The structure of the reflex arc is simple drawing. The structure of the reflex arc and the functions of its links. Reflex arc and nerve centers

Reflex arc is a chain nerve cells, necessarily including the first - sensitive and the last - motor (or secretory) neurons.

Reflex arc

The most simple reflex arcs are two- and three-neuron, closing at the level of one segment spinal cord.

In a three-neuronal reflex arc, the first neuron is represented by a sensitive cell, which moves first along the peripheral process, and then along the central one, heading towards one of the nuclei rear horn spinal cord.

Here the impulse is transmitted to the next neuron, the process of which is directed from the posterior horn to the anterior, to the cells of the nuclei (motor) of the anterior horn.

This neuron performs a conductive (conductor) function. It transmits an impulse from a sensitive (afferent) neuron to a motor (efferent) one. The body of the third neuron (efferent, effector, motor) lies in the anterior horn of the spinal cord, and its axon is part of the anterior root, and then spinal nerve extends to the working organ (muscle).

With the development of the spinal cord and brain, the connections in the nervous system also became more complex.

Formed multi-neuronal complex reflex arcs, in the construction and functions of which nerve cells are involved, located in the overlying segments of the spinal cord, in the nuclei brain stem, hemispheres and even in the cortex large brain... The processes of nerve cells that conduct nerve impulses from the spinal cord to the nuclei and cortex of the brain and in the opposite direction form bundles,fasciculi.

The bundles of nerve fibers are called conductive paths.

Pathways

In the spinal cord and brain, according to structure and function, three groups of pathways are distinguished: associative, commissural and projection.

Associative nerve fibers

neurofibrae associationes, connect areas of gray matter, various functional centers (cerebral cortex, nuclei) within one half of the brain. Allocate short and long associative fibers (paths). Short ones connect nearby areas of gray matter and are located within one lobe of the brain (intralobar bundles of fibers). Long associative fibers connect areas of gray matter that are far apart from each other, belonging to different lobes (interlobar bundles of fibers). Long associative paths include the following: upper longitudinal bundle,fasciculus longitudinalis superior; lower longitudinal bundle,fasci culus longitudinalis inferior; hooked bundle,fasciculus uncindtus... In the spinal cord, associative fibers connect cells of the gray matter belonging to different segments and form anterior, lateral and posterior intrinsic bundles(intersegmental beams), fasciculi proprii ventrales, laterales, dorsales

Commissural nerve fibers

neurofibrae commissurales, connect Gray matter the right and left hemispheres, similar centers of the right and left halves of the brain in order to coordinate their functions. Commissural fibers pass from one hemisphere to another, forming adhesions (corpus callosum, vault adhesion, anterior commissure).

Projection nerve fibers

neurofibraeprojectiones, connect underlying departments brain (spinal) with the brain, as well as the brain stem nucleus with the basal nuclei (striatum) and the cortex and, conversely, the cerebral cortex, the basal nuclei with the brain stem nuclei and with the spinal cord. With the help of projection nerve fibers, the ascending and descending systems of fibers are distinguished in the group of projection pathways.

The reflex concept is very important in physiology. This concept explains the automated work of the body to quickly adapt to changes in the environment.

With the help of reflexes, the nervous system coordinates the activity of the body with signals coming from the surrounding external and internal environment.

Reflex (reflection) is the basic principle and way of working nervous system... More general concept - reactivity ... These concepts imply that the reason for the behavioral activity of the organism lies not in the psyche, but outside the psyche , outside the nervous system, and is triggered by signals external to the psyche and to the nervous system - stimuli. Also implied determinism , i.e. predetermined behavior due to the causal relationship between the stimulus and the body's response to it.

The concepts of "reflex" and "reflex arc" refer to in the field of physiology of the nervous system and they must be understood to the level of complete understanding and clarity in order to understand many other topics and sections of physiology.

Definition of the concept

A simple definition of "reflex"

Reflex is responsiveness. You can give such a definition of a reflex, but after that it is necessary to name 6 important criteria (signs) of a reflex that characterize it. They are listed in below, in full definition reflex concepts.

The reflex is a stereotypical automated adaptive responsiveness to a stimulus (irritant).

Reflex in the general broad sense is secondary a phenomenon caused by another phenomenon (primary), i.e. reflection, a consequence in relation to something original. In physiology, a reflex is responsiveness organism to an incoming signal, the source of which is outside the psyche, when the triggering signal (stimulus) is a primary phenomenon, and the reaction to it is a secondary, responsive one.

