“Sens” is translated as “feeling”, “sensation”.
Sensory systems are the perceptive systems of the body (visual, auditory, olfactory, tactile, gustatory, pain, tactile, vestibular, proprioceptive, interoceptive).
We can say 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 - on the letter “e”. Therefore, technical perceptive systems are sensory, and physiological ones are sensory.
Perception is the translation of the characteristics of external stimulation 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 an internal image that reflects the essential characteristics of the external stimulus. The internal sensory image of a stimulus is a neural model consisting of a system of nerve cells. It is important to understand that this neural model cannot completely correspond to the real stimulus and will always differ from it in at least some detail.
For example, the cubes in the picture on the right form a model that is close to reality, but cannot exist in reality...
2) Analyzers and sensor systems
Analyzers are a part of the nervous system consisting of many specialized perceptual receptors, as well as intermediate and central nerve cells and the nerve fibers connecting them.
I.P. Pavlov created the doctrine of analyzers. This is a simplified idea of perception. It divided the analyzer into 3 sections.
Analyzer structure
· Peripheral part (remote) - these are receptors that perceive irritation and convert it into nervous excitation.
· The conduction section (afferent or sensory nerves) are pathways that transmit sensory excitation generated in the receptors.
· The central section is a section of the cerebral cortex that analyzes sensory stimulation received by it and builds a sensory image through the synthesis of stimulation.
Thus, for example, final visual perception occurs in the brain, not in the eye.
The concept of a sensor system is broader than an analyzer. It includes additional devices, adjustment systems and self-regulation systems. The sensory system provides feedback between the brain's analyzing structures and the perceptive receptive apparatus. Sensory systems are characterized by a 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 “sensory system” and “analyzer”
1) The sensory system is active, not passive, in transmitting excitation.
2) The sensory system includes auxiliary structures that ensure optimal adjustment and operation of the receptors.
3) The sensory system includes auxiliary lower nerve centers, which not only transmit sensory stimulation further, but change its characteristics and divide it into several streams, sending them in different directions.
4) The sensory system has feedback connections between subsequent and preceding structures that transmit sensory excitation.
5) Processing and processing of sensory stimulation occurs not only in the cerebral cortex, but also in underlying structures.
6) The sensory system actively adapts to the perception of the stimulus and adapts to it, i.e. its adaptation occurs.
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 from 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 minimal strength of stimulation.
The activity of sensory receptors is a necessary condition to carry out all functions of the central nervous system. Touch receptors are the first link in the reflex pathway and the peripheral part of a more complex structure - analyzers. The set of receptors, the stimulation of which leads to a change in the activity of any nerve structures, is called the receptive field.
Classification of receptors
The nervous system is different great variety 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 depending on depending on the type of stimulus perceived. There are 5 types of receptors:
Ш Mechanoreceptors are excited by mechanical deformation. They are located in the skin, blood vessels, internal organs, musculoskeletal system, auditory and vestibular systems.
Ш 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, carotid and aortic bodies, hypothalamus and medulla oblongata.
Ш Thermoreceptors sense changes in temperature. They are divided into heat and cold receptors and are found in the skin, blood vessels, internal organs, hypothalamus, mid, medulla and spinal cord.
Ш Photoreceptors in the retina of the eye perceive light (electromagnetic) energy.
Ш Nociceptors (pain receptors) - their excitation is accompanied by pain sensations. The irritants for them are mechanical, thermal and chemical factors. Painful stimuli are perceived by free nerve endings, which 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 generated into visual, auditory, gustatory, olfactory and tactile.
IN. By location in the body receptors are divided into extero- and interoreceptors. Exteroceptors include receptors of the skin, visible mucous membranes and sensory organs: visual, auditory, taste, olfactory, tactile, cutaneous, 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 (proprioceptors) and vestibular receptors. If the same type of receptors is 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 sensitivity to adequate is much greater than that to inadequate stimuli, then these are monomodal receptors. Monomodality is especially characteristic of extroreceptors. Polymodal receptors are adapted to perceive several adequate stimuli, for example mechanical and temperature or mechanical, chemical and pain. These include irrital receptors of the lungs.
D. According to structural and functional organization distinguish between primary and secondary receptors. In the primary receptor, the stimulus acts directly on the ending of the sensory neuron: olfactory, tactile, temperature, pain receptors, proprioceptors, receptors of internal organs. In the secondary receptors there is a special cell synaptically connected to the end of the dendrite of the sensory neuron, which transmits the signal through the end of the dendrite to the conductive pathways: auditory, vestibular, taste buds, retinal photoreceptors.
E. By speed of adaptation receptors are divided into 3 groups: phase (quickly adapting): vibration and touch receptors of the skin, tonic (slowly adapting): proprioceptors, lung stretch receptors, some pain receptors, phase-tonic (mixed, adapting at an average speed): retinal photoreceptors, thermoreceptors skin.
RECEPTOR PROPERTIES
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 transmit information to the central nervous system about all changes in the external and internal environment. Moreover, the excitability of different types of receptors is not the same. In exteroceptors it is higher than in intero ones. Pain receptors have low excitability; they are evolutionarily adapted to respond to stimuli of extreme strength.
Adaptation of receptors is a decrease in their excitability during prolonged exposure to a stimulus. An exception is the use of the term “dark adaptation” for photoreceptors, the excitability of which increases in the dark. The significance of adaptation is that it reduces the perception of stimuli that have properties (long-lasting action, low dynamics of force) that reduce their significance for the life of the body.
Spontaneous receptor activity. Many types of receptors are capable of generating impulses in a neuron without the action of a stimulus on them. This is called background activity and the excitability of such receptors is higher than those without such activity. The background activity of the receptors is involved in maintaining the tone of the nerve centers under conditions of physiological rest.
The excitability of receptors is under neurohumoral control of the entire 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, and muscle.
Among the efferent ones, inhibitory effects (negative feedback) have been better studied. In this way, the effects of strong stimuli are limited. An activating effect on receptors can also be exerted through efferent pathways.
Also, the nervous system regulates the activity of receptors through changes in the concentration of hormones (for example, increasing the sensitivity of visual and auditory receptors under the influence of adrenaline, thyroxine); through 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 regulating the activity of receptors lies in the best coordination of their excitability with the strength of stimulation.
4) General principles of sensor systems
1. The principle of multi-story
In each sensory system, there are several transfer intermediate instances on the way from the receptors to the cerebral cortex. In these intermediate lower nerve centers, partial processing of excitation (information) occurs. Already at the level of the lower nerve centers, unconditioned reflexes are formed, i.e., responses to stimulation; they do not require the participation of the cerebral cortex and are carried out very quickly.
For example: A midge flies straight 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; simple detection of the fact that an object is quickly approaching the eye is sufficient.
One of the peaks of the multi-layered sensory system is the auditory sensory system. It has 6 floors. There are also additional bypass routes to higher cortical structures that bypass several lower floors. In this way, the cortex receives a preliminary signal to increase its readiness for the main flow of sensory excitation.
Illustration of the multi-story principle:
2. Multichannel principle
Excitation is transmitted from receptors to the cortex always along several parallel paths. Excitation flows are partially duplicated and partially separated. They transmit information about various properties of the stimulus.
An example of parallel pathways in the visual system:
1st pathway: retina - thalamus - visual cortex.
2nd path: retina - quadrigeminal region (superior colliculi) of the midbrain (nuclei of the oculomotor nerves).
3rd pathway: retina - thalamus - thalamic cushion - parietal associative cortex.
When different pathways are damaged, the results are different.
For example: if you destroy the external geniculate body of the thalamus (ECT) in visual pathway 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 visual field is disrupted; If you destroy the thalamic cushion in path 3, then object recognition and visual memorization disappear.
In all sensory systems, there are necessarily three ways (channels) of excitation transmission:
1) specific path: it leads to the primary sensory projection zone of the cortex,
2) nonspecific path: it provides general activity and tone of the cortical part of the analyzer,
3) associative pathway: it determines the biological significance of the stimulus and controls attention.
Illustration of the multi-channel principle:
In the evolutionary process, the multistory and multichannel nature of the structure of sensory pathways increases.
3. The principle of convergence
Convergence is the convergence of neural pathways in the form of a funnel. Due to convergence, a neuron at the upper level receives excitation from several neurons at a lower level.
For example: in the retina of the eye there is a large convergence. There are several tens of millions of photoreceptors, and no more than one million ganglion cells. That is, There are many times fewer nerve fibers transmitting excitation from the retina than photoreceptors.
4. The principle of divergence
Divergence is the divergence of the flow of excitation into several flows from the lowest floor to the highest (reminiscent of a diverging funnel).
5. Feedback principle
Feedback usually means the influence of the controlled element on the control element. For this, there are corresponding excitation paths from lower and higher centers back to the receptors.
