The Seven Essential Virtues of TV Stars. Hypersensitivity, HSP: what is it? What is the name of sensitivity

One of the most important indicators of the quality of the receiving path is the sensitivity of the receiver. It characterizes the ability of the receiver to receive weak signals. Receiver sensitivity is defined as the minimum input signal level of the device required to provide the required quality of the received information. The quality can be estimated by a given bit error rate (BER), error message reception probability (MER), or signal-to-noise ratio SNR (Signal-to-Noise Ratio) at the input of the receiver demodulator. If the receiver sensitivity is limited, then it can be estimated by the actual or marginal receiver sensitivity, noise figure, or noise temperature.

The sensitivity of a receiver with low gain, at the output of which there is practically no noise, is determined by the emf, (or nominal power) of the signal in the antenna (or its equivalent), at which a given voltage (power) of the signal at the output of the receiver is provided.

The sensitivity of the receiver is determined by its gain K US. The receiver must provide amplification of even the weakest input signals to the output level necessary for the normal operation of the device, however, interference and noise act at the receiver input, which are also amplified in the receiver and can degrade the quality of its operation. In addition, amplified internal noise appears at the output of the receiver. The less internal noise, the better the quality of the receiver, the higher the sensitivity of the receiver.

Real Sensitivity receiver is equal to emf. (or nominal power) of the signal in the antenna, at which the voltage (power) of the signal at the output of the receiver exceeds the voltage (power) of the interference by a given number of times. Ultimate sensitivity receiver is equal to emf. or the nominal power of the RAP signal in the antenna, at which at the output of its linear part (i.e., at the input of the detector), the signal power is equal to the power of the internal noise.

When setting the sensitivity of the receiver in the form of emf, it is measured in microvolts. Modern mobile communication receivers have a sensitivity of tenths of a microvolt. The method of setting the sensitivity of the receiver in the form of emf. leads to the fact that with a different input resistance of the receiver, we will get a different emf value. Therefore, despite the fact that all modern receivers of mobile communication systems have an input impedance of 50 ohms, the sensitivity of the receivers is specified in terms of the signal power at the receiver input. Sensitivity is defined as the ratio of the power at the receiver input to the 1 mW power level and is expressed on a logarithmic scale in dBm.

The ultimate sensitivity of the receiver can also be characterized by the noise figure N 0 , equal to the ratio of the noise power generated at the output of the linear part of the receiver by the antenna equivalent (at room temperature T 0 = 290 K) and the linear part, to the noise power generated only by the antenna equivalent. Obviously,

where k= 1.38 10 –23 J/deg is the Boltzmann constant;
Pw is the noise band of the linear part of the receiver, Hz;
R AP is the signal power, W.

From (1) it can be seen that the signal power corresponding to its limiting sensitivity and related to the frequency band unit can be expressed in units kT 0:

The maximum sensitivity of the receiver can also be characterized by the noise temperature of the receiver T pr, for which it is necessary to additionally heat the equivalent of the antenna, so that at the output of the linear part of the receiver, the power of the noise generated by it is equal to the noise power of the linear part. Obviously, where

A real antenna is affected by external noise, the rated power of which is ,
where T A is the noise temperature of the antenna. Therefore, at the output of the linear part

To obtain equality of signal and noise powers, power is required

Literature:

1. "Design of radio receivers" ed. A.P. Sievers - M .: "Higher School" 1976 pp. 7-8
2. "Radio receivers" ed. Zhukovsky - M .: "Sov. Radio" 1989 pp. 8 - 10
3. Palshkov V.V. "Radio receivers" - M .: "Radio and communication" 1984 pp. 12 - 14

Together with the article "Receiver Sensitivity" they read:

Depending on the value of the received frequency, the circuit and design solutions of radio receivers can vary significantly.
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Adjacent channel selectivity is the ability of a receiver to receive a useful signal at a given channel frequency with a given error probability
https://website/WLL/ChastotIzbirat.php

Intermodulation, blocking, one decibel compression point, these are the main sources of reception side channels! To know and be able to deal with these phenomena is the task of any technical specialist.
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The dynamic range of the receiver, on the one hand, determines the ability of the receiver to detect a weak input signal, on the other hand, to process high-level signals without distortion.
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Naturally, we are interested in reducing the probability of a type II error as much as possible, that is, increasing the sensitivity of the criterion. To do this, you need to know what it depends on. In principle, this problem is similar to the one that was solved in relation to type I errors, but with one important exception.

