Other

Conditioned and unconditioned reflexes. Reflex concept

When classifying the diverse reflexes of the human and animal body, they are taken into account various signs and manifestations. All reflexes by origin are divided into unconditional (congenital or specific) and conditional (acquired during the individual life of an animal or person, developed under certain conditions).

Based on biological significance reflexes for the body are divided into:

– on protective, aimed at moving away from the stimulus;
– food, ensuring the acquisition, consumption and digestion of food;
– sexual, ensuring continuation of the family;
– indicative, or research, ensuring body rotation and movement towards a new stimulus;
– postural-tonic, or reflexes of body position in space ;
– locomotor, providing movement of the body in space.

Depending on the location of the reflex arc receptors, there are:

– exteroceptive reflexes that occur in response to irritation of body surface receptors;
– proprioceptive reflexes that occur in response to irritation of receptors in muscles, tendons and joints;
– visceroceptive reflexes that occur in response to receptor stimulation internal organs.

Depending on the organs whose activity is ensured by this reflex, cardiac, respiratory, vascular and other reflexes are distinguished.

Reflexes are also distinguished by the nature of the responses: secretory, expressed in the release of secretion produced by the gland; trophic, associated with changes in metabolism; motor, or motor, characterized by the contractile activity of striated and smooth muscles(the most diverse group of reflexes). Motor reflexes include flexion, rubbing, scratching reflexes and others that occur when the skin is irritated; sucking reflex in a child; protective reflex when the cornea of the eye is irritated - blinking; pupillary reflex- constriction of the pupil when exposed to light and dilation in the dark.

Motor proprioceptive reflexes occur when muscle and tendon receptors are stimulated. So, when the tendon of the quadriceps femoris is hit, as a result of its stretching, a reflex extension of the leg at the knee occurs - the knee reflex; when the Achilles tendon is hit - the Achilles reflex.

Vasomotor reflexes involve the constriction and dilation of blood vessels.

Visceromotor reflexes are motor reflexes that occur when receptors are stimulated smooth muscle internal organs, they ensure the movements of the stomach, intestines, bladder, ureters, etc.

All the reflexes described above, depending on which parts of the central nervous system are involved in their implementation, are divided:

– on spinal (carried out with the participation of spinal cord neurons);
– bulbar (involving neurons medulla oblongata);
– mesencephalic (involving the midbrain);
– diencephalic (featuring diencephalon);
– cortical (involving cortical neurons cerebral hemispheres brain).

Spinal reflexes include flexion, which occurs when pinching a frog’s leg with tweezers, rubbing, which occurs when the frog’s skin is irritated with a piece of paper soaked in sulfuric acid, etc., as well as reflexes from the tendons of the limbs. The sucking and blinking reflexes are carried out with the participation of the medulla oblongata, and the pupillary reflexes - the midbrain.

The regulation of any function involves the participation of different parts of the central nervous system, therefore the classification of reflexes according to the parts of the brain involved in their implementation is relative. It's about only about the leading importance of neurons of one or another part of the central nervous system.

Inhibition in the central nervous system – active process, manifested in the suppression or weakening of excitation. In contrast to excitation, inhibition by nerve fibers does not apply.

The phenomenon of inhibition in nerve centers was described by I.M. Sechenov in 1862. Much later, the English physiologist Sherrington discovered that the processes of excitation and inhibition are involved in any reflex act.

Braking value:

– coordination - the process of inhibition ensures orderliness or coordination in the work of nerve centers, for example, to bend an arm, it is necessary to excite the flexion center, which sends nerve impulses to the biceps, and inhibit the extension center, which sends nerve impulses to the triceps;
– protective – under the influence of super-strong stimuli in the nerve center, not excitation, but inhibition develops, as a result, reserves of ATP and transmitter are restored;
– limitation the influx of afferent impulses into the central nervous system of secondary information of little significance for life.

There are presynaptic and postsynaptic inhibition. With presynaptic inhibition, the inhibitory effect is realized on the presynaptic membrane; this type of inhibition is involved in limiting the influx of sensory impulses into the brain. Postsynaptic inhibition occurs on the postsynaptic membrane. This is the main type of inhibition; it develops in special inhibitory synapses with the participation of inhibitory mediators that suppress the ability nerve cell generate excitation processes.

According to neural organization, inhibition is divided into translational, recurrent, lateral (side) and reciprocal.