5) Operation of analyzers and sensor systems
In the functioning of sensory systems, certain receptors correspond to their own areas of cortical cells.
The specialization of each sense organ is based not only on the structural features of the receptors of the analyzers, but also on the specialization of the neurons that are part of the central nervous apparatus, which receive signals perceived by the peripheral sense organs. The analyzer is not a passive receiver of energy; it reflexively adapts 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 world occurs as follows:
1) the stimulus causes certain energy changes 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 human brain and sensory systems, but also on the characteristics of the person himself, his development and condition. When sick or tired, a person's sensitivity to certain influences changes.
There are also cases of pathologies when a person is deprived, for example, of hearing or vision. If this problem is congenital, then there is a disruption in the flow of information, which can lead to mental development delays. If these children were taught special techniques that compensate for their deficiencies, 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:
b quality,
b intensity,
b duration,
b spatial localization.
But not every irritation causes a sensation. The minimum magnitude of the stimulus at which sensation appears is the absolute threshold of sensation. The value of this threshold characterizes absolute sensitivity, which is numerically equal to a value inversely proportional to the absolute threshold of sensations. And sensitivity to changes in the stimulus is called relative or differential sensitivity. The minimum difference between two stimuli that causes a slightly noticeable difference in sensation 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. Conversion of the force of stimulation into a frequency code of impulses is a 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 influence of a stimulus (irritant), stimulus-gated ion channels must open in the cell receptor membrane (and, on the contrary, close in photoreceptors). The flow of ions begins through them and a state of membrane depolarization develops.
2. Topical correspondence - the excitation flow (information flow) in all transmission structures corresponds significant characteristics irritant. 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 - a neural model of the stimulus.
3. Detection is the selection of qualitative features. Detector neurons respond to certain features of an object and do not respond to everything else. Detector neurons mark contrast transitions. Detectors make a complex signal meaningful and unique. They highlight the same parameters in different signals. 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 transmission.
5. Specificity of receptors and sensory organs. Their sensitivity is maximum to a certain type of stimulus with a certain intensity.
6. The law of specificity of sensory energies: sensation is determined not by the stimulus, but by the irritated sensory organ. Even more precisely, we 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 painful 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 flow of excitation coming 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.
General information
Adhering to the cognitive approach to describing the psyche, we imagine a person as a kind of system that processes symbols when solving its problems, then we can imagine the most important feature of a person’s individuality - the sensory organization of the personality.
Sensory organization of personality
The sensory organization of a personality is the level of development of individual sensitivity systems and the possibility of their unification. Human sensory systems are his sense organs, like receivers of his sensations, in which the transformation of sensation into perception occurs.
Any 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 characteristic. For example, bats have developed sensitivity to the perception of short ultrasonic pulses, and dogs have olfactory sensitivity.
The main feature of a person’s sensory organization is that it develops as a result of his entire life path. A person’s sensitivity is given to him at birth, but its development depends on the circumstances, desires and efforts of the person himself.
What do we know about the world and ourselves? Where do we get this knowledge? 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 a 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 phenomena of the external world is delivered to the brain. In the same way, a loop is closed through sensations to receive feedback about the current physical and partly mental state of the body.
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 occurs in the human sensory systems and, on its basis, cognitive processes that are more complex in structure arise: perceptions, ideas, memory, thinking.
No matter how simple the primary cognitive process may be, it is precisely it that is the basis of mental activity; only through the “inputs” of sensory systems does the surrounding world penetrate into our consciousness.
Processing sensations
After the brain receives information, the result of its processing is the development of a response action or strategy aimed, for example, at improving physical tone, focusing more attention on the current activity, or setting up an accelerated involvement in mental activity.
Generally speaking, the response or strategy developed at any given time is the best choice of the options available to a person at the time of decision making. However, it is clear that the number of options available and the quality of choice varies from person to person and depends, for example, on:
mental properties of the individual,
strategies for relationships with others,
partly physical condition,
experience, the presence of the necessary information in memory and the ability to retrieve it.
degree of development and organization of higher nervous processes, etc.
For example, a baby goes out undressed into the cold, his skin feels cold, perhaps chills appear, he becomes uncomfortable, a signal about this is sent to the brain and a deafening roar is heard. An adult’s reaction to cold (stimulus) may be different; he will either rush to get dressed or jump into warm room, or will try to warm up in another way, for example, by running or jumping.
Improving higher mental functions of the brain
Over time, children improve their reactions, greatly increasing the effectiveness of the results achieved. But after growing up, opportunities for improvement do not disappear, despite the fact that an adult’s sensitivity to them decreases. This is exactly what “Effecton” sees as part of its mission: increasing the efficiency of intellectual activity by training the higher mental functions of the brain.
Effecton's software products allow you to measure various indicators of the human sensorimotor system (in particular, the Jaguar package contains time tests for simple audio and visual-motor reactions, complex visual-motor reactions, and accuracy of perception of time intervals). Other packages of the Effecton complex evaluate the properties of cognitive processes at higher levels.
Therefore, it is necessary to develop the child’s perception, and using the “Jaguar” package can help you with this.
Physiology of sensations
Analyzers
The physiological mechanism of sensations is the activity of nervous apparatus - analyzers, consisting of 3 parts:
receptor - the perceiving part of the analyzer (converts external energy into a nervous process)
central section of the analyzer - afferent or sensory nerves
cortical sections of the analyzer, in which nerve impulses are processed.
Certain receptors correspond to their own areas 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 are part of the central nervous apparatus, which receive signals perceived by the peripheral sense organs. The analyzer is not a passive receiver of energy; it reflexively adapts under the influence of stimuli.
Movement of a stimulus from the external to the internal world
According to the cognitive approach, the movement of a stimulus during its transition from the external world to the internal world occurs as follows:
the stimulus causes certain energy changes 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 human brain and sensory systems, but also on the characteristics of the person himself, his development and condition. When sick or tired, a person's sensitivity to certain influences changes.
There are also cases of pathologies when a person is deprived, for example, of hearing or vision. If this problem is congenital, then there is a disruption in the flow of information, which can lead to mental development delays. If these children were taught special techniques that compensate for their deficiencies, 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:
quality,
intensity,
duration,
spatial localization.
But not every irritation causes a sensation. The minimum magnitude of the stimulus at which sensation appears is the absolute threshold of sensation. The value of this threshold characterizes absolute sensitivity, which is numerically equal to a value inversely proportional to the absolute threshold of sensations. And sensitivity to changes in the stimulus is called relative or differential sensitivity. The minimum difference between two stimuli that causes a slightly noticeable difference in sensation is called the difference threshold.
Based on this, we can conclude that it is possible to measure sensations. And once again you are amazed by the amazing, finely working instruments - human sense organs or human sensory systems.
Effecton's software products allow you to measure various indicators of the human sensory system (for example, the Jaguar package contains speed tests for simple audio and visual-motor reactions, complex visual-motor reactions, accuracy of time perception, accuracy of space perception and many others). Other packages of the Effecton complex also evaluate the properties of cognitive processes at higher levels.
Classification of sensations
Five main types of sensations: vision, hearing, touch, smell and taste - were already known to the ancient Greeks. Currently, 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.
The classification of sensations is carried out 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 occur in the presence or absence of direct contact of the receptor with the stimulus. Vision, hearing, and smell are distant sensations. These types of sensations provide orientation in the immediate environment. Taste, pain, tactile sensations are contact.
According to the location of the receptors on the surface of the body, in muscles and tendons or inside the body, they are distinguished accordingly:
exteroception - visual, auditory, tactile and others;
proprioception - sensations from muscles, tendons;
interoception - sensations of hunger, thirst.
During the evolution of all living things, sensitivity has undergone changes from the most ancient to the modern. Thus, distant sensations can be considered more modern than contact ones, but in the structure of the contact analyzers themselves it is also possible to identify more ancient and completely new functions. For example, pain sensitivity is more ancient than tactile sensitivity.
Such classification principles help to group all types of sensations into systems and see their interactions and connections.
Types of sensations
Vision, hearing
Let's consider different kinds sensations, keeping in mind that vision and hearing are the most well studied.
The question of the process of transforming sensory stimuli into sensations, their localization, as well as the mechanism and place of formation of a general idea of an object (perception) in modern psychophysiology is resolved on the basis of the teachings of I.P. Pavlova about analyzers (sensory systems).
The analyzer (sensory system) is a unified physiological system that is adapted to perceive stimuli from external or inner world, their processing into a nerve impulse and the formation of sensation and perception.
The following analyzers (sensory systems) are distinguished: pain, vestibular, motor, visual, introceptive, skin, olfactory, auditory, temperature and others.
Any analyzer has a fundamentally identical structure (Fig. 14.1). It consists of three parts:
1. The initial - perceiving part of the analyzer is represented by receptors. They developed in the process of evolution as a result of the increased sensitivity of some cells to a certain type of energy (thermal, chemical, mechanical, etc.). The stimulus to which the receptor is specially adapted is called adequate; all others will be inadequate.
