of its development.

Joint receptors react to the position of the joint and to changes in the joint angle, thus participating in the feedback system from the motor system and in its control. Articular receptors inform about the position of individual parts of the body in space and relative to each other. These receptors are free nerve endings or endings enclosed in a special capsule. Some joint receptors send information about the size of the joint angle, i.e., about the position of the joint. Their impulse continues throughout the entire period of maintaining a given angle. The greater the angle shift, the higher the frequency. Other joint receptors are excited only at the moment of movement in the joint, i.e. they send information about the speed of movement. The frequency of their impulses increases with the increase in the rate of change in the joint angle.

Conductive and cortical sections proprioceptive analyzer of mammals and humans. Information from muscle, tendon and joint receptors enters through the axons of the first afferent neurons located in the spinal ganglia into the spinal cord, where it is partially switched to alpha motor neurons or interneurons (for example, to Renshaw cells), and partially sent along ascending pathways to higher parts of the brain. In particular, along the Flexig and Gowers pathways, proprioceptive impulses are delivered to the cerebellum, and through the Gaulle and Burdach bundles, passing in the dorsal cords of the spinal cord, it reaches the neurons of the nuclei of the same name located in the medulla oblongata.

The axons of thalamic neurons (third-order neurons) end in the cerebral cortex, mainly in the somatosensory cortex (postcentral gyrus) and in the area of ​​the Sylvian fissure (areas S-1 and S-2, respectively), and also partially in the motor ( prefrontal) region of the cortex. This information is used quite widely by the motor systems of the brain, including for making decisions about the intention of movement, as well as for its implementation. In addition, based on proprioceptive information, a person forms ideas about the state of muscles and joints, as well as, in general, about the position of the body in space.

Signals coming from receptors of muscle spindles, tendon organs, joint capsules and tactile receptors of the skin are called kinesthetic, i.e., informing about body movement. Their participation in the voluntary regulation of movements varies. Signals from joint receptors cause a noticeable reaction in the cerebral cortex and are well recognized. Thanks to them, a person perceives differences in joint movements better than differences in the degree of muscle tension during static positions or supporting weight. Signals from other proprioceptors, arriving primarily in the cerebellum, provide unconscious regulation, subconscious control of movements and postures.

Thus, proprioceptive sensations give a person the opportunity to perceive changes in the position of individual parts of the body at rest and during movements. Information coming from the proprioceptors allows him to constantly control the posture and accuracy of voluntary movements, dose the force of muscle contractions when counteracting external resistance, for example, when lifting or moving a load.

Sensory systems, their meaning and classification. Interaction of sensory systems.

To ensure the normal functioning of an organism*, the constancy of its internal environment, communication with the continuously changing external environment and adaptation to it are necessary. The body receives information about the state of the external and internal environments with the help of sensory systems that analyze (distinguish) this information, ensure the formation of sensations and ideas, as well as specific forms of adaptive behavior.

The idea of ​​sensory systems was formulated by I. P. Pavlov in the doctrine of analyzers in 1909 during his study of higher nervous activity. Analyzer- a set of central and peripheral formations that perceive and analyze changes in the external and internal environments of the body. The concept of “sensory system”, which appeared later, replaced the concept of “analyzer”, including the mechanisms of regulation of its various departments using direct and feedback connections. Along with this, the concept of “sense organ” still exists as a peripheral formation that perceives and partially analyzes environmental factors. The main part of the sensory organ is the receptors, equipped with auxiliary structures that ensure optimal perception.

When directly exposed to various environmental factors with the participation of sensory systems in the body, Feel, which are reflections of the properties of objects in the objective world. The peculiarity of sensations is their modality, those. a set of sensations provided by any one sensory system. Within each modality, in accordance with the type (quality) of the sensory impression, different qualities can be distinguished, or valence. Modalities are, for example, vision, hearing, taste. Qualitative types of modality (valence) for vision are different colors, for taste - the sensation of sour, sweet, salty, bitter.

The activity of sensory systems is usually associated with the emergence of five senses - vision, hearing, taste, smell and touch, through which the body communicates with the external environment. However, in reality there are much more of them.

The classification of sensory systems can be based on various features: the nature of the current stimulus, the nature of the sensations that arise, the level of receptor sensitivity, the speed of adaptation, and much more.