Complete definition of "reflex"

Physiological definition of the term "reflex arc"

Reflex arc is a schematic pathway for the movement of excitation from the receptor to the effector.

We can say that this is the path of nervous excitement from the place of its birth to the place of application, as well as the path from the information input to the information output from the body. This is what a reflex arc is from a physiological point of view.

Anatomical definition of the term "reflex arc"

Reflex arc is a set of nerve structures involved in the implementation of a reflex act.

Both of these definitions reflex arc are correct, but more often for some reason anatomical definition is used, although the concept of a reflex arc refers to physiology, not anatomy.

Remember that the diagram of any reflex arc must begin with irritant , although the stimulus itself is not part of the reflex arc. The reflex arc ends with an organ effector , which gives a response.

Stimulus - it's such physical factor, which, when exposed to sensory receptors adequate for it, generates nervous excitement in them.

An irritant triggers transduction in the receptors, as a result of which irritation is converted into excitation.

Electric current is a universal irritant, since it is capable of generating excitation not only in sensory receptors, but also in neurons, nerve fibers, glands and muscles.

Variants of the result of the effect of an irritant on the body

1. Launching an unconditioned reflex.

2. Launching a conditioned reflex.

3. Launching an orientation reflex.

4. Launch of the dominant.

5. Launching the functional system.

6. Run emotions.

7. Launching the creation of a neural model (in particular, a sensory image), the learning / memorization process.

8. Launching memories.

There are not so many types of effectors.

Types of effector v:

1) striated muscles of the body (fast white and slow red),

2) vascular smooth muscles and internal organs,

3) external secretion glands (for example, salivary glands),

4) glands internal secretion(for example, the adrenal glands).

Accordingly, the responses will be the result of the activity of these effectors, i.e. contraction or relaxation of muscles, leading to movements of the body or internal organs and blood vessels, or the secretion of secretions by the glands.

The concept of a temporary neural connection

"Temporary connection is a set of biochemical, neurophysiological and, possibly, ultrastructural changes in the brain that arise in the process of a combination of conditioned and unconditioned stimuli and form strictly defined relationships between structural formations underlying various brain mechanisms. The memory mechanism fixes these relationships, ensuring their retention. and reproduction ". (Khananashvili M.M., 1972).

Meanwhile, the meaning of this tricky definition boils down to the following:

Temporary neural connection is the flexible part capaciously reflex arc, formed during the development of a conditioned reflex to connect two undoubtedly reflex arcs. It provides for the conduction of excitation between the nerve centers of two different unconditioned reflexes. Initially, one of these two unconditioned reflexes is triggered by a weak stimulus ("conditioned"), and the second - by a strong ("unconditioned" or "reinforcement"), but when a conditioned reflex has already been developed, then a weak conditioned stimulus is able to trigger an "alien" unconditioned reaction for due to the transition of excitation from its nerve center to the nerve center of a strong unconditioned stimulus.

Types of reflex arcs:

This reflex arc is the simplest, it contains only 5 elements. Although the figure shows more elements, but of them we single out 5 basic and necessary: receptor (2) - afferent ("bringing") neuron (4) - intercalary neuron (6) - efferent ("outgoing") neuron (7, 8 ) - effector (13).

It is important to understand the meaning of each arc element. Receptor : Converts irritation to nervous excitement. Afferent neuron : Delivers sensory stimulation to the central nervous system, to the interneuron. Intercalary neuron : transforms the incoming excitement and directs it along the desired path. So, for example, an intercalary neuron can receive sensory ("signal") excitation, and then transmit another excitation - motor ("control"). Efferent neuron : delivers control excitement to the effector organ. For example, motor stimulation is directed to the muscle. Effector carries out a response.

The figure on the right shows an elementary reflex arc using the knee reflex as an example, which is so simple that it even lacks intercalary neurons.

Pay attention to the fact that on the motor neuron, which ends the reflex arc, many endings of neurons located on different levels nervous system and striving to control the activity of this motoneuron.

4. Double-sided arc conditional reflex E.A. Asratyan. It shows that during the development of a conditioned reflex, counter temporary connections are formed and both stimuli used are both conditioned and unconditioned at the same time.