Rice. 14.1.
Depending on the location, the following receptors are distinguished:
A) Exteroceptors (visual, auditory, olfactory, gustatory, tactile), which lie on the surface of the body and respond to external influences, providing an influx of sensory information from the external environment. B) Interoreceptors are located in the tissues of internal organs in the lumen of large vessels (for example, chemoreceptors, baroreceptors) and are sensitive to certain parameters of the internal environment (concentrations of chemical active substances, blood pressure, etc.); they are important for obtaining information about the functional state of the body and its internal environment. C) Proprioceptors lie in muscles, tendons and perceive information about the degree of stretching and contraction of muscles, due to which a “body sense” is formed (a sense of one’s own body and the relative location of its parts).
The perceptive part of the analyzer is sometimes represented by the corresponding sensory organ (eye, ear, etc.). A sensory organ is a structure containing receptors and auxiliary structures that provide the perception of specific energy. For example, the eye contains visual receptors and structures such as the eyeball, membranes of the eyeball, eye muscles, pupil, lens, vitreous body, which provide the effect of light on the visual receptors.
The function of the receptors is to perceive the energy of the stimulus and convert it into nerve impulses of a certain frequency (sensory code).
2. The conductive section of each analyzer is represented by a sensory nerve, along which excitation goes from the receptors to the subcortical and cortical centers of this analyzer. In this case, two interconnected pathways are distinguished: the first, the so-called specific analyzer pathway, goes through specific nuclei of the brain stem and plays a major role in the transmission of sensory information and the occurrence of sensations of a certain type; the second, nonspecific pathway is represented by neurons of the reticulatory formation. The flow of impulses traveling along it changes the functional state of the structures of the spinal cord and brain, i.e. has an activating effect on nerve centers. The role of the conductive section of each analyzer is not limited to transmitting excitation from receptors to the cortex: it also takes part in the occurrence of sensations. For example, the subcortical centers of the visual analyzer, located in the midbrain (in the superior colliculus), receive information from visual receptors and tune the organ of vision to more accurately perceive visual information. In addition, already at the level of the diencephalon, unclear, rough sensations arise (for example, light and shadow, light and dark objects). Considering the conductive part of the analyzers as a whole, you should pay attention to the thalamus. In this part of the diencephalon, the afferent (sensitive) pathways of all analyzers (with the exception of the olfactory one) converge. This means that the thalamus receives information from extero-, proprio- and interoreceptors about the environment and the state of the body.
Thus, all sensory information is collected and analyzed in the thalamus. Here it is partially processed and in this processed form is transferred to various areas of the cortex. Most sensory information does not reach the higher part of the central nervous system (and therefore does not cause clear and conscious sensations), but becomes a component of motor and emotional responses and, possibly, “material” for intuition.
Rice. 14.2.
Each analyzer contains descending, efferent neurons that “turn on” motor reactions. For example, visual information arriving at the superior colliculus causes “local” reflexes—involuntary eye movements behind a moving object, one of the elements of the orienting reflex. In the cortex, the central ends of all analyzers are connected to the motor zone, which is the central section of the motor analyzer. Thus, the motor zone receives information from all sensory systems of the body and serves as a link in interanalyzer relationships, thereby ensuring a connection between sensations and movements.
The structural elements of analyzers are not isolated in the nervous system, but are anatomically and functionally connected with speech centers, with the limbic system, subcortical sections, with autonomic centers of the trunk, etc., which ensures the relationship of sensations with emotions, movements, behavior, speech, and explains influence of sensory information on the human body.
Operating principles of analyzers (sensory systems)
Analyzers are figuratively called windows to the world, or channels of communication between a person and the outside world and his own body. Already “at the input” the information is analyzed, which is achieved by the selective response of receptors.
Within one modality there is a huge variety of signals: for example, sounds vary in pitch, timbre, origin; visual information - by color, brightness, shape, size, etc. The ability to perceive the difference between them is due to the fact that different sensory signals arise in the analyzers for different stimuli. This function is called signal discrimination. It is achieved by the formation of nerve impulses of different frequencies at the receptor level (sensory code) and the inclusion of differentiation processes at all levels of the sensory system - from receptors to the cortex. Essentially, signal discrimination - an integral part of analysis process.
As the child develops and his interaction with the outside world becomes more complex, differentiations become more subtle due to the development of differentiation inhibition in the cortex. This is also facilitated by the development of each analyzer separately, as well as the complication of their interaction. Movement plays a major role in this process: motor differentiation helps sensory differentiation. Thus, to distinguish visual information, eye movements are necessary, which inevitably accompany the process of viewing an object, as well as various hand positions that arise when feeling it. The same principle applies to the formation of phonemic hearing. To distinguish speech sounds well - phonemes - it is not enough to hear the speech of another person (even with excellent diction of the speaker), you also need to have a good feel for your own articulatory apparatus (lips, tongue, palate, larynx, cheeks), and feel the differences in its positions when reproducing sounds. Many methods of teaching preschool and younger children school age, as well as correction techniques rely on this mechanism.
A subtle analysis of stimuli requires the activity of the subject of cognition himself. If a person himself wants to participate in a particular activity, and it evokes positive emotions (interest, joy), then his sensory sensitivity to various signals increases significantly. Voluntary attention plays an active role in this process. This result is achieved due to control from the cerebral cortex and the nearest subcortex of the underlying sections of the analyzers with the help of efferent neurons (see Fig. 14.1).
Thus, sensory processes cannot be considered only as a physiological reflection of the objective properties of objects, since they also reflect a subjective factor - the needs, emotions and associated behavior of the subject, which influence the emerging sensory images.
One of the questions that arises when studying sensory systems is how information is transmitted in analyzers. In the receptors, under the influence of a stimulus, nerve impulses of a certain frequency are formed, which propagate along the afferent pathways in groups - “volleys” or “packs” (sensory frequency code). It is believed that the number of impulses and their frequency is the language with which receptors transmit information to the brain about the properties of the reflected object.
On modern stage It is impossible to establish a clear correspondence between one or another property of the stimulus and the method of its fixation in the nervous system. Existing scientific information describes only some general principles of information transmission in the nervous system (Fig. 14.3).
Rice. 14.3.
The scheme of this process is as follows. The sensory code in the form of nerve impulses comes from receptors to the subcortical centers of the brain, where they are partially decoded, filtered, and then sent to specific centers of the cortex - the centers of the analyzer, where sensations are born. Then a synthesis of various sensations occurs, from where impulses are sent to the hippocampus (memory) and the structures of the limbic system (emotions), and then return to the cortex, including the motor center of the frontal lobe. The excitement is summed up and a sensory image is built.
Thus, not only sensations, but also movements, memory and emotions are involved in constructing a holistic image of an object and recognizing it. Previously encountered impressions (sensory images) are stored in memory, and emotions signal the significance of the information received.
Perception does not arise mechanically or purely physiologically. The subject himself, his consciousness, his attention take an active part in its formation. In other words, the person himself must pay attention to the object, isolate it, voluntarily switch attention from the whole to the parts and have a desire for this, some kind of goal. That is why children's education can only be successful when it makes them want to know what is offered to them, if it is of interest to them.
Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.
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1. SENSORY SYSTEMS
1.1 General overview about sensory systems
Sensory - from the Latin sensus - feeling, sensation.
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) peripheral department - a receptor that receives and transforms external energy into a nervous process, and an effector - an organ or system of organs that responds to the actions of external or internal stimuli, acting as the executive element of the reflex act; sensory visual sensitivity sensitization
2) conducting pathways - afferent (ascending) and efferent (descending), connecting the peripheral part of the analyzer with the central one;
3) the central section - represented by the subcortical and cortical nuclei and projection sections of the cerebral cortex, where the processing of nerve impulses coming from the peripheral sections occurs.
Each analyzer has a core, i.e. the central part, where the bulk of the receptor cells is concentrated, and the periphery, consisting of scattered cellular elements, which are located in varying quantities 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. The scattered (peripheral) elements of this analyzer are included in areas adjacent to the cores of other analyzers. This ensures the participation of a large part of the entire cerebral cortex in a separate sensory act. The analyzer core performs the function of fine analysis and synthesis, for example, it differentiates sounds by height. Scattered elements are associated with the function of coarse analysis, for example, distinguishing between musical sounds and noise.
Certain cells of the peripheral parts of the analyzer correspond to certain areas of cortical cells. Thus, spatially different points in the cortex represent, for example, different points of the retina; The spatially different arrangement of cells is represented in the cortex and the organ of hearing. The same applies to other senses.
Numerous experiments carried out using artificial stimulation methods now make it possible to quite definitely establish the localization in the cortex of certain types 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. Touch-motor sensitivity is represented in the posterior central gyrus, etc.
