sensory properties. Types of sensory systems
Properties of the conductor section of the analyzers
This department of analyzers is represented by afferent pathways and subcortical centers. The main functions of the conductor department are: analysis and transmission of information, implementation of reflexes and inter-analyzer interaction. These functions are provided by the properties of the conductive section of the analyzers, which are expressed in the following.
1. From each specialized formation (receptor), there is a strictly localized specific sensory path. These pathways usually transmit signals from receptors of the same type.
2. Collaterals depart from each specific sensory pathway 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 non-specific pathways, in addition, the reticular formation is a place of interanalyzer interaction.
3. There is a multi-channel conduction of excitation from receptors to the cortex (specific and non-specific pathways), which ensures the reliability of information transmission.
4. During the transfer of excitation, there is a multiple switching of excitation at different levels of the central nervous system. There are three main switching levels:
- spinal or stem (medulla oblongata);
- visual tubercle;
- the corresponding projection area of the cerebral cortex.
At the same time, within the sensory pathways, there are afferent channels for the urgent transmission of information (without switching) to higher brain centers. It is believed that through these channels, the pre-adjustment of higher brain centers to the perception of subsequent information is carried out. The presence of such pathways is a sign of improving the design of the brain and increasing the reliability of sensory systems.
5. In addition to specific and non-specific 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 intersensory assessment of the biological significance of the stimulus, etc. Thus, the sensory function is carried out on the basis of the interconnected activity of specific, non-specific and associative formations of the brain, which ensure the formation of an adequate adaptive behavior of the body.
Central, or cortical, part 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 cortical zones are distinguished. Excitation from the corresponding receptors to the primary zones is directed along fast-conducting specific pathways, while the activation of secondary and tertiary (associative) zones occurs along polysynaptic non-specific 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 feelings that arise in a person when they are irritated. Distinguish visual, auditory, olfactory, gustatory, tactile receptors thermoreceptors, proprio and vestibuloreceptors (receptors of 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 exteroreceptors, And domestic , or interoreceptors. Exteroreceptors include auditory, visual, olfactory, taste and tactile receptors. Interoreceptors include vestibuloreceptors and proprioreceptors (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 that receive information at a distance from the source of irritation (visual, auditory and olfactory), and contact - excited by direct contact with the 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
excited by their mechanical deformation; located in the skin, blood vessels, internal organs, musculoskeletal, 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 voltage, osmolarity and pH, glucose levels and other substances). Such receptors are found in the mucous membrane of the tongue and nose, the carotid and aortic bodies, the hypothalamus, and the 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, middle, medulla and spinal cord.
· Photoreceptors in the retina, the eyes perceive light (electromagnetic) energy.
· Nociceptors , the excitation of which is accompanied by pain 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 that are found in the skin, muscles, internal organs, dentin, and blood vessels. From a psychophysiological point of view, receptors are divided into visual, auditory, gustatory, olfactory And tactile.
Depending on the structure of the receptors they are subdivided into primary , or primary sensory, which are specialized endings of a sensitive neuron, and secondary , or secondary-sensing, which are cells of epithelial origin, capable of generating a receptor potential in response to the action of an adequate stimulus.
Primary sensory receptors can themselves generate action potentials in response to stimulation by an adequate stimulus, if the value of their receptor potential reaches a threshold value. These include olfactory receptors, most skin mechanoreceptors, thermoreceptors, pain receptors or nociceptors, proprioceptors, and most internal organ interoreceptors. The body of the neuron is located in the spinal ganglion or in the ganglion of the cranial nerves. 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 the stimulus only by the appearance of a receptor potential, the magnitude of which determines the amount of mediator secreted by these cells. With its help, secondary receptors act on the nerve endings of sensory neurons that generate action potentials depending on the amount of mediator released from the secondary sensory 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 more often referred to as primary receptors, but their lack of the ability to generate action potentials indicates their similarity to secondary receptors.
According to the speed of adaptation Receptors are divided into three groups: adaptable (phase), slowly adapting (tonic) and mixed (phasnotonic), adapting at an average speed. Examples of rapidly adapting receptors are the receptors for vibration (Pacini corpuscles) and touch (Meissner corpuscles) 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 the action of stimuli of only one physical nature and therefore belong to monomodal . They can also be excited by some inadequate 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 polymodal receptors, adequate stimuli of which can serve as stimuli of a different nature. To this type of receptors belong some pain receptors, or nociceptors (lat. nocens - harmful), which can be excited by mechanical, thermal and chemical stimuli. Polymodality is present in thermoreceptors that respond to an increase in the concentration of potassium 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, due 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 outside world, the degree of illumination and the length of the daylight hours.
The visual sensory system, like any other, consists of three departments:
1. Peripheral department - the eyeball, in particular - the retina of the eye (perceives light irritation)
2. Conductor department - axons of ganglion cells - optic nerve - optic chiasm - optic tract - diencephalon (geniculate bodies) - midbrain (quadrigemina) - thalamus
3. The central section - the occipital lobe: the region of the spur groove and adjacent convolutions.
optic tract make up several neurons. Three of them - photoreceptors (rods and cones), bipolar cells and ganglion cells - are located in the retina.
After decussation, the optic fibers form optic tracts, which, on the basis of the brain, go around the gray tubercle, pass along the lower surface of the legs of the brain and end in the lateral geniculate body, the cushion of the optic tubercle (thalamus opticus) and the anterior quadrigemina. Of these, only the first is a continuation of the visual path and the primary visual center.
At the ganglion cells of the external geniculate body, the fibers of the optic tract end and the fibers of the central neuron begin, which pass through the posterior knee of the internal capsule and then, as part of the Graziole bundle, go to the cortex of the occipital lobe, cortical visual centers, in the region of the spur groove.
So, the nerve path of the visual analyzer begins in the layer of retinal ganglion cells and ends in the cortex of the occipital lobe 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. Here begins the central neuron, which ends in the cortex of the occipital lobe of the brain.
The physiological significance of the visual pathway is determined by its function, which conducts 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 that have great value in the diagnosis of diseases of the central nervous system and in the dynamics of monitoring the patient.
For a clear vision of an object, it is necessary that the rays of each of its points be focused on the retina. If you look into the distance, then close objects are not clearly visible, blurry, since the rays from near points are focused behind the retina. It is impossible to see objects equally clearly at different distances from the eye 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 the rays passing through the peripheral parts of the lens are refracted more strongly than the 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 a 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), that is, the ability of the eye to refract, is measured in conventional units - diopters. The diopter is the refractive power of a lens, in which parallel rays, after refraction, are collected at a focus at a distance of 1 m.
We see the world around us clearly when all departments of the visual analyzer "work" harmoniously and without interference. In order for the image to be sharp, the retina must obviously be in the back focus of the optical system of the eye. Various violations of 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, hyperopia, age-related farsightedness and astigmatism (Fig. 5).
Fig.5. The course of rays in 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 see two separate points, visible at an angle of 1 minute.
With an anomaly of refraction, visual acuity is always below 1. There are three main types of refractive error - astigmatism, myopia (myopia) and farsightedness (hypermetropia).
Refractive errors cause nearsightedness or farsightedness. The refraction of the eye changes with age: it is less than normal in newborns, in old age it can decrease again (the so-called senile farsightedness or presbyopia).
Astigmatism due to the fact that, due to congenital features, the optical system of the eye (cornea and lens) refracts rays differently 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). So, if the curvature of the surface of the cornea in a vertical section is greater than in a horizontal one, 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. Therefore, the rays of light passing through the astigmatic eye will be focused in different planes: if the horizontal lines of the object are focused on the retina, then the vertical lines are in front of it. Wearing cylindrical lenses, matched to the real defect in the optical system, to a certain extent compensates for this refractive error.
Nearsightedness and farsightedness due to changes in the length of the eyeball. With normal refraction, the distance between the cornea and the central fovea (yellow spot) is 24.4 mm. With myopia (nearsightedness), the longitudinal axis of the eye is more than 24.4 mm, so the 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 lenses in front of myopic eyes, which will push the focused image onto the retina. In a far-sighted eye, the longitudinal axis of the eye is shortened; 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 an accommodative effort, i.e. an increase in the convexity of the lens. Therefore, a far-sighted person strains the accommodative muscle, considering not only close, but also distant objects. When viewing close objects, the accommodative efforts of far-sighted people are insufficient. Therefore, for reading, farsighted people should wear glasses with biconvex lenses that enhance the refraction of light.
Refractive errors, in particular myopia and hyperopia, are also common among animals, for example, in 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. They are located in the subcutaneous fat. They are fast-adapting (they react only at the moment of the beginning of the impact), that is, they register the force of pressure. They have large receptive fields, that is, they represent rough sensitivity.
- Meissner bodies are pressure receptors located in the dermis. They are a layered structure with a nerve ending passing between the layers. They are fast adapting. They have small receptive fields, that is, they represent a subtle sensitivity.
- Merkel discs are non-encapsulated pressure receptors. They are slowly adapting (they respond to the entire duration of exposure), that is, they record the duration of pressure. They have small receptive fields.
- Hair follicle receptors - respond to hair deflection.
- Ruffini's endings are stretch receptors. They are slowly adapting, 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, tears, stretching, radiation exposure, chemical irritants; immune function of the skin. T-lymphocytes present in the skin recognize exogenous and endogenous antigens; Largenhans 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 irritation; 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 drugs; The secretory function is carried out by the sebaceous and sweat glands of the skin, which secrete lard and sweat, which, when mixed, form a thin film of water-fat emulsion on the surface of the skin; Respiratory function - the ability of the skin to absorb oxygen and release carbon dioxide, which increases with an increase in 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 integumentary 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.
Pain classification. There are two types of pain:
1. Somatic, arising from damage to the skin and the musculoskeletal system. 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 is manifested in tingling, tingling. Deep pain, as a rule, is dull, poorly localized, has a tendency to radiate to surrounding structures, is accompanied by discomfort, nausea, severe sweating, and a drop in blood pressure.
2. Visceral, arising from damage to internal organs and having a similar picture with deep pain.
Projection and reflected pain. There are special types of pain - projection and reflected.
As an example projection pain you can cause a sharp blow to the ulnar nerve. Such a blow causes an unpleasant, hard to describe sensation that spreads to those parts of the hand 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 region of the receptors of this sensory pathway. One of the most 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 cartilage discs. Afferent impulses in nociceptive fibers in such a pathology cause pain sensations that are projected into the area associated with the injured spinal nerve. Projection (phantom) pain also includes pain that patients feel in the area of the remote part of the limb.
Reflected pains pain sensations are called not in the internal organs, from which pain signals are received, but in certain parts of the skin surface (Zakharyin-Ged zones). So, with angina pectoris, in addition to pain in the region of the heart, pain is felt in the left arm and shoulder blade. Reflected pain differs from projection pain in that it is not caused 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 that conduct pain impulses from the receptors of the affected organ and the receptors of the corresponding skin area converge on the same neuron of the spinothalamic pathway. 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.
Anti-pain (antinociceptive) system. In the second half of the twentieth century, data were obtained on 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 exert a downward activating effect on the inhibitory neurons of the spinal cord. These include the central gray matter, the raphe nuclei, the locus coeruleus, the lateral reticular nucleus, the paraventricular and preoptic nuclei of the hypothalamus. The somatosensory area of the cortex integrates and controls the activity of the structures of the analgesic system. Violation of this function can cause unbearable pain.
The most important role in the mechanisms of the analgesic function of the CNS is played by the endogenous opiate system (opiate receptors and endogenous stimulants).
Endogenous stimulants of opiate receptors are enkephalins and endorphins. Some hormones, such as corticoliberin, can stimulate their formation. Endorphins act mainly through morphine receptors, which are especially abundant in the brain: in the central gray matter, raphe nuclei, and the middle thalamus. Enkephalins act through receptors located predominantly 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 arises under the action of superstrong stimuli on the receptors of the five sense organs. 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.
However, in modern theory pain, the position on the role of central summation and convergence in the mechanisms of pain was used. The most important achievement in the development of modern pain theory is the study of the mechanisms of the central perception of pain and the analgesic system of the body.
Functions of proprioreceptors
Proprioreceptors include muscle spindles, tendon organs (or Golgi organs), and articular receptors (receptors for the articular capsule and articular ligaments). All these receptors are mechanoreceptors, the specific stimulus of which is their stretching.
muscle spindles human, are elongated 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 a few to hundreds.
Thus, muscle spindles, as sensors of the state of muscle strength and the rate 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 the spindles in the conditions of natural muscle activity are quite complex. When a passive muscle is stretched, activation of spindle receptors is observed; it causes the myotatic reflex, or stretch reflex. With active muscle contraction, a decrease in its length has a deactivating effect on the spindle receptors, and excitation of gamma motor neurons, accompanying excitation of alpha motor neurons, leads to reactivation of the receptors. As a result, the impulse from the spindle receptors during movement depends on the length of the muscle, the speed of its shortening and the force of contraction.
Tendon organs (Golgi receptors) of a person are located in the area of \u200b\u200bconnection of muscle fibers with a tendon, sequentially with respect to muscle fibers.