The figure on the right shows an animated diagram of a double conditioned reflex arc. It actually consists of two unconditioned reflex arcs: the left one is a blinking unconditioned reflex to irritation of the eye with an air stream (the effector is the contracting muscle of the eyelid), the right is the salivary unconditioned relex to irritation of the tongue with acid (effector is salivary gland secreting saliva). Due to the formation of temporary conditioned reflex connections in the cerebral cortex, the effectors begin to respond to stimuli that are inadequate for them normally: blinking in response to acid in the mouth and salivation in response to air blowing into the eye.

5. Reflex ring ON. Bernstein. This diagram shows how the movement is reflexively corrected depending on the achievement of the set goal.

6. Functional system to ensure the appropriate behavior of P.K. Anokhin. This diagram shows the management of complex behavioral acts aimed at achieving a useful planned result. The main features of this model: acceptor of the result of action and feedback between elements.

7. Double arc of the conditioned salivary reflex. This diagram shows that any conditioned reflex should consist of two reflex arcs formed by two different unconditioned reflexes since each stimulus (conditioned and unconditioned) generates its own unconditioned reflex.

An example of an experiment protocol on the development of a conditioned pupillary reflex to sound in a laboratory lesson

Experience number	UR (conditioned stimulus) inadequate for the pupil	Pupil RBR (conditioned response)	BR (unconditioned stimulus) adequate for the pupil	BOR (unconditioned response) of the pupil	Note
Stimuli and reactions	Sound (knock or ringing of a bell)	Extension/Constriction pupil	Darkness/Light(blackout of one eye)	Extension/Constriction pupil	Unconditional response to sound do not register, even if it is. We evaluate only the reaction to blackout.
*Series 1. Obtaining an unconditional response to darkness in the form of pupil dilation*
1.	(-)	(-)	(+)	(+)	Only BOR is observed
…	(-)	(-)	(+)	(+)	Only BOR is observed
10.	(-)	(-)	(+)	(+)	Only BOR is observed
Output : The unconditioned response of the pupil to an adequate BR (darkness) is constantly manifested.
*Series 2. Obtaining an indifferent (indifferent) action of an inadequate conditioned stimulus (sound) on the pupil*
1.	(+)	(+) ?	(-)	(+) ?
2.	(+)	(+)	(-)	(+)	OER (indicative response)
…	(+)	(+)	(-)	(+)	OER (indicative response)
10.	(+)	(-)	(-)	(-)	The irritant is already indifferent
Output : After several repetitions of stimulation inadequate for the pupil, OER disappears and the stimulus becomes indifferent (indifferent).
*Series 3. Development of a conditioned reflex (conditioned response)*
1.	(+)	(-)	(+)	(+)	Only BOR is observed
…	(+)	(-)	(+)	(+)	Only BOR is observed
15.	(+)	(+)	(+)	(+)	UOR appears
16.	(+)	(+)	(-)	(-)	RBB (conditioned response) appears even in the absence of RBB (unconditioned response)
Output : After repeated combination of conditioned and unconditioned stimuli, a conditioned response of the pupil to a conditioned stimulus (sound) that was previously indifferent to it appears.
*Series 4. Obtaining inhibition of a conditioned reflex (extinction)*
1.	(+)	(+)	(-)	(-)
…	(+)	(+)	(-)	(-)	RBM (conditioned response) is observed
6.	(+)	(-)	(-)	(-)
Output : After repeated conditioned stimuli without reinforcement by unconditioned stimuli, the UOR disappears, i.e. the conditioned reflex is inhibited.
*Series 5. Secondary development (restoration) of an inhibited conditioned reflex*
1.	(+)	(-)	(+)	(+)	Only BOR is observed
…	(+)	(-)	(+)	(+)	Only BOR is observed
5.	(+)	(+)	(+)	(+)	UOR appears
6.	(+)	(+)	(-)	(-)	RBR (conditioned reaction) is manifested in the absence of BR (unconditioned stimulus) and BOR caused by it (unconditioned response)
Output : The secondary development (restoration) of conditioned reflexes is faster than the initial development.
*Series 6. Obtaining secondary inhibition of conditioned reflexes (repeated extinction)*
1.	(+)	(+)	(-)	(-)	RBM (conditioned response) is observed
…	(+)	(+)	(-)	(-)	RBM (conditioned response) is observed
4.	(+)	(-)	(-)	(-)	The disappearance of the conditioned response
Conclusion: Secondary inhibition of the conditioned reflex is developed faster than its primary inhibition.
Legend: (-) - no irritation or reaction, (+) - presence of irritation or reaction

Basic form nervous activity is a reflex. Reflex is a causal reaction of the body to changes in the external or internal environment, carried out with the obligatory participation of the central nervous system in response to irritation of the receptors. Due to reflexes, the emergence, change or termination of any activity of the body occurs.