For the sensory process to occur, the entire analyzer as a whole must work. The impact of an irritant on the receptor causes irritation. The beginning of this irritation is 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's response to irritation occurs. We perceive 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 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 was considered to be the basis on which the entire mental life of a person is built with the help of associations. 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, proposing to divide the sense of touch into: the sense of touch, the sense of weight, the sense of temperature.
In addition, he identified a special group of feelings: the feeling of pain, the sense of balance, the sense of movement, the 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 by 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 a modern modification of this classification, the additional concept of submodality is used, for example, in a modality such 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 analyzer, he used the physicochemical characteristics of the signal. Hence the names of the analyzers: light, sound, skin-mechanical, olfactory, etc., and not visual, auditory, etc., as analyzers were usually classified.
The classifications discussed above did not allow us to reflect the multi-level nature of different types of receptions, some of which are earlier and lower in level of development, while others are later and more differentiated. Ideas about the multi-level affiliation 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) proposed a genetic classification principle in 1920. He distinguished between protopathic sensitivity (lower) and epicritic sensitivity (highest).
Tactile sensitivity was identified as epicritic, or discriminative, sensitivity of the highest level; and protopathic sensitivity, archaic, lower level - painful. He proved that protopathic and epicritic components can be both inherent in different modalities and occur within one modality. Younger and more advanced epicritic sensitivity allows you to accurately localize an object in space, it provides objective information about the phenomenon. For example, touch allows you to accurately determine the location of a touch, and hearing allows you to determine the direction in which the sound was heard. Relatively ancient and primitive sensations do not provide 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 constant affective overtones, and they reflect subjective states rather than objective processes. The ratio of protopathic and epicritic components in different types of sensitivity turns out to be different.
Alexey Alekseevich Ukhtomsky (1875-1942), an outstanding Russian physiologist, one of the founders of the physiological school of St. Petersburg University, also used the genetic principle of classification. The highest receptions according to Ukhtomsky are hearing and vision, which are in constant interaction with the lower ones, thanks to which they improve and develop. For example, the genesis of visual reception lies in the fact that first tactile reception turns 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 receptive surfaces and the function they perform:
1. Exteroception (external reception): a) contact; b) distant; c) contact-distant;
2. Proprioception (reception in muscles, ligaments, etc.): a) static; b) kinesthetic.
3. Interoception (reception of internal organs).
Charles Sherrington's systemic classification divided all sensory systems into three main blocks.
The first block is exteroception, which brings to a person information coming from the outside world and is the main reception that connects a person with the outside world. It includes: vision, hearing, touch, smell, taste. All exteroception is divided into three subgroups: contact, distant and contact-distant.
Contact exteroception occurs when a stimulus is applied directly to the surface of the body or the corresponding receptors. Typical examples include sensory acts of touch and pressure, touch, and taste.
Distant exteroception occurs 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. This includes vision, hearing, and smell.
Contact-distant exteroception is carried out both in direct contact with the stimulus and remotely. This includes temperature, skin and pain. vibratory sensory acts.
The second block is proprioception, which conveys to a 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 located in muscles and articular surfaces (tendons, ligaments). Excitations that occur when muscles are stretched or joints change position cause kinesthetic reception.
The third block includes interoception, signaling the state of a person’s internal organs. These receptors are located in the walls of the stomach, intestines, heart, blood vessels and other visceral formations. Interoceptive are the feelings of hunger, thirst, sexual sensations, feelings of malaise, etc.
Modern authors use Aristotle's expanded classification, distinguishing between reception: touch and pressure, touch, temperature, pain, taste, olfactory, visual, auditory, position and movement (static and kinesthetic) and organic (hunger, thirst, sexual sensations, pain, internal sensations). organs, etc.), structuring it with the classification of Ch. Sherrington. The levels of organization of sensory systems are based on the genetic principle of G. Head's classification.
1.3 Chuvalidity 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 for mental reflection in the form of a sensory act.
There are absolute and differential sensitivity. Absolute sensitivity - the ability to perceive stimuli of minimal strength (detection). Differential sensitivity is the ability to perceive a change in a stimulus or distinguish between similar stimuli within the same modality.
Sensitivity is measured or determined by the strength of the stimulus, which under given conditions is capable of causing sensation. Feeling - active mental process partial reflections of objects or phenomena of the surrounding world, as well as internal states of the body, in the human mind under the direct influence of stimuli on the senses.
The minimum strength of the stimulus that can cause 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 age, the nature of the activity, the functional state of the body, the strength and duration of the current stimulus.
The upper absolute threshold of sensation is determined by the maximum strength of the stimulus, which also causes a sensation characteristic of a given 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 discrimination threshold. Difference sensitivity is inversely proportional to the discrimination threshold.
The French physicist P. Bouguer in 1729 came to the conclusion that the difference threshold of visual perception is directly proportional to its initial level. 100 years after P. Bouguer, 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 is the difference threshold, I is the original stimulus.
The ratio of the difference threshold to the value of the original stimulus is a constant value and is called relative difference or differential threshold.
According to the Bouguer-Weber law, the differential threshold is a certain constant part of the value of the original stimulus by which it must be increased or decreased in order to obtain a barely noticeable change in sensation. The magnitude of the differential threshold depends on the modality of sensation. For vision it is approximately 1/100, for hearing 1/10, for kinesthesia 1/30, etc.
The reciprocal of the differential threshold is called differential sensitivity. Subsequent studies showed that the law is valid only for the middle part of the dynamic range of the sensor system, where differential sensitivity is maximum. The limits of this zone vary 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 the science of the natural connection between physical and mental phenomena, using a number of psychophysical laws 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 active stimulus, that is, the sensation changes much more slowly than the strength of irritation increases.
As signal intensity increases, an increasingly large difference between intensity units (i) is required to keep the differences between the sensation units (S) equal. 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 is called the basic psychophysical law in psychology.
Stevens' law (power law) is a variant of the basic psychophysical law proposed by the American psychologist Stanley Stevens (1906-1973), which 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 the sensation, i is the strength of the stimulus, k is a constant depending on the unit of measurement, n is the exponent of the function. The exponent n of the power function is different for 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 difficulty of detecting thresholds and recording 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 simply in the inability to perceive the signal due to its weakness, but in the fact that it is always present against the background of interference or “noise” masking it " The sources of this “noise” are numerous. Among them are extraneous stimuli, spontaneous activity of receptors and neurons in the central nervous system, changes 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 confidence when the signal was presented and when it was not. As a result, the signal detection process itself becomes probabilistic. This feature of the occurrence of sensations of near-threshold intensity is taken into account in a number of works created in Lately mathematical models, describing this sensory activity.
1.4 Variability of sensitivity
The sensitivity of analyzers, determined by the magnitude of absolute and difference thresholds, is not constant and can change. This variability in sensitivity depends both on environmental conditions and on a number of internal physiological and psychological conditions. There are two main forms of changes in sensitivity:
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 body to the actions of the environment due to changes in sensitivity under the influence of an active stimulus. There are three types of adaptation:
1. Adaptation as the complete disappearance of sensation during the prolonged action of a stimulus. In the case of constant stimuli, the sensation tends to fade. For example, clothes, a watch on your hand, soon cease to be felt. A common fact is the distinct disappearance of olfactory sensations soon after we enter an atmosphere with any persistent odor. The intensity of the taste sensation weakens 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 intensity level of a constantly acting stimulus. The phenomenon is typical for all modalities except visual.
Full adaptation of the visual analyzer under the influence of a constant and motionless stimulus does not occur under normal conditions. This is explained by compensation for the constant stimulus due to movements of the receptor apparatus itself. Constant voluntary and involuntary eye movements ensure continuity of visual sensation. Experiments in which conditions were artificially created to stabilize the image relative to the retina of the eyes 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 followed by recovery is a protective adaptation.
So, for example, when we find ourselves from a dimly lit room into a brightly lit space, we are first blinded and unable to discern any details around us. After some time, the sensitivity of the visual analyzer is restored, and we begin to see normally. The same thing happens when we find ourselves in a weaving workshop and at first, apart from the roar of the machines, we cannot perceive speech and other sounds. After some time, 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 with the subsequent restoration of these thresholds in accordance with the intensity of the current 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 existing stimuli and helps 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 type of adaptation, characteristic of certain types of sensations, can be defined as positive adaptation.
In the visual analyzer, this is a dark adaptation, when the sensitivity of the eye increases under the influence of being in the dark. A similar form of auditory adaptation is adaptation to silence. In temperature sensations, positive adaptation is detected 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, while others detect slow adaptation. For example, tactile receptors adapt very quickly. The visual receptor adapts relatively slowly (dark adaptation time reaches several tens of minutes), olfactory and gustatory.
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 core.