The tendon organs are an elongated spindle-shaped or cylindrical structure, the length of which in humans can reach 1 mm. This primary sensory receptor. At rest, i.e. when the muscle is not contracted, background impulses come from the tendon organ. Under conditions of muscle contraction, the impulse frequency increases in direct proportion to the magnitude of muscle contraction, which makes it possible 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 the tendon organs to the muscle fibers (and in some cases to the muscle spindles), the tendon mechanoreceptors are stretched when the 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.
Articular receptors react to the position of the joint and to changes in the articular angle, thus participating in the system feedback from the motor apparatus and in its management. 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 articular receptors send information about the magnitude of the articular angle, i.e., about the position of the joint. Their impulsation continues throughout the entire period of conservation of this angle. It is the greater the frequency, the greater the angle shift. Other articular receptors are excited only at the moment of movement in the joint, that is, they send information about the speed of movement. The frequency of their impulses increases with an increase in the rate of change in the articular angle.
Conductor and cortical departments proprioceptive analyzer of mammals and humans. Information from muscle, tendon and joint receptors enters the spinal cord through the axons of the first afferent neurons located in the spinal ganglia, where it partially switches to alpha motor neurons or interneurons (for example, to Renshaw cells), and partially goes 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 along 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.
Axons of thalamic neurons (neurons of the third order) terminate in the cerebral cortex, mainly in the somatosensory cortex (postcentral gyrus) and in the region of the Sylvian sulcus (regions S-1 and S-2, respectively), and also partially in the motor ( prefrontal) area of the cortex. This information is used by the motor systems of the brain quite widely, including for making a decision about the idea of movement, as well as for its implementation. In addition, on the basis of 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 the receptors of muscle spindles, tendon organs, articular bags and tactile skin receptors are called kinesthetic, that is, informing about the movement of the body. Their participation in voluntary regulation of movements is different. Signals from articular receptors cause a noticeable reaction in the cerebral cortex and are well understood. Thanks to them, a person perceives differences in joint movements better than differences in the degree of muscle tension in static positions or weight maintenance. Signals from other proprioceptors, coming mainly to the cerebellum, provide unconscious regulation, subconscious control of movements and postures.
Thus, proprioceptive sensations enable a person to perceive changes in the position of individual parts of the body at rest and during movements. Information coming from proprioceptors allows him to constantly control the posture and accuracy of voluntary movements, dose the strength 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, connection with the constantly 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, provide the formation of sensations and ideas, as well as specific forms of adaptive behavior.
The concept of sensory systems was formulated by I. P. Pavlov in the study 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 with the help of direct and feedback connections. Along with this, there is still the concept of "sense organ" as a peripheral entity that perceives and partially analyzes environmental factors. The main part of the sense organ are receptors, equipped with auxiliary structures that provide optimal perception.
With the direct impact of various environmental factors with the participation of sensory systems in the body, there are Feel, which are reflections of the properties of objects of the objective world. The peculiarity of sensations is their modality, those. the totality of sensations provided by any one sensory system. Within each modality, according to the type (quality) of the sensory impression, different qualities can be distinguished, or valency. Modalities are, for example, sight, hearing, taste. Qualitative types of modality (valency) for vision are various colors, for taste - the sensation of sour, sweet, salty, bitter.
The activity of sensory systems is usually associated with the emergence of five senses - sight, hearing, taste, smell and touch, through which the organism is connected 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 acting stimulus, the nature of the sensations that arise, the level of sensitivity of receptors, the rate of adaptation, and much more.
The most significant is the classification of sensory systems, which is based on their purpose (role). In this regard, there are several types of sensory systems.
External sensory systems perceive and analyze changes in the external environment. This should include visual, auditory, olfactory, gustatory, tactile and temperature sensory systems, the excitation of which is perceived subjectively in the form of sensations.
Internal (visc
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1. SENSOR SYSTEMS
1.1 Understanding sensory systems
Sensory - from the Latin sensus - feeling, feeling.
The sensory system is an integral nervous mechanism that receives and analyzes sensory information. A synonym for the sensory system in Russian psychology is the term "analyzer", which was first introduced by the outstanding Russian physiologist I.P. Pavlov.
The analyzer consists of three parts:
1) the peripheral section - a receptor that receives and transforms external energy into a nervous process, and an effector - an organ or system of organs that reacts to the actions of external or internal stimuli, acting as the executive link of a reflex act; sensory visual sensitivity sensitization
2) pathways - afferent (ascending) and efferent (descending), connecting the peripheral section of the analyzer with the central one;
3) the central section - represented by the subcortical and cortical nuclei and the projection sections of the cerebral cortex, where the processing of nerve impulses coming from the peripheral sections takes place.
Each analyzer has a core, i.e. the central part, where the main mass of receptor cells is concentrated, and the periphery, consisting of scattered cellular elements, which are located in one quantity or another in various areas of the cortex. The nuclear part of the analyzer consists of a large mass of cells that are located in the area of the cerebral cortex where the centripetal nerves from the receptor enter. Scattered (peripheral) elements of this analyzer enter the regions adjacent to the nuclei of other analyzers. This ensures participation in a separate sensory act of a large part of the entire cerebral cortex. The analyzer core performs the function of fine analysis and synthesis, for example, it differentiates sounds by pitch. Scattered elements are associated with a coarse analysis function, such as distinguishing musical sounds and noise.
Certain cells of the peripheral parts of the analyzer correspond to certain parts of the cortical cells. So, spatially different points in the cortex are represented, for example, different points retina; spatially different arrangement of cells is presented in the cortex and the organ of hearing. The same applies to other sense organs.
Numerous experiments carried out by methods of artificial stimulation make it possible at the present time to quite definitely establish the localization in the cortex of one or another type of sensitivity. Thus, the representation of visual sensitivity is concentrated mainly in the occipital lobes of the cerebral cortex. Auditory sensitivity is localized in the middle part of the superior temporal gyrus. Tactile-motor sensitivity is represented in the posterior central gyrus, etc.
For the emergence of a sensory process, the work of the entire analyzer as a whole is necessary. The impact of the stimulus on the receptor causes the appearance of irritation. The beginning of this irritation lies in the transformation of external energy into a nervous process, which is produced by the receptor. From the receptor, this process reaches the nuclear part of the analyzer along ascending pathways. When excitation reaches the cortical cells of the analyzer, the body responds to irritation. We sense light, sound, taste, or other qualities of stimuli.
Thus, the analyzer constitutes the initial and most important part of the entire path of nervous processes, or the reflex arc. The reflex arc consists of a receptor, pathways, a central part, and an effector. The interconnection of the elements of the reflex arc provides the basis for the orientation of a complex organism in the surrounding world, the activity of the organism, depending on the conditions of its existence.
1.2 Types of sensory systems
For a long time, visual, auditory, tactile, olfactory and gustatory sensitivity seemed to be the basis on which, with the help of associations, the entire mental life of a person is built. In the 19th century, this list began to expand rapidly. Sensitivity to the position and movement of the body in space was added to it, vestibular sensitivity, tactile sensitivity, etc. were discovered and studied.
The first classification was put forward by Aristotle, who lived in 384-322. BC, who identified 5 types of "external senses": visual, auditory, olfactory, tactile, gustatory.
The German physiologist and psychophysicist Ernst Weber (1795-1878) expanded the Aristotelian classification by proposing to divide the sense of touch into: the sense of touch, the sense of weight, the sense of temperature.
In addition, he singled out a special group of feelings: a sense of pain, a sense of balance, a sense of movement, a sense of internal organs.
The classification of the German physicist, physiologist, psychologist Hermann Helmholtz (1821-1894) is based on the categories of modality, in fact this classification is also an extension of Aristotle's classification. Since modalities are distinguished according to the corresponding sense organs, for example, sensory processes associated with the eye belong to the visual modality; sensory processes associated with hearing - to the auditory modality, etc. In the modern modification of this classification, an additional concept of submodality is used, for example, in such a modality as skin feeling, submodalities are distinguished: mechanical, temperature and pain. Similarly, within the visual modality, achromatic and chromatic submodalities are distinguished.
German psychologist, physiologist, philosopher Wilhelm Wundt (1832-1920) is considered the founder of the classification of sensory systems based on the type of energy of an adequate stimulus for the corresponding receptors: physical (vision, hearing); mechanical (touch); chemical (taste, smell).
This idea was not widely developed, although it was used by I.P. Pavlov to develop the principles of physiological classification.
The classification of sensations by the outstanding Russian physiologist Ivan Petrovich Pavlov (1849-1936) is based on the physicochemical characteristics of stimuli. To determine the quality of each of the analyzers, he used the physico-chemical characteristics of the signal. Hence the names of analyzers: light, sound, skin-mechanical, odor, etc., and not visual, auditory, etc., as analyzers were usually classified.
The classifications considered above did not allow reflecting the multi-level nature of different types of receptions, some of which are earlier and lower in terms of development, while others are later and more differentiated. Ideas about the multi-level belonging of certain sensory systems are associated with the model of human skin receptions developed by G.Head.
The English neurologist and physiologist Henry Head (1861-1940) in 1920 proposed the genetic principle of classification. He distinguished between protopathic sensitivity (lower) and epicritical sensitivity (higher).
Tactile sensitivity was singled out as the epicritical, or discriminative, sensitivity of the highest level; and protopathic sensitivity, archaic, lower level - pain. He proved that protopathic and epicritical components can be both inherent in different modalities and can occur within one modality. The younger and more perfect epicritical sensitivity makes it possible to accurately localize an object in space, it provides objective information about the phenomenon. For example, touch allows you to accurately determine the place of touch, and hearing - to determine the direction in which the sound was heard. Relatively ancient and primitive sensations do not give precise localization either in external space or in the space of the body. For example, organic sensitivity - a feeling of hunger, a feeling of thirst, etc. They are characterized by a constant affective coloration, and they reflect subjective states rather than objective processes. The ratio of protopathic and epicritical components in different types of sensitivity are different.
Aleksey Alekseevich Ukhtomsky (1875-1942), an outstanding Russian physiologist, one of the founders of the physiological school of St. Petersburg University, also applied the genetic principle of classification. According to Ukhtomsky, the highest receptions are hearing, vision, which are in constant interaction with the lower ones, thanks to which they improve and develop. For example, the genesis of visual reception is that first tactile reception passes into tactile-visual, and then into purely visual reception.
The English physiologist Charles Sherrington (1861-1952) in 1906 developed a classification that takes into account the location of the receptor surfaces and the function they perform:
1. Exteroception (external reception): a) contact; b) distant; c) contact-distance;
2. Proprioception (reception in muscles, ligaments, etc.): a) static; b) kinesthetic.
3. Interoception (reception of internal organs).
Ch. Sherrington's system classification divided all sensory systems into three main blocks.
The first block is exteroception, which brings to the person information coming from the outside world and is the main reception that connects the person with the outside world. It includes: sight, hearing, touch, smell, taste. All exteroception is divided into three subgroups: contact, distant and contact-distant.
Contact exteroception is carried out when the stimulus is exposed directly to the surface of the body or the corresponding receptors. A typical example is the sensory acts of touch and pressure, touch, taste.
Distant exteroception is carried out without direct contact of the stimulus with the receptor. In this case, the source of irritation is located at some distance from the receptive surface of the corresponding sensory organ. It includes sight, hearing, smell.
Contact-distant exteroception is carried out both in direct contact with the stimulus, and remotely. It includes temperature, skin and pain. vibrational sensory acts.
The second block is proprioception, which brings to the person information about the position of his body in space and the state of his musculoskeletal system. All proprioception is divided into two subgroups: static and kinesthetic reception.
Static reception signals the position of the body in space and balance. Receptor surfaces that report changes in body position in space are located in the semicircular canals of the inner ear.
Kinesthetic reception signals the state of movement (kinesthesia) of individual parts of the body relative to each other, and the positions of the musculoskeletal system. Receptors for kinesthetic, or deep, sensitivity are found in muscles and articular surfaces (tendons, ligaments). Excitations arising from muscle stretching, changing the position of the joints, cause kinesthetic reception.
The third block includes interoception, signaling the state of the internal organs of a person. These receptors are found in the walls of the stomach, intestines, heart, blood vessels, and other visceral structures. Interoceptive are the feeling of hunger, thirst, sexual sensations, sensations of malaise, etc.
Modern authors use the supplemented classification of Aristotle, distinguishing between reception: touch and pressure, touch, temperature, pain, taste, olfactory, visual, auditory, positions and movements (static and kinesthetic) and organic (hunger, thirst, sexual sensations, pain, sensations of internal organs, etc.), structuring it by C. Sherrington's classification. The levels of organization of sensory systems are based on the genetic principle of G.Head's classification.
1.3 Chusensitivity of sensory systems
Sensitivity - the ability of the sense organs to respond to the appearance of a stimulus or its change, i.e. the ability to mental reflection in the form of a sensory act.
Distinguish between absolute and differential sensitivity. Absolute sensitivity - the ability to perceive stimuli of minimal strength (detection). Differential sensitivity - the ability to perceive a change in a stimulus or distinguish between close stimuli within the same modality.
