REFLEX (Latin reflexus turned back, reflected) - the emergence, change or the termination of functional activity of bodies, fabrics or a complete organism which is carried out with the participation of c. N of page in response to irritation of receptors of an organism.
Ideas of the «reflected» activity of an organism as the principle of its organization — i.e. that activity of a complete organism (or its separate parts) on external manifestation is «reflected» at impact on its special structures physical. or chemical environmental factors — were for the first time formulated by the philosopher and the scientist R. Descartes. The term for designation of such activity was offered and entered into physiology by the Czech physiologist I. Prokhaska. As the example characterizing automatic and involuntary reflex activity of an organism, R. Descartes gave a blinking of the person at sudden emergence of a light irritant before eyes and otdergivany hands at sudden painful influence. An important contribution to development of ideas of R. were researches of the Scottish doctor Ch. Bella and the physiologist F. Marangdi. By them it is shown, that sensitive nerve fibrils enter in spinal cord (see) as a part of Back roots, and motive nerve fibrils come out a spinal cord as a part of ventral roots (Bella — Marangdi the law). The determined consistent pattern in distribution of afferent and efferent pathways of spread of activation in a nervous system allowed the English physiologist and the doctor Hall (M. of Hall) in 1850 to offer and prove the term «reflex arc» and to use ideas of a reflex and a reflex arc in clinic. Histologic researches of S. Ra-mon-i-Kakhal put the doctrine about neuron as to a base unit of a nervous system. On the basis of this representation the English physiologist Ch. Sherrington formulated the principles of the neural organization of reflex arcs and proved a concept about synapse (see) as device of inter-neural communication. He considered R. as a functional unit of nervous activity and offered the principles of integration of R. at the level of a spinal cord.
In the second half of 19 century the reflex principle was extended not only to activity of a brain, but gained universal value for an explanation of mechanisms of regulation of functions of separate bodies and a complete organism (see. Reflex theory ). The merit in it belongs to I. M. Sechenov, to-ry in 1863 in the work «Reflexes of a brain» vyskazat a thought that «all acts of adult and unconscious life on a way of an origin an essence reflexes». Based on theoretical provisions, I. M. Sechenova, I. P. Pavlov developed idea of adaptive value of reflex activity in life of zhivoty: and the person also developed the doctrine about conditioned reflexes (see) as to the highest form of adaptation of an organism to living conditions (see. Higher nervous activity ). Works of other domestic physiologists (H. E. Vvedensky, A. A. Ukhtomsky, I. S. Beritashvili) were proved modern ideas of mechanisms of coordination and integration of River. Results of a research of the central mechanisms of formation of R. formed a basis for development by school of P. K. Anokhin of the system principles of the organization of brain processes of a tsra formation of purposeful behavioural acts of animals and the person (see. Functional systems ).
Structural basis of implementation of R. is the so-called reflex arc (fig. 1). Are its part: receptors (see), the perceiving irritants influencing an organism; afferent neurons, to-rye the shoots tie receptors with the centers of a nervous system and provide centripetal: carrying out excitement; structures back and a brain where afferent excitement arrives and where there is its analysis and synthesis; the efferent neurons which are a terminal point of escaping of c. N, page. excitement (see), extending tsentrobezhno on nerve fibrils to the periphery to bodies and fabrics; effectors, or executive bodies (skeletal muscles, glands, internals) realizing the River. Specific reflex reactions can include various number of receptors, afferent and efferent neurons and complex processes of interaction of vozbuzhdeniye in centers of a nervous system (see). Areas of a body, in limits to-rykh are located specialized receptors, irritation to-rykh causes strictly certain R., received the name of receptive (receptor) fields, or reflexogenic zones (see). Napr, irritation of a mucous membrane of a nose causes River. sneezing (see), and a mucous membrane of an eyeglobe — River. blinkings (see). Reflexogenic zones form according to the inborn program of development and maturing of a nervous system of an individual owing to what are a «rigid» link in R.'s implementation on the «incentive — reaction» type.