To evaluate the sensitivity of a test, you need to specify the amount of difference that it should detect. This value is determined by the objectives of the study. In the diuretic example, the sensitivity was low - 55%. But, perhaps, the researcher simply did not consider it necessary to detect an increase in diuresis from 1200 to 1400 ml / day, that is, by only 17%?

As the data scatter increases, the probability of both types of errors increases. As we will see shortly, it is more convenient to account for the magnitude of the differences and the spread of the data together by calculating the ratio of the magnitude of the differences to the standard deviation.

The sensitivity of a diagnostic test can be increased by reducing its specificity - a similar relationship exists between the level of significance and the sensitivity of the criterion. The higher the significance level (that is, the smaller a), the lower the sensitivity.

As we have already said, the most important factor that affects the probability of both type I and type II errors is the sample size. As the sample size increases, the probability of error decreases. In practice, this is very important, since it is directly related to the design of the experiment.

Before proceeding to a detailed consideration of the factors affecting the sensitivity of the criterion, we list them again.

Significance level a. The smaller a, the lower the sensitivity.

The ratio of the size of the differences to the standard deviation. The larger this ratio, the more sensitive the criterion.

Sample size. The larger the volume, the higher the sensitivity of the criterion.

Significance level

To get a visual representation of the relationship between the sensitivity of the criterion and the level of significance, let's return to Fig. 6.3. By choosing the significance level a, we thereby set the critical value of t. We choose this value so that the proportion of values ​​that exceed it - provided that the drug has no effect - is equal to a (Fig. 6.3A). The sensitivity of the criterion is the proportion of those values ​​of the criterion that exceed the critical one, provided that the treatment has an effect (Fig. 6.3B). As can be seen from the figure, if the critical value is changed, this share will also change.

Let's take a closer look at how this happens.

On fig. 6.4A shows the distribution of Student's t-test values. Difference from fig. 6.3 is that this is now the distribution obtained for all 1027 possible pairs of samples. The top graph is the distribution of t values ​​for the case when the drug does not have a diuretic effect. Suppose we chose a significance level of 0.05, that is, we took a = 0.05. In this case, the critical value is 2.101, which means we reject the null hypothesis and accept the differences as statistically significant at t > +2.101 or t. 6.4B. It shows the same distributions of t values. The difference in the chosen significance level is a = 0.01. The critical value of t has increased to 2.878, the dotted line has shifted to the right and cuts off only 45% of the lower plot. Thus, when moving from 5% to 1% significance level, the sensitivity decreased from 55 to 45%. Accordingly, the probability of a type II error increased to 1 - 0.45 = 0.55.

So, by reducing a, we reduce the risk of rejecting the correct null hypothesis, that is, finding differences (effect) where there are none. But by doing so, we also reduce sensitivity - the probability of detecting differences that actually exist.