Sensitivity is measured or determined by the strength of the stimulus, which, under given conditions, is capable of causing a sensation. Feeling is an active mental process partial reflections of objects or phenomena of the surrounding world, as well as the internal states of the body, in the mind of a person with the direct impact of stimuli on the senses.
The minimum strength of the stimulus that can cause a sensation is determined by the lower absolute threshold of sensation. Stimuli of lesser strength are called subthreshold. The lower threshold of sensations determines the level of absolute sensitivity of this analyzer. The lower the threshold value, the higher the sensitivity.
where E is sensitivity, P is the threshold value of the stimulus.
The value of the absolute threshold depends on the age, the nature of the activity, the functional state of the organism, the strength and duration of the acting stimulus.
The upper absolute threshold of sensation is determined by the maximum strength of the stimulus, which also causes a sensation characteristic of this modality. There are suprathreshold stimuli. They cause pain and destruction of the receptors of the analyzers, which are affected by suprathreshold stimulation. The minimum difference between two stimuli that causes different sensations in the same modality determines the difference threshold, or threshold of discrimination. Difference sensitivity is inversely proportional to the discrimination threshold.
The French physicist P. Buger in 1729 came to the conclusion that the difference threshold of visual perception is directly proportional to its initial level. 100 years after P. Buger, the German physiologist Ernst Weber established that this pattern is also characteristic of other modalities. Thus, a very important psychophysical law was found, which was called the Bouguer-Weber law.
Bouguer-Weber law:
where? I - difference threshold, I - initial stimulus.
The ratio of the difference threshold to the value of the initial stimulus is a constant value and is called relative difference or differential threshold.
According to the Bouguer-Weber law, the differential threshold is some constant part of the magnitude of the original stimulus, by which it must be increased or decreased in order to obtain a barely noticeable change in sensation. The value of the differential threshold depends on the modality of sensation. For vision, it is about 1/100, for hearing 1/10, for kinesthesia 1/30, etc.
The reciprocal of the differential threshold is called the differential sensitivity. Subsequent studies have shown that the law is valid only for the middle part of the dynamic range of the sensory system, where the differential sensitivity is maximum. The limits of this zone are different for different sensory systems. Outside this zone, the differential threshold increases, sometimes very significantly, especially when approaching the absolute lower or upper threshold.
The German physicist, psychologist and philosopher Gustav Fechner (1801-1887), the founder of psychophysics as a science of the regular connection of physical and mental phenomena, using a number of psychophysical regularities found by that time, including the Bouguer-Weber law, formulated the following law.
Fechner's law:
where S is the intensity of sensation, i is the strength of the stimulus, K is the Bouguer-Weber constant.
The intensity of sensations is proportional to the logarithm of the strength of the acting stimulus, that is, the sensation changes much more slowly than the strength of the irritation grows.
As the intensity of the signal increases, in order for the differences between the units of measurement of sensations (S) to remain equal, an increasingly significant difference between the units of intensity (i) is required. In other words, while the sensation increases uniformly (in an arithmetic progression), the corresponding increase in signal intensity occurs physically unevenly, but proportionally (in a geometric progression). The relationship between quantities, one of which changes in an arithmetic progression, and the second in a geometric progression, is expressed by a logarithmic function.
Fechner's law has received in psychology the name of the basic psychophysical law.
Stevens' law (power law) is a variant of the basic psychophysical law proposed by the American psychologist Stanley Stevens (1906-1973), and establishes a power-law, rather than a logarithmic relationship between the intensity of sensation and the strength of stimuli:
where S is the intensity of sensation, i is the strength of the stimulus, k is a constant that depends on the unit of measurement, n is the exponent of the function. The exponent n of the power function is different for the sensations of different modalities: the limits of its variation are from 0.3 (for sound volume) to 3.5 (for the strength of an electric shock).
The complexity of detecting thresholds and fixing changes in the intensity of sensation is the object of research at the present time. Modern researchers studying the detection of signals by various operators have come to the conclusion that the complexity of this sensory action lies not only in the impossibility of perceiving the signal due to its weakness, but in the fact that it is always present against the background of masking interference or "noise". ". The sources of this "noise" are numerous. Among them are extraneous stimuli, spontaneous activity of receptors and neurons in the central nervous system, a change in the orientation of the receptor relative to the stimulus, fluctuations in attention, and other subjective factors. The action of all these factors leads to the fact that the subject often cannot say with complete certainty when the signal was presented and when it was not. As a result, the signal detection process itself acquires a probabilistic character. This feature of the appearance of sensations of near-threshold intensity is taken into account in a number of recently created mathematical models that describe this sensory activity.
1.4 Sensitivity variability
The sensitivity of the analyzers, determined by the magnitude of the absolute and difference thresholds, is not constant and can change. This variability of sensitivity depends both on the conditions of the external environment and on a number of internal physiological and psychological conditions. There are two main forms of sensitivity change:
1) sensory adaptation - a change in sensitivity under the influence of the external environment;
2) sensitization - a change in sensitivity under the influence of the internal environment of the body.
Sensory adaptation - adaptation of the organism to the actions of the environment due to a change in sensitivity under the influence of an acting stimulus. There are three types of adaptation:
1. Adaptation as the complete disappearance of sensation in the process of prolonged action of the stimulus. In the case of constant stimuli, the sensation tends to fade. For example, clothes, watches on the hand, soon cease to be felt. The distinct disappearance of olfactory sensations soon after we enter the atmosphere with any persistent odor is also a common fact. The intensity of the taste sensation is weakened if the corresponding substance is kept in the mouth for some time.
And, finally, the sensation may fade away completely, which is associated with a gradual increase in the lower absolute threshold of sensitivity to the level of intensity of a permanent stimulus. The phenomenon is characteristic of all modalities, except visual.
Complete adaptation of the visual analyzer under the action of a constant and immobile stimulus does not occur under normal conditions. This is due to the compensation of a constant stimulus due to the movements of the receptor apparatus itself. Constant voluntary and involuntary eye movements ensure the continuity of the visual sensation. Experiments in which the conditions for stabilizing the image relative to the retina of the eyes were artificially created showed that in this case the visual sensation disappears 2–3 seconds after its occurrence.
2. Adaptation as a dulling of sensation under the influence of a strong stimulus. A sharp decrease in sensation with subsequent recovery is a protective adaptation.
So, for example, when we get from a semi-dark room into a brightly lit space, we are first blinded and unable to distinguish any details around. After some time, the sensitivity of the visual analyzer is restored, and we begin to see normally. The same thing happens when we get into the weaving workshop and for the first time, apart from the roar of the machines, we cannot perceive speech and other sounds. After a while, the ability to hear speech and other sounds is restored. This is explained by a sharp increase in the lower absolute threshold and the discrimination threshold, followed by the restoration of these thresholds in accordance with the intensity of the acting stimulus.
Types of adaptation described 1 and 2 can be combined under the general term "negative adaptation", since their result is a general decrease in sensitivity. But "negative adaptation" is not a "bad" adaptation, since it is an adaptation to the intensity of the acting stimuli and helps to prevent the destruction of sensory systems.
3. Adaptation as an increase in sensitivity under the influence of a weak stimulus (decrease in the lower absolute threshold). This kind of adaptation, which is characteristic of certain types of sensations, can be defined as positive adaptation.
In the visual analyzer, this is dark adaptation, when the sensitivity of the eye increases under the influence of being in the dark. A similar form of auditory adaptation is silence adaptation. In temperature sensations, positive adaptation is found when a pre-cooled hand feels warm, and a pre-heated hand feels cold when immersed in water of the same temperature.
Studies have shown that some analyzers detect fast adaptation, others slow. For example, touch receptors adapt very quickly. The visual receptor adapts relatively slowly (the time of dark adaptation reaches several tens of minutes), the olfactory and gustatory receptors.
The phenomenon of adaptation can be explained by those peripheral changes that occur in the functioning of the receptor under the influence of direct and feedback from the analyzer nucleus.
Adaptive regulation of the level of sensitivity, depending on which stimuli (weak or strong) affect the receptors, is of great biological importance. Adaptation helps to catch weak stimuli through the sense organs and protects the sense organs from excessive irritation in case of unusually strong influences.
So, adaptation is one of the most important types of changes in sensitivity, indicating a greater plasticity of the organism in its adaptation to environmental conditions.
Another type of change in sensitivity is sensitization. The process of sensitization differs from the process of adaptation in that in the process of adaptation, the sensitivity changes in both directions - that is, it increases or decreases, and in the process of sensitization - only in one direction, namely, an increase in sensitivity. In addition, the change in sensitivity during adaptation depends on environmental conditions, and during sensitization - mainly on the processes occurring in the body itself, both physiological and mental. Thus, sensitization is an increase in the sensitivity of the sense organs under the influence of internal factors.
There are two main directions of increasing sensitivity according to the type of sensitization. One of them is of a long-term permanent nature and depends mainly on stable changes occurring in the body, the second is of a non-permanent nature and depends on temporary effects on the body.
The first group of factors that change sensitivity include: age, endocrine changes, dependence on the type of nervous system, the general state of the body associated with the compensation of sensory defects.
Studies have shown that the acuteness of the sensitivity of the sense organs increases with age, reaching its maximum by the age of 20-30, in order to gradually decrease in the future.
The essential features of the functioning of the sense organs depend on the type of the human nervous system. It is known that people with a strong nervous system show more endurance and less sensitivity, and people with a weak nervous system with less endurance have more sensitivity.
Of great importance for sensitivity is the endocrine balance in the body. For example, during pregnancy, olfactory sensitivity is sharply aggravated, while visual and auditory sensitivity decreases.
Compensation for sensory defects leads to an increase in sensitivity. Thus, for example, loss of sight or hearing is compensated to a certain extent by an exacerbation of other types of sensitivity. People deprived of sight have a highly developed sense of touch, they are able to read with their hands. This hand-reading process has a special name - haptics. People who are deaf have a strong vibrational sensitivity. For example, the great composer Ludwig van Beethoven in last years life, when he lost his hearing, he used vibrational sensitivity to listen to musical works.
The second group of factors that change sensitivity include pharmacological effects, a conditioned reflex increase in sensitivity, the influence of the second signal system and set, the general state of the body associated with fatigue, and the interaction of sensations.
There are substances that cause a distinct exacerbation of sensitivity. These include, for example, adrenaline, the use of which causes excitation of the autonomic nervous system. Phenamine and a number of other pharmacological agents can have a similar effect, exacerbating the sensitivity of receptors.
The conditioned reflex increase in sensitivity can include situations in which there were harbingers of a threat to the functioning of the human body, fixed in memory by previous situations. For example, a sharp exacerbation of sensitivity is observed in members of operational groups who participated in hostilities during subsequent combat operations. Taste sensitivity is aggravated when a person enters an environment similar to that in which he previously participated in a plentiful and pleasant feast.
An increase in the sensitivity of the analyzer can also be caused by exposure to second-signal stimuli. For example: a change in the electrical conductivity of the eyes and tongue in response to the words "sour lemon", which actually occurs with direct exposure to lemon juice.
An exacerbation of sensitivity is also observed under the influence of the installation. Thus, auditory sensitivity rises sharply when waiting for an important phone call.
Changes in sensitivity occur even in a state of fatigue. Fatigue first causes an exacerbation of sensitivity, that is, a person begins to acutely feel extraneous sounds, smells, etc., not related to the main activity, and then, with the further development of fatigue, a decrease in sensitivity occurs.
A change in sensitivity can also be caused by the interaction of different analyzers.
The general pattern of the interaction of analyzers is that weak sensations cause an increase, and strong sensations cause a decrease in the sensitivity of the analyzers during their interaction. Physiological mechanisms in this case, underlying sensitization. - these are the processes of irradiation and concentration of excitation in the cerebral cortex, where the central sections of the analyzers are represented. According to Pavlov, a weak stimulus causes an excitation process in the cerebral cortex, which easily radiates (spreads). As a result of irradiation, the sensitivity of other analyzers increases. Under the action of a strong stimulus, a process of excitation occurs, which, on the contrary, causes a process of concentration, which leads to inhibition of the sensitivity of other analyzers and a decrease in their sensitivity.
During the interaction of analyzers, intermodal connections may arise. An example of this phenomenon is the fact of the occurrence of panic fear when exposed to the sound of ultra-low frequencies. The same phenomenon is confirmed when a person feels the effect of radiation or feels a look in the back.
An arbitrary increase in sensitivity can be achieved in the process of targeted training activities. So, for example, an experienced turner is able to "by eye" determine the millimeter dimensions of small parts, tasters of various wines, spirits, etc., even having extraordinary innate abilities, in order to become real masters of their craft, are forced to train the sensitivity of their analyzers for years.
The considered types of sensitivity variability do not exist in isolation precisely because the analyzers are in constant interaction with each other. Related to this is the paradoxical phenomenon of synesthesia.