An afferent way of carrying out excitement from receptors in c. the N of page can include from one up to several afferent nervous cells (see. Nervous cell ). The first nervous cell which is directly connected with a receptor is called receptor, the subsequent — often call touch, or sensitive. They can be located at various levels of c. N of page, beginning from a spinal cord and finishing afferent zones of bark of big hemispheres (see. Cerebral cortex ). The afferent nerve fibrils which are shoots of receptor neurons carry out excitement from various receptors with various speed (see. Nerve fibrils ). On J. Erlan-ger and G. Gasser (1937) classification the majority of afferent nerve fibrils concerns to group A (to subgroups α, β, γ) and carry out excitement with a speed from 12 to 120 m/s. Afferent fibers belong to this group, to-rye depart from tactile, temperature, pain receptors and mechanioreceptors (see). Different excitability of receptors and various speed of carrying out impulses on afferent fibers create a geterokhroniya of receipt of vozbuzhdeniye in structures back and a brain (a so-called heterochronic reflex arc).
Processes of transition of excitement from afferent neurons to efferent are carried out in nerve centers. The simple reflex arc consists of two neurons — receptor and effector (so-called two-neural, or monosinaptiche-Skye a reflex arc). It means that excitement from group of afferent nervous cells passes directly to group of motor-neurons, to-rye send excitement to muscles, causing their reduction (e.g., knee R.). In the majority of reflex arcs distribution of impulses from afferent neurons on effector is carried out through numerous inserted (intermediate) nervous cells (so-called polisinaptichesky reflex arcs). Depending on the level of an arrangement of nerve centers of various reflex arcs distinguish R.: spinal (are located in segments of a spinal cord); bulbar (are located in a myelencephalon); mezentsefalny (are located in structures of a mesencephalon); diencephalic (neurons of a diencephalon are involved); cortical (i.e. with participation of various areas of a cerebral cortex). The structural organization of a nerve center is most studied at the level of back and a myelencephalon; in overlying departments of a brain millions and billions of neurons, morphological bonds between are involved in reflex reactions to-rymi are still insufficiently studied.
Effector neurons are final instance of an exit of excitement from a nerve center to executive body (effector).
Mechanisms of formation and R.'s implementation are connected with structurally functional features of all links of a reflex arc. The time slice from the moment of impact of an irritant on receptors prior to change of a functional condition of an effector is designated as the latent (hidden) period, or R.'s time E.g., at the person knee R.'s time makes 0,0196 — 0,0238 sec., R.'s time of a blinking at bright illumination of eyes — 0,05 — 0,2 sec., and R.'s time of expansion of skin vessels reaches 20 sec.
Rate of propagation of excitement on afferent and efferent fibers is size rather stable. Duration of implementation of reflex reaction more depends on time of passing of excitement through a nerve center (so-called central time of R.). It depends on quantity of interneuronels, on the number of synoptic switchings between neurons and on time of a synaptic delay in the course of transfer of excitement from neuron to neuron. So, the central time of knee R. makes only 0,003 sec., and R. blinkings — 0,036 — 0,186 sec.
Fiziol. properties P. (size, duration, dynamics of implementation) and feature of carrying out excitement are determined by reflex arcs by conditions of irritation — adequacy of the influencing irritant, physical. parameters of an irritant, level of excitability of receptors, and also functional condition of nerve centers (mainly condition of the synoptic device).
Thus, in reflex arcs excitement is always carried out in one direction — from receptors to afferent neurons and from them to efferent neurons. It is caused by the unipolar conductivity in mezhneyronalny synapses connected with the mechanism of chemical transfer of an impulse from a presynaptic membrane on postsynaptic. Existence of genetically programmed «rigid» bonds between neurons in a nerve center causes structural isolation of carrying out excitement on reflex arcs. However due to formation of dynamic functional linkages between nervous cells in the course of post-natal development of an individual there is an association P. in the composite reactions of a complete organism providing its viability in the changing conditions of the environment.
Fiziol. patterns of spread of activation between neurons in the reflex center are rather well studied at the level of a spinal cord on the example of segmented motive Rubles. Segmented reactions to external irritation represent the most elementary form P., and all further evolution of a nervous system went on the way of development of the nadsegmentar-ny device. From this point of view segmented R. is the main type of reaction to external irritation, and all highest forms of these reactions are essentially gradual complication of the reflex act. Neyrofiziol. mechanisms of transition of excitement from afferent ways on motor-neurons at the level of segments of a spinal cord can be investigated by electrophysiologic methods (see. Electrophysiology ). So, in an experiment on an animal the irritation impulses of electric current of the central end of the cut back root is followed by emergence in a ventral root of the same segment of the bioelectric phenomena accompanying segmented R. (fig. 2). The first monophase fluctuation of potential appears with stage of latency about 1,5 ms, lasting 1 — 3 ms and reflects synchronous volley of impulses in axons of many motor-neurons. This answer is called monosinaptichesky (monosinaptichesky carrying out). It is followed by a series of fluctuations of potential with a smaller amplitude lasting 10 — 15 ms and representing the late activity of other motor-neurons (polisinaptichesky carrying out).