1. Progressive inhibition is caused by the inclusion of inhibitory neurons along the path of excitation.
2. Returnable inhibition is carried out by intercalary inhibitory neurons (Renshaw cells). Impulses from motor neurons through collaterals extending from its axon activate the Renshaw cell, which, in turn, causes inhibition of the discharges of this neuron. This inhibition is realized through inhibitory synapses, formed by a cell Renshaw on the body of the motor neuron that activates it. Thus, a circuit with negative feedback is formed from two neurons, which makes it possible to suppress excessive activity of the motor neuron.
3. Lateral inhibition is the process of inhibiting a group of neurons located next to a group of excited cells. This type of inhibition is common in sensory systems.
4. Reciprocal, or conjugate, inhibition is based on the fact that signals along the same afferent pathways provide excitation of one group of neurons, and through intercalary inhibitory cells cause inhibition of another group of neurons. It manifests itself, for example, at the level of motor neurons of the spinal cord innervating antagonist muscles (flexors - extensors of the limbs). When bending an arm or leg, the centers of the extensor muscles are inhibited. A reflex act is possible only with conjugate inhibition of antagonist muscles. When walking, bending the leg is accompanied by relaxation of the extensors, and vice versa, when extending, the flexor muscles are inhibited. If this did not happen, then a mechanical struggle of the muscles, convulsions, would arise, and not adaptive motor acts. Violation reciprocal inhibition underlies motor disorders accompanying many motor development disorders in childhood.

During ontogenesis, due to the development of inhibitory neurons, inhibitory mechanisms of the central nervous system are formed. Their early form is postsynaptic inhibition, later presynaptic inhibition is formed. Thanks to the formation of inhibitory mechanisms, the irradiation of excitation into the central nervous system, characteristic of newborns, is significantly limited, unconditioned reflexes become more accurate and localized.

Coordination of reflex activity- this is the coordinated interaction of nerve centers to ensure any process. Coordination of functions ensures reflex acts corresponding to influences external environment and manifested from the outside various systems(muscular, endocrine, cardiovascular). For example, when running, the flexor and extensor muscles reflexively work, increasing blood pressure, the lumen of blood vessels increases, the heartbeat and breathing become more frequent. Coordination of functions is determined by the characteristics of the relationship between reflex manifestations on the part of various body systems for the implementation of a certain physiological act. Coordination mechanisms develop throughout childhood and reach their perfection by the age of 18-20.

Mechanisms for coordinating reflex activity:

1. Irradiation of excitation. Neurons of different centers are interconnected by numerous interneurons Therefore, when receptors are stimulated, excitation can spread not only to the neurons of the center of a given reflex, but also to other neurons (the phenomenon of irradiation). The stronger and longer the afferent stimulation and the higher the excitability of surrounding neurons, the more neurons the irradiation process covers. Inhibition processes limit irradiation and contribute to the concentration of excitation at the starting point of the central nervous system.

The process of irradiation plays an important positive role in the formation of new reactions of the body (indicative reactions, conditioned reflexes). Thanks to the irradiation of excitation between different nerve centers, new functional connections arise - conditioned reflexes. Excessive irradiation of excitation can have a negative impact on the state and actions of the body, disrupting the delicate relationships between excited and inhibited nerve centers and causing impaired coordination of movements.

2. Relief and occlusion. Facilitation is the excess of the effect of the simultaneous action of two weak stimuli over the sum of their separate effects. Occlusion (blockage) is the opposite phenomenon of relief. Occlusion occurs under the influence of strong stimuli and leads to a decrease in the strength of the total response.
3. The principle of a common final path. There are several times more afferent neurons in the central nervous system than efferent ones. In this regard, different afferent influences arrive at the same intercalary and efferent neurons, which are their common final paths to the working organs. Many different stimuli can cause the same motor neurons in the spinal cord to act. For example, motor neurons, which control the respiratory muscles, in addition to providing inhalation, are involved in reflex reactions such as sneezing, coughing, etc.

Distinguish allied And antagonistic reflexes (first identified by the English physiologist C. Sherrington, who established the principle of a common final path). Meeting on common final paths, allied reflexes mutually reinforce each other, and antagonistic reflexes inhibit each other. In the first case, in the neurons of the common terminal pathway, nerve impulses are summed up (for example, the flexion reflex is enhanced by simultaneous irritation of several areas of the skin). In the second case, competition occurs for the possession of a common final path, as a result of which only one reflex is carried out, while the others are inhibited. The ease of performing mastered movements is explained by the fact that they are based on time-ordered, synchronized flows of impulses that pass through finite paths more easily than impulses arriving in a random order.