Synesthesia - the occurrence under the influence of irritation of one analyzer of a sensation characteristic of another (for example: cold light, warm colors). This phenomenon is widely used in art. It is known that some composers had the ability to "color hearing", including Alexander Nikolaevich Skryabin, who owns the first color musical work in history - the symphony "Prometheus", presented in 1910 and including a party of light. The Lithuanian painter and composer Čiurlionis Mykolojus Konstantinas (1875-1911) is known for his symbolic paintings, in which he reflected the visual images of his musical works - “Sonata of the Sun”, “Sonata of Spring”, “Symphony of the Sea”, etc.
The phenomenon of synesthesia characterizes the constant interconnection of the sensory systems of the body and the integrity of the sensory reflection of the world.
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General information
Adhering to the cognitive approach to the description of the psyche, we represent a person as a kind of system that processes symbols in solving its problems, then we can imagine the most important feature of a person's personality - the sensory organization of the personality.
Sensory organization of personality
The sensory organization of personality is the level of development individual systems sensitivity and the possibility of their combination. The sensory systems of a person are his sense organs, as if receivers of his sensations, in which sensation is transformed into perception.
Every receiver has a certain sensitivity. If we turn to the animal world, we will see that the predominant level of sensitivity of any species is a generic trait. For example, bats have developed sensitivity to the perception of short ultrasonic pulses, dogs have olfactory sensitivity.
The main feature of the sensory organization of a person is that it develops as a result of all his life path. The sensitivity of a person is given to him at birth, but its development depends on the circumstances, desire and efforts of the person himself.
What do we know about the world and about ourselves? Where do we get this knowledge from? How? The answers to these questions come from the depths of centuries from the cradle of all living things.
Feel
Sensation is a manifestation of the general biological property of living matter - sensitivity. Through sensation there is a psychic connection with the external and internal world. Thanks to sensations, information about all the phenomena of the external world is delivered to the brain. In the same way, a loop closes through sensations to receive feedback about the current physical and, to some extent, mental state of the organism.
Through sensations, we learn about taste, smell, color, sound, movement, the state of our internal organs, etc. From these sensations, holistic perceptions of objects and the whole world are formed.
It is obvious that the primary cognitive process takes place in human sensory systems, and already on its basis, cognitive processes that are more complex in their structure arise: perceptions, representations, memory, thinking.
No matter how simple the primary cognitive process may be, but it is precisely this that is the basis of mental activity, only through the “entrances” of sensory systems does the world around us penetrate into our consciousness.
Sensation Processing
After the information is received by the brain, the result of its processing is the development of a response or strategy aimed, for example, at improving physical tone, focusing more on current activities, or setting up for accelerated inclusion in mental activity.
Generally speaking, the response or strategy worked out at any given time is the best choice of the options available to the person at the time of the decision. However, it is clear that the number of options available and the quality of choice vary from person to person and depend on, for example:
mental properties of personality,
strategies for interacting with others
some of the physical condition,
experience, the availability of the necessary information in memory and the possibility of retrieving it.
the degree of development and organization of higher nervous processes, etc.
For example, the baby went out naked in the cold, his skin feels cold, perhaps chills appear, he becomes uncomfortable, a signal about this enters the brain and a deafening roar is heard. The reaction to cold (stimulus) in an adult may be different, he will either rush to get dressed, or jump into a warm room, or try to warm himself in another way, for example, by running or jumping.
Improving the higher mental functions of the brain
Over time, children improve their reactions, multiplying the effectiveness of the result achieved. But after growing up, the opportunities for improvement do not disappear, despite the fact that the adult's susceptibility to them decreases. It is in this that "Effekton" sees part of its mission: increasing the efficiency of intellectual activity by training the higher mental functions of the brain.
Effekton's software products make it possible to measure various indicators of the human sensorimotor system (in particular, the Jaguar package contains tests of the time of a simple audio and visual-motor reaction, a complex visual-motor reaction, and the accuracy of perception of time intervals). Other packages of the "Effekton" complex evaluate the properties of cognitive processes of higher levels.
Therefore, it is necessary to develop the perception of the child, and the use of the package "Jaguar" can help you with this.
Physiology of sensations
Analyzers
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 conversion of external energy into a nervous process)
central part of the analyzer - afferent or sensory nerves
cortical sections of the analyzer, in which the processing of nerve impulses takes place.
Certain receptors correspond to their sections of cortical cells.
The specialization of each sense organ is based not only on the structural features of the receptor analyzers, but also on the specialization of the neurons that make up the central nervous apparatus, which receive signals perceived by the peripheral senses. The analyzer is not a passive receiver of energy; it is reflexively rebuilt under the influence of stimuli.
The movement of stimulus from the outer to the inner world
According to the cognitive approach, the movement of a stimulus during its transition from the external world to the internal one occurs as follows:
the stimulus causes certain changes in energy in the receptor,
energy is converted into nerve impulses
information about nerve impulses is transmitted to the corresponding structures of the cerebral cortex.
Sensations depend not only on the capabilities of the brain and sensory systems of a person, but also on the characteristics of the person himself, his development and condition. With illness or fatigue, a person changes sensitivity to certain influences.
There are also cases of pathologies when a person is deprived, for example, of hearing or sight. If this trouble is congenital, then there is a violation of the flow of information, which can lead to delays mental development. If these children were taught special techniques to compensate for their shortcomings, then some redistribution within the sensory systems is possible, thanks to which they will be able to develop normally.
Properties of sensations
Each type of sensation is characterized not only by specificity, but also has general properties with other types:
quality,
intensity,
duration,
spatial localization.
But not every irritation causes a sensation. The minimum value of the stimulus at which a sensation appears is the absolute threshold of sensation. The value of this threshold characterizes the absolute sensitivity, which is numerically equal to the value inversely proportional to the absolute threshold of sensations. And sensitivity to a change in the stimulus is called relative or difference sensitivity. The minimum difference between two stimuli, which causes a slightly noticeable difference in sensations, is called the difference threshold.
Based on this, we can conclude that it is possible to measure sensations. And once again you come to admire the amazing finely working devices - human organs human senses or sensory systems.
Effekton's software products allow you to measure various indicators of the human sensory system (for example, the Jaguar package contains tests of the speeds of a simple audio and visual-motor reaction, a complex visual-motor reaction, the accuracy of time perception, the accuracy of space perception, and many others). Other packages of the "Effekton" complex also evaluate the properties of cognitive processes of higher levels.
Classification of sensations
Five basic types of sensations: sight, hearing, touch, smell and taste - were already known to the ancient Greeks. At present, ideas about the types of human sensations have been expanded; about two dozen different analyzer systems can be distinguished, reflecting the impact of the external and internal environment on receptors.
Sensations are classified according to several principles. 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 arise in the presence or absence of direct contact of the receptor with the stimulus. Sight, hearing, smell are distant sensations. These types of sensations provide orientation in the nearest environment. Taste, pain, tactile sensations - contact.
According to the location of receptors on the surface of the body, in muscles and tendons, or inside the body, they are distinguished, respectively:
exteroception - visual, auditory, tactile and others;
proprioception - sensations from muscles, tendons;
interoception - feelings of hunger, thirst.
In the course of the evolution of all living things, sensitivity has undergone changes from the most ancient to the modern. So, distant sensations can be considered more modern than contact ones, but in the structure of the contact analyzers themselves, one can also reveal more ancient and completely new functions. So, for example, pain sensitivity is more ancient than tactile.
Such classification principles help to group all kinds of sensations into systems and see their interaction and connections.
Types of sensations
Vision, hearing
Let us consider various types of sensations, bearing in mind that vision and hearing are the most well studied.
1) Sensor systems
"Sens" - translated as "feeling", "feeling".
Sensory systems are the perceiving systems of the body (visual, auditory, olfactory, tactile, gustatory, pain, tactile, vestibular apparatus, proprioceptive, interoceptive).
It can be said that sensory systems are the "information inputs" of the organism for its perception of the characteristics of the environment, as well as the characteristics of the internal environment of the organism itself. In physiology, it is customary to emphasize the letter "o", while in technology - the letter "e". Therefore, technical perceiving systems are sensory, and physiological systems are sensory.
Perception is the translation of the characteristics of an external stimulus into internal neural codes available for processing and analysis by the nervous system (coding), and the construction of a neural model of the stimulus (sensory image).
Perception allows you to build internal image, reflecting the essential characteristics of the external stimulus. The internal sensory image of the stimulus is a neural model consisting of a system of nerve cells. It is important to understand that this neural model cannot fully correspond to the real stimulus and will always differ from it at least in some details.
For example, the cubes in the picture on the right form a model close to reality, but not able to exist in reality...
2) Analyzers and sensor systems
Analyzers are called part of the nervous system, consisting of many specialized perceiving receptors, as well as intermediate and central nerve cells and nerve fibers connecting them.
I.P. Pavlov created the doctrine of analyzers. This is a simplified representation of perception. He divided the analyzer into 3 links.
The structure of the analyzer
The peripheral part (remote) is the receptors that perceive irritation and turn it into nervous excitation.
Conductor department (afferent or sensory nerves) - these are pathways that transmit sensory excitation born in receptors.
The central section is a section of the cerebral cortex that analyzes the sensory excitation that has come to it and builds a sensory image due to the synthesis of excitations.
Thus, for example, the final visual perception occurs in the brain and not in the eye.
The concept of a sensory system is broader than an analyzer. It includes additional devices, adjustment systems and self-regulation systems. The sensory system provides for feedback between the brain's analyzing structures and the perceiving receptive apparatus. Sensory systems are characterized by the process of adaptation to stimulation.
Adaptation is the process of adapting the sensory system and its individual elements to the action of a stimulus.
Differences between the concepts of "sensor system" and "analyzer"
1) The sensory system is active, not passive in excitation transfer.
2) The sensory system includes auxiliary structures that ensure optimal tuning and operation of the receptors.
3) The sensory system includes auxiliary lower nerve centers, which not only transmit sensory excitation further, but change its characteristics and divide it into several streams, sending them in different directions.
4) The sensory system has feedback between subsequent and previous structures that transmit sensory excitation.
5) Processing and processing of sensory excitation occurs not only in the cerebral cortex, but also in the underlying structures.
6) The sensory system actively adjusts to the perception of the stimulus and adapts to it, that is, it adapts.
7) The sensor system is more complex than the analyzer.
Conclusion: Sensory system = analyzer + regulation system.
3) Sensory receptors
Sensory receptors are specific cells that are tuned to perceive various stimuli of the external and internal environment of the body and are highly sensitive to an adequate stimulus. An adequate stimulus is a stimulus that gives the maximum response, with a minimum strength of irritation.
The activity of sensory receptors is a necessary condition for the implementation of all the functions of the central nervous system. Sensory receptors are the first link in the reflex pathway and the peripheral part of a more complex structure - analyzers. A set of receptors, the stimulation of which leads to a change in the activity of any nerve structures, is called the receptive field.
Receptor classification
The nervous system is characterized by a wide variety of receptors, Various types which are shown in the figure:
Rice.
Receptors are classified according to several criteria:
A. The central place is occupied by the division of dependence on the type of perceived stimulus. There are 5 such types of receptors:
III Mechanoreceptors are excited during mechanical deformation. They are located in the skin, blood vessels, internal organs, musculoskeletal system, auditory and vestibular systems.
III 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. Such receptors are found in the mucous membrane of the tongue and nose, the carotid and aortic bodies, the hypothalamus, and the medulla oblongata.
III Thermoreceptors perceive changes in temperature. They are divided into heat and cold receptors and are located in the skin, blood vessels, internal organs, hypothalamus, middle, medulla oblongata and spinal cord.
III Photoreceptors in the retina of the eye perceive light (electromagnetic) energy.
Ш Nociceptors (pain receptors) - their excitation is accompanied by pain sensations. Irritants for them are mechanical, thermal and chemical factors. Painful stimuli are perceived by free nerve endings that are found in the skin, muscles, internal organs, dentin, and blood vessels.
B. From a psychophysiological point of view Receptors are divided according to the sense organs and the sensations formed into visual, auditory, gustatory, olfactory and tactile.
IN. Location in the body Receptors are divided into extero- and interoreceptors. Exteroreceptors include receptors of the skin, visible mucous membranes and sensory organs: visual, auditory, taste, olfactory, tactile, skin, pain and temperature. Interoreceptors include receptors of internal organs (visceroreceptors), blood vessels and the central nervous system, as well as receptors of the musculoskeletal system (proprioreceptors) and vestibular receptors. If the same kind of receptors are localized both in the central nervous system and in other places (vessels), then such vessels are divided into central and peripheral.
G. Depending on the degree of receptor specificity, i.e. from their ability to respond to one or more types of stimuli, monomodal and polymodal receptors are distinguished. In principle, each receptor can respond not only to an adequate, but also to an inadequate stimulus, however, the sensitivity to them is different. If the sensitivity to adequate is much greater than that to inadequate stimuli, then these are monomodal receptors. Monomodality is especially characteristic of extreroreceptors. Polymodal receptors are adapted to the perception of several adequate stimuli, such as mechanical and temperature or mechanical, chemical and pain. These include the irritant receptors of the lungs.