The nervous pathway along which excitement spreads during the implementation of reflexes is called reflex arc.

Reflex arcs consist of five components: 1) receptor; 2) afferent nervous way; 3) reflex center; 4) efferent nerve pathway; 5) effector (working body).

Receptor is a sensitive nerve ending that perceives irritation. In the receptors, the energy of the stimulus is converted into the energy of a nerve impulse. Distinguish: 1) exteroreceptors- are excited under the influence of irritations from environment(skin receptors, eyes, inner ear, nasal mucosa and oral cavity); 2) interoreceptors- perceive irritations from the internal environment of the body (receptors of internal organs, blood vessels); 3) proprioceptors- react to changes in the position of individual parts of the body in space (receptors of muscles, tendons, ligaments, joint capsules).

Afferent nerve pathway represented by the processes of receptor neurons carrying excitations to the central nervous system.

Reflex center consists of a group of neurons located at different levels of the central nervous system and transmitting nerve impulses from the afferent to the efferent nerve pathway.

Efferent nerve pathway conducts nerve impulses from the central nervous system to the effector.

Effector- an executive organ, the activity of which changes under the influence of nerve impulses coming to it through the formations of the reflex arc. The effectors can be muscles or glands.

Reflex arcs can be simple or complex. A simple reflex arc consists of two neurons - a perceiving one and an effector one, between which there is one synapse. A diagram of such a two-neural reflex arc is shown in Fig. 71.

An example of a simple reflex arc is a tendon reflex arc, such as a knee reflex arc.

The reflex arcs of most reflexes include not two, but a larger number of neurons: receptor, one or more intercalated, and effector. Such reflex arcs are called complex, multi-neuronal. A diagram of a complex (three-neuron) reflex arc is shown in Fig. 72.

It has now been established that during the response of the effector, numerous nerve endings present in the working organ are excited. Nerve impulses now from the effector again enter the central nervous system and inform it about the correct response of the working organ. Thus, reflex arcs are not open, but ring formations.

Reflexes are very diverse. They can be classified according to a number of characteristics: 1) by biological significance(food, defensive, sexual); 2) depending on the type of stimulated receptors: exteroceptive, interoceptive and proprioceptive; 3) by the nature of the response: motor or motor (executive organ - muscle), secretory (effector - gland), vasomotor (narrowing or expansion of blood vessels).

All reflexes of the whole organism can be divided into two large groups: unconditioned and conditioned. The differences between them will be discussed in Chapter XII.

Reflex and reflex arc

Reflex(from Lat. "reflexus" - reflection) - the body's response to changes in the external or internal environment, carried out through the central nervous system in response to stimulation of receptors.

Reflexes are manifested in the emergence or termination of any activity of the body: in the contraction or relaxation of muscles, in the secretion or cessation of secretion of the glands, in the narrowing or expansion of blood vessels, etc.

Thanks to reflex activity, the body is able to quickly respond to various changes in the external environment or its internal state and adapt to these changes. In vertebrates, the meaning reflex function The central nervous system is so large that even partial loss of it (with the prompt removal of individual parts of the nervous system or with its diseases) often leads to profound disability and the inability to carry out the necessary vital functions without constant careful care.

The significance of the reflex activity of the central nervous system was fully revealed in the classical works of I.M.Sechenov and I.P. Pavlov. As early as 1862, IM Sechenov in his epoch-making work "Reflexes of the Brain" asserted: "All acts of conscious and unconscious life, according to the mode of origin, are reflexes."

Types of reflexes

All reflex acts of the whole organism are divided into unconditional and conditioned reflexes .

Unconditioned reflexes are inherited, they are inherent in every biological species; their arcs are formed by the time of birth and normally persist throughout life. However, they can change under the influence of the disease.

Conditioned reflexes arise when individual development and the accumulation of new skills. The development of new temporary connections depends on changing environmental conditions. Conditioned reflexes are formed on the basis of unconditioned and with the participation of the higher parts of the brain.

Unconditioned and conditioned reflexes can be classified into various groups on a number of grounds.