The most significant is the classification of sensory systems, which is based on their purpose (role). In this regard, several types of sensory systems are distinguished.

External sensor systems perceive and analyze changes in the external environment. This should include the visual, auditory, olfactory, gustatory, tactile and temperature sensory systems, the excitation of which is perceived subjectively in the form of sensations.

Internal (visc

The sensory organization of a personality is the level of development of individual sensitivity systems and the possibility of their unification. Human sensory systems are his sense organs, like receivers of his sensations, in which the transformation of sensation into perception occurs.

The main feature of a person’s sensory organization is that it develops as a result of his entire life path. A person’s sensitivity is given to him at birth, but its development depends on the circumstances, desires and efforts of the person himself. Feeling – lower mental process of reflecting individual properties of objects or phenomena of the internal and external world through direct contact.

It is obvious that the primary cognitive process occurs in the human sensory systems and, on its basis, cognitive processes that are more complex in structure arise: perceptions, ideas, memory, thinking. No matter how simple the primary cognitive process may be, it is precisely it that is the basis of mental activity; only through the “inputs” of sensory systems does the surrounding world penetrate into our consciousness. The physiological mechanism of sensations is the activity of the nervous apparatus - analyzers, consisting of 3 parts:

· receptor- the perceiving part of the analyzer (carries out the transformation of external energy into a nervous process)

· central section of the analyzer- afferent or sensory nerves

· cortical sections of the analyzer, in which nerve impulses are processed.

Each type of sensation is characterized not only by specificity, but also has common properties with other types: quality, intensity, duration, spatial localization. The minimum magnitude of the stimulus at which the sensation appears is absolute threshold of sensation. The value of this threshold characterizes absolute sensitivity, which is numerically equal to a value inversely proportional to the absolute threshold of sensations. Sensitivity to changes in stimulus is called relative or difference sensitivity. The minimum difference between two stimuli that causes a slightly noticeable difference in sensation is called difference threshold.

Classification of sensations

A widespread classification is based on the modality of sensations (specificity of the sense organs) - this is the division of sensations into visual, auditory, vestibular, tactile, olfactory, gustatory, motor, visceral. There are intermodal sensations - synesthesia. The main and most significant group of sensations brings information from the outside world to a person and connects him with the external environment. These are exteroceptive - contact and distant sensations; they occur in the presence or absence of direct contact of the receptor with the stimulus. Vision, hearing, and smell are distant sensations. These types of sensations provide orientation in the immediate environment. Taste, pain, tactile sensations are contact. According to the location of the receptors on the surface of the body, in muscles and tendons or inside the body, they are distinguished accordingly:

– exteroceptive sensations (arising from the influence of external stimuli on receptors located on the surface of the body, externally) visual, auditory, tactile;

– proprioceptive(kinesthetic) sensations (reflecting the movement and relative position of body parts with the help of receptors located in muscles, tendons, joint capsules);

– interoceptive(organic) sensations - arising from the reflection of metabolic processes in the body with the help of specialized receptors, hunger and thirst.

In order for a sensation to arise, it is necessary that the stimulus reaches a certain value, which is called threshold of perception.
Relative threshold- the magnitude that the stimulus must reach for us to feel this change.
Absolute thresholds– these are the upper and lower limits of the organ’s resolution. Threshold research methods:

Bounds method

consists in gradually increasing the stimulus from subthreshold, then the reverse procedure

Installation method

the subject independently distinguishes the magnitude of the stimulus

All sensory systems are built on the same principle and consist of three sections: peripheral, conductive and central.

Peripheral department represented by a sense organ. It consists of receptors - the endings of sensory nerve fibers or specialized cells. They ensure the conversion of stimulus energy into nerve impulses.

Receptors differ in location (internal and external), structure and characteristics of perception of the energy of the stimulus (some perceive mechanical, others chemical, and still others light stimuli).

In addition to receptors, sensory organs include auxiliary structures that perform protective, supportive and some other functions. For example, the auxiliary apparatus of the eye is represented by the extraocular muscles, eyelids and lacrimal glands.

