Sensory systems

Definition of the concept

Sensory systems

Sensory systems –

E ABOUT rnye.

So, sensory systems

Types of sensory systems

1) Nociceptive (painful).

homeostasis

(sensory image).

Analyzer structure

1. Peripheral part

2. Wiring department

3. Central department

Concept of sensory system wider than the analyzer.

Adaptation

General principles of sensor systems

Departments of the sensory system:

1. Receptors. Auxiliary structures are also possible (for example, the eyeball, ear, etc.).
2. Afferent (sensitive) nerve pathways (afferent neurons).
3. Lower nerve centers.
4. Higher nerve center in the cortex cerebral hemispheres brain.

Multi-storey principle.

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, i.e. responses to irritation, 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.

The principle of multi-channel.

Excitation is always transmitted from receptors to the cortex along several parallel pathways. Excitation flows are partially duplicated and partially separated. They transmit information about various properties of the stimulus.

Example of parallel paths visual system:

1st pathway: retina - thalamus - visual cortex.

2nd path: retina - quadrigeminal (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 cortex zone,

2) non-specific 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.

In the evolutionary process, the multistory and multichannel nature of the structure of sensory pathways increases.

Illustration of the Multichannel Principle: Sensory Pathways

The principle of convergence.

Convergence is the convergence of neural pathways in the form of a funnel. Due to convergence neuron top 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.

The principle of divergence.

Divergence is the divergence of the excitation flow 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 appropriate ways of excitation from lower and higher centers back to receptors

General principles of operation of sensor systems:

1. Conversion the forces of stimulation into the 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 properties 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. Topic matching - the flow of excitation (information flow) in all transmission structures corresponds to the significant characteristics of the stimulus. It means that important signs 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. "Topical" means "spatial".

3. Detection - this is a selection qualitative signs. 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 information about the original object at each level of excitation transmission.

5. Specificity 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: 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 preceding 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.

Adequate stimulus- this is an irritant that gives a maximum response, with a minimum force of irritation.

Specificity of sensory systems predetermined by their structure. The structure limits their responses to one stimulus and facilitates the perception of others.

General overview

Physiology of vision

Vision is provided by the visual sensory system, or visual analyzer, according to I.P. Pavlova.

Visual perception– this is the construction of a neural model of light stimulation due to excitation and inhibition of the photoreceptors of the retina. The model is built from neurons in the visual zone of the cerebral cortex based on the visual excitation that the retina produces when irritated by light.

This neural pattern represents a subjective visual image, which in its most important details coincides with real light stimulation. However, there is no doubt that this image has great distortions compared to reality, but we simply do not notice this. Do you think the image below is moving? No! It's your eyes that are moving...

And as a result, the subjective image of the image moves, which in reality is motionless. There are many known visual illusions based on subjective distortions of the real image.

Physiology of hearing

The auditory sensory system provides perception sounds and construction auditory images, i.e. hearing. An adequate stimulus for her is sound. This means that it is to sounds that the auditory sensory system has increased sensitivity and susceptibility, and also creates sensory images that correctly reflect important characteristics sound stimuli and allow you to navigate sound signals.

To understand the physiology of hearing, we will need to explain the emergence of the auditory sensory flow of excitation, its movement through the nervous system and, finally, the formation of the auditory sensory image.

Plan for explaining auditory perception:

1. Irritant.

2. Conducting stimulation (sound) to receptors

3. Molecular mechanisms of sound reception (transduction) point by point

4. Conductive section: conduction of auditory sensory stimulation to the auditory cortex

5. Transformation of the flow of auditory excitation in the lower auditory nerve centers

6. Analyzing cortical department - auditory areas of the cortex

7. Adaptation of the auditory sensory system to sounds

6. General scheme mechanism of auditory perception

Stimulus

The stimulus for the auditory sensory system is sound.

Sound is longitudinal vibration particles of the medium that transmits sound. Sound vibrations are transmitted through air, water, skull bones, i.e. for gaseous, liquid and solid media.

The main parameters of sound waves are the vibration frequency, their amplitude and timbre (frequency spectrum). Frequency is the tone of a sound. The higher the pitch of the sound, the higher the frequency sound vibrations. The range of human perception of sound is approximately from 20 to 20,000 Hz (hertz - one vibration per second).