By biological value

defensive
indicative
postural-tonic (reflexes of body position in space)
locomotor (reflexes of body movement in space)

By the location of the receptors, the irritation of which is caused by this reflex act

exteroreceptive reflex - irritation of receptors on the external surface of the body
viscero- or interoreceptive reflex - arising from irritation of the receptors of internal organs and blood vessels
proprioceptive (myotatic) reflex - irritation of the receptors of skeletal muscles, joints, tendons

By the location of the neurons involved in the reflex

spinal reflexes - neurons are located in the spinal cord
bulbar reflexes - carried out with the obligatory participation of neurons of the medulla oblongata
mesencephalic reflexes - carried out with the participation of neurons in the midbrain
diencephalic reflexes - diencephalon neurons are involved
cortical reflexes - carried out with the participation of neurons of the cerebral cortex

NB!(Nota bene - pay attention!)

In reflex acts, carried out with the participation of neurons located in the higher parts of the central nervous system, neurons located in the lower parts - in the intermediate, middle, medulla, oblong and spinal cord always participate. On the other hand, with reflexes that are carried out by the spinal cord or the medulla oblongata, the midbrain or the diencephalon, nerve impulses reach the higher parts of the central nervous system. Thus, this classification of reflex acts is to some extent arbitrary.

By the nature of the response, depending on which organs are involved in it

motor, or motor reflexes - muscles serve as the executive organ;
secretory reflexes - end with glandular secretion;
vasomotor reflexes - manifested in the narrowing or expansion of blood vessels.

NB! This classification is applicable to more or less simple reflexes aimed at combining functions within the body. With complex reflexes, in which neurons located in the higher parts of the central nervous system are involved, as a rule, various executive organs are involved in the implementation of the reflex reaction, as a result of which there is a change in the ratio of the organism with external environment, changes in the behavior of the organism.

Examples of some relatively simple reflexes most often studied in a laboratory experiment on an animal or in a clinic for diseases of the human nervous system [show] .

As noted above, such a classification of reflexes is conditional: if any reflex can be obtained with the preservation of one or another section of the central nervous system and destruction of the overlying sections, this does not mean that this reflex is carried out in a normal organism only with the participation of this section: in each reflex, all parts of the central nervous system are involved in one way or another.

Any reflex in the body is carried out using a reflex arc.

Reflex arc- this is the path along which stimulation (signal) from the receptor passes to the executive organ. The structural basis of the reflex arc is formed by neural circuits consisting of receptor, insertion and effector neurons. It is these neurons and their processes that form the path along which nerve impulses from the receptor are transmitted to the executive organ during the implementation of any reflex.

In the peripheral nervous system, reflex arcs (neural circuits) are distinguished

somatic nervous system, innervating the skeletal and musculature

autonomic nervous system, innervating internal organs: heart, stomach, intestines, kidneys, liver, etc.

The reflex arc consists of five sections:

receptors who perceive irritation and respond to it with excitement. The receptors can be the endings of long processes of centripetal nerves or microscopic bodies of various shapes from epithelial cells, on which the processes of neurons end. Receptors are located in the skin, in all internal organs, accumulations of receptors form the sense organs (eye, ear, etc.).

sensitive (centripetal, afferent) nerve fiber transmitting excitement to the center; a neuron with this fiber is also called a sensitive neuron. The bodies of sensory neurons are found outside the central nervous system - in nerve nodes along the spinal cord and near the brain.

nerve center where the switching of excitation from sensory neurons to motor neurons occurs; The centers of most motor reflexes are located in the spinal cord. In the brain, centers of complex reflexes are located, such as protective, food, orientation, etc. In the nerve center, a synaptic connection of the sensory and motor neurons takes place.

motor (centrifugal, efferent) nerve fiber carrying excitement from the central nervous system to the working organ; Centrifugal fiber - long process motor neuron. A neuron is called a motor neuron, the process of which approaches the working organ and transmits a signal to it from the center.

effector- a working organ that carries out an effect, a reaction in response to stimulation of the receptor. The effectors can be muscles that contract when excitation arrives at them from the center, gland cells that secrete juice under the influence of nervous excitement, or other organs.

The simplest reflex arc can be schematically represented as formed by only two neurons: receptor and effector, between which there is one synapse. This reflex arc is called bineural and monosynaptic. Monosynaptic reflex arcs are very rare. An example of them is the arc of the myotatic reflex.