In normal operating conditions of a nervous system receptors, signals to-rykh go to any segment of a spinal cord, are never excited at the same time. The first volleys of impulses coming to a nerve center cannot cause in effector neurons of the extending excitement, but cause partial depolarization of many motor-neurons. This depolarization remains during several milliseconds and can be summed up with the depolarization caused by the following volley of impulses from receptors that leads to response of nervous cells. Such phenomenon received the name consecutive, or temporary, summations of vozbuzhdeniye. Along with temporary summation in segments of a spinal cord summation of vozbuzhdeniye can be carried out simultaneous, or space. It is expressed that R. arises at simultaneous irritation of several receptors territorially remote from each other, but belonging to the same receptor field. In this case the separate neuron is excited, as a rule, if several synapses located on it give at the same time exciting postsynaptic potentials (EPP). The phenomenon of summation of vozbuzhdeniye in segments of a spinal cord is possible thanks to convergence (convergence) of vozbuzhdeniye to one nervous cell. The mechanism of convergence provides a possibility of integration of two or more arriving to neuron vozbuzhdeniye, coming from various sources. E.g., motor-neurons of a spinal cord can receive impulses on fibers from peripheral receptors, on the fibers connecting segments of a spinal cord on a reticulospinal way and on box-Tiko-spinal fibers. Interaction of the heterogeneous vozbuzhdeniye converging to neurons can be shown in phenomena of occlusion or simplification. The phenomenon of occlusion consists in change of amount of the excited neurons at simultaneous irritation of two afferent entrances to segments of a spinal cord that leads to decrease in strength of the expected Ruble. The central simplification is characterized by opposite effect when at simultaneous irritation of afferent entrances R.'s force appears more arithmetic sum of reactions at separate afferent irritation.
A necessary condition of optimum transfer of vozbuzhdeniye from an afferent part of a reflex arc on efferent through a nerve center is the sufficient metabolic rate of nervous cells and their supply with oxygen. Even insignificant hypoxia (see) leads to disturbance of mezhneyronalny transfer of vozbuzhdeniye and disorder of reflex reactions. Sharply also narcotic substances (morphine, alcohols, strychnine) changing excitability of nervous cells and interfering with mechanisms of synoptic transfer of vozbuzhdeniye break reflex activity.
Idea of a reflex arc and R. should be considered only as the scheme, convenient for the analysis, in a cut the neurons which are surely participating in this or that reflex act are shown. It is always necessary to consider that nervous impulses (see. Nervous impulse ) at any R. are capable to extend widely in c. N of page on numerous conduction paths. Even at a spinal animal where integrity of a nervous system is sharply broken, R. is carried out not by one reflex arc, but several. Morphological researches at the level of segments of a spinal cord convincingly show that through one afferent entrance, impact on considerable number of efferent neurons (fig. 3) can be made.
The general principles of spread of activation in the centers of a nervous system allow to understand nek-ry mechanisms of coordination of River. In particular, relationship between R. can be expressed in mutually assistance each other (alliirovanny R.), rendering at each other the braking influence (antagonistic R.); difficult reflex acts, in to-rykh one R. emergence of the following etc. causes, received chain R.' name (see. Chain reflex ).
Classification of reflexes
the Uniform standard classification does not exist. All R. of animals and the person are divided by I. P. Pavlov's classification on inborn (unconditional), being specific and rather constant (see. Instinctive reflex ), and individually acquired (conditional), carrying changeable and temporality (see. Conditioned reflex ). Then, on the biological importance for an organism, food, sexual, defensive, approximate and research, homeostatic Rubles allocate. According to a type of receptors, on to-rye the specific irritant works, and the place of their arrangement distinguish the interoceptive R. (arising at impact of factors of internal environment of an organism on interoretseptor, e.g. R. with osmo-, chemo - or baroreceptors), the exteroceptive R. (arising at action of irritants of the environment, napr, visual, acoustical, olfactory R.), the proprioceptive R. (arising at mechanical irritation of muscle and tendinous receptors during reduction and stretching of skeletal muscles).