Sounds by tone below 20 Hz are called infrasound, consciousness does not perceive them, but there may be subconscious reactions (worry, anxiety, fear and even inexplicable horror). Infrasounds with a frequency of 4 Hz are considered the most dangerous, with a frequency of 8-14 Hz - they correspond to the alpha rhythm of the brain and, apparently, can cause a trance state. Infrasounds of this frequency can be produced by professional equipment at discos and in this way cause a special altered state of consciousness in the people present there.

Sounds by tone above 20000 Hz are called ultrasound, humans do not perceive them (however, cats, dogs and other animals do).

The greatest sensitivity of the ear is in the range from 1000 to 3000 Hz - this is exactly the range of sounds of human speech.

Music playback devices have a wider range from 12-14 Hz to 16000.

2. Conducting stimulation (sound) to receptors

Definition of the concept

Types of smell impairment

Definition of the concept

Olfactory (olfactory) sensory system, or olfactory analyzer, is a neural system for recognizing volatile and water-soluble substances by the configuration of their molecules, creating subjective sensory images in the form of odors.

Just like the gustatory sensory system, the olfactory system is a chemical sensitivity system.

Pain sensory system

(pain analyzer)

Pain sensory system - is a collection nerve structures, perceiving damaging irritations and forming painful sensations, i.e. pain. The concept of “pain sensory system” is clearly broader than the concept of “pain analyzer”, since the pain sensory system necessarily includes a system for counteracting pain - the “antinociceptive system”. The concept of “pain analyzer” can do without the antinociceptive system, but this would be a significant simplification.

Important Feature pain analyzer is that adequate (suitable) stimuli for it can be among the most different classes. The irritation is a damaging effect, therefore, stimuli for the pain analyzer are damaging factors.

What is damaged and disrupted:

Integrity of body coverings and organs.
Integrity of cell membranes and cells.
The integrity of the nociceptives themselves nerve endings.
Optimal course of oxidative processes in tissues.

In general, damage is a signal of disruption of normal functioning.

Definition of “pain”

There are two approaches to understanding pain:

1. Pain is feeling . It has a signaling value for the body, just like sensations of another modality (vision, hearing, etc.).

Pain- it is unpleasant, causing suffering feeling, which occurs under the influence of extremely strong irritants, as a result of tissue damage or oxygen starvation.

Pain - it's psychophysical state discomfort.

It is accompanied by changes in the activity of organs and systems, the emergence of new emotions and motivations. In this approach, pain is seen as a consequence of the primary pain implied by the first approach. Perhaps a more accurate expression in this case would be "painful condition" .

Components of the pain response

1. Motor component.

Excitation from the motor cortex reaches the motor neurons spinal cord, they transmit it to the muscles that carry out motor reactions. In response to pain, motor reflexes, reflexes of flinching and alertness, protective reflexes and behavior aimed at eliminating the action of the harmful factor arise.

2. Vegetative component.

It is caused by inclusion in the systemic pain reaction hypothalamus- higher vegetative center. This component manifests itself in changes in vegetative functions necessary to ensure the body’s protective response. The value changes blood pressure, heart rate, breathing, metabolic changes occur, etc.

3. Emotional component.

It manifests itself in the formation of negative emotional reaction, which is due to the inclusion of emotiogenic areas of the brain in the process of excitation. This negative emotion, in turn, provokes various behavioral reactions: flight, attack, hiding.

Each component of the pain response can be used to assess the specificity of the pain sensation.

Types of pain

Depending on the path of pain stimulation:

1. Primary pain is epicritic. This pain is clear localized, usually has a sharp, stabbing character, occurs when mechanoreceptors are activated, excitation moves along A-fibers, along the neospinothalamic tract to the projection zones of the somatosensory cortex.

2. Secondary pain is protopathic. This pain arises slowly, has unclear localization, and is characterized by an aching character. Occurs when chemonociceptors are activated, excitation moves along C-fibers, the paleospinothalamic tract to the nonspecific nuclei of the thalamus, from there they spread along various areas bark. This type of pain is usually accompanied by motor, autonomic and emotional reactions.

Depending on nociceptors:

1. Somatic, occurs in the skin, muscles, joints, etc. It is two-phase: first epicritic and then protopathic. The intensity depends on the degree and area of damage.

2. Visceral, occurs in internal organs and is difficult to localize. Pain can be projected onto completely different areas, not those where the nociceptors that generated it are located.