The conduction section of the sensory system consists of sensory nerve fibers, which in most cases form a specialized nerve. It delivers information from receptors to the central part of the sensory system.

And finally, the central section is located in the cerebral cortex. Here are the higher sensory centers, which provide the final analysis of incoming information and the formation of corresponding sensations.

Thus, the sensory system is a set of specialized structures of the nervous system that carry out the processes of receiving and processing information from the external and internal environment, and also form sensations.

There are visual, auditory, vestibular, gustatory, olfactory and other sensory systems.

Visual sensory system

Its peripheral part is represented by the organ of vision (eye), the conductive part is represented by the optic nerve, and the central part is represented by the visual zone, located in the occipital lobe of the cerebral cortex.

Light rays from the objects in question act on the light-sensitive cells of the eye and cause excitement in them. It is transmitted along the optic nerve to the cerebral cortex. Here, in the occipital lobes, visual sensations of shape, color, size, location and direction of movement of objects arise.

Auditory sensory system plays a very important role. Its activity underlies the teaching of speech. It is represented by the ear - the organ of hearing (peripheral section), the auditory nerve (conducting section) and the auditory zone located in the temporal lobe of the cerebral cortex (central section).

Vestibular sensory system provides spatial orientation of a person. With its help, we receive information about accelerations and decelerations that occur during movement. It is represented by the organ of balance, the vestibular nerve and the corresponding zone in the temporal lobes of the cerebral cortex.

The sense of body position in space is especially necessary for pilots, scuba divers, acrobats, etc. If the organ of balance is damaged, a person cannot stand and walk confidently.

Taste sensory system carries out analysis of soluble chemical irritants acting on the organ of taste (tongue). With its help, the suitability of food is determined.

Our tongue is covered with a mucous membrane, the folds of which contain taste buds (Fig.). Inside each kidney there are receptor cells with microvilli.

The receptors are associated with nerve fibers that enter the brain as part of the cranial nerves. Through them, impulses reach the posterior part of the central gyrus of the cerebral cortex, where taste sensations are formed.

There are four main taste sensations: bitter, sweet, sour and salty. The tip of the tongue shows the highest sensitivity to sweets, the edges to salty and sour, and the root to bitter substances.

Olfactory sensory system Perceives and analyzes chemical stimuli in the external environment.

The peripheral section of the olfactory sensory system is represented by the epithelium of the nasal cavity, which contains receptor cells with microvilli. The axons of these sensory cells form the olfactory nerve, which is directed into the cranial cavity (Fig.).

Through it, excitation is carried to the olfactory centers of the cerebral cortex, where odors are recognized.

The sense of touch plays a significant role in human cognition of the external world. It provides the ability to perceive and distinguish the shape, size and nature of the surface of an object. The receptors involved in the processes of perception of stimuli acting on the skin are very diverse. They respond not only to touch, but also to heat, cold and pain. The most tactile receptors are on the lips and the palmar surface of the fingers, the least on the torso. Excitation from receptors is transmitted through sensory neurons to the skin sensitivity zone of the cerebral cortex, where corresponding sensations arise.

The sensory system (analyzer) is a complex system consisting of a peripheral receptor formation - a sensory organ, pathways - cranial and spinal nerves and a central section - the cortical section of the analyzer, i.e. a specific area of ​​the cerebral cortex in which information received from the senses is processed. The following sensory systems are distinguished: visual, auditory, gustatory, olfactory, somatosensory, vestibular.

Visual sensory system represented by the perceptive department - the receptors of the retina of the eye, the conducting system - the optic nerves, and the corresponding areas of the cortex in the occipital lobes of the brain.

Structure of the organ of vision: The basis of the organ of vision is the eyeball, which is placed in the orbit and has an irregular spherical shape. Most of the eye consists of auxiliary structures, the purpose of which is to project the field of vision onto the retina. The eye wall consists of three layers:

sclera (tunica albuginea). It is the thickest, strongest and provides the eyeball with a certain shape. This shell is opaque and only in the anterior section does the sclera merge into the cornea;

choroid. It is abundantly supplied with blood vessels and pigment containing a coloring matter. The part of the choroid located behind the cornea forms the iris, or iris. In the center of the iris there is a small hole - the pupil, which, narrowing or expanding, lets in more or less light. The iris is separated from the choroid proper by the ciliary body. In its thickness there is the ciliary muscle, on the thin elastic threads of which the lens is suspended - a biconvex lens with a diameter of 10 mm.

retina. This is the innermost layer of the eye. It contains rod and cone photoreceptors. The human eye contains approximately 125 million of these rods, which allow it to see well in dim light. The retina of the human eye contains 6-7 million cones; They function best in bright light. It is believed that there are three types of cones, each of which perceives light of a specific wavelength - red, green or blue. Other colors are created by combining these three primary colors.