D. By structural and functional organization distinguish between primary and secondary receptors. In the primary receptor, the stimulus acts directly on the end of the sensory neuron: olfactory, tactile, temperature, pain receptors, proprioceptors, receptors of internal organs. In the secondary receptors there is a special cell that is synaptically connected to the end of the dendrite of the sensory neuron, and it transmits a signal through the end of the dendrite to the conduction pathways: auditory, vestibular, taste receptors, retinal photoreceptors.
E. According to the speed of adaptation receptors are divided into 3 groups: phasic (quickly adapting): vibration and skin touch receptors, tonic (slowly adapting): proprioreceptors, lung stretch receptors, part of pain receptors, phasic-tonic (mixed, adapting at an average speed): retinal photoreceptors, thermoreceptors skin.
PROPERTIES OF RECEPTORS
High excitability of receptors. For example, 1 quantum of light is enough to excite the retina, and one molecule of an odorous substance is enough for the olfactory receptor. This property allows you to quickly transfer information to the central nervous system about all changes in the external and internal environment. At the same time, the excitability of different types of receptors is not the same. In exteroceptors, it is higher than in intero. Pain receptors have low excitability, they are evolutionarily adapted to respond to the action of extreme stimuli.
Adaptation of receptors - a decrease in their excitability with prolonged exposure to an irritant. An exception is the use of the term "dark adaptation" for photoreceptors, which increase in excitability in the dark. The value of adaptation is that it reduces the perception of stimuli that have properties (long-term action, low dynamics of force), which reduce their importance for the life of the organism.
Spontaneous activity of receptors. Many types of receptors are capable of generating impulses in a neuron without the action of an irritant on them. This is called background activity and the excitability of such receptors is higher than those without such activity. The background activity of receptors is involved in maintaining the tone of the nerve centers under conditions of physiological rest.
The excitability of receptors is under the neurohumoral control of the whole organism. The nervous system can influence the excitability of receptors in different ways. It has been established that the nerve centers exercise efferent (descending) control over many receptors - vestibular, auditory, olfactory, muscle.
Among efferent inhibitory effects (negative feedback) are better studied. Thus, the effects of strong stimuli are limited. Through efferent pathways, an activating effect on receptors can also be exerted.
Also, the nervous system regulates the activity of receptors through a change in the concentration of hormones (for example, an increase in the sensitivity of visual and auditory receptors under the influence of adrenaline, thyroxine); through the regulation of blood flow in the receptor zone and through pre-receptor influence, i.e. changing the strength of the stimulus to the receptor (for example, changing the flow of light using the pupillary reflex).
The importance for the body of regulation of receptor activity lies in the best coordination of their excitability with the strength of irritation.
4) General principles for the design of sensor systems
1. The principle of multi-storey
In each sensory system, there are several transmission intermediate instances on the way from receptors to the cerebral cortex. In these intermediate lower nerve centers, a partial processing of excitation (information) occurs. Already at the level of the lower nerve centers, unconditioned reflexes are formed, that is, responses to irritation, they do not require the participation of the cerebral cortex and are carried out very quickly.
For example: The midge flies right into the eye - the eye blinked in response, and the midge did not hit it. For a response in the form of blinking, it is not necessary to create a full-fledged image of a midge, a simple detection that an object is rapidly approaching the eye is sufficient.
One of the pinnacles of the multi-storey sensory system device is the auditory sensory system. It has 6 floors. There are also additional detours to higher cortical structures that bypass several of the lower floors. In this way, the cortex receives a preliminary signal to increase its readiness to the main flow of sensory excitation.
Illustration of the multi-storey principle:
2. The principle of multichannel
Excitation is always transmitted from the receptors to the cortex along several parallel pathways. The excitation flows are partially duplicated and partially separated. They transmit information about the various properties of the stimulus.
An example of parallel paths in the visual system:
1st path: retina - thalamus - visual cortex.
2nd path: retina - quadrigemina (upper hills) of the midbrain (nucleus of the oculomotor nerves).
3rd way: retina - thalamus - thalamus cushion - parietal associative cortex.
When different paths are damaged, the results are different.
For example: if you destroy the lateral geniculate body of the thalamus (NKT) in the visual path 1, then complete blindness occurs; if the superior colliculus of the midbrain is destroyed in path 2, then the perception of the movement of objects in the field of view is disturbed; if the thalamic cushion is destroyed in path 3, object recognition and visual memory are lost.
In all sensory systems, there are necessarily three ways (channels) for the transmission of excitation:
1) a specific path: it leads to the primary sensory projection zone of the cortex,
2) non-specific way: it provides general activity and tone of the cortical part of the analyzer,
3) associative path: it determines the biological significance of the stimulus and controls attention.
Illustration of the multichannel principle:
In the evolutionary process, multi-storey and multi-channel in the structure of sensory pathways is enhanced.
3. Principle of convergence
Convergence is the convergence of neural pathways in the form of a funnel. Due to convergence, an upper-level neuron receives excitation from several lower-level neurons.
For example: there is a large convergence in the retina of the eye. There are several tens of millions of photoreceptors, and no more than one million of ganglion cells. nerve fibers that transmit excitation from the retina are many times smaller than photoreceptors.
4. Principle of divergence
Divergence is a divergence of the excitation flow into several flows from the lowest floor to the highest (resembles a divergent funnel).
5. Feedback principle
Feedback usually means the influence of a managed element on a managing one. For this, there are corresponding paths of excitation from the lower and higher centers back to the receptors.
5) Operation of analyzers and sensor systems
In the work of sensory systems, certain receptors correspond to their own sections of cortical cells.
The specialization of each sense organ is based not only on the structural features of the analyzer receptors, but also on the specialization of the neurons that make up the central nervous apparatus, which receive signals perceived by the peripheral senses. The analyzer is not a passive receiver of energy; it is reflexively rebuilt under the influence of stimuli.
According to the cognitive approach, the movement of a stimulus during its transition from the external world to the internal one occurs as follows:
1) the stimulus causes certain changes in energy in the receptor,
2) energy is converted into nerve impulses,
3) information about nerve impulses is transmitted to the corresponding structures of the cerebral cortex.
Sensations depend not only on the capabilities of the brain and sensory systems of a person, but also on the characteristics of the person himself, his development and condition. With illness or fatigue, a person changes sensitivity to certain influences.
There are also cases of pathologies when a person is deprived, for example, of hearing or sight. If this trouble is congenital, then there is a violation of the flow of information, which can lead to mental retardation. If these children were taught special techniques to compensate for their shortcomings, then some redistribution within the sensory systems is possible, thanks to which they will be able to develop normally.
Properties of sensations
Each type of sensation is characterized not only by specificity, but also has common properties with other types:
l quality,
b intensity,
b duration,
l spatial localization.
But not every irritation causes a sensation. The minimum value of the stimulus at which a sensation appears is the absolute threshold of sensation. The value of this threshold characterizes the absolute sensitivity, which is numerically equal to the value inversely proportional to the absolute threshold of sensations. And sensitivity to a change in the stimulus is called relative or difference sensitivity. The minimum difference between two stimuli, which causes a slightly noticeable difference in sensations, is called the difference threshold.
Based on this, we can conclude that it is possible to measure sensations.
General principles of operation of sensor systems:
1. The transformation of the strength of stimulation into a frequency code of impulses is the universal principle of operation of any sensory receptor.
Moreover, in all sensory receptors, the transformation begins with a stimulus-induced change in the properties of the cell membrane. Under the action of a stimulus (stimulus), stimulus-gated ion channels should open in the cell receptor membrane (and, on the contrary, close in photoreceptors). Through them, the flow of ions begins and the state of membrane depolarization develops.
2. Topical correspondence - the flow of excitation (information flow) in all transmission structures corresponds to the significant characteristics of the stimulus. This means that important signs of the stimulus will be encoded in the form of a stream of nerve impulses, and the nervous system will build an internal sensory image similar to the stimulus - the neural model of the stimulus.
3. Detection is the selection of qualitative features. Neurons-detectors respond to certain features of the object and do not respond to everything else. Detector neurons mark contrast transitions. Detectors add meaning and uniqueness to a complex signal. In different signals, they allocate the same parameters. For example, only detection will help you separate the contours of a camouflaged flounder from its surrounding background.
4. Distortion of information about the original object at each level of excitation transfer.
5. Specificity of receptors and sense organs. Their sensitivity is maximum to a certain type of stimulus with a certain intensity.
6. The law of specificity of sensory energies: the sensation is determined not by the stimulus, but by the irritated sensory organ. Even more precisely, one can say this: the sensation is determined not by the stimulus, but by the sensory image that is built in the higher nerve centers in response to the action of the stimulus. For example, the source of pain irritation may be located in one place of the body, and the sensation of pain may be projected to a completely different area. Or: the same stimulus can cause very different sensations depending on the adaptation of the nervous system and / or sensory organ to it.
7. Feedback between subsequent and previous structures. Subsequent structures can change the state of the previous ones and in this way change the characteristics of the excitation flow that comes to them.
The specificity of sensory systems is predetermined by their structure. The structure limits their responses to one stimulus and facilitates the perception of others.
The concept 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. concept sensor system, which appeared later, replaced the concept of the analyzer, including the mechanisms of regulation of its various departments with the help of direct and feedback links. Along with this, there is still the concept sense organ as a peripheral entity that perceives and partially analyzes environmental factors. The main part of the sense organ are receptors, equipped with auxiliary structures that provide optimal perception. Thus, the organ of vision consists of the eyeball, the retina, which contains visual receptors, and a number of support structures Key words: eyelids, muscles, lacrimal apparatus. The organ of hearing consists of the outer, middle and inner ear, where, in addition to the spiral (Corti) organ and its hair (receptor) cells, there are also a number of auxiliary structures. The tongue is the organ of taste. Under the direct influence of various environmental factors with the participation of analyzers in the body, Feel, which are reflections of the properties of objects of the objective world. The peculiarity of sensations is their modality, those. a set of sensations provided by any one analyzer. Within each modality, according to the type (quality) of the sensory impression, different qualities can be distinguished, or valency. Modalities are, for example, sight, hearing, taste. Qualitative types of modality (valency) for vision are various colors, for taste - the sensation of sour, sweet, salty, bitter.
The activity of analyzers is usually associated with the emergence of five senses - sight, hearing, taste, smell and touch, through which the body is connected with the external environment. However, in reality, there are much more of them. For example, the sense of touch in a broad sense, in addition to tactile sensations arising from touch, includes a sense of pressure and vibration. The temperature sensation includes sensations of heat or cold, but there are also more complex sensations, such as sensations of hunger, thirst, sexual desire (libido), due to a special (motivational) state of the body. The sensation of the position of the body in space is associated with the activity of the vestibular, motor analyzers and their interaction with the visual analyzer. A special place in the sensory function is occupied by the sensation of pain. In addition, we can, although "vaguely", perceive other changes, not only in the external, but also in the internal environment of the body, while emotionally colored sensations are formed. So, coronary spasm in the initial stage of the disease, when pain does not yet occur, can cause a feeling of melancholy, despondency. Thus, the structures that perceive irritation from the environment and the internal environment of the body are actually much larger than is commonly believed.
The classification of analyzers can be based on various signs: the nature of the acting stimulus, the nature of the sensations that arise, the level of sensitivity of receptors, the speed of adaptation, and much more.
But the most significant is the classification of analyzers, which is based on their purpose (role). In this regard, there are several types of analyzers.
External Analyzers perceive and analyze changes in the external environment. This should include visual, auditory, olfactory, gustatory, tactile and temperature analyzers, the excitation of which is perceived subjectively in the form of sensations.
Internal (visceral) analyzers, perceiving and analyzing changes in the internal environment of the body, indicators of homeostasis. Fluctuations in the indicators of the internal environment within the physiological norm in a healthy person are usually not perceived subjectively in the form of sensations. So, we cannot subjectively determine the value of blood pressure, especially if it is normal, the state of the sphincters, etc. However, information coming from the internal environment plays an important role in regulating the functions of internal organs, ensuring the adaptation of the body to various conditions of its life. The significance of these analyzers is studied in the course of physiology (adaptive regulation of the activity of internal organs). But at the same time, a change in some constants of the internal environment of the body can be perceived subjectively in the form of sensations (thirst, hunger, sexual desire) that are formed on the basis of biological needs. To meet these needs, behavioral responses are included. For example, when a feeling of thirst arises due to the excitation of osmo- or volumic receptors, behavior is formed that is aimed at finding and taking water.
Body position analyzers perceive and analyze changes in the position of the body in space and body parts relative to each other. These include vestibular and motor (kinesthetic) analyzers. As we evaluate the position of our body or its parts relative to each other, this impulse reaches our consciousness. This is evidenced, in particular, by the experience of D. Maklosky, which he set on himself. Primary afferent fibers from muscle receptors were irritated by threshold electrical stimuli. An increase in the frequency of impulses of these nerve fibers evoked subjective sensations in the subject of a change in the position of the corresponding limb, although its position did not actually change.
Pain Analyzer should be singled out separately in connection with its special significance for the body - it carries information about damaging effects. Pain can occur with irritation of both extero- and interoreceptors.