Depending on the location of the pain:

1. Local pain, localized directly at the site of nociceptive influence.

2. Projection pain, a sensation that spreads along the nerve and is transmitted to its individual sections from the point of origin.

3. Referring pain is felt not in the area of impact, but where the other branch of the excited nerve is located.

4. Referred pain is felt in the superficial areas of the skin, which are innervated from the same segment of the spinal cord as the internal organs, generating nociceptive effects. Initially, excitation occurs on the nociceptors of the affected internal organs, then it is projected outside the diseased organ, to various areas of the skin or to other organs. Interneurons of the spinal cord are responsible for reflected pain, on which excitations from internal organs and skin areas converge. Painful excitation that occurs in an internal organ activates a common interneuron, and excitation from it runs along the same pathways as during skin irritation. Pain can be reflected in areas significantly removed from the organ that gave rise to it.

5. Phantom pain occurs after organ removal (amputation). Responsibility for it lies with persistent foci of excitation located in the nociceptive structures of the central nervous system. This is usually accompanied by a deficiency of inhibition in the central nervous system. Entering the cerebral cortex, excitation from the generator of this excitation (pain nerve center) is perceived as prolonged, continuous and excruciating pain.

Definition

Antinociceptive systemis a hierarchical set of nervous structures on different levels The central nervous system, with its own neurochemical mechanisms, is capable of inhibiting the activity of the pain (nociceptive) system.

In the ANC system it is mainly used opiatergic regulatory system , based on the interaction of opioid ligands with opiate receptors.

The antinociceptive system suppresses pain at several different levels. If it weren’t for her pain-relieving work, then I’m afraid that pain would become the leading feeling in our lives. But fortunately, after the first sharp attack of pain, it recedes, giving us the opportunity to rest. This is the result of the antinociceptive system, which suppresses pain some time after its occurrence.

The antinociceptive system also causes increased interest because it was she who gave rise to interest in drugs. After all, drugs were originally used precisely as painkillers, helping the antinociceptive system suppress pain, or replacing it in suppressing pain. And still medical use drugs are justified precisely by their analgesic effect. Unfortunately, the side effects of drugs make a person dependent on them and over time turn him into a special suffering creature, and then ensure his premature death...

In general, the "pain analyzer", which provides the perception of pain, provides a good example of the difference between the concepts of "sensory system" and "analyzer". The analyzer (i.e., the perceiving device) is only a certain part of the whole nociceptive sensory system. Together with the antinociceptive system, they no longer constitute just an analyzer, but a more complex self-regulating sensory system.

There are, for example, people with a congenital absence of the feeling of pain, while their nociceptive pain pathways are preserved, which means that they have a mechanism for suppressing pain activity.

In the 70s of the twentieth century, the idea of the antinociceptive system was formed. This system limits pain excitation and prevents overexcitation of nociceptive structures. The stronger the painful nociceptive stimulation, the stronger the inhibitory effect of the antinociceptive system.

With extremely strong painful effects, the antinociceptive system cannot cope, and then a painful shock occurs. With a decrease in the inhibitory effect of the antinociceptive system pain system can become overexcited and give rise to a sensation of spontaneous (spontaneous) psychogenic pain even in healthy organs.

Sensory systems

“Sens” is translated as “feeling”, “sensation”.

Definition of the concept

Sensory systems– these are the perceptive systems of the body (visual, auditory, olfactory, tactile, gustatory, pain, tactile, vestibular, proprioceptive, interoceptive).

Sensory systems –

These are specialized subsystems of the nervous system that provide it with the perception and input of information through the formation of subjective sensations based on objective stimuli.

Sensory systems include peripheral sensory receptors along with auxiliary structures (sensory organs), nerve fibers extending from them (pathways) and sensory nerve centers (lower and higher).

Lower nerve centers transform (process) incoming sensory stimulation into output, and higher nerve centers, along with this function, form screen structures that form a nervous model of irritation - a sensory image.

We can say that sensory systems are the “information inputs” of the body for its perception of characteristics environment, as well as characteristics internal environment the body itself. In physiology, it is customary to emphasize the letter “o,” while in technology, the emphasis is on the letter “e.” Therefore, technical perceiving systems - with E sensory, and physiological - sensory ABOUT rnye.