The predominance of one or another reflex reaction on the final paths is due to its significance for the life of the organism in at the moment. In such a selection important role plays the presence of a dominant in the central nervous system (see below). It ensures the flow main reaction, suppressing secondary ones.

4. Feedback, or secondary afferentation. Any motor act caused by an afferent stimulus is accompanied by excitation of receptors in muscles, tendons, joint capsules. Signals from proprioceptors secondarily enter the central nervous system, which allows for correction of its activity and self-regulation in accordance with the current needs of the body and environment. This important principle reflex self-regulation of body functions is called the feedback principle. In addition, due to feedback, the tone of the nerve centers is maintained.
5. Reciprocal (conjugate) relationships between nerve centers. The basis of the relationship between nerve centers is the process of induction - stimulation (induction) of the opposite process. Induction limits the spread (irradiation) of nervous processes and ensures the concentration of excitation.

There are simultaneous and sequential induction. Strong process excitation in the nerve center causes (induces) inhibition in neighboring nerve centers, and a strong inhibitory process induces excitation in neighboring nerve centers. Thus, when the extensor centers of the muscles are excited, the flexor centers are inhibited and vice versa.

When the processes of excitation and inhibition change within one center, they speak of sequential negative or positive induction. She has great value when organizing rhythmic activity, providing alternate contraction and relaxation of muscles, and underlies many acts of life support, such as breathing and heartbeat.

In children, clear inductive relationships between the processes of inhibition and excitation begin to develop between the ages of 3 and 5 years, since at this age the strength and differentiation of nervous processes increases.

6. Dominant – temporary predominance of one nerve center or group of centers over others, determining the current activity of the body. In 1923, A. A. Ukhtomsky formulated the principle of dominance as a working principle of the activity of nerve centers.

The dominant is characterized by:

– increased excitability of the nerve centers included in the dominant focus;
– persistence of excitation of the centers of the dominant focus over time;
– the ability to increase one’s arousal through summation nerve impulses, going to other centers (“attract” impulses going to other centers, as a result, irritation of various receptor fields begins to cause a reflex response characteristic of the activity of a given dominant center);
– the ability of the dominant center, through the mechanism of simultaneous induction, to cause inhibition of the activity of other centers.

A dominant focus in the central nervous system can arise under the influence various factors, in particular, strong afferent stimulation, hormonal influences, changes in blood chemistry, motivation, etc. The central nervous system has the ability to rearrange dominant relationships in accordance with the changing needs of the body, and throughout a person’s life, one dominant replaces another.

A dominant focus in a child arises faster and easier than in adults, but it is characterized by low resistance to external stimuli. This is largely associated with the instability of attention in children: new stimuli easily evoke a new dominant, and indicative reactions themselves early age are dominant.

7. Plastic nerve centers - functional variability and adaptability of nerve centers, their ability to perform new, unusual reflex acts. This is especially pronounced after removal various departments brain If some parts of the cerebellum or cerebral cortex were partially removed, the impaired function may be partially or completely restored over time.

A living organism to a certain influence, taking place with the participation of. By generally accepted classification reflexes are divided into unconditioned and conditioned.

Unconditioned reflexes are innate, characteristic this species, responses to environmental influences.

1. Vital (life). The instincts of this group ensure the preservation of the life of the individual. They are characterized by the following signs:

a) failure to satisfy the corresponding requirement leads to the death of the individual; And

b) no other individual of a given species is needed to satisfy a particular need.

Vital instincts include:

– food,

- drinking,

– defensive,

– sleep-wake regulation,

- energy saving reflex.

2. Zoosocial (role-playing). Reflexes of this group arise only when interacting with individuals of their own species. These include:

– sexual,

– parental,

– reflex of emotional resonance (empathy),

– territorial,

– hierarchical (reflexes of dominance or submission).

3. Self-development reflexes (satisfying ideal needs).

These reflexes are not associated with individual or species adaptation to the existing situation. They are directed to the future. These reflexes cannot be derived from other needs discussed in the previous groups; These are independent reflexes. Self-development reflexes include:

– research

– imitation and game

– reflex of overcoming (resistance, freedom).

Conditioned reflexes are divided as follows.

By biological trait:

– food;

– sexual;

– defensive;

– motor;

– indicative – reaction to a new stimulus.