The entire internal cavity of the eye is filled with a jelly-like mass - the vitreous body. Nerve fibers extend from the rods and cones of the retina, which then form the optic nerve. The optic nerve penetrates through the eye sockets into the cranial cavity and ends in the occipital lobe of the cerebral hemispheres - the visual cortex.

The accessory apparatus of the eye includes the protective devices and muscles of the eye. Protective devices include the eyelids with eyelashes, the conjunctiva and the lacrimal apparatus. The eyelids are paired skin-conjunctival folds that cover the eyeball in front. The anterior surface of the eyelid is covered with thin, easily folded skin, under which lies the muscle of the eyelid and which on the periphery passes into the skin of the forehead and face. The posterior surface of the eyelid is lined with the conjunctiva. The eyelids have anterior edges of the eyelids that bear eyelashes and posterior edges of the eyelids that merge into the conjunctiva. Eyebrows and eyelashes protect the eye from dust. The conjunctiva covers the back surface of the eyelids and the front surface of the eyeball. There is a distinction between the conjunctiva of the eyelid and the conjunctiva of the eyeball. The lacrimal gland is located in the fossa of the same name in the upper outer corner of the orbit; its excretory ducts (5-12 in number) open in the area of ​​the upper fornix of the conjunctival sac. The lacrimal gland secretes a clear, colorless liquid called tears, which protects the eye from drying out. The lower end of the lacrimal sac passes into the nasolacrimal duct, which opens into the inferior nasal meatus.

The eye is the most mobile of all organs of the body. Various eye movements, sideways, up, down movements are provided by the extraocular muscles located in the orbit. There are 6 of them in total, 4 rectus muscles are attached to the front of the sclera (top, bottom, right, left) and each of them turns the eye in its own direction. And 2 oblique muscles, superior and inferior, are attached to the back of the sclera.

Auditory sensory system – a set of structures that ensure the perception of sound information, convert it into nerve impulses, and its subsequent transmission and processing in the central nervous system. In the auditory analyzer: - the peripheral section is formed by auditory receptors located in the organ of Corti of the inner ear; - conduction section – vestibulocochlear nerves; - central section - auditory zone of the temporal lobe of the cerebral cortex.

The hearing organ is represented by the outer, middle and inner ear.

The outer ear consists of the pinna and the external auditory canal. Both formations perform the function of capturing sound vibrations. The boundary between the outer and middle ear is the eardrum - the first element of the apparatus for the mechanical transmission of vibrations of sound waves.

The middle ear consists of the tympanic cavity and the auditory (Eustachian) tube.

The tympanic cavity lies deep within the pyramid of the temporal bone. Its capacity is approximately 1 cubic meter. cm. The walls of the tympanic cavity are lined with mucous membrane. The cavity contains three auditory ossicles (hammer, incus and stapes), connected by joints. The chain of auditory ossicles transmits mechanical vibrations of the eardrum to the membrane of the oval window and the structures of the inner ear.

The auditory (Eustachian) tube connects the tympanic cavity with the nasopharynx. Its walls are lined with mucous membrane. The pipe serves to equalize the internal and external air pressure on the eardrum.

The inner ear is represented by a bony and membranous labyrinth. The bony labyrinth includes: the cochlea, the vestibule, the semicircular canals, and the last two formations do not belong to the organ of hearing. They represent the vestibular apparatus, regulating the position of the body in space and maintaining balance.