Structural and functional organization of analyzers
According to I.P. Pavlov (1909), any analyzer has three sections: peripheral, conductive and central, or cortical. The peripheral section of the analyzer is represented by receptors. Its purpose is the perception and primary analysis of changes in the external and internal environments of the body. In receptors, the stimulus energy is transformed into a nerve impulse, as well as signal amplification due to the internal energy of metabolic processes. Receptors are characterized by specificity (modality), i.e. the ability to perceive a certain type of stimulus to which they have adapted in the process of evolution (adequate stimuli), on which the primary analysis is based. So, the receptors of the visual analyzer are adapted to the perception of light, and the auditory receptors are adapted to sound, etc. That part of the receptor surface from which one afferent fiber receives a signal is called its receptive field. Receptive fields can have a different number of receptor formations (from 2 to 30 or more), among which there is a leader receptor, and overlap each other. The latter provides greater reliability of the function and plays a significant role in compensation mechanisms.
Receptors are characterized by great diversity.
In classification receptors the central place is occupied by their division depending on the type of perceived stimulus. There are five types of such receptors.
1. Mechanoreceptors are excited during their mechanical deformation, they are located in the skin, blood vessels, internal organs, musculoskeletal system, auditory and vestibular systems.
2. 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 voltage, osmolarity and pH, glucose levels and other substances). Such receptors are found in the mucous membrane of the tongue and nose, the carotid and aortic bodies, the hypothalamus, and the medulla oblongata.
3. Thermoreceptors perceive temperature changes. They are divided into heat and cold receptors and are found in the skin, mucous membranes, blood vessels, internal organs, hypothalamus, middle, medulla and spinal cord.
4. Photoreceptors in the retina of the eye perceive light (electromagnetic) energy.
5. Nociceptors, the excitation of which is accompanied by pain sensations (pain receptors). These receptors are irritated by mechanical, thermal and chemical (histamine, bradykinin, K+, H+, etc.) factors. Painful stimuli are perceived by free nerve endings that 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 formed into visual, auditory, gustatory, olfactory and tactile.
Location in the body Receptors are divided into extero- and interoreceptors.
Exteroreceptors include receptors of the skin, visible mucous membranes and sensory organs: visual, auditory, gustatory, olfactory, tactile, pain and temperature. Interoreceptors include receptors of internal organs (visceroreceptors), vessels and the central nervous system. A variety of interoreceptors are receptors of the musculoskeletal system (proprioreceptors) and vestibular receptors. If the same type of receptors (for example, chemoreceptors sensitive to CO 3) is localized both in the central nervous system (in the medulla oblongata) and in other places (vessels), then such receptors are divided into central and peripheral.
According to the speed of adaptation Receptors are divided into three groups: rapidly adapting (phasic), slowly adapting (tonic) and mixed (phasic-tonic), adapting at an average speed. Examples of rapidly adapting receptors are the receptors for vibration (Pacini corpuscles) and touch (Meissner corpuscles) on the skin. Slowly adapting receptors include proprioceptors, lung stretch receptors, and pain receptors. Retinal photoreceptors and skin thermoreceptors adapt at an average speed.
By structural and functional organization distinguish between primary and secondary receptors. Primary receptors are sensitive endings of the dendrite of the afferent neuron. The body of the neuron is located in the spinal ganglion or in the ganglion of the cranial nerves. 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.
In the 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.
This classification allows us to understand how the excitation of receptors occurs.
The mechanism of excitation of receptors. When a stimulus acts on a receptor cell in the protein-lipid layer of the membrane, a change in the spatial configuration of protein receptor molecules occurs. This leads to a change in the permeability of the membrane for certain ions, most often for sodium ions, but in recent years the role of potassium in this process has also been discovered. Ion currents arise, the membrane charge changes, and the receptor potential (RP) is generated. And then the excitation process proceeds in different receptors in different ways. In the primary sensory receptors, which are free bare endings of a sensitive neuron (olfactory, tactile, proprioceptive), RP acts on the neighboring, most sensitive areas of the membrane, where an action potential (AP) is generated, which then propagates in the form of impulses along the nerve fiber. The conversion of external stimulus energy into AP in primary receptors can occur either directly on the membrane or with the participation of some auxiliary structures. So, for example, occurs in the body of Pacini. The receptor here is represented by the bare end of the axon, which is surrounded by a connective tissue capsule. When squeezing the Pacinian corpuscle, RP is recorded, which is further converted into an impulse response of the afferent fiber. In secondary sensory receptors, which are represented by specialized cells (visual, auditory, gustatory, vestibular), RP leads to the formation and release of the mediator from the presynaptic section of the receptor cell into the synaptic cleft of the receptor-afferent synapse. This mediator acts on the postsynaptic membrane of the sensitive neuron, causes its depolarization and the formation of a postsynaptic potential, which is called the generator potential (GP). GP, acting on the extrasynaptic regions of the membrane of the sensitive neuron, causes the generation of AP. GP can be both de- and hyperpolarization and, accordingly, cause excitation or inhibit the impulse response of the afferent fiber.
Properties and features of receptor and generator potentials
Receptor and generator potentials are bioelectrical processes that have the properties of a local or local response: they propagate with a decrement, i.e. with damping; the value depends on the strength of the irritation, since they obey the "law of force"; the value depends on the rate of increase of the stimulus amplitude in time; are capable of summing up when applying quickly following each other irritations.
So, in the receptors, the stimulus energy is converted into a nerve impulse, i.e. primary coding of information, transformation of information into a sensory code.
Most of the receptors have the so-called background activity, i.e. in them there is excitation in the absence of any irritants.
Conductor section of the analyzer includes afferent (peripheral) and intermediate neurons of the stem and subcortical structures of the central nervous system (CNS), which form, as it were, a chain of neurons located in different layers at each level of the CNS. The conductor section provides for the conduction of excitation from receptors to the cerebral cortex and partial processing of information. The conduction of excitation along the conduction section is carried out in two afferent ways:
1) by a specific projection path (direct afferent paths) from the receptor along strictly designated specific paths with switching at different levels of the central nervous system (at the level of the spinal cord and medulla oblongata, in the visual tubercles and in the corresponding projection zone of the cerebral cortex);
2) in a non-specific way, with the participation of the reticular formation. At the level of the brainstem, collaterals depart from a specific path to the cells of the reticular formation, to which various afferent excitations can converge, ensuring the interaction of analyzers. In this case, afferent excitations lose their specific properties (sensory modality) and change the excitability of cortical neurons. Excitation is conducted slowly through a large number of synapses. Due to the collaterals, the hypothalamus and other parts of the limbic system of the brain, as well as the motor centers, are included in the excitation process. All this provides the vegetative, motor and emotional components of sensory reactions.
Central, or cortical, analyzer department, according to I.P. Pavlov, consists of two parts: the central part, i.e. "nucleus", represented by specific neurons that process afferent impulses from receptors, and the 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 cortical zones are distinguished. Excitation from the corresponding receptors to the primary zones is directed along fast-conducting specific pathways, while the activation of secondary and tertiary (associative) zones occurs along polysynaptic non-specific pathways. In addition, the cortical zones are interconnected by numerous associative fibers. Neurons are unevenly distributed throughout the thickness of the cortex and usually form six layers. The main afferent pathways to the cortex end on the neurons of the upper layers (III - IV). These layers are most strongly developed in the central sections of the visual, auditory and skin analyzers. Afferent impulses involving the stellate cells of the cortex (layer IV) are transmitted to pyramidal neurons (layer III), from here the processed signal leaves the cortex to other brain structures.
In the cortex, the input and output elements, together with stellate cells, form the so-called columns - functional units of the cortex, organized in the vertical direction. The column has a diameter of about 500 µm and is defined by the area of distribution of collaterals of the ascending afferent thalamocortical fiber. Neighboring columns have relationships that organize the participation of multiple columns for the implementation of a particular reaction. The excitation of one of the columns leads to the inhibition of the neighboring ones.
Cortical projections of sensory systems have a topical principle of organization. The volume of the cortical projection is proportional to the density of the receptors. Due to this, for example, the central fovea of the retina in the cortical projection is represented by a larger area than the periphery of the retina.
To determine the cortical representation of various sensory systems, the method of registration of evoked potentials (EP) is used. EP is one of the types of induced electrical activity in the brain. Sensory EPs are recorded during stimulation of receptor formations and are used to characterize such an important function as perception.
From the general principles of organizing analyzers, one should single out multi-level and multi-channel.
Multilevel provides the possibility of specialization of different levels and layers of the CNS for processing certain types information. This allows the body to respond more quickly to simple signals that are already analyzed at separate intermediate levels.
The existing multichannel nature of analyzer systems is manifested in the presence of parallel neural channels, i.e. in the presence in each of the layers and levels of a plurality of nerve elements associated with a plurality of nerve elements of the next layer and level, which in turn transmit nerve impulses to elements of a higher level, thereby ensuring the reliability and accuracy of the analysis of the influencing factor.
At the same time, existing hierarchical principle building sensory systems creates conditions for fine regulation of perception processes through influences from higher levels to lower ones.
These structural features of the central section ensure the interaction of various analyzers and the process of compensating for impaired functions. At the level of the cortical section, the highest analysis and synthesis of afferent excitations is carried out, providing a complete picture of the environment.
The main properties of analyzers are as follows.
1. High sensitivity to an adequate stimulus. All parts of the analyzer, and above all the receptors, are highly excitable. Thus, retinal photoreceptors can be excited by the action of only a few photons of light, olfactory receptors inform the body about the appearance of single molecules of odorous substances. However, when considering this property of the analyzers, it is preferable to use the term "sensitivity" rather than "excitability", since in humans it is determined by the appearance of sensations.
Sensitivity is assessed using a number of criteria.
Threshold of sensation(absolute threshold) - the minimum strength of irritation that causes such excitation of the analyzer, which is perceived subjectively in the form of a sensation.
Discrimination Threshold(differential threshold) - the minimum change in the strength of the acting stimulus, perceived subjectively in the form of a change in the intensity of sensation. This pattern was established by E. Weber in an experiment with determining the force of pressure on the palm by the test subjects. It turned out that under the action of a load of 100 g it was necessary to add a load of 3 g to feel the increase in pressure, with a load of 200 g it was necessary to add 6 g, 400 g - 12 g, etc. In this case, the ratio of the increase in the strength of irritation (L) to the strength of the acting stimulus (L) is a constant value (C):
For different analyzers, this value is different, in this case it is approximately 1/30 of the strength of the acting stimulus. A similar pattern is observed with a decrease in the strength of the acting stimulus.
Feeling intensity with the same strength of the stimulus, it can be different, since it depends on the level of excitability of the various structures of the analyzer at all its levels. This pattern was studied by G. Fechner, who showed that the intensity of sensation is directly proportional to the logarithm of the strength of stimulation. This position is expressed by the formula:
where E is the intensity of sensations,
K is a constant,
L is the strength of the acting stimulus,
L 0 - sensation threshold (absolute threshold).
Weber's and Fechner's laws are not accurate enough, especially at low stimulation strength. Psychophysical research methods, although they suffer from some inaccuracy, are widely used in the study of analyzers in practical medicine, for example, in determining visual acuity, hearing, smell, tactile sensitivity, and taste.
2. inertia- relatively slow emergence and disappearance of sensations. The latent time of the appearance of sensations is determined by the latent period of excitation of receptors and the time required for the transition of excitation in synapses from one neuron to another, the time of excitation of the reticular formation and generalization of excitation in the cerebral cortex. Preservation for a certain period of sensations after the stimulus is turned off is explained by the phenomenon of aftereffect in the central nervous system - mainly by the circulation of excitation. Thus, a visual sensation does not arise and does not disappear instantly. The latent period of the visual sensation is 0.1 s, the aftereffect time is 0.05 s. Light stimuli (flickering) rapidly following one after another can give a sensation of continuous light (the phenomenon of "flicker merging"). The maximum frequency of flashes of light, which are still perceived separately, is called the critical flicker frequency, which is the greater, the stronger the stimulus brightness and the higher the excitability of the central nervous system, and is about 20 flickers per second. Along with this, if two motionless stimuli are successively projected at different parts of the retina with an interval of 20–200 ms, a sensation of the movement of the object arises. This phenomenon is called "Phi-phenomena". This effect is observed even when one stimulus is somewhat different in form from another. These two phenomena, "flicker fusion" and "Phi-phenomenon" are at the heart of cinematography. Due to the inertia of perception, the visual sensation from one frame lasts until the appearance of another, which is why the illusion of continuous movement arises. Typically, this effect occurs with the rapid sequential presentation of still images on the screen at a speed of 18-24 frames per second.
3. Ability sensory system to adaptation at a constant strength of a long-acting stimulus, it consists mainly in a decrease in absolute and an increase in differential sensitivity. This property is inherent in all parts of the analyzer, but it manifests itself most clearly at the level of receptors and consists in a change not only in their excitability and impulsation, but also in indicators of functional mobility, i.e. in changing the number of functioning receptor structures (P.G. Snyakin). According to the rate of adaptation, all receptors are divided into quickly and slowly adapting, sometimes a group of receptors with an average rate of adaptation is also distinguished. In the conductive and cortical sections of the analyzers, adaptation is manifested in a decrease in the number of activated fibers and nerve cells.