Adaptive regulation of the level of sensitivity depending on what stimuli (weak or strong) affects the receptors is of great biological importance. Adaptation helps the sensory organs to detect weak stimuli and protects the sensory organs from excessive irritation in the event of unusually strong influences.
So adaptation is one of the most important species changes in sensitivity, indicating 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 during the adaptation process sensitivity changes in both directions - that is, it increases or decreases, but in the process of sensitization - only in one direction, namely, increasing sensitivity. In addition, changes in sensitivity during adaptation depend on environmental conditions, and during sensitization - mainly on processes occurring in the body itself, both physiological and mental. Thus, sensitization is an increase in the sensitivity of the senses under the influence of internal factors.
There are two main directions for increasing sensitivity according to the type of sensitization. One of them is of a long-term, permanent nature and depends primarily on sustainable changes occurring in the body, the second is of an unstable 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, and the general condition of the body associated with compensation of sensory defects.
Studies have shown that the sensitivity of the sensory organs increases with age, reaching its maximum by 20-30 years, in order to gradually decrease thereafter.
Essential features of the functioning of the senses depend on the type of human nervous system. It is known that people with a strong nervous system exhibit greater endurance and less sensitivity, while people with a weak nervous system and less endurance have greater sensitivity.
The endocrine balance in the body is very important for sensitivity. For example, during pregnancy, olfactory sensitivity sharply worsens, while visual and auditory sensitivity decreases.
Compensation for sensory defects leads to increased sensitivity. So, for example, the loss of vision or hearing is to a certain extent compensated by the exacerbation of other types of sensitivity. People deprived of vision have a highly developed sense of touch and are able to read with their hands. This process of reading with your hands has a special name - haptics. In people who are deaf, vibration sensitivity develops greatly. For example, the great composer Ludwig van Beethoven last years life, when he lost his hearing, he used vibration sensitivity to listen musical works.
The second group of factors that change sensitivity includes pharmacological influences, conditioned reflex increases in sensitivity, the influence of the second signaling system and attitudes, the general state of the body associated with fatigue, as well as the interaction of sensations.
There are substances that cause a distinct exacerbation of sensitivity. These include, for example, adrenaline, the use of which causes stimulation of the autonomic nervous system. A similar effect, exacerbating the sensitivity of receptors, can have phenamine and a number of other pharmacological agents.
Conditioned reflex increases in sensitivity 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 increase in sensitivity is observed among members of operational groups who participated in combat operations during subsequent combat operations. Taste sensitivity is heightened when a person finds himself in an environment similar to the one in which he previously participated in a rich and pleasant feast.
An increase in the sensitivity of the analyzer can also be caused by exposure to secondary signal stimuli. For example: a change in the electrical conductivity of the eyes and tongue in response to the words “sour lemon,” which in fact occurs when directly exposed to lemon juice.
An aggravation of sensitivity is also observed under the influence of the installation. Thus, hearing sensitivity increases sharply when anticipating an important phone call.
Changes in sensitivity also occur in a state of fatigue. Fatigue first causes an exacerbation of sensitivity, that is, a person begins to acutely sense extraneous sounds, smells, etc. not related to the main activity, and then when further development Fatigue causes a decrease in sensitivity.
A change in sensitivity can also be caused by the interaction of different analyzers.
The general pattern of interaction between analyzers is that weak sensations cause an increase, and strong ones cause a decrease in the sensitivity of the analyzers during their interaction. Physiological mechanisms in 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. When exposed to 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.
When analyzers interact, intermodal connections may arise. An example of this phenomenon is the occurrence of panic fear when exposed to ultra-low frequency sound. The same phenomenon is confirmed when a person feels the effects of radiation or feels someone staring at their back.
A voluntary increase in sensitivity can be achieved in the process of targeted training activities. For example, an experienced turner is able to “by eye” determine the millimeter dimensions of small parts; tasters of various wines, perfumes, etc., even with 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 analyzers are in constant interaction with each other. Associated with this is the paradoxical phenomenon of synesthesia.
Synesthesia is the occurrence, under the influence of stimulation 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 possessed the ability of “color hearing,” including Alexander Nikolaevich Scriabin, who wrote the first color-musical work in history - the Prometheus symphony, presented in 1910 and including the light part. Lithuanian painter and composer Čiurlionis Mikolojus Konstantinas (1875-1911) is known for his symbolic paintings, in which he reflected 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 body’s sensory systems and the integrity of the sensory reflection of the world.
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Structural complexity of human sensations. Main types of sensations. The concept of sensor and sensory systems. Human sense organs. The concept of adaptation in modern psychology. Interaction of sensations, sensitization, synesthesia, Weber-Fechner law.
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Formation of domestic neuropsychology as an independent science. Sensory and gnostic visual, skin-kinesthetic and auditory disorders. Visual, tactile and auditory agnosia. Auditory analyzer, sensory auditory disorders.
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The concept of sensation and its physiological basis. Types and classification of sensations: visual, auditory, vibration, olfactory, gustatory, skin and others. Definition of perception as a psychological process, its properties. Types and ways of thinking.
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Human sensory systems, the degree of their development, their role and place in the formation of human behavior. Properties of sensory systems and regulation of their activity. Emotions as an element of human life, their psychological essence and influence on individual behavior.
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Classification and basic properties of human perception. System of sensory standards. Absolute sensitivity and sensitivity to discrimination. Mastering the means and methods of perception in early childhood. Psychological foundations of sensory education.
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The formation of psychophysiology as one of the branches of neuroscience. The concept of sensory systems, their main functions and properties, adaptation and interaction. Physiological basis dreams and the cause of somnambulism. Psychophysiology of creative activity and speech.
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Five sensory systems and the function of forming ideas about the world. Characteristics of representative systems. Auditory, visual, kinesthetically focused people. Predicates, their role in establishing rapport with people. Tuning and predicative phrases.
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The idea of sensory systems was formulated by I.P. Pavlov in the doctrine of analyzers in 1909 during his study of higher nervous activity. Analyzer- a set of central and peripheral formations that perceive and analyze changes in the external and internal environments of the body. Concept 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, the concept still exists sense organ as a peripheral formation that perceives and partially analyzes environmental factors. The main part of the sensory organ is the receptors, equipped with auxiliary structures that ensure optimal perception. Thus, the organ of vision consists of the eyeball, the retina, which contains visual receptors, and a number of auxiliary structures: 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 can be considered an organ of taste. When directly exposed to various environmental factors with the participation of analyzers in the body, Feel, which are reflections of the properties of objects in the objective world. The peculiarity of sensations is their modality, those. a set of sensations provided by any one analyzer. Within each modality, in accordance with the type (quality) of the sensory impression, different qualities can be distinguished, or valence. Modalities are, for example, vision, hearing, taste. Qualitative types of modality (valence) for vision are different colors, for taste - the sensation of sour, sweet, salty, bitter.
The activity of analyzers is usually associated with the emergence of five senses - vision, hearing, taste, smell and touch, through which the body communicates with the external environment. However, in reality there are much more of them. For example, the sense of touch in a broad sense, in addition to the tactile sensations arising from touch, includes the feeling of pressure and vibration. The temperature sense includes sensations of warmth or cold, but there are also more complex sensations, such as sensations of hunger, thirst, sexual need (libido), due to the special (motivational) state of the body. The sense of body position in space is associated with the activity of the vestibular and motor analyzers and their interaction with the visual analyzer. Special place the sensory function is occupied by the sensation of pain. In addition, we can, albeit “vaguely,” perceive other changes, not only in the external, but also in the internal environment of the body, and in this case emotionally charged sensations are formed. So, coronary spasm in initial stage illness, when pain does not yet occur, can cause a feeling of melancholy and despondency. Thus, there are actually much more structures that perceive irritation from the living environment and the internal environment of the body than is commonly believed.
The classification of analyzers can be based on various characteristics: the nature of the current stimulus, the nature of the sensations that arise, the level of receptor sensitivity, the speed of adaptation, and much more.
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 indicators of the internal environment within the physiological norm in a healthy person are usually not perceived subjectively in the form of sensations. Thus, 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 body’s adaptation to different conditions his life activity. The significance of these analyzers is studied as part of a physiology course (adaptive regulation of the activity of internal organs). But at the same time, changes in some constants of the internal environment of the body can be perceived subjectively in the form of sensations (thirst, hunger, sexual desire) formed on the basis of biological needs. To satisfy these needs, behavioral responses are activated. For example, when a feeling of thirst arises due to stimulation of osmo- or volume receptors, behavior is formed aimed at searching for and receiving 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 the 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 experiment of D. McLosky, which he performed on himself. Primary afferent fibers from muscle receptors were stimulated by threshold electrical stimuli. An increase in the frequency of impulses of these nerve fibers caused the subject to have subjective sensations of a change in the position of the corresponding limb, although its position did not actually change.