Size of difference

Considering the influence of the significance level, we took the magnitude of the differences constant: our drug increased the daily diuresis from 1200 to 1400 ml, that is, by 200 ml. Now let's accept

constant significance level a = 0.05 and see how the sensitivity of the test depends on the magnitude of the differences. It is clear that large differences are easier to identify than small ones. Consider the following examples. On fig. 6.5A shows the distribution of t values ​​for the case when the study drug does not have a diuretic effect. Hatched are 5% of the largest absolute values ​​of t located to the left - 2.101 or to the right +2.101. On fig. 6.5B shows the distribution of t values ​​for the case when the drug increases the daily

Increase in daily diuresis, ml

diuresis by an average of 200 ml (we have already considered this situation). Above the right critical value lies 55% of the possible values ​​of t: the sensitivity is 0.55. Next, in fig. 6.5B shows the distribution of t values ​​for the case when the drug increases diuresis by an average of 100 ml. Now only 17% of t values ​​exceed 2.101. Thus, the sensitivity of the test is only 0.17. In other words, the effect will be found in less than one out of every five comparisons between the control and experimental groups. Finally, fig. 6.5D represents a case of increased diuresis by 400 ml. 99% of the values ​​of t fell into the critical region. The sensitivity of the test is 0.99: differences will almost certainly be detected.

By repeating this thought experiment, one can determine the sensitivity of the test for all possible effect values, from zero to "infinite". Plotting the results on a graph, we get Fig. 6.6, where the sensitivity of the test is shown as a function of the magnitude of the differences. From this graph, you can determine what the sensitivity will be for a particular effect size. So far, the graph is not very convenient to use, because it is only suitable for this group size, standard deviation, and significance level. We'll build another graph shortly that's more suitable for research planning, but first we need to understand more about the role of scatter and group size.

Scatter of values

The sensitivity of the test increases with the observed differences; as the spread of values ​​increases, the sensitivity, on the contrary, decreases.

Recall that Student's t-test is defined as follows:

where X1 and X2 are averages, s is the combined score of the standard

deviations a, n1 and n2 are sample sizes. Note that x1 and

X2 are estimates of two (different) means - p and p2. For simplicity, we assume that the volumes of both samples are equal, that is, n1 = n2. Then the computed value of t is an estimate of the quantity P1-P2 P-P

Let's look at a few examples. The standard deviation in our study population is 200 ml (see Fig. 6.1). In this case, an increase in daily diuresis by 200 or 400 ml is equal to one or two standard deviations, respectively. These are very noticeable changes. If the standard deviation were 50 ml, then the same changes in diuresis would be even more significant, amounting to 4 and 8 standard deviations, respectively. Conversely, if the standard deviation were, for example, 500 ml, then the change in urine output in 200 ml would be 0.4 standard deviation. Finding such an effect would be difficult and hardly worth it at all.

So, the sensitivity of the test is affected not by the absolute magnitude of the effect, but by its ratio to the standard deviation. Let's denote it f (Greek "phi"); this ratio φ = 5/a is called the noncentrality parameter.

Sample size

We have learned about two factors that affect the sensitivity of a test: the significance level a and the non-centrality parameter φ. The more a and the more f, the more feeling
validity. Unfortunately, we cannot influence at all, and as for a, its increase increases the risk of rejecting the correct null hypothesis, that is, finding differences where there are none. However, there is one more factor that we can, within certain limits, change at our discretion without sacrificing the level of significance. We are talking about the sample size (number of groups). With an increase in the sample size, the sensitivity of the test increases.

There are two reasons why increasing the sample size increases the sensitivity of the test. First, increasing the sample size increases the number of degrees of freedom, which in turn reduces the critical value. Secondly, as can be seen from the formula just obtained

the value of t grows with the sample size n (this is also true for many other criteria).

Figure 6.7A reproduces the distributions from fig. 6.4A. The upper graph corresponds to the case when the drug does not have a diuretic effect, the lower one - when the drug increases daily diuresis by 200 ml. The number of each group is 10 people. Figure 6.7B shows similar distributions. The difference is that now each group included not 10, but 20 people. Since the size of each of the groups is 20, the number of degrees of freedom is V = 2(20 - 1) = 38. From Table 4.1, we find that the critical value of t at the 5% significance level is 2.024 (in the case of samples of size 10, it was 2.101). On the other hand, an increase in the sample size led to an increase in the values ​​of the criterion. As a result, not 55, but 87% of the values ​​of t exceed the critical value. So, increasing the size of the groups from 10 to 20 people led to an increase in sensitivity from 0.55 to 0.87.