On localization of an efferent part of reflex arcs of R. are subdivided into two big groups: 1) the somatic R. having the effector device cross-striped (skeletal) muscles and which are shown in motive acts, napr, static and statokinetic (locomotory) R.; 2) vegetative reflexes (see), the effector device to-rykh are smooth muscles of internals, a muscle of heart, secretory glands; allocate also somato-vegetative R.' group (e.g., oculocardic and palatal and cordial reflexes). All motive R. (see. Motor reactions ) are grouped or designated separately depending on change of a functional condition of the corresponding muscle or group of muscles (e.g., vypryamitelny R., pharyngeal R., scapular R., buttock R., bottom R.). Vegetative R. differentiate on the functions changing in various bodies and fabrics (e.g., secretory, vascular, respiratory R.). Practically any R. can be designated on any compound component of a reflex arc — i.e. on receptors, with to-rykh R. (hemoretseptivny, baroretseptivny, etc. R.), on the level of structures ts.n is caused. page where there is the main center of implementation of R. (spinal, bulbar, etc. R.) and on effector changes (deglutitory, blink, tussive, etc. R.). On the nature of influences on activity of an effector of R. can be exciting, defiant or strengthening functioning of body, and brake, suppressing its work (e.g., reflex strengthening of action of the heart at sympathetic influences and braking at parasympathetic).
Evidence of communication of an organism with the outside world by means of R. made it the philosophy for an explanation of any forms of behavior of animals and the person, and the three-membered reflex arc was the convenient schematized structure for understanding of mechanisms of implementation of River. Manifestation of rigid communication between the operating incentive and response formed base for the formulation of original positions of the reflex theory: 1) exclusive value of an incentive; 2) the forward course of excitement on a reflex arc; 3) The river comes to an end with a reflex effect. The last provision of the reflex theory in essence «stopped» understanding of dynamics of development of behavior of an organism and did not disclose adaptive value P. The doctrine about a conditioned reflex of I. P. Pavlov allowed to take a step forward in development of the reflex theory and knowledge of mechanisms of a reflex effect. Conditional R.'s understanding as adaptive act of a live organism to changes of the environment inevitably led to formulation of the question about usefulness of result of a reflex effect, and its development led P. K. Anokhin to justification of ideas of the physiological device of anticipation and assessment of results of action on the basis of receipt in a brain of the «return» afferentation (see. Acceptor of results of action ). The analysis of mechanisms of functioning of an acceptor of results of action allowed P. K. Anokhin to formulate bases of the theory of functional system and to develop the principles of the system organization of processes vts. N of page during the formation of any behavioural act of the person and animals. System ideas of the organization of brain processes replaced former views of linear distribution of vozbuzhdeniye in the central part of a reflex arc from afferent structures to efferent. The system organization of processes in c. the N of page first of all includes synthesis of all afferent vozbuzhdeniye on the basis of the dominating motivation and mechanisms of memory (see. Afferent synthesis ). Prestarting integration of vozbuzhdeniye is as a result created, edges it is developed finally in efferent processes. Thus, exclusiveness of the operating irritant concerning the determined reflex reaction is lost, and focus of behavior will be defined by internal state of an organism and character of the environment at the moment.
In the comparative and physiological plan of reaction, externally similar R., and proceeding on the «incentive — reaction» type are observed already at infusorians, at to-rykh a role of receptors carry out special fibers of cilia, and a role of an effector — cytoplasm. At sponges irritants are perceived by special epithelial cells, and at the highest coelenterates communication of the perceiving cells of an epithelium with muscle cells is carried out through neurosaws. Nervous a ganglion of worms already have internuncial neurons between sensory and motive cells. Development of a ganglionic nervous system correlated with segmentation of a body; arthropods to complication of bodies of the head have a further differentiation of head nerve knots. At vertebrate animals the general type of the organization of a nervous system sharply becomes complicated, various departments of a brain begin to develop. Sharp increase in true R. with wide specific receptive fields and a variety of reflex answers also is connected with it. At mammal R. are made out already during pre-natal development, and their formation in pre-and postnatal-number ontogenesis is connected with dynamics of myelination of nerve fibrils and ways to c. N of page (see. Nervous system ).