In most cases, reflex arcs include not two, but more neurons: receptor, one or more intercalated and effector. Such reflex arcs are called multi-neuronal and polysynaptic. An example of a polysynaptic reflex arc is the withdrawal reflex of a limb in response to pain stimulation.

The reflex arc of the somatic nervous system on the way from the central nervous system to the skeletal muscle is not interrupted anywhere, unlike the reflex arc of the autonomic nervous system, which on the way from the central nervous system to the innervated organ is necessarily interrupted with the formation of a synapse - the autonomic ganglion.

The vegetative ganglia, depending on their location, can be divided into three groups:

vertebral (vertebral) ganglia - belong to the sympathetic nervous system. They are located on both sides of the spine, forming two borderline trunks (they are also called sympathetic chains)

the prevertebral (prevertebral) ganglia are located at a greater distance from the spine, at the same time they are at some distance from the organs they innervate. The prevertebral ganglia include the ciliary node, the upper and middle cervical sympathetic nodes, solar plexus, superior and inferior mesenteric nodes.

intraorgan ganglia are located in internal organs: in the muscular walls of the heart, bronchi, middle and lower third of the esophagus, stomach, intestines, gallbladder, Bladder, as well as in the glands of external and internal secretion. Parasympathetic fibers are interrupted on the cells of these ganglia.

This difference between the somatic and autonomic reflex arcs is due to the anatomical structure of the nerve fibers that make up the neural circuit, and the speed of conduction of a nerve impulse through them.

For the implementation of any reflex, the integrity of all links of the reflex arc is necessary. Violation of at least one of them leads to the disappearance of the reflex.

Reflex implementation scheme

In response to stimulation of the receptor, the nervous tissue enters a state of excitement, which is a nervous process that causes or enhances the activity of an organ. The excitation is based on a change in the concentration of anions and cations on both sides of the membrane of the processes of the nerve cell, which leads to a change in the electrical potential on the cell membrane.

In a two-neuron reflex arc (the first neuron is a cell of the spinal ganglion, the second neuron is a motor neuron [motoneuron] of the anterior horn of the spinal cord), the dendrite of the spinal ganglion cell has a considerable length, it follows to the periphery as part of the sensory fibers of the nerve trunks. The dendrite ends with a special device for the perception of irritation - a receptor.

Excitation from the receptor along the nerve fiber is transmitted centripetally (centripetally) to the spinal ganglion. The axon of the neuron of the spinal ganglion is part of the posterior (sensory) root; this fiber reaches the motoneuron of the anterior horn and via the synapse, in which signal transmission occurs via chemical- a mediator, establishes contact with the body of the motor neuron or with one of its dendrites. The axon of this motor neuron is part of the anterior (motor) root, through which a centrifugal (centrifugal) signal is sent to the executive organ, where the corresponding motor nerve ends with a motor plaque in the muscle. The result is muscle contraction.

Excitation is carried out along the nerve fibers at a speed of 0.5 to 100 m / s, in isolation and does not pass from one fiber to another, which is impeded by the sheaths covering the nerve fibers.

The process of inhibition is the opposite of arousal: it stops activity, weakens or prevents its occurrence. Excitation in some centers of the nervous system is accompanied by inhibition in others: nerve impulses entering the central nervous system can delay certain reflexes.

Both processes - excitation and inhibition - are interconnected, which ensures the coordinated activity of organs and the whole organism as a whole. For example, while walking, the contraction of the flexor and extensor muscles alternates: when the center of flexion is excited, the impulses follow to the flexor muscles, at the same time the extension center is inhibited and does not send impulses to the extensor muscles, as a result of which the latter relax, and vice versa.

The relationship that determines the processes of excitation and inhibition, i.e. self-regulation of body functions is carried out using direct and feedback connections between the central nervous system and the executive organ. Feedback ("reverse afferentation" according to P.K. Anokhin), i.e. connection between executive body and the central nervous system, implies the transmission of signals from the working organ to the central nervous system about the results of its work at any given moment.

According to reverse afferentation, after the executive organ receives an efferent impulse and fulfills the working effect, the executive organ signals the central nervous system to execute the order at the periphery.