Going through all possible sample sizes, you can plot the sensitivity of the test as a function of the size of the groups (Fig. 6.8). With increasing volume sensitivity

is growing. At first, it grows rapidly, then, starting from a certain sample size, the growth slows down.

Sensitivity calculation is an essential part of medical research planning. Now, having become acquainted with the most important factor that determines sensitivity, we are ready to solve this problem.

How to determine the sensitivity of a criterion?

On fig. 6.9 the sensitivity of the Student's test is presented as a function of the non-centrality parameter f = 5/s at a significance level a = 0.05. The four curves correspond to the four sample sizes.

The samples are assumed to be of equal size. What if it's not? If you refer to Fig. 6.9 when planning a study (which is very reasonable), then you need to consider the following. For a given total number of patients, it is precisely the equal number of groups that ensures maximum sensitivity. So, an equal number of groups should be planned. If, however, you decide to calculate sensitivity after the study, when, having found no statistically significant difference, you want to determine the extent to which this can be considered evidence of no effect, then you should take the size of both groups equal to the smaller of them. This calculation will give a somewhat underestimated sensitivity, but will save you from being overly optimistic.

Let's apply curves from fig. 6.9 for example with a diuretic (see fig. 6.1). We want to calculate the sensitivity of Student's t-test at a significance level of a = 0.05. The standard deviation is 200 ml. What is the probability of detecting an increase in daily diuresis by 200 ml?

The number of control and experimental groups is ten. We choose in Fig. 6.9 the corresponding curve and find that the sensitivity of the criterion is 0.55.

So far, we have been talking about the sensitivity of the Stew test.

Halothane and morphine in open heart surgery

In ch. In Table 4, we compared the cardiac index during halothane and morphine anesthesia (see Table 4.2) and did not find statistically significant differences. (Recall that the cardiac index is the ratio of the minute volume of the heart to the surface area of ​​the body.) However, the groups were small - 9 and 16 people. The mean CI in the halothane group was 2.08 L/min/m2; in the morphine group 1.75 l/min/m2, i.e. 16% less. Even if the differences were statistically significant, such a small difference would hardly be of any practical interest.

So let's put the question this way: what was the probability of detecting a difference of 25%? The combined variance estimate is s2 = 0.89, so the standard deviation is 0.94 l/min/m2. Twenty five percent of 2.08 l/min/m2 is 0.52 l/min/m2.

Thereby,

5 _ 0.52 o ~ 0.94

Since the sizes of the groups do not match, we will choose the smallest of them - 9 - to estimate the sensitivity. 6.9 it follows that in this case the sensitivity of the criterion is 0.16.

The chances of detecting even a 25% difference were very small. Let's summarize.

The sensitivity of a test is the probability of rejecting the false hypothesis of no difference.

The sensitivity of the test is affected by the significance level: the smaller a, the lower the sensitivity.

The larger the effect size, the greater the sensitivity.

The larger the sample size, the greater the sensitivity.

Sensitivity is calculated differently for different criteria.

Sensitivity I

the ability of the organism to perceive various stimuli emanating from the external and internal environment, and to respond to them.

Ch. is based on the processes of reception, the biological significance of which lies in the perception of stimuli acting on them, their transformation into excitation processes (Excitation) , which are the source of the corresponding sensations (pain, temperature, light, auditory, etc.). Subjectively experienced appears with threshold stimulation of certain receptors (Receptors) . In those cases when the incoming receptors in the c.n.s. below the threshold of sensation, it does not cause this or that sensation, however, it can lead to certain reflex reactions of the body (vegetative-vascular, etc.).