Pain analyzer should be highlighted separately due to its special significance for the body - it carries information about damaging actions. Painful sensations can occur when both extero- and interoreceptors are irritated.
Structural and functional organization of analyzers
According to the presentation of 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 the receptors, the energy of the stimulus is transformed into a nerve impulse, as well as the signal is amplified 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. Thus, the receptors of the visual analyzer are adapted to the perception of light, and the auditory receptors are adapted to perceive sound, etc. That part of the receptor surface from which one afferent fiber receives the 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 ensures 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 by mechanical deformation and 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 tension, osmolarity and pH, glucose levels and other substances). Such receptors are found in the mucous membrane of the tongue and nose, carotid and aortic bodies, hypothalamus and medulla oblongata.
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, midbrain, medulla oblongata and spinal cord.
4. Photoreceptors in the retina of the eye perceive light (electromagnetic) energy.
5. Nociceptors, the excitation of which is accompanied by painful sensations (pain receptors). The irritants of these receptors are mechanical, thermal and chemical (histamine, bradykinin, K +, H +, etc.) factors. Painful stimuli are perceived by free nerve endings, which are found in the skin, muscles, internal organs, dentin, and blood vessels.
From a psychophysiological point of view receptors are divided according to the sense organs and the sensations generated into visual, auditory, gustatory, olfactory and tactile.
By location in the body receptors are divided into extero- and interoreceptors.
Exteroceptors 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), blood vessels and the central nervous system. A variety of interoreceptors are receptors of the musculoskeletal system (proprioceptors) 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.
By speed of adaptation receptors are divided into three groups: rapidly adapting (phasic), slowly adapting (tonic) and mixed (phasotonic), adapting at an average speed. An example of rapidly adapting receptors are the vibration (Pacini corpuscles) and touch (Meissner corpuscles) receptors on the skin. Slowly adapting receptors include proprioceptors, lung stretch receptors, and pain receptors. Retinal photoreceptors and skin thermoreceptors adapt at an average speed.
According to structural and functional organization distinguish between primary and secondary receptors. Primary receptors are the sensory endings of the dendrite of the afferent neuron. The neuron body is located in the spinal ganglion or cranial nerve ganglion. In the primary receptor, the stimulus acts directly on the endings of the sensory neuron. Primary receptors are phylogenetically more ancient structures; they include olfactory, tactile, temperature, pain receptors and proprioceptors.
In secondary receptors there is a special cell that is 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 receptor excitation occurs.
Mechanism of receptor excitation. When a stimulus acts on a receptor cell, a change in the spatial configuration of protein receptor molecules occurs in the protein-lipid layer of the membrane. This leads to a change in the permeability of the membrane to certain ions, most often sodium ions, but in recent years the role of potassium in this process has also been discovered. Ionic currents arise, the membrane charge changes, and a receptor potential (RP) is generated. And then the process of excitation occurs in different receptors in different ways. In the primary sensory receptors, which are the free bare ends of a sensitive neuron (olfactory, tactile, proprioceptive), the RP acts on the adjacent, most sensitive areas of the membrane, where an action potential (AP) is generated, which then spreads in the form of impulses along the nerve fiber. The conversion of external stimulus energy into AP in primary receptors can occur both directly on the membrane and with the participation of some auxiliary structures. This, for example, happens in the Pacinian corpuscle. The receptor here is represented by a bare axon ending, which is surrounded by a connective tissue capsule. When the Pacinian corpuscle is compressed, 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 a transmitter from the presynaptic section of the receptor cell into the synaptic cleft of the receptor-afferent synapse. This transmitter acts on the postsynaptic membrane of the sensitive neuron, causing its depolarization and the formation of a postsynaptic potential, which is called the generator potential (GP). GP, acting on extrasynaptic areas of the membrane of a sensitive neuron, causes the generation of APs. GP can be both de- and hyperpolarizing 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 bioelectric processes that have the properties of a local or local response: they spread with decrement, i.e. with attenuation; the magnitude depends on the strength of irritation, since they obey the “law of force”; the value depends on the rate of increase in the stimulus amplitude over time; can be summed up when applying rapidly successive irritations.
So, the transformation of stimulus energy into a nerve impulse occurs in the receptors, i.e. primary coding of information, transformation of information into sensory code.
Most receptors have so-called background activity, i.e. excitation occurs in them in the absence of any stimuli.
Conductor section of the analyzer includes afferent (peripheral) and intermediate neurons of the stem and subcortical structures of the central nervous system (CNS), which constitute a chain of neurons located in different layers at each level of the CNS. The conduction section ensures the conduction of excitation from receptors to the cerebral cortex and partial processing of information. The conduction of excitation through the conduction section is carried out by two afferent pathways:
1) 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 and medulla oblongata, in the visual thalamus and in the corresponding projection zone of the cerebral cortex);
2) in a nonspecific way, with the participation of the reticular formation. At the level of the brain stem, collaterals extend from a specific pathway 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 carried out slowly through a large number of synapses. Due to collaterals, the hypothalamus and other parts of the limbic system of the brain, as well as motor centers, are included in the excitation process. All this provides the autonomic, 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. “core”, 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 zones of the cortex are distinguished. Excitation from the corresponding receptors to the primary zones is directed along fast-conducting specific pathways, while activation of the secondary and tertiary (associative) zones occurs along polysynaptic nonspecific pathways. In addition, the cortical zones are interconnected by numerous associative fibers. Neurons are distributed unevenly 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 parts of the visual, auditory and skin analyzers. Afferent impulses with the participation of stellate cells of the cortex (IV layer) are transmitted to pyramidal neurons (III layer), from here the processed signal leaves the cortex to other brain structures.
In the cortex, input and output elements, together with stellate cells, form so-called columns - functional units of the cortex, organized in the vertical direction. The column has a diameter of about 500 μm and is determined by the distribution zone of collaterals of the ascending afferent thalamocortical fiber. Adjacent columns have relationships that organize the participation of multiple columns to carry out a particular reaction. Excitation of one of the columns leads to inhibition of neighboring ones.
Cortical projections of sensory systems have a topical principle of organization. The volume of the cortical projection is proportional to the receptor density. 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 recording evoked potentials (EP) is used. EP is a type of evoked electrical activity in the brain. Sensory EPs are recorded during stimulation of receptor formations and are used to characterize such important function as perception.
From general principles The organization of analyzers should be multi-level and multi-channel.
Multilevelness provides the possibility of specialization of different levels and layers of the central nervous system for processing certain types of information. This allows the body to more quickly respond to simple signals that are analyzed at individual intermediate levels.
The existing multichannel nature of analyzer systems is manifested in the presence of parallel neural channels, i.e. in each of the layers and levels there are many nerve elements connected with many 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 the construction of sensory systems creates conditions for fine regulation of perception processes through influences from higher levels to lower ones.
These structural features of the central department ensure the interaction of various analyzers and the process of compensation for impaired functions. At the level of the cortical region, a higher analysis and synthesis of afferent excitations is carried out, providing a complete picture of the environment.
The main properties of the analyzers are the following.
1. High sensitivity to an adequate stimulus. All parts of the analyzer, and especially the receptors, are highly excitable. Thus, the photoreceptors of the retina can be excited by the action of only a few quanta of light, and the olfactory receptors inform the body about the appearance of single molecules of odorous substances. However, when considering this property of analyzers, it is preferable to use the term “sensitivity” rather than “excitability”, since in humans it is determined by the occurrence of sensations.
Sensitivity is assessed using a number of criteria.
Threshold of sensation(absolute threshold) - the minimum force of irritation that causes such excitation of the analyzer, which is perceived subjectively in the form of a sensation.
Discrimination threshold(differential threshold) - a minimal change in the strength of the current 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 the determination of the force of pressure on the palm by the test subject’s sensation. It turned out that when a load of 100 g was applied, it was necessary to add a load of 3 g to feel an increase in pressure, when a load of 200 g was applied, it was necessary to add 6 g, 400 g - 12 g, etc. In this case, the ratio of the increase in the strength of stimulation (L) to the strength of the active stimulus (L) is a constant value (C):
This value is different for different analyzers, in this case it is equal to approximately 1/30 of the strength of the current stimulus. A similar pattern is observed when the strength of the current stimulus decreases.
Intensity of sensations with the same stimulus strength can be different, since it depends on the level of excitability of 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 - constant,
L is the strength of the current stimulus,
L 0 - sensation threshold (absolute threshold).
Weber's and Fechner's laws are not accurate enough, especially with low irritation strength. Psychophysical research methods, although they suffer from some inaccuracy, are widely used in studies of analyzers in practical medicine, for example, in determining visual acuity, hearing, smell, tactile sensitivity, and taste.