Development of reflex activity
Development of reflex activity takes place several stages in an embryogenesis: 1. Primary motive R.' stage (the first R. are found in embryos of the person on the 3rd month of prenatal development and are shown in the form of bending of a neck, the movement of parts of a trunk and extremities at irritation of lips and wings of a nose, and implementation of reactions is provided with the reflex arcs passing through kernels of a trifacial in a myelencephalon and through a cervical thickening of a spinal cord). 2. A stage of primary generalization of R. (reactions are shown in the form of bystry movements of the head, trunk and konechg awns). 3. A stage of secondary generalization of R. (any body part becomes a reflexogenic zone practically, and big groups of muscles are involved in motor reactions; thus broad irradiation of excitement in c, N of page is observed, edges in later period of embryonic development goes down and R. become more limited and specialized). 4. A stage of specialization of R. (difficult food — sucking, deglutitory, protective — chesatel-ny, otryakhivatelny and adjusting — cervical, labyrinth R. form). Very much early are found in a human fruit bottom, knee and prehensile
R. V the post-natal period there is a bystry consolidation of R., ready at the birth, and also formation new within the developing analizatorny systems. Further coordination of reflex acts happens due to maturing of synoptic structures and mechanisms of central braking (see). In later terms of the post-natal period such composite specialized reactions as, e.g., form approximate and research reaction (see).
Various age periods of the person are characterized also by distinctions in degree sformirovannostp for century of N and stability of the main inborn Rubles. In process of aging of all organism in nervous cells there are irreversible structural changes reducing them functionality (falling of excitability, reduction of speed of carrying out excitement). Inertness of processes develops in c. N of page, are weakened brake processes, time of reflex reactions increases.
The research P. is conducted by means of the special refleksometr allowing to determine key parameters and extent of manifestation of reflex reactions (see. Refleksometriya ). In a wedge, practice the main somatic and vegetative R. of the person estimate visually during the drawing irritations on razlich-iy reflexogenic zones. Technology of calling of R. consists in striking a blow by a percussion hammer on a sinew or a periosteum; the irritation of skin, mucous membranes carry out special objects (a stupid needle, a voloskovy brush, a paper strip). For the analysis of the central mechanisms of implementation of R. use widely applied electrophysiologic methods of a research.
Reflexes in neuropathology
In neurologic clinic especially often investigate the instinctive somatic reflexes which are shown reduction of one or several skeletal muscles in extremities, a trunk or the head, and R. classify but to the location of the receptor perceiving irritation.' The group of reflexes has essential practical value in clinic, in to-rykh a receptor is in depth of the muscle (deep reflexes, or proprpotsep-tivny R.).
In the following group P. the receptors which are stuffed up in skin or mucous membranes (superficial, or exteroceptive R.) are exposed to irritation. The irritation of receptors of internals, mucous digestive tract, respiratory tracts, etc. is the cornerstone of studying of interoceptive reflexes. Allocate also so-called telereceptive R.' group, at to-rykh irritation it is perceived at distance (visual, acoustical, olfactory R.).
About a wedge, the points of view it is important to represent accurately an arrangement of the neurons making an arch everyone explored by the River. On safety or these R.' change judge extent of functional and morphological disturbance of the specified structures of a brain. In it major importance of reflexes consists in topical diagnosis of defeat of a nervous system (see. Topical diagnosis ). The more simply the reflex arc is constructed, the value of this reflex for topical diagnosis is more.
And constant the proprioceptive R.' arches consisting of two neurons are the simplest (receptor and effector). For an example it is possible to give an arch of the knee jerk which is constantly investigated at patients in clinic. Knee jerk (see) is caused by blow of the neurologic hammer in a patellar ligament (lig. patellae). The chetyrekhglavy muscle of a hip is in reply reduced and there is an extension of a shin. An afferent neuron of an arch of this R. is the sensory cell of an intervertebral ganglion (L2 — L4). The dendrite of this neuron has a spiral-shaped receptor in a muscle spindle the four-head of a muscle of a hip and is a part of a femoral nerve. The axon of a sensory cell as a part of the corresponding back spinal root enters a back horn of a spinal cord and comes to an end with synoptic communication with an efferent neuron (and - motor-neuron) a front horn of a spinal cord. The axon of this motor-neuron as a part of a ventral spinal root goes out of the vertebral channel through an intervertebral opening, passes through a lumbar texture and as a part of a femoral nerve reaches the four-head of a muscle of a hip, coming to an end with a neuromuscular synapse with its extrafusal muscle fibers. A long time this R.'s mechanism contacted irritation of Golgi's receptor who is in a sinew. However in fiziol. experiments it was established that tendon jerks by the nature are reflexes on stretching.