So, sensory systems- These are information inputs into the nervous system.

Types of sensory systems

1. Auditory. An adequate stimulus is sound.

2. Visual. An adequate stimulus is light.

3. Vestibular. An adequate stimulus is gravity, acceleration.

4. Taste. An adequate stimulus is taste (bitter, sour, sweet, salty).

5. Olfactory. An adequate irritant is smell.

6. Kinesthetic = tactile (tactile) + temperature (heat and cold). An adequate stimulus is pressure, vibration, heat (increased temperature), cold (low temperature).

7. Motor. Provides a sense of the relative position of body parts in space, a sense of one’s body). It is the motor sensory system that allows us to touch, for example, our nose or other parts of the body with our hand, even with our eyes closed.

8. Muscular (proprioceptive). Provides a feeling of the degree of muscle tension. Adequate stimulus - muscle contraction and tendon strain.

9. Painful. An adequate stimulus is damage to cells, tissues or pain mediators.
1) Nociceptive (painful).
2) Antinociceptive (painkiller).

10. Interoceptive. Provides internal sensations. It is poorly controlled by consciousness and, as a rule, gives vague sensations. However, in a number of cases, people can say that they feel not just discomfort in any internal organ, but a state of “pressure”, “heaviness”, “distension”, etc. The interoceptive sensory system maintains homeostasis, and at the same time it does not necessarily generate any sensations perceived by consciousness, i.e. does not create perceptual sensory images.

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...

Analyzers and sensor systems

I.P. Pavlov created the doctrine of analyzers. This is a simplified idea of perception. It divided the analyzer into 3 sections.

Analyzer structure

1. Peripheral part(remote) are receptors that perceive irritation and transform it into nervous excitation.

2. Wiring department- these are pathways that transmit sensory excitation generated in receptors.

3. Central department- this is a section of the cerebral cortex that analyzes the 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.

Concept of sensory system wider than the 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 adaptation of the sensory system and its individual elements to the action of a stimulus.

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

The sensor system includes 3 parts

1. Receptors - sense organs

2. Conductor section connecting receptors to the brain

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

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

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

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

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

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

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

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

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

Functions of touch systems

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

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

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

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

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

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

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

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

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

Classification of receptors.

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

By the nature of information perception

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

Mechanisms of receptor excitation

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

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

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

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

Threshold of irritation and threshold of entertainment.

Threshold of irritation- minimum strength stimulus that causes sensation.

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

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

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

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

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

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

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

For tactile receptors S=9.4*I d 0.52

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

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

Sensory hearing system

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

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

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

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

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

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

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

Inner ear

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

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

Visual system.

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

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

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

Refractive errors of the eye.

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

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

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

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

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

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

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

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

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

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

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

Retinal neurons.

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

Nerve pathways.

The 1st neuron is bipolar.

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

Visual functions.

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

Visual alaptation.

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

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

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

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

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

Color vision.

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

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

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

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

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

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

Perception of space.

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

“Sens” is translated as “feeling”, “sensation”.

Definition of the concept

Sensory systems– these are the perceptive systems of the body (visual, auditory, olfactory, tactile, gustatory, pain, tactile, vestibular, proprioceptive, interoceptive).

Sensory systems - these are specialized subsystems of the nervous system that provide it with the perception and input of information through the formation of subjective sensations based on objective stimuli. Sensory systems include peripheral sensory receptors along with auxiliary structures (sensory organs), nerve fibers extending from them (pathways) and sensory nerve centers (lower and higher). Lower nerve centers transform (process) incoming sensory stimulation into output, and higher nerve centers, along with this function, form screen structures that form a nervous model of irritation - a sensory image. © Sazonov V.F., 2012-2016. © kineziolog.bodhu.ru, 2012-2016..

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, the emphasis is on the letter “e.” Therefore, technical perceiving systems - with E sensory, and physiological - sensory ABOUT rnye.

So, sensory systems- These are information inputs into the nervous system.

Types of sensory systems

Analyzers and sensor systems

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) are receptors that perceive irritation and transform it into nervous excitation.

Wiring department - these are pathways that transmit sensory excitation generated in receptors.

Central department - this is a section of the cerebral cortex that analyzes the 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.

Concept of sensory system wider than the 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 adaptation of the sensory system and its individual elements to the action of a stimulus.