2. Inertia- relatively slow onset and disappearance of sensations. The latent time for the occurrence 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. The persistence of sensations for a certain period after the stimulus is turned off is explained by the phenomenon of aftereffects in the central nervous system - mainly by the circulation of excitation. Thus, a visual sensation does not arise and disappear instantly. The latent period of visual sensation is 0.1 s, the aftereffect time is 0.05 s. Light stimuli (flickers) quickly following one after another can give a feeling of continuous light (the phenomenon of “flickering fusion”). The maximum frequency of light flashes, which are perceived separately, is called the critical flickering frequency, which is greater, the stronger the brightness of the stimulus and the higher the excitability of the central nervous system, and is about 20 flickers per second. Along with this, if two stationary stimuli are projected sequentially with an interval of 20-200 ms onto different parts of the retina, a sensation of object movement arises. This phenomenon is called the “Phi Phenomenon.” This effect is observed even when one stimulus is slightly different in shape from the other. These two phenomena: “flicker fusion” and “Phi-phenomenon” are the basis 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 when still images are presented on the screen in rapid succession at a speed of 18-24 frames per second.
3. Ability sensory system to adaptation with a constant strength of a long-acting stimulus, it mainly consists of a decrease in absolute and an increase in differential sensitivity. This property is inherent in all sections of the analyzer, but it is most clearly manifested at the level of receptors and consists in a change not only in their excitability and impulses, but also in indicators of functional mobility, i.e. in changing the number of functioning receptor structures (P.G. Snyakin). Based on the speed of adaptation, all receptors are divided into quickly and slowly adapting, and sometimes a group of receptors with an average speed 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 through descending influences that change the activity of the underlying structures of the sensory system. Thanks to this, the phenomenon of “tuning” sensory systems to 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 in the environment, the beneficial and negative aspects of their impact on the body. Therefore, dysfunction of external analyzers, especially visual and auditory, makes it extremely difficult to understand the outside world (the outside world is very poor for a blind or deaf person). However, only analytical processes in the central nervous system cannot create a real picture of the environment. The ability of analyzers to interact with each other provides a figurative and holistic view of objects in the external world. For example, we evaluate the quality of a lemon slice 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 holistic image of the perceived object is created. The interaction of analyzers when assessing phenomena and objects also underlies compensation for impaired functions when one of the analyzers is lost. Thus, in blind people the sensitivity of the auditory analyzer increases. Such people can determine the location of large objects and walk around them if there is no extraneous noise. This is done by reflecting sound waves from an object in front. American researchers observed a blind man who quite 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. Thus, listening to music can cause pain relief during dental procedures (audioanalgesia). Noise impairs visual perception; bright light increases the perception of sound volume. The process of interaction between sensory systems can manifest itself at various levels. The reticular formation of the brain stem, the cerebral cortex, plays a particularly important role in this. Many cortical neurons have the ability to respond to complex combinations of signals from different modalities (multisensory convergence), which is very important for cognition of the environment and the evaluation of 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 analyzer departments is coding. In the auditory analyzer, the mechanical vibration of the membrane and other sound-conducting elements is at the first stage converted into a receptor potential, the latter ensures the release of the transmitter 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, at the synapse of which the electrical signal again turns into a chemical signal, 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 is where physiological coding differs from most technical systems communications, where the message is usually restored to its original form.
Nervous system codes. IN Computer technology uses 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 larger number of combinations with the same code length. The universal code of the nervous system is nerve impulses that travel along nerve fibers. In this case, 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. The transmission of a signal from one cell to another in all sections of the analyzer is carried out using a chemical code, i.e. various mediators. To store information in the central nervous system, encoding is carried out using structural changes in neurons (memory mechanisms).
Coded characteristics of the stimulus. The analyzers encode the qualitative characteristics of the stimulus (for example, light, sound), the strength of the stimulus, the time of its action, as well as space, i.e. the place of action of the stimulus and its localization in the environment. All sections of the analyzer take part in encoding all the characteristics of the stimulus.
In the peripheral part 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 an adequate stimulus. Thus, a light beam excites only the receptors of the retina; 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 the 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. Moreover, with increasing stimulus strength, 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 may also change; in addition, the strength of the stimulus can be encoded by varying the latency period and reaction time. A strong stimulus reduces the latency period, increases the number of impulses and lengthens the reaction time. Space is encoded by the size of the area over which the receptors are excited; this is spatial encoding (for example, we can easily determine whether a pencil touches the surface of the skin with a sharp or blunt end). Some receptors are more easily excited when a stimulus acts on them at a certain angle (Pacinian corpuscles, retinal receptors), which is an assessment of the direction of action of the stimulus on the receptor. The localization of the action of the stimulus is encoded by the fact that receptors in different parts of the body send impulses to certain areas of the cerebral cortex.
The time of action of the stimulus on the receptor is encoded by the fact that it begins to be excited with the onset 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 encoded accurately enough due to their rapid adaptation and cessation of excitation with a constant strength of the stimulus. This inaccuracy is partially compensated by the presence of on-, off- and on-off receptors, which are excited respectively when the stimulus is turned on, 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., sensitization of the receptor to changes in this stimulus develops. An increase in 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 conductor section of the analyzer, coding is carried out only at “switching stations,” that is, when transmitting a signal from one neuron to another, where the code changes. Information is not encoded in nerve fibers; they act as wires through which information encoded in receptors and processed in the centers of the nervous system is transmitted.
There can be different intervals between impulses in a separate nerve fiber, impulses are formed into packets with different numbers, and there can also be different intervals between individual packets. All this reflects the nature of the information encoded in the receptors. In this case, the number of excited nerve fibers in the nerve trunk 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, by changing the volume of impulses at the input and output, and secondly, by spatial coding, i.e. due to the connection of certain neurons with certain receptors. In both cases, the stronger the stimulus, the more neurons are excited.
In the overlying parts of the central nervous system, 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 stimulus parameter, for example, to a stimulus moving in space, or to a light or dark stripe 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 analyzer function. In the sensory nuclei, inhibitory processes occur that filter and differentiate sensory information. These processes provide control of sensory information. This reduces noise and changes the ratio of spontaneous and evoked neuronal activity. This mechanism is realized through 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 arriving in the form of nerve impulses is recoded into structural and biochemical changes in neurons (memory mechanisms). The cerebral cortex carries out the highest analysis and synthesis of incoming information.
Analysis consists in the fact that, with the help of the sensations that arise, we distinguish between the current 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 or phenomenon encountered for the first time.
There are cases where blind people from birth began to see only in adolescence. Thus, a girl who gained sight only at the age of 16 could not use her vision to recognize objects that she had used many times before. But as soon as she took the object in her hands, she happily named it. Thus, she had to practically re-learn the world around her with the participation of the visual analyzer, reinforced by information from other analyzers, in particular from the tactile one. In this case, tactile sensations turned out to be decisive. This is evidenced, for example, by the long-standing experience of Strato. It is known that the image on the retina is reduced and inverted. A newborn sees the world exactly like this. 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 they appear in reality, although the image on the retina remains inverted. Straton put on glasses with lenses that turned the image on the retina to a position corresponding to reality. The observed world around us 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, and 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, incoming information is compared with traces of memory about other similar objects or phenomena. Information received in the form of nerve impulses is encoded using long-term memory mechanisms.
So, the process of transmitting a sensory message is accompanied by repeated recoding and ends with higher analysis and synthesis, which occurs in the cortical section of the analyzers. After this, the choice or development of a program for the body’s response takes place.