For understanding the physiological mechanisms of Ch., the teachings of I.P. Pavlova about analyzers (Analyzers) . As a result of the activity of all parts of the analyzer, a subtle and synthesis of stimuli acting on irritations is carried out. In this case, not only the transmission of impulses from receptors to the central analyzer occurs, but also a complex process of reverse (efferent) regulation of sensitive perception (see Self-regulation of physiological functions) . The excitability of the receptor apparatus is determined both by the absolute intensity of stimulation, and by the number of simultaneously stimulated receptors or by the quality of their repeated irritations - the law of summation of receptor irritations. the excitability of the receptor depends on the influence of the central nervous system. and sympathetic innervation.

Sensory impulses from the peripheral receptor apparatus reach the cerebral cortex along specific pathways and non-specific pathways of the reticular formation (Reticular formation) Non-specific afferent impulses travel along the spinoreticular pathway, which at the level of the brainstem (Brainstem) has connections with the cells of the reticular formation . The activating and inhibitory systems of the reticular formation (see Functional systems) carry out the regulation of afferent impulses, participate in the selection of information coming from the periphery to the higher parts of the Ch. system, passing some impulses and blocking others.

There are general and special Ch. General Ch. is divided into exteroceptive, proprioceptive and interoceptive. Exteroceptive (superficial, skin) include pain, temperature (thermal and cold) and tactile Ch. () with their varieties (for example, electrocutaneous - sensations caused by various types of electric current; feeling of moisture - hygroesthesia , it is based on a combination of tactile sensation with temperature; a feeling of itching is a variant of tactile Ch., etc.).

Proprioceptive (deep) Ch. - bathiesthesia includes muscular-articular Ch. (a sense of the position of the body and its parts in space), vibration (), pressure (). To interoceptive (vegetative-visceral) is Ch., associated with the receptor apparatus in the internal organs and blood vessels. There are also complex types of sensitivity: two-dimensional-spatial feeling, localization, discriminatory sensitivity, stereognosis, etc.

The English neurologist Ged (N. Head) proposed to divide the general sensitivity into protopathic and epicritical. Protopathic Ch. is phylogenetically older, associated with the thalamus, and serves to perceive nociceptive stimuli that threaten the body with tissue destruction or even death (for example, strong pain stimuli, sudden temperature effects, etc.). Epicritical Ch., phylogenetically younger, is not associated with the perception of damaging effects. It enables the organism to navigate in the environment, to perceive weak stimuli, to which the organism can respond with a choice reaction (an arbitrary motor act). Epicritical Ch. include tactile, low temperature fluctuations (from 27 to 35 °), irritation, their difference (discrimination), and muscular-articular feeling. Decrease or function of epicritical Ch. leads to disinhibition of the function of the protopathic Ch. system and makes the perception of nociceptive irritations unusually strong. At the same time, pain and temperature stimuli are perceived as especially unpleasant, they become more diffuse, spilled and do not lend themselves to precise localization, which is indicated by the term "".

Special Ch. is associated with the function of the sense organs. It includes Vision , Hearing , Smell , Taste , Body balance . Taste Ch. is associated with contact receptors, other types - with distant receptors.

Ch.'s differentiation is connected with structural and physiological features of a peripheral sensitive neuron - its receptor and a dendrite. Normal for 1 cm 2 skin has an average of 100-200 pain, 20-25 tactile, 12-15 cold and 1-2 heat receptors. Peripheral sensory nerve fibers (dendrites of the cells of the spinal node, trigeminal node, jugular node, etc.) conduct excitatory impulses at different speeds depending on the thickness of their myelin layer. Group A fibers, covered with a thick layer of myelin, conduct an impulse at a speed of 12-120 m/s; group B fibers, which have a thin myelin layer, drive impulses at a speed of 3-14 m/s; group C fibers - unmyelinated (have only one) - at a speed of 1-2 m/s. Group A fibers serve to conduct impulses of tactile and deep Ch., but they can also conduct pain stimuli. Group B fibers conduct pain and tactile stimuli. Group C fibers are conductors of mainly pain stimuli.