The cochlea is the seat of the hearing organ. It looks like a bone canal with 2.5 turns and constantly expanding. The bony canal of the cochlea, due to the vestibular and basal plates, is divided into three narrow passages: upper (scalena vestibule), middle (cochlear duct), lower (scalena tympani). Both scalae are filled with fluid (perilymph), and the cochlear duct contains endolymph. On the basement membrane of the cochlear duct is the organ of hearing (organ of Corti), consisting of hair receptor cells. These cells convert mechanical sound vibrations into bioelectric impulses of the same frequency, which then travel along the fibers of the auditory nerve to the auditory zone of the cerebral cortex.

The vestibular organ (organ of balance) is located in the vestibule and semicircular canals of the inner ear. Semicircular canals are narrow bony passages located in three mutually perpendicular planes. The ends of the canals are somewhat expanded and are called ampoules. The semicircular ducts of the membranous labyrinth lie in the canals.

The vestibule contains two sacs: elliptical (uterus, utriculus) and spherical (sacculus). In both vestibular sacs there are elevations called spots. Receptor hair cells are concentrated in the spots. The hairs are directed inside the sacs and attached to crystalline pebbles - otoliths and the jelly-like otolith membrane.

In the ampoules of the semicircular ducts, receptor cells form a cluster - ampullary cristae. Excitation of the receptors here occurs due to the movement of endolymph in the ducts.

Irritation of otolithic receptors or receptors of the semicircular ducts occurs depending on the nature of the movement. The otolithic apparatus is excited by accelerating and decelerating rectilinear movements, shaking, rolling, tilting the body or head to the side, during which the pressure of the otoliths on the receptor cells changes. The vestibular apparatus is involved in the regulation and redistribution of muscle tone, which ensures the preservation of posture and compensation for the state of unstable balance when the body is in an upright position (standing).

Taste sensory system - a set of sensory structures that provide the perception and analysis of chemical irritants and stimuli when they act on the receptors of the tongue, as well as forming taste sensations. The peripheral parts of the taste analyzer are located on the taste buds of the tongue, the soft palate, the posterior wall of the pharynx and the epiglottis. The conductive section of the taste analyzer is the taste fibers of the facial and glossopharyngeal nerves, along which taste stimuli follow through the medulla oblongata and visual thalamus to the lower surface of the frontal lobe of the cerebral cortex (central section).

Olfactory sensory system – a set of sensory structures that provide perception and analysis of information about substances in contact with the mucous membrane of the nasal cavity and form olfactory sensations. In the olfactory analyzer: peripheral section - receptors of the upper nasal passage of the mucous membrane of the nasal cavity; conduction section - olfactory nerve; The central section is the cortical olfactory center, located on the lower surface of the temporal and frontal lobes of the cerebral cortex. Olfactory receptors are located in the mucous membrane that occupies the upper part of the nasal concha. The mucous membrane, or olfactory membrane, has three layers of cells: structural cells, olfactory cells and basal cells. Olfactory cells transmit nerve impulses to the olfactory bulb, and from there to the olfactory centers of the cerebral cortex, where the sensation is evaluated and deciphered.

Somatosensory system – a set of sensory systems that provide coding of temperature, pain, and tactile stimuli that act directly on the human body. The receptor section is the skin receptors, the conductor section is the spinal nerves, and the brain section of the somatosensory system is concentrated in the cortex of the parietal lobes of the brain.

Structure and functions of human skin. The skin surface area of ​​an adult is 1.5-2 m2. The skin is rich in muscle and elastic fibers that have the ability to stretch, give it elasticity and resist pressure. Thanks to these fibers, the skin can return to its original state after stretching. The skin consists of two sections: the upper - the epidermis, or outer layer, and the lower - the dermis, or the skin itself. Both departments are separate from each other and at the same time closely interconnected. The dermis (or skin itself) in the lower section directly passes into the subcutaneous fatty tissue. The epidermis consists of 5 layers: the basal layer, subulate, granular, shiny, or vitreous, and the most superficial - horny. The last, stratum corneum of the epidermis, is in direct contact with the external environment. Its thickness varies in different areas of the skin. The most powerful is on the skin of the palms and soles, the thinnest is on the skin of the eyelids. The stratum corneum consists of keratinized anucleate cells resembling flat scales, closely fused to each other in the depths of the stratum corneum and less compact on its surface. Obsolete epithelial elements are constantly separated from the stratum corneum (so-called physiological desquamation). Horny plates consist of horny substance - keratin.