1. Touch systemactive , and not passive in the transmission of excitation.

2. The sensor system includessupport structures , ensuring optimal adjustment and operation of receptors.

3. The sensory system includes auxiliary , which not only transmit sensory stimulation further, but change its characteristics and divide it into several streams, sending them in different directions.

4. The sensor system hasfeedbacks between subsequent and preceding structures transmitting 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. it occursadaptation .

7. The sensor system is more complex than the analyzer.

Conclusion:

Sensory system = analyzer + lower nerve center (or several centers) + regulatory system.

Departments of the sensory system:

1. Receptors. Auxiliary structures are also possible (for example, the eyeball, ear, etc.).
2. Afferent (sensitive) (afferent neurons).
3. .
4. The highest nerve center in the cerebral cortex.

1. The principle of multi-story building.

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.

Illustration of the multi-story principle:

2. The principle of multi-channel.

An example of parallel pathways in the visual system:

1st pathway: retina - thalamus - visual cortex.

2nd path: retina - quadrigeminal (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.

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.

In the evolutionary process, the multistory and multichannel nature of the structure of sensory pathways increases.

Illustration of the multi-channel principle:

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.

4. The principle of divergence.

Divergence is the divergence of the excitation flow into several flows from the lowest floor to the highest (reminiscent of a diverging funnel).

5. Feedback principle.

1. Conversion the forces of stimulation into the 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. Look: Reception and transduction

2. Topic matching - excitation flow (information flow)in all transmission structures corresponds to significantcharacteristics of the stimulus. This means that important signs of the stimulus will be encoded in the form of a stream of nerve impulses and the nervous system will build an internal sensory image similar to the stimulus - a neural model of the stimulus. "Topical" means "spatial".

3. Detection - this is the selection of qualitative characteristics. 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 information about the original object at each level of excitation transmission.

5. Specificity 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: 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 preceding 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.

Adequate stimulus - this is an irritant that gives a maximum response, with a minimum force of irritation.

The adequacy of the stimulus is a relative concept. For example, there is a protein called tuamatin, which has a molecular weight of 22 thousand, consists of 207 amino acid residues and is 8 thousand times sweeter than sucrose. But exactly water solution sucrose is accepted as the standard of sweet taste.

Specificity of sensory systems predetermined by their structure. The structure limits their responses to one stimulus and facilitates the perception of others.

Details on sensor systems for reports and abstracts can be found here:

Rebrova N.P. Physiology of sensory systems: Educational and methodological manual. St. Petersburg, Future Strategy, 2007. Read

bibliotekar.ru/447/213.htm

humbio.ru/humbio/ssb/00000aa0.htm Electronic textbook in human biology, section Sensory systems.

medbiol.ru/medbiol/physiology/001b2075.htm Electronic textbook, section Sensory systems

http://website-seo.ru/read/page/15/ Basic electronic resources on psychophysiology (allowed to download).

website-seo.ru/read/page/2/ Additional electronic resources on psychophysiology (allowed to download).

www.maik.ru/cgi-bin/list.pl?page=sensis elibrary.ru/title_about.asp?id=8212 Journal of Sensory Systems.

ito.osu.ru/resour/el_book/courses/temp3/glava_4_1.html Sensory systems in brief.

www.ozrenii.ru/ About vision (not the classical presentation of information about the visual system).

The sensor system includes 3 parts

1. Receptors - sense organs

2. Conductor section connecting receptors to the brain

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

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

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

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

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

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

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

Functions of touch systems

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

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

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

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

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

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

Classification of receptors.

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

By the nature of information perception

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

Mechanisms of receptor excitation

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

Threshold of irritation and threshold of entertainment.

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

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

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

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

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

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

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

For tactile receptors S=9.4*I d 0.52

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

Sensory hearing system

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

Inner ear

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

Visual system.

Refractive errors of the eye.

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

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

Photoreceptors. The flasks are responsible for color vision, there are 6-7 million of them. The sticks are for twilight vision, there are 110-123 million of them. They are located unevenly. In the central fovea there are only bulbs; here is the greatest visual acuity. Sticks are more sensitive than flasks.

Retinal neurons.

Nerve pathways.

The 1st neuron is bipolar.

Visual functions.

Visual alaptation.

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

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

Blinding brightness of light. Light that is too bright causes an unpleasant feeling of being blinded. The upper limit of glare depends on the adaptation of the eye. The longer the dark adaptation, the less brightness causes blinding.