The bodies of the first neurons of all types of Ch. are located in the spinal ganglia ( rice. one ) and in the nodes of sensory cranial nerves (Cranial nerves) . The axons of these neurons, as part of the posterior roots of the spinal nerves and the sensory roots of the corresponding cranial nerves, also enter the brain stem, forming two groups of fibers. Short fibers end in a synapse at the cells of the posterior horn of the spinal cord (their analogue in the brainstem is the descending spinal tract of the trigeminal nerve), which is the second sensitive neuron. The axons of most of these neurons, having risen by 2-3 segments, pass through the anterior white commissure to the opposite side of the spinal cord and go up as part of the lateral spinothalamic tract, ending in a synapse at cells of specific ventrolateral nuclei of the thalamus. These fibers carry pain and temperature pulses. Another part of the fibers of the spinothalamic pathway, passing through the simplest types of tactile sensitivity (, hair sensitivity, etc.), is located in the anterior funiculus of the spinal cord and makes up the anterior spinothalamic tract, which also reaches the thalamus. cells of the nuclei of the thalamus (third sensitive neurons) axons, forming the posterior third of the posterior thigh of the inner capsule, reach the sensitive neurons of the cerebral cortex (cerebral cortex) ( posterior central and parietal).

A group of long fibers from the posterior root passes uninterruptedly in the same direction, forming thin and wedge-shaped bundles. As part of these bundles, axons, without crossing, rise to the medulla oblongata, where they end in nuclei of the same name - in the thin and wedge-shaped nuclei. Thin (Goll) contains fibers that conduct Ch. from the lower half of the body, wedge-shaped (Burdaha) - from the upper half of the body. The axons of the cells of the thin and sphenoid nuclei pass at the level of the medulla oblongata to the opposite side - the upper sensitive medial loops. After this decussation in the suture, the fibers of the medial loop go up in the posterior part (tire) of the pons and midbrain and, together with the fibers of the spinothalamic tract, approach the ventrolateral nucleus of the thalamus. Fibers from the thin nucleus approach the cells located laterally, and from the sphenoid nucleus - to more medial groups of cells. The axons of sensitive cells of the nuclei of the trigeminal nerve also fit here. neurons of the thalamic nuclei, axons pass through the posterior third of the posterior thigh of the internal capsule and, ending at the cells of the cortex of the postcentral gyrus (fields 1, 2, 3), the upper parietal lobule (fields 5 and 7) of the cerebral hemispheres. These long fibers carry out muscular-articular, vibrational, complex types of tactile, two-dimensional, spatial, discriminatory Ch., feelings of pressure, stereognosis - from the receptors of the same half of the body to the medulla oblongata. Above the medulla oblongata, they reconnect with conductors of pain and temperature sensitivity of the corresponding side of the body.

Research methods sensitivity is divided into subjective and objective. Subjective methods are based on the psychophysiological study of sensation (absolute and differential thresholds of sensitivity). Clinical study Ch. (see Examination of the patient , neurological examination) should be carried out in a warm and quiet room. In order to better focus on the perception and analysis of sensations, he should lie with his eyes closed. The results of Ch.'s research depend on the patient's reaction, his attention, the safety of consciousness, etc.

Pain sensitivity is examined by a pin prick or other sharp object; temperature - by touching the skin with test tubes filled with cool (not higher than 25 °) and hot (40-50 °) water. More accurately, temperature Ch. can be examined using a thermoesthesiometer, and pain - with a Rudzit algesimeter. The threshold characteristic of pain and tactile sensitivity can be obtained by examining graduated bristles and hairs using the Frey method. Tactile Ch. is examined by lightly touching the skin with a brush, pieces of cotton wool, soft paper, etc. Discriminatory Ch. is examined with Weber's compass. Normally, two separate irritations on the palmar surface of the fingers are perceived when one is removed from the other by 2 mm, on the palmar surface of the hand, this distance reaches 6-10 mm, on the forearm and dorsum of the foot - 40 mm, and on the back and hips - 65-67 mm.