So, when the hand picks up an object, the eyes continuously measure the distance between the hand and the target and send their information in the form of afferent signals to the brain. In the brain, there is a short circuit to efferent neurons, which transmit motor impulses to the muscles of the arm, which produce the actions necessary for taking the object by it. Muscles simultaneously act on receptors located in them, which continuously send sensory signals to the brain informing about the position of the hand at any given moment. This two-way signaling along the chains of reflexes continues until the distance between the hand and the object is equal to zero, i.e. until the hand picks up the object. Consequently, all the time there is a self-examination of the organ's work, which is possible due to the mechanism of "reverse afferentation", which has the character of a vicious circle.

The existence of such a closed circular, or circular, chain of reflexes of the central nervous system provides all the most complex corrections of the processes occurring in the body with any changes in internal and external conditions (V.D. Moiseev, 1960). Without feedback mechanisms, living organisms would not be able to intelligently adapt to their environment.

Consequently, instead of the previous idea that the structure and function of the nervous system is based on an open reflex arc, the theory of information and feedback ("reverse afferentation") gives a new understanding of a closed circular chain of reflexes, a circular system of efferent-afferent signaling. Not an open arc, but a closed circle - this is the latest understanding of the structure and function of the nervous system.

Nervous activity human body involves the conversion of incoming signals. As a result of the transformations that have taken place, there will be responses to stimuli. In order to implement them, the body needs an established relationship from receiving an impulse to responding to a stimulus.

Almost all reflexes are closed within the brain and spinal cord. However, there are those in which the arc is closed outside the central nervous system in the autonomic ganglia or even within the boundaries of a specific internal organ (for example, the heart). The proper functioning of reflexes is the basis for the full flow of impulses, which determines the activity of the central nervous system.

General information

Reflex - a holistic reaction to a stimulus, which is carried out by the central nervous system. It manifests itself in controlled and uncontrolled movements, in the work of the body, in behavioral changes, emotions and receptivity.

The perception of the stimulus is carried out through the activity of the receptors. They are nerve fibers and structures that are susceptible to stimuli. These receptors are able to perceive some of them - sound, light, temperature changes, pressure, etc. Based on these criteria, receptors are divided into corresponding types.

In the process of irritation, excitation is carried out inside the receptor. It begins to convert energy into pulses of electrical origin. The perceived data is received as an electrical signal and is directed along the nerve endings of neurons before contacting with the rest of the nerve fibers. The impulse is transmitted to interneurons, and then to motor neurons. It acts in the same way as from receptive neurons.

Neural circuits enter the central nervous system, where they form the nerve center. The received data is processed, as a result of which a control command is formed. Further, it is sent to the working organ, where the impulse provokes muscle contraction.

Types of reflexes

The reflex involves the body's response to changes in the external or internal environment due to the effect on receptors. They are located on top layer the skin, forming exteroreceptive reflexes inside the vessels.

The response to stimuli by its origin can be conditional or unconditioned.

The latter include reflexes, whose arc was formed even before birth. In the conditional, it is formed under the influence of various external provoking factors.

Classification

The arc is the path through which the impulse is directed to the working body. It is made up of neural circuits. Directly they and their endings form a path through which a signal is transmitted during the implementation of a reflex. There is a certain classification that divides these formations into types.

Polysynaptic arcs

This type includes a 3-neural arc, inside which a nerve center is located in the middle of the receptor and effector. Its manifestation will be withdrawal of the limb as a response to pain.

The polysynaptic arc has a specific structure. Such a chain is bound to go through the brain. Taking into account the location of the neural circuits that process the impulse, the following are distinguished:

spinal;
bulbar;
mesencephalic;
cortical.

When the reflex is perceived upper sections CNS, then neuronal circuits in the lower parts are involved in its processing.

Regardless of the reflex, when the constancy of the arc is disturbed, it disappears. Often, such a rupture can occur due to injury or illness. In complex reflexes, other organs are included in the reaction process, which can cause a behavioral change within the body.

Blink reflex arc

This reaction of the body, due to its own complexity, makes it possible to study such a movement of excitation along an arc, which is extremely difficult to study in other situations. It begins with the activation of the processes of excitation and inhibition at the same time. Given the nature of the lesion, they may become active different areas arcs. Able to induce a blinking reflex trigeminal nerve- reaction to touch, auditory - reaction to noise, visual - response to light amplitudes or perceived threat.

The response is characterized by early and late components. The second is responsible for inhibiting the reaction. For example, touching skin century. The eye will close instantly. With a second touch of the dermis, the reflex will be slower. When the received data is processed, a controlled slowdown of the received reflex is carried out. This slowdown, for example, teaches women to use eye makeup extremely quickly, overcoming the eyelid's natural tendency to close the cornea. Other variations of such arcs are also being studied, but they often have an overly complex structure and do not differ in clarity.