An important role in sensory adaptation is played by efferent regulation, which is carried out by descending influences that change the activity of the underlying structures of the sensory system. Due to this, the phenomenon of "tuning" of sensory systems to the optimal perception of stimuli in a changed environment arises.
4. Interaction of analyzers. With the help of analyzers, the body learns the properties of objects and phenomena of the environment, the beneficial and negative aspects of their impact on the body. Therefore, violations of the function of external analyzers, especially visual and auditory, make it extremely difficult to understand the outside world (the surrounding world is very poor for the blind or deaf). However, only analytical processes in the CNS cannot create a real idea of the environment. The ability of analyzers to interact with each other provides a figurative and holistic view of the objects of the outside world. For example, we evaluate the quality of a lemon wedge using visual, olfactory, tactile and taste analyzers. At the same time, an idea is formed both about individual qualities - color, consistency, smell, taste, and about the properties of the object as a whole, i.e. a certain integral image of the perceived object is created. The interaction of analyzers in assessing phenomena and objects also underlies the compensation of impaired functions in the event of the loss of one of the analyzers. So, in the blind, the sensitivity of the auditory analyzer increases. Such people can determine the location of large objects and bypass them if there is no extraneous noise. This is done by reflecting sound waves from the object in front. American researchers observed a blind man who accurately determined the location of a large cardboard plate. When the subject's ears were covered with wax, he could no longer determine the location of the cardboard.
Interactions of sensory systems can manifest themselves in the form of the influence of excitation of one system on the state of excitability of another according to the dominant principle. For example, listening to music can cause pain relief during dental procedures (audio analgesia). Noise impairs visual perception, bright light increases the perception of sound volume. The process of interaction of sensory systems can manifest itself at various levels. A particularly important role in this is played by the reticular formation of the brain stem, the cerebral cortex. Many cortical neurons have the ability to respond to complex combinations of signals of different modalities (multisensory convergence), which is very important for learning about the environment and evaluating new stimuli.
Encoding information in analyzers
Concepts. Coding- the process of converting information into a conditional form (code), convenient for transmission over a communication channel. Any transformation of information in the departments of the analyzer is coding. In the auditory analyzer, the mechanical vibration of the membrane and other sound-conducting elements at the first stage is converted into a receptor potential, the latter ensures the release of the mediator into the synaptic cleft and the emergence of a generator potential, as a result of which a nerve impulse arises in the afferent fiber. The action potential reaches the next neuron, in the synapse of which the electrical signal is again converted into a chemical one, i.e., the code changes many times. It should be noted that at all levels of analyzers there is no restoration of the stimulus in its original form. This physiological coding differs from most technical communication systems, where the message, as a rule, is restored in its original form.
Codes of the nervous system. IN Computer technology uses a binary code, when two symbols are always used to form combinations - 0 and 1, which represent two states. Encoding of information in the body is carried out on the basis of non-binary codes, which makes it possible to obtain a greater number of combinations with the same code length. The universal code of the nervous system is the nerve impulses that propagate along the nerve fibers. At the same time, the content of information is determined not by the amplitude of the pulses (they obey the “All or Nothing” law), but by the frequency of the pulses (time intervals between individual pulses), their combination into bursts, the number of pulses in a burst, and the intervals between bursts. Signal transmission from one cell to another in all parts of the analyzer is carried out using a chemical code, i.e. various mediators. To store information in the CNS, coding is carried out using structural changes in neurons (mechanisms of memory).
Encoded characteristics of the stimulus. In analyzers, the qualitative characteristic of the stimulus (for example, light, sound), the strength of the stimulus, the time of its action, and also the space, i.e., are encoded. the place of action of the stimulus and its localization in the environment. All departments of the analyzer take part in coding all the characteristics of the stimulus.
In the peripheral section of the analyzer coding of the quality of the stimulus (type) is carried out due to the specificity of the receptors, i.e. the ability to perceive a stimulus of a certain type, to which it is adapted in the process of evolution, i.e. to the appropriate stimulus. Thus, a light beam excites only retinal receptors, other receptors (smell, taste, tactile, etc.) usually do not respond to it.
The strength of the stimulus can be encoded by a change in the frequency of impulses generated by receptors when the strength of the stimulus changes, which is determined by the total number of impulses per unit time. This is the so-called frequency coding. In this case, with an increase in the strength of the stimulus, the number of impulses arising in the receptors usually increases, and vice versa. When the strength of the stimulus changes, the number of excited receptors can also change, in addition, the coding of the strength of the stimulus can be carried out by different values of the latent period and reaction time. A strong stimulus reduces the latent period, increases the number of impulses and lengthens the reaction time. The space is encoded by the size of the area on which the receptors are excited, this is spatial coding (for example, we can easily determine whether a pencil touches the skin surface with a sharp or blunt end). Some receptors are more easily excited when exposed to a stimulus at a certain angle (Pacini bodies, retinal receptors), which is an assessment of the direction of the stimulus to the receptor. The localization of the action of the stimulus is encoded by the fact that the receptors of various parts of the body send impulses to certain areas of the cerebral cortex.
The duration of the action of the stimulus on the receptor is encoded by the fact that it begins to be excited with the onset of the action of the stimulus and stops being excited immediately after the stimulus is turned off (temporal coding). It should be noted that the time of action of the stimulus in many receptors is not coded accurately enough due to their rapid adaptation and cessation of excitation with a constantly acting stimulus strength. This inaccuracy is partly compensated by the presence of on-, off-, and on-off receptors, which are excited, respectively, when the stimulus is turned on and off, and also when the stimulus is turned on and off. With a long-acting stimulus, when adaptation of the receptors occurs, a certain amount of information about the stimulus (its strength and duration) is lost, but sensitivity increases, i.e., receptor sensitization develops to a change in this stimulus. Strengthening the stimulus acts on the adapted receptor as a new stimulus, which is also reflected in a change in the frequency of impulses coming from the receptor.
In the conductive section of the analyzer, coding is carried out only at "switching stations", i.e., when a signal is transmitted from one neuron to another, where the code is changed. Information is not encoded in nerve fibers, they play the role of wires through which information is transmitted, encoded in receptors and processed in the centers of the nervous system.
There can be different intervals between impulses in a single nerve fiber, impulses are formed into bundles with a different number, and there can also be different intervals between individual bundles. All this reflects the nature of the information encoded in the receptors. In the nerve trunk, the number of excited nerve fibers can also change, which is determined by a change in the number of excited receptors or neurons at the previous signal transition from one neuron to another. At switching stations, for example, in the thalamus, information is encoded, firstly, due to a change in the volume of impulses at the input and output, and secondly, due to spatial coding, i.e. due to the connection of certain neurons with certain receptors. In both cases, the stronger the stimulus, the greater the number of neurons fired.
In the overlying parts of the CNS, a decrease in the frequency of neuronal discharges and the transformation of long-term impulses into short bursts of impulses are observed. There are neurons that are excited not only when a stimulus appears, but also when it is turned off, which is also associated with the activity of receptors and the interaction of the neurons themselves. Neurons, called "detectors", respond selectively to one or another parameter of the stimulus, for example, to a stimulus moving in space, or to a light or dark strip located in a certain part of the visual field. The number of such neurons, which only partially reflect the properties of the stimulus, increases at each subsequent level of the analyzer. But at the same time, at each subsequent level of the analyzer there are neurons that duplicate the properties of the neurons of the previous section, which creates the basis for the reliability of the function of the analyzers. In the sensory nuclei, inhibitory processes occur that filter and differentiate sensory information. These processes provide control of sensory information. This reduces the noise and changes the ratio of spontaneous and evoked activity of neurons. Such a mechanism is implemented due to the types of inhibition (lateral, recurrent) in the process of ascending and descending influences.
At the cortical end of the analyzer frequency-spatial coding occurs, the neurophysiological basis of which is the spatial distribution of ensembles of specialized neurons and their connections with certain types of receptors. Impulses arrive from receptors in certain areas of the cortex at different time intervals. Information coming in the form of nerve impulses is recoded into structural and biochemical changes in neurons (mechanisms of memory). In the cerebral cortex, the highest analysis and synthesis of the information received is carried out.
The analysis consists in the fact that with the help of the sensations that arise, we distinguish between the acting stimuli (qualitatively - light, sound, etc.) and determine the strength, time and place, i.e. the space on which the stimulus acts, as well as its localization (source of sound, light, smell).
Synthesis is realized in the recognition of a known object, phenomenon or in the formation of an image of an object, phenomenon encountered for the first time.
There are cases when blind from birth vision appeared only in adolescence. So, a girl who gained sight only at the age of 16 could not recognize objects with the help of sight, which she had repeatedly used before. But as soon as she took the object in her hands, she happily called it. She thus had to practically re-study the world around her with the participation of the visual analyzer, reinforced by information from other analyzers, in particular from the tactile one. At the same time, tactile sensations were decisive. This is evidenced, for example, by the long experience of Strato. It is known that the image on the retina is reduced and inverted. The newborn sees the world that way. However, in early ontogenesis, the child touches everything with his hands, compares and compares visual sensations with tactile ones. Gradually, the interaction of tactile and visual sensations leads to the perception of the location of objects as it is in reality, although the image remains upside down on the retina. Strato put on glasses with lenses that turned the image on the retina into a position corresponding to reality. The observed surrounding world turned upside down. However, within 8 days, by comparing tactile and visual sensations, he again began to perceive all things and objects as usual. When the experimenter took off his glasses, the world turned upside down again, normal perception returned after 4 days.
If information about an object or phenomenon enters the cortical section of the analyzer for the first time, then an image of a new object or phenomenon is formed due to the interaction of several analyzers. But even at the same time, the incoming information is compared with traces of memory about other similar objects or phenomena. The information received in the form of nerve impulses is encoded using the mechanisms of long-term memory.
So, the process of transmitting a sensory message is accompanied by multiple recoding and ends with a higher analysis and synthesis that occurs in the cortical section of the analyzers. After that, the choice or development of a program for the body's response already takes place.