The muscular-articular feeling is examined in the position of the patient lying down, always with his eyes closed. produces an unsharp passive in individual small or large joints - extension, adduction, etc. The subject must determine the direction, volume and these movements. You can use a kinesthesiometer. With a pronounced violation of the muscular-articular feeling, a sensitive (Ataxia) .

The feeling of pressure is determined by distinguishing pressure from a light touch, and also by detecting the difference in the degree of pressure applied. The study is performed using a baresthesiometer - a spring apparatus with a pressure intensity scale expressed in grams. Normally, it distinguishes between an increase or decrease in pressure on the arm by 1/10 - 1/20 of the original pressure.

Vibrating frequency is examined with a tuning fork 64-128 Hz. The leg of a sounding tuning fork is placed on protrusions (ankles, forearms, iliac crest, etc.). Normal vibration at the ankles lasts 8-10 from, on the forearm - 11-12 from.

The ability to recognize two-dimensional stimuli is examined by asking the patient to determine, with his eyes closed, the numbers, letters and figures that he draws with a pencil or the blunt end of a pin on the skin of the subject.

The stereognostic sense is defined by the ability to recognize coins, a pencil, a key, etc. when touched with closed eyes. The subject evaluates the shape, consistency, temperature, surfaces, approximate mass and other qualities of the object. The complex act of stereognosis is associated with the associative activity of the brain. With the defeat of general types of sensitivity, this is impossible - secondary (pseudoastereognosis). Primary happens with a disorder of higher brain (cortical) functions - gnosis (see Agnosia) .

Sensitivity disorders are often observed in various diseases of the nervous system and, as a rule, are used to clarify the tonic diagnosis, as well as to control the dynamics of the pathological process under the influence of the patient's treatment. Distinguish between quantitative and qualitative violations of Ch. Quantitative are a decrease in the intensity of sensation - or a complete loss of Ch. -. This applies to all types of Ch., analgesia - a decrease or absence of pain Ch., thermoanesthesia - a decrease or absence of temperature Ch., topohypesthesia, topanesthesia - a decrease or loss of localization of irritation, etc. An increase in Ch. - is associated with a decrease in the threshold of perception of one or another irritation . Qualitative disturbances of Ch. include a perversion of the perception of external stimuli, for example: the occurrence of a sensation of pain during cold or thermal irritation, a sensation of a larger size of a palpated object - macroesthesia, a sensation of many objects instead of one - polyesthesia, a sensation of pain in another zone in relation to the injection site - synalgia, sensation of irritation not in the place of its application - alloesthesia, sensation of irritation in a symmetrical area on the other hand -, inadequate perception of various irritations -. Ch. represents a special form of qualitative change - a kind of painful perception of various sharp irritations. With hyperpathy, excitability increases (light irritations are perceived less clearly in the zone of hyperpathy than normal, and intense irritations are sharply painful, extremely unpleasant, painful), irritations are poorly localized by the patient, they are noted for a long time.

Ch.'s disorders include paresthesia - various sensations not associated with any external influence - goosebumps, numbness, tingling, stiffness of skin areas, pain in the hair roots (trichalgia), a feeling of skin moisture, drops of liquid on it (). Especially often, a variety of paresthesias are observed with dorsal tabes (Tapes dorsalis) , funicular myelosis (Funicular myelosis) and other diseases of the nervous system, in which the posterior cords of the spinal cord and posterior roots are involved in the process.

Depending on the localization of the pathological process in the nervous system, various types of disorders of Ch. are observed. When the receptor apparatus is damaged, a local one is observed due to a decrease in the number of receptor points, as well as changes in the threshold characteristics of different types of Ch. .