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

Color vision.

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

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

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

Consistent color images. If you look at a painted object and then at a white background, the background will take on a complementary color. The reason is color adaptation.

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

Perception of space.

Visual sensory system. Organ of hearing and balance. Smell and taste analyzers. Cutaneous sensory system.

The human body as a single whole is a unity of functions and forms. Regulation of the body's life support, mechanisms for maintaining homeostasis.

Theme for self-study: Structure of the eye. Structure of the ear. The structure of the tongue and the location of sensitivity zones on it. The structure of the nose. Tactile sensitivity.

Sense organs (analyzers)

A person perceives the world around him through the senses (analyzers): touch, sight, hearing, taste and smell. Each of them has specific receptors that perceive a certain type of irritation.

Analyzer (sense organ)- consists of 3 sections: peripheral, conduction and central. Peripheral (perceiving) link analyzer - receptors. They transform signals from the outside world (light, sound, temperature, smell, etc.) into nerve impulses. Depending on the method of interaction of the receptor with the stimulus, there are contact(skin, taste receptors) and distant(visual, auditory, olfactory) receptors. Conductor link analyzer - nerve fibers. They conduct excitation from the receptor to the cerebral cortex. Central (processing) link analyzer - a section of the cerebral cortex. A malfunction of one part causes a malfunction of the entire analyzer.

There are visual, auditory, olfactory, gustatory and skin analyzers, as well as a motor analyzer and a vestibular analyzer. Each receptor is adapted to its own specific stimulus and does not perceive others. Receptors are able to adapt to the strength of the stimulus by reducing or increasing sensitivity. This ability is called adaptation.

Visual analyzer. Receptors are excited by light quanta. The organ of vision is the eye. It consists of the eyeball and an auxiliary apparatus. Auxiliary apparatus represented by eyelids, eyelashes, lacrimal glands and muscles of the eyeball. Eyelids formed by folds of skin lined from the inside with mucous membrane (conjunctiva). Eyelashes protect the eyes from dust particles. Lacrimal glands located in the outer upper corner of the eye and produce tears that wash the front of the eyeball and enter the nasal cavity through the nasolacrimal duct. Muscles of the eyeball set it in motion and orient it towards the object in question.

Eyeball located in the orbit and has a spherical shape. It contains three shells: fibrous(external), vascular(average) and mesh(internal), as well as inner core, consisting of lens, vitreous And aqueous humor anterior and posterior chambers of the eye.

The posterior part of the fibrous membrane is a dense opaque connective tissue tunica albuginea (sclera), front - transparent convex cornea. The choroid is rich in blood vessels and pigments. It actually distinguishes choroid(rear end), ciliary body And iris. The bulk of the ciliary body is the ciliary muscle, which changes the curvature of the lens through its contraction. Iris ( iris) has the appearance of a ring, the color of which depends on the amount and nature of the pigment it contains. There is a hole in the center of the iris - pupil. It can contract and expand due to the contraction of muscles located in the iris.

The retina has two parts: rear- visual, perceiving light stimuli, and front- blind, not containing photosensitive elements. The visual part of the retina contains light-sensitive receptors. There are two types of visual receptors: rods (130 million) and cones (7 million). Sticks are excited by weak twilight light and are unable to distinguish color. Cones are excited by bright light and are able to distinguish color. The rods contain red pigment - rhodopsin, and in cones - iodopsin. Directly opposite the pupil there is yellow spot - the place of best vision, which contains only cones. Therefore, we see objects most clearly when the image falls on the yellow spot. Towards the periphery of the retina, the number of cones decreases, and the number of rods increases. Only sticks are located on the periphery. The place on the retina from which the optic nerve emerges is devoid of receptors and is called blind spot.

Most of the cavity of the eyeball is filled with a transparent gelatinous mass, forming vitreous body, which maintains the shape of the eyeball. Lens It is a biconvex lens. Its back part is adjacent to the vitreous body, and its front part is facing the iris. When the muscle of the ciliary body associated with the lens contracts, its curvature changes and light rays are refracted so that the image of the object of vision falls on the macula of the retina. The ability of the lens to change its curvature depending on the distance of objects is called accommodation. If accommodation is disturbed, there may be myopia(the image is focused in front of the retina) and farsightedness(the image is focused behind the retina). With myopia, a person sees distant objects unclearly, with farsightedness - near objects. With age, the lens hardens, accommodation deteriorates, and farsightedness develops.