sensory receptor visual analyzer
General plan of the structure of sensory systems
|
Name of analyzer |
The nature of the stimulus |
Peripheral department |
conductor department |
Central hotel |
|
visual |
Electromagnetic oscillations reflected or radiated by objects of the outside world and perceived by the organs of vision. |
Rod and cone neurosensory cells, the outer segments of which are, respectively, rod-shaped (“rods”) and cone-shaped (“cones”) shapes. Rods are receptors that perceive light rays in low light conditions, i.e. colorless or achromatic vision. Cones, on the other hand, function in bright light conditions and are characterized by different sensitivity to the spectral properties of light (color or chromatic vision) |
The first neuron of the conduction section of the visual analyzer is represented by bipolar cells of the retina. Axons of bipolar cells, in turn, converge to ganglion cells (the second neuron). Bipolar and ganglion cells interact with each other due to numerous lateral connections formed by collaterals of dendrites and axons of the cells themselves, as well as with the help of amacrine cells. |
Located in the occipital lobe. There are complex and supercomplex receptive fields of the detector type. This feature allows you to select from the whole image only separate parts of lines with different locations and orientations, while the ability to selectively respond to these fragments is manifested. |
|
auditory |
Sounds, i.e., oscillatory motions of particles of elastic bodies propagating in the form of waves in the most various environments, including the air environment, and perceived by the ear |
Converting the energy of sound waves into the energy of nervous excitation, it is represented by receptor hair cells of the organ of Corti (the organ of Corti), located in the cochlea. The inner ear (sound-receiving apparatus), as well as the middle ear (sound-transmitting apparatus) and the outer ear (sound-catching apparatus) are combined into the concept hearing organ |
It is represented by a peripheral bipolar neuron located in the spiral ganglion of the cochlea (the first neuron). The fibers of the auditory (or cochlear) nerve, formed by the axons of the neurons of the spiral ganglion, end on the cells of the nuclei of the cochlear complex of the medulla oblongata (the second neuron). Then, after a partial decussation, the fibers go to the medial geniculate body of the metathalamus, where the switch again occurs (the third neuron), from here the excitation enters the cortex (the fourth neuron). In the medial (internal) geniculate bodies, as well as in the lower tubercles of the quadrigemina, there are centers of reflex motor reactions that occur under the action of sound. |
Located in the upper part of the temporal lobe of the brain. Importance for the function of the auditory analyzer, they have transverse temporal gyrus (Geshl's gyrus). |
|
Vestibular |
Provides the so-called acceleration feeling, i.e. a sensation that occurs with rectilinear and rotational acceleration of the movement of the body, as well as with changes in the position of the head. The vestibular analyzer plays a leading role in the spatial orientation of a person, maintaining his posture. |
It is represented by hair cells of the vestibular organ, located, like the cochlea, in the labyrinth of the pyramid of the temporal bone. The vestibular organ (the organ of balance, the organ of gravity) consists of three semicircular canals and the vestibule. The vestibule consists of two sacs: round (sacculus), located closer to the cochlea, and oval (utriculus), located closer to the semicircular canals. For the hair cells of the vestibule, adequate stimuli are the acceleration or deceleration of the rectilinear movement of the body, as well as head tilts. For the hair cells of the semicircular canals, an adequate stimulus is the acceleration or deceleration of rotational movement in any plane. |
Peripheral fibers of bipolar neurons of the vestibular ganglion located in the internal auditory canal (the first neuron) approach the receptors. The axons of these neurons as part of the vestibular nerve are sent to the vestibular nuclei of the medulla oblongata (the second neuron). The vestibular nuclei of the medulla oblongata (upper - Bechterew's nucleus, medial - Schwalbe's nucleus, lateral - Deiters' nucleus and lower - Roller's nucleus) receive additional information on afferent neurons from the proprioreceptors of the muscles or from the articular joints of the cervical spine. These nuclei of the vestibular analyzer are closely connected with various parts of the central nervous system. This ensures control and management of somatic, vegetative and sensory effector reactions. The third neuron is located in the nuclei of the thalamus, from where the excitation is sent to the cortex of the hemispheres. |
The central department of the vestibular analyzer is localized in the temporal region of the cerebral cortex, somewhat anterior to the auditory projection zone (fields 21–22 according to Brodmann, the fourth neuron). |
|
Motor |
Provides the formation of the so-called muscle feeling when the tension of the muscles, their membranes, articular bags, ligaments, tendons changes. Three components can be distinguished in a muscular sense: a sense of position, when a person can determine the position of his limbs and their parts relative to each other; a sense of movement, when, by changing the angle of flexion in the joint, a person is aware of the speed and direction of movement; a sense of strength, when a person can assess the muscle strength needed to move or hold joints in a certain position when lifting or moving a load. Along with the skin, visual, vestibular motor analyzer evaluates the position of the body in space, posture, participates in the coordination of muscle activity |
It is represented by proprioceptors located in muscles, ligaments, tendons, articular bags, fascia. These include muscle spindles, Golgi bodies, Pacini bodies, and free nerve endings. The muscle spindle is a collection of thin short striated muscle fibers that are surrounded by a connective tissue capsule. The muscle spindle with intrafusal fibers is located parallel to the extrafusal ones, therefore, they are excited during relaxation (lengthening) of the skeletal muscle. Golgi bodies are found in tendons. These are grape-shaped sensitive endings. The Golgi bodies, located in the tendons, are connected sequentially relative to the skeletal muscle, so they are excited when it contracts due to the tension of the muscle tendon. Golgi receptors control the force of muscle contraction, i.e. voltage. Panina's bodies are encapsulated nerve endings, localized in the deep layers of the skin, in tendons and ligaments, they respond to pressure changes that occur during muscle contraction and tension in tendons, ligaments and skin. |
It is represented by neurons that are located in the spinal ganglia (the first neuron). The processes of these cells in the bundles of Gaulle and Burdach (posterior columns of the spinal cord) reach the delicate and sphenoid nuclei of the medulla oblongata, where the second neurons are located. From these neurons, the fibers of the muscular-articular sensitivity, having crossed, as part of the medial loop, reach the thalamus, where third neurons are located in the ventral posterolateral and posteromedial nuclei. |
The central section of the motor analyzer is the neurons of the anterior central gyrus. |
|
Internal (visceral) |
They analyze and synthesize information about the state of the internal environment of the body and participate in the regulation of the work of internal organs. Can be distinguished: 1) an internal analyzer of pressure in blood vessels and pressure (fillings) in internal hollow organs (mechanoreceptors are the peripheral part of this analyzer); 2) temperature analyzer; 3) an analyzer of the chemistry of the internal environment of the body; 4) analyzer of the osmotic pressure of the internal environment. |
Mechanoreceptors include all receptors for which pressure is an adequate stimulus, as well as stretching, deformation of the walls of organs (vessels, heart, lungs, gastrointestinal tract and other internal hollow organs). Chemoreceptors include the entire mass of receptors that respond to various chemical substances: these are receptors of the aortic and carotid glomeruli, mucosal receptors digestive tract and respiratory organs, receptors of serous membranes, as well as chemoreceptors of the brain. Osmoreceptors are localized in the aortic and carotid sinuses, in other vessels of the arterial bed, in the interstitial tissue near the capillaries, in the liver and other organs. Some osmoreceptors are mechanoreceptors, some are chemoreceptors. Thermoreceptors are localized in the mucous membranes of the digestive tract, respiratory organs, bladder, serous membranes, in the walls of arteries and veins, in the carotid sinus, and also in the nuclei of the hypothalamus. |
From interoreceptors, excitation mainly takes place in the same trunks with the fibers of the autonomic nervous system. The first neurons are located in the corresponding sensory ganglia, the second neurons are in the spinal or medulla oblongata. The ascending paths from them reach the posteromedial nucleus of the thalamus (the third neuron) and then rise to the cerebral cortex (the fourth neuron). |
The cortical region is localized in zones C 1 and C 2 of the somatosensory cortex and in the orbital region of the cerebral cortex. The perception of some interoceptive stimuli may be accompanied by the appearance of clear, localized sensations, for example, when the walls of the bladder or rectum are stretched. But visceral impulses (from the interoreceptors of the heart, blood vessels, liver, kidneys, etc.) may not cause clearly conscious sensations. This is due to the fact that such sensations arise as a result of irritation of various receptors that are part of a particular organ system. In any case, changes in internal organs have a significant impact on emotional condition and the nature of human behavior |
|
Temperature |
Provides information about the temperature of the external environment and the formation of temperature sensations |
It is represented by two types of receptors: some respond to cold stimuli, others to heat. Heat receptors are Ruffini bodies, and cold receptors are Krause flasks. Cold receptors are located in the epidermis and directly below it, and heat receptors are located mainly in the lower and upper layers of the skin itself and the mucous membrane. |
Myelinated type A fibers depart from cold receptors, and unmyelinated type C fibers depart from heat receptors, so information from cold receptors propagates at a faster rate than from thermal ones. The first neuron is localized in the spinal ganglia. The cells of the posterior horns of the spinal cord represent the second neuron. Nerve fibers extending from the second neurons of the temperature analyzer pass through the anterior commissure to opposite side in the lateral columns and as part of the lateral spinal thalamic tract they reach the visual mound, where the third neuron is located. From here, excitation enters the cortex of the cerebral hemispheres. |
The central section of the temperature analyzer is localized in the region of the posterior central gyrus of the cerebral cortex. |
|
Tactile |
Provides sensations of touch, pressure, vibration and tickling. |
It is represented by various receptor formations, the irritation of which leads to the formation of specific sensations. On the surface of the skin devoid of hair, as well as on the mucous membranes, special receptor cells (Meissner bodies) located in the papillary layer of the skin react to touch. On the skin covered with hair, the hair follicle receptors, which have moderate adaptation, respond to touch. |
From most mechanoreceptors in the spinal cord, information enters the central nervous system via A-fibers, and only from tickle receptors - via C-fibers. The first neuron is located in the spinal ganglia. In the posterior horn of the spinal cord, the first switch to interneurons (second neuron) occurs, from which the ascending path as part of the posterior column reaches the nuclei of the posterior column in the medulla oblongata (third neuron), where the second switch occurs, then through the medial loop the path follows to the ventrobasal nuclei of the thalamus opticus (fourth neuron), the central processes of the neurons of the thalamus go to the cerebral cortex. |
It is localized in zones 1 and 2 of the somatosensory region of the cerebral cortex (posterior central gyrus). |
|
Taste |
The resulting sense of taste is associated with irritation of not only chemical, but also mechanical, temperature and even pain receptors of the oral mucosa, as well as olfactory receptors. The taste analyzer determines the formation of taste sensations, is a reflexogenic zone. |
Taste receptors (taste cells with microvilli) are secondary receptors, they are an element of taste buds, which also include supporting and basal cells. Taste buds contain serotonin-containing cells and histamine-producing cells. These and other substances play a role in the formation of the sense of taste. Individual taste buds are polymodal formations, as they can perceive various types of taste stimuli. Taste buds in the form of separate inclusions are located on the back wall of the pharynx, soft palate, tonsils, larynx, epiglottis and are also part of the taste buds of the tongue as an organ of taste. |
Inside the taste bud are nerve fibers that form receptor-afferent synapses. The taste buds of different areas of the oral cavity receive nerve fibers from different nerves: the taste buds of the anterior two-thirds of the tongue - from the tympanic string, which is part of the facial nerve; kidneys of the posterior third of the tongue, as well as the soft and hard palate, tonsils - from the glossopharyngeal nerve; taste buds located in the pharynx, epiglottis and larynx - from the upper laryngeal nerve, which is part of the vagus nerve |
It is localized in the lower part of the somatosensory zone of the cortex in the area of representation of the language. Most of the neurons in this area are multimodal; reacts not only to taste, but also to temperature, mechanical and nociceptive stimuli. The taste sensory system is characterized by the fact that each taste bud has not only afferent, but also efferent nerve fibers that are suitable for taste cells from the central nervous system, which ensures the inclusion of the taste analyzer in the integral activity of the body. |
|
Olfactory |
Primary sensory receptors, which are the ends of the dendrite of the so-called neurosecretory cell. The upper part of the dendrite of each cell carries 6-12 cilia, and an axon departs from the base of the cell. Cilia, or olfactory hairs, are immersed in a liquid medium - a layer of mucus produced by Bowman's glands. The presence of olfactory hairs significantly increases the contact area of the receptor with molecules of odorous substances. The movement of the hairs provides an active process of capturing the molecules of the odorous substance and contact with it, which underlies the targeted perception of odors. The receptor cells of the olfactory analyzer are immersed in the olfactory epithelium lining the nasal cavity, in which, in addition to them, there are supporting cells that perform a mechanical function and are actively involved in the metabolism of the olfactory epithelium. Part of the supporting cells located near the basement membrane is called basal |
The first neuron of the olfactory analyzer should be considered a neurosensory or neuroreceptor cell. The axon of this cell forms synapses, called glomeruli, with the main dendrite of the mitral olfactory bulb cells, which represent the second neuron. The axons of the mitral cells of the olfactory bulbs form the olfactory tract, which has a triangular extension (olfactory triangle) and consists of several bundles. The fibers of the olfactory tract go in separate bundles to the anterior nuclei of the optic tubercle. Some researchers believe that the processes of the second neuron go directly to the cerebral cortex, bypassing the visual tubercles. |
It is localized in the anterior part of the pear-shaped lobe of the cortex in the region of the sea horse gyrus. |
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|
Pain is a "sensory modality" like hearing, taste, vision, etc., it performs a signaling function, which consists in information about the violation of such vital body constants as the integrity of the integumentary membranes and a certain level of oxidative processes in tissues that ensure their normal functioning. . At the same time, pain can be considered as a psychophysiological state, accompanied by changes in the activity of various organs and systems, as well as the emergence of emotions and motivations. |
It is represented by pain receptors, which, at the suggestion of C. Sherrington, are called nociceptors. These are high-threshold receptors that respond to destructive influences. According to the mechanism of excitation, nociceptors are divided into mechanociceptors and chemociceptors. Mechanociceptors are located mainly in the skin, fascia, tendons, articular bags and mucous membranes of the digestive tract. Chemonociceptors are also located on the skin and in the mucous membranes, but prevail in the internal organs, where they are localized in the walls of small arteries. |
Conduction of pain excitation from receptors is carried out along the dendrites of the first neuron, located in the sensory ganglia of the corresponding nerves that innervate certain parts of the body. The axons of these neurons enter the spinal cord to the intercalary neurons of the posterior horn (the second neuron). Further excitation in the central nervous system It is carried out in two ways: specific (lemniscus) and nonspecific (extralemniscal). The specific path starts from the intercalary neurons of the spinal cord, the axons of which, as part of the spinothalamic tract, enter the specific nuclei of the thalamus (in particular, the ventrobasal nucleus), which represent the third neurons. The processes of these neurons reach the cortex. The nonspecific pathway also starts from the intercalary neuron of the spinal cord and goes through collaterals to various brain structures. Depending on the place of termination, three main tracts are distinguished - neospinothalamic, spinoreticular, spinomesencephalic. The last two tracts are combined into the spinothalamic. Excitation through these tracts enters the nonspecific nuclei of the thalamus and from there to all parts of the cerebral cortex. |
The specific pathway ends in the somatosensory area of the cerebral cortex. According to modern concepts, two somatosensory zones are distinguished. The primary projection zone is located in the region of the posterior central gyrus. Here there is an analysis of nociceptive influences, the formation of a sensation of acute, precisely localized pain. In addition, due to close connections with the motor cortex, motor acts are carried out when exposed to damaging stimuli. The secondary projection zone, which is located deep in the Sylvian sulcus, is involved in the processes of awareness and the development of a program of behavior in case of pain. The non-specific pathway extends to all areas of the cortex. A significant role in the formation of pain sensitivity is played by the orbitofrontal region of the cortex, which is involved in the organization of the emotional and autonomic components of pain. |
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