The dermis (the skin itself) consists of connective tissue and is divided into two layers: subepithelial (papillary) and reticular. The presence of papillae greatly increases the area of ​​contact between the epidermis and the dermis and thus provides better nutritional conditions for the epidermis. The reticular layer of the dermis, without sharp boundaries, passes into the subcutaneous fatty tissue. The reticular layer is somewhat different from the papillary layer in the nature of its fibrousness. The strength of the skin mainly depends on its structure. An extremely important functional feature of the dermis is the presence of elastic and other fibers in it, which, having great elasticity, maintain the normal shape of the skin and protect the skin from injury. With age, when elastic fibers degenerate, skin folds and wrinkles appear on the face and neck. The dermis contains hair follicles, sebaceous and sweat glands, as well as muscles, blood vessels, nerves and nerve endings. The skin is covered almost all over with hair. The palms and soles, the lateral surfaces and nail phalanges of the fingers, the border of the lips and some other areas are free from hair.

Hair is keratinized thread-like appendages of the skin, 0.005-0.6 mm thick and from a few millimeters to 1.5 m long, their color, size and distribution are related to age, gender, race and body area. Of the 2 million hairs on the human body, about 100,000 are found on the scalp. They are divided into three types:

long – thick, long, pigmented, covering the scalp, and after puberty – the pubis, armpits, and in men – also the mustache, beard and other parts of the body;

bristly - thick, short, pigmented, forming eyebrows, eyelashes, found in the external auditory canal and the vestibule of the nasal cavity;

vellus – thin, short, colorless, covering the rest of the body (numerically dominant); under the influence of hormones during puberty, some parts of the body can turn into long ones.

The hair consists of a shaft protruding above the skin and a root immersed in it to the level of subcutaneous fatty tissue. The root is surrounded by a hair follicle - a cylindrical epithelial formation, protruding into the dermis and hypodermis and braided with a connective tissue hair bursa. Near the surface of the epidermis, the follicle forms an expansion - a funnel into which the ducts of the sweat and sebaceous glands flow. At the distal end of the follicle there is a hair bulb, into which a connective tissue hair papilla grows with a large number of blood vessels that feed the bulb. The bulb also contains melanocytes, which cause hair pigmentation.

Nail is a formation in the form of a plate lying on the dorsal surface of the distal phalanx of the fingers. It consists of the nail plate and the nail bed. The nail plate consists of hard keratin, formed by many layers of horny scales, firmly connected to each other, and lies on the nail bed. Its proximal part, the root of the nail, is located in the posterior nail fissure and is covered with the cuticle, with the exception of a small light crescent-shaped zone (luna). Distally, the plate ends with a free edge lying above the subungual plate.

Skin glands. Sweat glands are involved in thermoregulation, as well as in the excretion of metabolic products, salts, drugs, and heavy metals. Sweat glands have a simple tubular structure and are divided into: eccrine and apocrine. Eccrine sweat glands are found in the skin of all areas of the body. Their number is 3-5 million (especially numerous on the palms, soles, forehead), and the total mass is approximately 150 g. They secrete transparent sweat with a low content of organic components and through the excretory ducts it reaches the surface of the skin, cooling it. Apocrine sweat glands, unlike eccrine ones, are located only in certain areas of the body: the skin of the armpits and perineum. They undergo final development during puberty. They produce milky sweat with a high content of organic substances. The structure is simple tubular-alveolar. The activity of the glands is regulated by the nervous system and sex hormones. Excretory ducts open into the mouths of hair follicles or onto the surface of the skin.

Sebaceous glands produce a mixture of lipids - sebum, which covers the surface of the skin, softening it and enhancing its barrier and antimicrobial properties. They are present in the skin everywhere except on the palms, soles and dorsum of the feet. Usually associated with hair follicles, they develop in adolescence during puberty under the influence of androgens (in both sexes). The sebaceous glands are located at the hair root on the border of the reticular and papillary layers of the dermis. They belong to simple alveolar glands. They consist of terminal sections and excretory ducts. The secretion of the sebaceous glands (20 g per day) occurs during contraction of the muscle that lifts the hair. Overproduction of sebum is characteristic of a disease called seborrhea.