When a sensory nerve is damaged, two zones of disturbance are detected: anesthesia in the zone of autonomic innervation of this nerve and hypesthesia with hyperpathy in the zone of mixed innervation (overlapping of innervation zones with another nerve). There is a discrepancy between the zones of violation of various types of Ch.: the largest surface is occupied by the area with violation of the temperature Ch., then the tactile one, and least of all - the area of ​​violation of the painful Ch. relatively high temperature (above 37 °) and low (below 20 °), injections are perceived as extremely unpleasant, diffuse, long-lasting sensations. Later (about 1 year later), tactile sensitivity is restored, the ability to distinguish between temperatures from 26 to 37 °, at the same time, the localization error and increased pain stimuli disappear (Ged's - Sherren's law). With damage to the peripheral nerve, all types of sensitivity are disturbed (see Neuritis) . For multiple symmetrical lesions of the peripheral nerves of the extremities (see Polyneuropathies) characteristic is a violation of all types of Ch. according to the polyneuritic or distal type - in the form of gloves on the hands and stockings (socks) on the legs ( rice. 2 ).

With damage to the posterior roots, disorders of all types of Ch. are localized in the corresponding dermatome ( rice. 3 ). With a viral lesion of the spinal node and sensitive root, paresthesia and hypesthesia are combined with herpetic eruptions in the same dermatome (see Ganglionitis) .

With the defeat of the entire diameter of the spinal cord, a conductor of all types develops with an upper border, which indicates the level of the spinal cord ( rice. 4 ). With the localization of the pathological focus above the cervical thickening of the spinal cord, the upper and lower extremities, the trunk appear. This is combined with central tetraparesis, dysfunction of the pelvic organs (see spinal cord) . The pathological focus at the level of the upper thoracic segments is manifested by anesthesia on the lower extremities, central lower paraparesis, and dysfunction of the pelvic organs. When the lumbar segments of the spinal cord are affected, conduction anesthesia captures the lower limbs and the anogenital zone.

The pathology of the thalamus causes Dejerine-Roussy, in which all types of Ch. decrease or disappear on the half of the body opposite to the focus, sensitive and moderate develop in the same limbs, contralateral hemianopsia . Characteristic of the defeat of the thalamus is hyperpathy and central against the background of hypesthesia on the entire half of the body. Thalamic pain is always very intense, diffuse, burning and resistant to analgesics.

With the defeat of the posterior thigh of the internal capsule, the so-called capsular one develops on the half of the body opposite to the focus. It is characterized by more pronounced Ch.'s disorders in the distal extremities, especially on the arm.

A pathological focus in the radiant crown or cerebral cortex ( postcentral) causes monoanesthesia on the face or only on the arm, or only on the leg (depending on the location of the focus and in accordance with the somatotopic representation of sensitivity). with cortical pathological foci, it is more pronounced in the distal parts of the limb, and the muscular-articular feeling and vibrational frequency are more disturbed than the superficial frequency.

When the pathological process is localized in the parasagittal region, both paracentral lobules are simultaneously disturbed and sensitivity is impaired on both feet.

Irritation of the sensitive zone of the cerebral cortex (with, cicatricial adhesive process, etc.) leads to Jacksonian sensitive seizures (see Jacksonian epilepsy) : paresthesias in the face, arm or leg, lasting from a few seconds to minutes without a change in consciousness. With damage to the parietal lobe, more complex types of Ch.'s disturbance develop, a weakening of the ability to discriminate, two-dimensional-spatial Ch., stereognosis, and to determine spatial relationships (topognosis).

Bibliography: Krol M.B. and Fedorova E.A. The main neuropathological syndromes, M,. 1966; Skoromets A.A. diseases of the nervous system, L., 1989.

Rice. 4. Scheme of conduction spinal paraanesthesia with an upper limit on Th X .

Rice. 1. Scheme of conductors of superficial (A) and deep (B) sensitivity: 1 - cell of the spinal ganglion; 2 - cell of the posterior horn of the spinal cord; 3 - spinothalamic tract; 4 - ; 5 - postcentral gyrus (zone of the leg); 6 - cell of the spinal ganglion; 7 - Gaulle's bundle; 8 - Gaulle's beam core; 9 - bulbotalamic tract ().