The main activator of tendinous R. is stretching of a muscle spindle that leads to irritation in his bag of a spiral-shaped receptor of a cell of a spinal ganglion. Thus, tendinous R.' mechanism is more difficult, than was considered earlier. It is more correct to call them not «tendinous», but myotatic or deep. The river on a muscle strain is carried out by the interfaced action and - and at - motor-neurons of front horns of a spinal cord. u-Motoneyrony can put intrafusal sokratitelny elements in action that facilitates formation of River. As for a tendinous receptor of Golgi, it is a receptor for carrying out impulses of the ss-motor-neurons braking activity. The axon of this sensitive neuron comes to an end at an inserted cell, by means of a cut contacts with and - motor-neuron. If stretching of a spindle is made slowly, the reflex gains tonic character. Degree of tension of a muscle coming at this moment is criterion for measurement of its tone. At short and abrupt irritation R.'s hammer becomes «phasic», the response movement has the nature of single short reduction of a muscle.
The three-neural arch is characteristic of exteroceptive R. Also more complex combinations of reflex mechanisms when between receptor and effector neurons there are internuncial neurons are possible. Such mnogozvenyevy chains of neurons are the cornerstone of difficult R. (see. Postural reflexes , Conditioned reflex , Chain reflex ).
In clinic the considerable number P., having a similar structure of a reflex arc is investigated (see the tab.). The special technique of a research is developed for each of them. Deep R. are caused by striking a blow a neurologic hammer on the corresponding sinew or ledges of shoots of a bone (periosteum). Blows a hammer should be struck with an identical force; at R.'s calling it is necessary to try to obtain from sick perhaps full relaxation of the studied extremity. At R.'s assessment pay attention to their expressiveness and symmetry. Therefore the same R. should be investigated on the right and at the left. R.'s expressiveness at healthy people can individually fluctuate.
R.'s changes can have quantitative and qualitative character. R.'s increase carries the name of a hyperreflexia, R.'s absence — areflexias (see), and irregularity — anizorefleksiya. R.'s irregularity usually indicates organic lesion of a brain or nerve. Localization and nature patol. process in a nervous system is established on the basis of comparison of irregularity of R. to other symptoms (prevalence of paralysis of muscles, a zone of disorders of sensitivity, etc.). For graphic reproduction of the reflex act and digital expression of its intensity it is possible to use refleksometra (see. Refleksometriya ).
At various diseases of a nervous system the following changes of R. are observed: decrease or loss (at damage of a reflex arc at any level), increase and a perversion (at defeat of pyramidal or extrapyramidal systems and a disinhibition of the segmented device of a spinal cord and a brain trunk). Decrease or loss of deep reflexes on hands is observed at neuritis (see), plexites (see), spondilogenny cervical radiculitises (see), myelosyringoses (see), hematomyelias (see), poliomyelitis (see), miyeloishemiya (see. Spinal cord ), polyneuritis (see), etc. On the lower extremities these R. are oppressed at discogenic lumbosacral radiculitis (see. Radiculitis , Osteochondrosis ), back to tabes (see), an injury of a spinal cord (see. Vertebral and spinal injury ) and others patol. states.
At damage pyramidal system (see), beginning from bark of a pretsentralny crinkle of a brain and finishing the level of decussation in a myelencephalon, deep R.' increase on extremities of the opposite side comes to light. If the pyramidal path is destroyed in a side cord of a spinal cord, then the hyperreflexia arises on the party patol. center.
At defeat of pyramidal system, except quantitative changes (deep R. are raised, superficial belly are reduced or lost), also qualitative changes are observed — the reflex reactions not inherent to a normality appear. These R. are designated as pathological (see. Reflexes pathological ).
To number patol. Rubles belong so-called inverted reflexes: at a certain R.'s calling there is a reflex reaction in the form of reduction of antagonists of those muscles, the irritation was directed to a reflexogenic zone to-rykh. E.g., during the calling of an akhillov of R. in response to blow in an Achilles tendon muscles of a front bed of a shin are reduced and foot makes a dorsiflexion instead of the expected bottom. Similar paradoxical R. can arise also on hands during the calling biceps reflexes (see). Paradoxical R. can be observed at flaccid and central paralyzes (see. Paralyses, paresis ). At the central paralyzes they are caused by irregularity of increase in excitability in various muscular groups. At flaccid paralyzes irradiation of irritation in the next segments or groups of neurons for antagonistic muscles is the main reason for paradoxical R., the innervation to-rykh is kept.