Monosynaptic

Education, consisting of 2 neural circuits, sufficient for the implementation of the signal. A striking example such a structure is a knee reflex. Characteristic feature there will be a lack of connection to the reaction of the parts of the brain. Such a reflex is referred to as unconditioned.

Directly such a reaction will be checked by a specialist as an indicator of the state of the somatosensory NS. In the process of hitting the knee with a hammer, the muscle begins to stretch. The irritant is directed through the afferent fiber to the spinal cord, and the impulse to the efferent fiber. In this experiment, skin receptors are not involved, but the result will be visible and the strength of the response is easily differentiated.

The vegetative arc can be interrupted in sections, forming a connection, while within the animal system, the direction that is overcome by the signal will not be interrupted by anything.

Reflex arc levels

This formation is the anatomical structure of the reaction. Consists of a chain of nerve endings that allows signals to be transmitted to the working organ.

The chain includes the following links:

A receptor that perceives irritation (internal or external). He is responsible for the production of nerve signals.
A sensitive pathway that consists of neurons. Directly through them, the impulse is directed to.
Nervous center with intercalary and motor neurons. The former direct the impulse to the latter, and the latter form teams.
Centrifugal path. Through it, the signal is sent to the working body.
Executive agency.

A necessary condition for a reflex is the integral structure of each section of the arc. The loss of one (due to injury or other circumstances) is associated with the absence of the reflex itself.

System properties

The education in question has the following characteristics:

Adequacy. The ability to respond to a particular stimulus that is formed for a given receptor in an evolutionary way (eye reaction to light changes).
Polymodality. The ability to respond to irritation.
The ability to react with several signals to a stimulus. Frequent signals are sent from some receptors, from 2 - rare, from 3 - in bursts. In view of this, the central nervous system is able to differentiate irritation (pain). The frequency of the signal depends on the strength of the stimulus.
The ability to convert energy into a signal.
Sudden agitation. Self-excitation without the influence of stimuli. It can provoke increased tone fibers of the vegetative NS.
Fluctuation. The ability to change the level of your own arousal. It fluctuates from the state of the fibers of the vegetative NS.
A device. The likelihood of adaptation to prolonged exposure to irritation.

These characteristics are important in the functioning of the reflex arc, which in turn is the basis for the proper functioning of the central nervous system.

Reflex arc implementation

As a reaction to the stimulus is excited, nervous processes occur that form or enhance the function of the organ. The basis of excitability will be a change in the content of anions and cations in the membrane of axons.

In the 2-neural arc, the dendrite of the cell has a significant length; it is directed to the periphery along with the receptive fibers of the nerve endings. It ends with a specific device for processing stimuli - a receptor. Excitability from it along the nerve ending centripetally enters the ganglion. The process of the neuron becomes a component of the dorsal root.

This fiber enters the motor neuron of the anterior horn and through the synapse, where the impulse is transmitted through a mediator, contacts the motor body. Its process becomes a component of the anterior root, through which the centrifugal impulse goes to the working organ. As a result, the muscle contracts.

Excitation is directed through the nerve fibers, separately and does not extend to the rest of the specified process. This is prevented by the sheaths that cover the fibers.

Taxiway braking value

Inhibition is the opposite of arousal. It ends the functioning of the second, slows down or prevents its appearance. Excitation in one center of the NS can accompany inhibition in another: the signals that enter the central nervous system can slow down various kinds of reflexes.

Each of the processes is interconnected, which guarantees the coordinated functioning of the internal organs and the body completely. For example, in the process motor activity there is an alternation muscle contraction flexors and extensors: When the flexor center is excited, signals are sent to the muscles that are responsible for this process. At the same time, the extensor center slows down and does not send signals to the extensor muscles, as a result, they will relax.

The interaction that determines the excitatory and inhibitory processes, that is, self-regulation of the work of internal organs, occurs through direct connections between the central nervous system and the working organ.

The functioning of the body is a conditioned reflex response to irritation. The reflex is his reaction to stimuli, carried out with the help of the central NN. Its anatomical basis is the reflex arc. It is a sequential chain of nerve cells that provide a response, a response to stimulation of receptors. For the body to respond appropriately, it requires a well-established interaction between receiving an impulse before responding to a stimulus.