sensory receptor visual analyzer
General plan of the structure of sensory systems
|
Analyzer name |
Nature of the stimulus |
Peripheral department |
Wiring department |
Central hotel |
|
visual |
Electromagnetic vibrations reflected or emitted by objects in the external world and perceived by the organs of vision. |
Rod and cone neurosensory cells, the outer segments of which are rod-shaped ("rods") and cone-shaped ("cones"), respectively. 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. The axons of the bipolar cells in turn converge on the 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 super complex receptive fields detector type. This feature allows you to isolate from a whole image only individual parts of lines with different locations and orientations, and the ability to selectively respond to these fragments is manifested. |
|
auditory |
Sounds, i.e. oscillatory movements of particles of elastic bodies, propagating in the form of waves in a wide variety of media, including air, and perceived by the ear |
Converting the energy of sound waves into the energy of nervous excitation, it is represented by the receptor hair cells of the organ of Corti (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-receiving apparatus) are combined into the concept organ of hearing |
Represented by a peripheral bipolar neuron located in the spiral ganglion of the cochlea (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 (second neuron). Then, after partial decussation, the fibers go to the medial geniculate body of the metathalamus, where switching occurs again (third neuron), from here the excitation enters the cortex (fourth neuron). In the medial (internal) geniculate bodies, as well as in the lower tuberosities of the quadrigeminal, there are centers of reflex motor reactions that occur when exposed to sound. |
Located in the upper part of the temporal lobe of the cerebrum. The transverse temporal gyrus (Heschl's gyrus) is important for the function of the auditory analyzer. |
|
Vestibular |
Provides the so-called acceleration feeling, i.e. a sensation that occurs during linear and rotational acceleration of body movement, as well as during changes in head position. The vestibular analyzer plays a leading role in the spatial orientation of a person and maintaining his posture. |
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 (organ of balance, organ of gravity) consists of three semicircular canals and the vestibule. The vestibule consists of two sacs: a round one (sacculus), located closer to the cochlea, and an oval one (utriculus), located closer to the semicircular canals. For the hair cells of the vestibule, adequate stimuli are acceleration or deceleration of the rectilinear movement of the body, as well as tilting of the head. For hair cells of the semicircular canals, an adequate stimulus is acceleration or deceleration rotational movement in any plane |
The peripheral fibers of the 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 directed to the vestibular nuclei of the medulla oblongata (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 muscle proprioceptors 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. Thanks to this, control and management of effector reactions of a somatic, vegetative and sensory nature are ensured. The third neuron is located in the nuclei of the visual thalamus, from where excitation is sent to the cerebral cortex. |
The central section of the vestibular analyzer is localized in the temporal region of the cerebral cortex, somewhat anterior to the auditory projection zone (Brodmann fields 21 - 22, fourth neuron). |
|
Motor |
Provides the formation of the so-called muscle feeling when the tension of muscles, their membranes, joint capsules, ligaments, and tendons changes. In the muscular sense, three components can be distinguished: 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 a joint, a person is aware of the speed and direction of movement; a sense of strength in which a person can estimate the muscle strength required to move or hold joints in a certain position when lifting or moving a load. Along with the cutaneous, visual, and vestibular motor analyzers, the motor analyzer evaluates the position of the body in space, posture, and is involved in the coordination of muscle activity. |
It is represented by proprioceptors located in muscles, ligaments, tendons, joint capsules, and fascia. These include muscle spindles, Golgi bodies, Pacinian 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 when the skeletal muscle relaxes (lengthens). Golgi bodies are found in tendons. These are grape-shaped sensory endings. Golgi corpuscles, located in the tendons, are connected in series relative to the skeletal muscle, so they are excited when it contracts due to tension in the muscle tendon. Golgi receptors control the force of muscle contraction, i.e. voltage. Panin's corpuscles are encapsulated nerve endings, localized in the deep layers of the skin, in tendons and ligaments, and respond to pressure changes that occur during muscle contraction and tension in tendons, ligaments and skin. |
Represented by neurons that are located in the spinal ganglia (first neuron). The processes of these cells in the bundles of Gaulle and Burdach (posterior columns spinal cord) reach the tender and sphenoid nuclei of the medulla oblongata, where the second neurons are located. From these neurons, the fibers of muscle-articular sensitivity, having crossed, as part of the medial loop, reach the visual 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 functioning of internal organs. We can highlight: 1) internal analyzer of pressure in blood vessels and pressure (filling) in internal hollow organs (mechanoreceptors are the peripheral part of this analyzer); 2) temperature analyzer; 3) analyzer of the chemistry of the internal environment of the body; 4) analyzer of osmotic pressure of the internal environment. |
Mechanoreceptors include all receptors for which adequate stimuli are pressure, as well as stretching and 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, receptors of the mucous membranes of the digestive tract and respiratory organs, receptors of the 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 interstitial tissue near 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, as well as in the nuclei of the hypothalamus. |
Excitation from interoreceptors mainly occurs in the same trunks as the fibers of the autonomic nervous system. The first neurons are located in the corresponding sensory ganglia, the second neurons are in the spinal cord or medulla oblongata. The ascending pathways from them reach the posteromedial nucleus of the thalamus (third neuron) and then ascend to the cerebral cortex (fourth neuron). |
The cortical section is localized in zones C 1 and C 2 of the somatosensory region of the 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 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 included in a particular organ system. In any case, changes in internal organs have a significant impact on the emotional state and nature of human behavior. |
|
Temperature |
Provides information about the external temperature and the formation of temperature sensations |
It is represented by two types of receptors: some respond to cold stimuli, others to heat ones. Heat receptors are Ruffini corpuscles, 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 the skin and mucous membrane itself. |
Cold receptors send out myelinated type A fibers, and heat receptors send out unmyelinated type C fibers, so information from cold receptors travels at a faster rate than from heat receptors. The first neuron is localized in the spinal ganglia. The cells of the dorsal horn 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 the opposite side into the lateral columns and, as part of the lateral spinothalamic tract, reach the visual thalamus, where the third neuron is located. From here the excitation enters the cerebral cortex. |
The central section of the temperature analyzer is localized in 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 hairless skin, as well as on the mucous membranes, special receptor cells (Meissner bodies) located in the papillary layer of the skin react to touch. On skin covered with hair, hair follicle receptors with 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 dorsal ganglia. In the dorsal horn of the spinal cord, the first switch to interneurons occurs (the second neuron), from them the ascending path as part of the dorsal column reaches the dorsal column nuclei in the medulla oblongata (the third neuron), where the second switch occurs, then through the medial loop the path follows to the ventro-basal nuclei of the visual thalamus (fourth neuron), the central processes of the neurons of the visual thalamus go to the cerebral cortex. |
Localized in zones 1 and 2 of the somatosensory area of the cerebral cortex (posterior central gyrus). |
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Flavoring |
The emerging 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 and 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 cells containing serotonin and cells that produce histamine. These and other substances play a certain role in the formation of the sense of taste. Individual taste buds are multimodal structures, as they can perceive different types of taste stimuli. Taste buds in the form of separate inclusions are located on back wall pharynx, soft palate, tonsils, larynx, epiglottis and are also part of the taste buds of the tongue as an organ of taste. |
The taste bud contains nerve fibers that form receptor-afferent synapses. Taste buds various areas the oral cavity receives nerve fibers from different nerves: the taste buds of the anterior two-thirds of the tongue - from the chorda tympani, which is part of the facial nerve; the 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 superior laryngeal nerve, which is part of the vagus nerve |
Localized in the lower part of the somatosensory cortex in the area of the language. Most of the neurons in this area are multimodal, i.e. reacts not only to taste, but also to temperature, mechanical and nociceptive stimuli. The gustatory sensory system is characterized by the fact that each taste bud has not only afferent, but also efferent nerve fibers that approach the taste cells from the central nervous system, which ensures the inclusion of the taste analyzer in the integral activity of the body. |
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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 bears 6-12 cilia, and an axon extends 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 area of contact of the receptor with molecules of odorant substances. The movement of hairs ensures the active process of capturing molecules of an odorous substance and contacting 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. Some of the supporting cells located near the basement membrane are called basal cells |
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 cells of the olfactory bulb, 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 visual thalamus. Some researchers believe that the processes of the second neuron go directly to the cerebral cortex, bypassing the visual thalamus. |
Localized in the anterior part of the piriform lobe of the cortex in the region of the seahorse gyrus. |
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Pain is a “sensory modality” like hearing, taste, vision, etc., it performs a signaling function, which consists of information about the violation of such vital constants of the body 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, according to the proposal of Ch. Sherrington, are called nociceptors. These are high-threshold receptors that respond to destructive influences. According to the mechanism of excitation, nociceptors are divided into mechanonociceptors and chemonociceptors. Mechanonociceptors are located mainly in the skin, fascia, tendons, joint capsules and mucous membranes of the digestive tract. Chemonociceptors are also located on the skin and mucous membranes, but they prevail in the internal organs, where they are localized in the walls of small arteries. |
Pain stimulation from receptors is carried out through the dendrites of the first neuron, located in the sensory ganglia of the corresponding nerves innervating certain areas of the body. The axons of these neurons enter the spinal cord to the interneurons of the dorsal horn (second neuron). Further, excitation in the central nervous system is carried out in two ways: specific (lemniscal) and nonspecific (extralemniscal). A specific path begins from interneurons of the spinal cord, the axons of which, as part of the spinothalamic tract, enter specific nuclei of the thalamus (in particular, the ventrobasal nucleus), which represent third neurons. The processes of these neurons reach the cortex. The nonspecific pathway also begins from the interneuron of the spinal cord and goes along collaterals to various brain structures. Depending on the place of termination, three main tracts are distinguished - neospinothalamic, spinoreticular, spinomesencephalic. The last two tracts unite to form the spinothalamic tract. Excitation along 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 ideas There are two somatosensory zones. The primary projection zone is located in the region of the posterior central gyrus. Here the analysis of nociceptive effects occurs, 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 in the depths of the Sylvian fissure, is involved in the processes of awareness and the development of a program of behavior during pain. The nonspecific pathway extends to all areas of the cortex. A significant role in the formation of pain sensitivity is played by the orbitofrontal cortex, which is involved in the organization of the emotional and autonomic components of pain. |