A pathological reflex — the reaction of a nervous system having diz-adaptive value for an organism as breaks adaptive opportunities of an organism and can play a role of the pathogenic factor promoting further development this or to emergence new patol. process (see. Adaptation ). These features distinguish pathological R. from physiological, arisen in the course of evolutionary as the mechanism «equilibrations of development of an organism with Wednesday and having adaptive value for an organism» (I. P. Pavlov).
Pathological R. forms on the basis of physiological R. and the corresponding physiological R. consists of the same structures, as, however functional relationship between these structures is changed. An indispensable condition of emergence of pathological R. is disturbance of activity of a nervous system of various character, beginning from disturbances molecular and membrane physical. - chemical mechanisms and finishing rough destructive changes and morfol. defects of fabric of a nervous system.
The etiological factors creating conditions for pathological R.'s emergence can be an exogenous and endogenous origin (effect of toxins, microbes, viruses, the general and local hypoxia of c. N of page, disturbance of microcirculation and exchange in these or those departments of c. N of page, cicatricial changes in nervous tissue, disturbances of endocrine system, etc.) * Pathological R. can arise also owing to an intensive afferent impulsation, the edge is not suppressed with physiological mechanisms. And; P. Pavlov described as unconditional pathological R. the ulceration and other changes in an oral cavity at dogs arising owing to visceral irritations at internals operations.
At the heart of pathological R. which are characterized by a functional hyperactivity hypersecretion lies mediators (see) or formation of generators patholologically the strengthened excitement in functionally important links of the reflex device (see. Nervous system, pathological physiology ). A pathogenetic condition of emergence and activity of such structures is insufficiency of brake control of secretion of mediators or activity of the corresponding population of neurons. These external irritants can matter only starting, provocative incentives, and then, already at height of development of process, patol. reactions can be provoked by other irritants.
Pathological R. can be various degree of complexity, be implemented by different departments of c. N of page and to cover various fields of activity of a nervous system, to be shown in the form of touch, motive, emotional, vegetative and other frustration. In neuropathology the pathological R. arising at damages of the central motive office are described (Babinski's reflexes, Rossoli-mo, a grasp reflex, a sucking reflex and so forth). Many of these reflexes represent the reactions characteristic of certain stages pre-and the early post-natal period. They are a consequence of universal pattern of a disinhibition in the conditions of pathology inhibited it is normal of mechanisms. Works of I. P. Pavlov and his employees described the conditional pathological R. arising at a combination of the indifferent irritations causing biologically useful, adaptive, reactions with patol. effects or patol. states; in these conditions the specified irritations become starting incentives for a call of pathological effects. Vegetative pathological R. can be shown in the form of vascular disorders, disturbances of secretion, diskineziya of band bodies, etc. Their special form as I. P. Pavlov and A. D. Speransky showed, dystrophic changes in various fabrics are.
Also R.'s perversions in the form of replacement of brake effects with exciting are among pathological R.; this phenomenon represents not true transformation of brake processes in exciting, and identification, in connection with loss of the brake control oppressed normal and strengthened in the conditions of pathology of an exciting component of brake reactions — disturbance of the principle of a dual functional innervation (see. Nervous system, pathological physiology ). Pathological R. can be expressed also as loss of functions if the structures providing normal brake influences are overstimulated. The phenomena of paresis at intensive afferent an incentive yatsrsh, suppression of spinal reflexes at hyper activation of nek-ry educations can be an example of such effects reticular formation (see), disbalance of tonic influences at damage cerebellum (see) or vestibular nuclei (see. Vestibular analyzer ), (inhibiting) influences patholologically strengthened dominant, etc.
Physiological R.' change and their turning into pathological can happen as well owing to changes in the device of their regulation, to-rye can arise at the different levels of regulation, including and at the level of working effector body at its damages, change of chemism of his environment, change of reactivity of the receptors connecting mediators, peptides, hormones, etc. In such conditions can arise pathological reaction (see), e.g., the perverted reaction (a spasm instead of expansion) coronary and brain vessels at effect of physiologically active agents, etc.
See also Reflexes pathological .
Table. The main reflexes investigated in neurologic practice, a way of their detection, manifestation, level of short circuit of a reflex arc
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Yu. A. Fadeyev; D. K. Bogorodinsky, A. A. Skoromets (not BP.), G. N. Kryzhanovsky (patol. reflex).