On the retina, the image appears inverted and reduced. Thanks to the processing in the cortex of information received from the retina and receptors of other senses, we perceive objects in their natural position.

Hearing analyzer. The receptors are excited by sound vibrations in the air. The organ of hearing is the ear. It consists of the outer, middle and inner ear. Outer ear consists of the auricle and auditory canal. Ears serve to capture and determine the direction of sound. External auditory canal begins with the external auditory opening and ends blindly eardrum, which separates the outer ear from the middle ear. It is lined with skin and has glands that secrete earwax.

Middle ear consists of the tympanic cavity, auditory ossicles and auditory (Eustachian) tube. Tympanic cavity filled with air and connected to the nasopharynx by a narrow passage - auditory tube, through which the same pressure is maintained in the middle ear and the space surrounding the person. Auditory ossicles - hammer, anvil And stirrup - movably connected to each other. Vibrations from the eardrum are transmitted through them to the inner ear.

Inner ear consists of a bony labyrinth and a membranous labyrinth located in it. Bone labyrinth contains three sections: vestibule, cochlea and semicircular canals. The cochlea belongs to the organ of hearing, the vestibule and semicircular canals belong to the organ of balance (vestibular apparatus). Snail- a bone canal twisted in the form of a spiral. Its cavity is divided by a thin membranous septum - the main membrane on which receptor cells are located. The vibration of the cochlear fluid irritates the auditory receptors.

The human ear perceives sounds with a frequency of 16 to 20,000 Hz. Sound waves reach the eardrum through the external auditory canal and cause it to vibrate. These vibrations are amplified (almost 50 times) by the ossicular system and transmitted to the fluid in the cochlea, where they are perceived by auditory receptors. Nerve impulse transmitted from auditory receptors through the auditory nerve to the auditory zone of the cerebral cortex.

Vestibular analyzer. The vestibular apparatus is located in the inner ear and is represented by the vestibule and semicircular canals. The vestibule consists of two bags. Three semicircular canals located in three mutually opposite directions corresponding to three dimensions of space. Inside the sacs and channels there are receptors that are able to sense fluid pressure. The semicircular canals perceive information about the position of the body in space. The bags perceive deceleration and acceleration, changes in gravity.

Excitation of the receptors of the vestibular apparatus is accompanied by a number of reflex reactions: changes in muscle tone, contraction of muscles that help straighten the body and maintain posture. Impulses from the receptors of the vestibular apparatus travel through the vestibular nerve to the central nervous system. The vestibular analyzer is functionally connected to the cerebellum, which regulates its activity.

Taste analyzer. Taste buds are irritated by chemicals dissolved in water. The organ of perception is taste buds- microscopic formations in the oral mucosa (on the tongue, soft palate, posterior pharyngeal wall and epiglottis). Receptors specific to the perception of sweet are located at the tip of the tongue, bitter - on the root, sour and salty - on the sides of the tongue. With the help of taste buds, food is tasted, its suitability or unsuitability for the body is determined, and when they are irritated, saliva and gastric and pancreatic juices are released. The nerve impulse is transmitted from the taste buds through the taste nerve to the taste zone of the cerebral cortex.

Olfactory analyzer. Smell receptors are irritated by gaseous chemicals. The sensory organ is the sensory cells in the nasal mucosa. The nerve impulse is transmitted from the olfactory receptors through the olfactory nerve to the olfactory zone of the cerebral cortex.

Skin analyzer. Skin contains receptors , perceiving tactile (touch, pressure), temperature (heat and cold) and pain stimuli. The organ of perception is the receiving cells in the mucous membranes and skin. The nerve impulse is transmitted from tactile receptors through the nerves to the cerebral cortex. With the help of tactile receptors, a person gets an idea of the shape, density, and temperature of bodies. There are most tactile receptors on the tips of the fingers, palms, soles of the feet, and tongue.

Motor analyzer. Receptors are excited when muscle fibers contract and relax. The organ of perception is the sensory cells in muscles, ligaments, and on the articular surfaces of bones.

How does an analyzer differ from a sensor system? Sensory systems

Analyzers and sensor systems

Sense organs (analyzers)