Differences orientation reflex from other conditioned reflexes:

– innate reaction of the body;

According to the nature of the conditional signal:

– natural – conditioned reflexes caused by those acting in natural conditions: view, conversation about food;

– artificial – caused by stimuli not associated with a given reaction under normal conditions.

According to the complexity of the conditional signal:

– simple – the conditioned signal consists of 1 stimulus (light causes salivation);

– complex – the conditioned signal consists of a complex of stimuli:

– conditioned reflexes that arise in response to a complex of simultaneously acting stimuli;

– conditioned reflexes that arise in response to a complex of sequentially acting stimuli, each of them “layers” on the previous one;

– conditioned reflex on a chain of stimuli, also acting one after another, but not “layered” on top of each other.

The first two are easy to develop, the last one is difficult.

By type of stimulus:

– exteroceptive – arise most easily;

The child's first to appear are proprioceptive reflexes (sucking reflex to posture).

By changing a particular function:

– positive – accompanied by increased function;

– negative – accompanied by weakening of function.

By the nature of the response:

– somatic;

– vegetative (vascular-motor).

Based on the combination of a conditioned signal and an unconditioned stimulus over time:

– cash – an unconditioned stimulus acts in the presence of a conditioned signal, the action of these stimuli ends simultaneously.

There are:

– coinciding existing conditioned reflexes – the unconditioned stimulus acts 1-2 s after the conditioned signal;

– delayed – the unconditioned stimulus acts 3-30 s after the conditioned signal;

– delayed – the unconditioned stimulus acts 1-2 minutes after the conditioned signal.

The first two arise easily, the last one is difficult.

– trace – the unconditioned stimulus acts after the termination of the conditioned signal. IN in this case a conditioned reflex occurs in response to trace changes in the brain section of the analyzer. The optimal interval is 1-2 minutes.

In different orders:

– conditioned reflex of the 1st order – developed on the basis of an unconditioned reflex;

– conditioned reflex of the 2nd order – is developed on the basis of the conditioned reflex of the 1st order, etc.

In dogs it is possible to develop conditioned reflexes up to the 3rd order, in monkeys - up to the 4th order, in children - up to the 6th order, in adults - up to the 9th order.

So, unconditioned reflexes- constant innate responses of the body to certain actions of stimuli, carried out with the help of the nervous system. Distinctive feature all unconditioned reflexes - their innateness, the ability to be inherited from generation to generation.

Among the characteristics of unconditioned reflexes, they also highlight the fact that they:

– are specific, i.e. characteristic of all representatives of a given species;

– have cortical representation, but can be carried out without the participation of the cerebral cortex;

– relatively constant, characterized by stability and great stability;

- are carried out in response to adequate stimulation applied to one specific receptive field.

Conditioned reflex- this is an acquired reflex characteristic of an individual (individual).

Conditioned reflexes:

– arise during the life of an individual and are not fixed genetically (not inherited);

– arise under certain conditions and disappear in their absence.

Types of reflexes
Congenital reflexes	Acquired reflexes
Unconditional	Conditional
Inherited by offspring from parents and maintained throughout the life of the organism	Easily acquired when needed necessary conditions, and are lost by the body throughout life
At birth, the body has ready-made reflex arcs	The body does not have ready-made nerve pathways
Provide adaptation of the organism only to changes in the environment, which have often been encountered by many generations of this species	Formed as a result of a combination of an indifferent stimulus with an unconditioned or previously developed conditioned reflex
Reflex arcs pass through the spinal cord or brain stem, the cerebral cortex is not involved in them	Reflex arcs pass through the cerebral cortex

Unconditional

Unconditioned reflexes are hereditarily transmitted (innate) reactions of the body, inherent to the entire species. Execute protective function, as well as the function of maintaining homeostasis (adaptation to conditions environment) .

Unconditioned reflexes are an inherited, unchangeable reaction of the body to external and internal signals, regardless of the conditions for the occurrence and course of reactions. Unconditioned reflexes ensure the body's adaptation to constant environmental conditions. The main types of unconditioned reflexes: food, protective, orientation, sexual.

An example of a defensive reflex is the reflexive withdrawal of the hand from a hot object. Homeostasis is maintained, for example, by a reflex increase in breathing when there is excess carbon dioxide in the blood. Almost every part of the body and every organ is involved in reflex reactions.

The simplest neural networks, or arcs (according to Sherrington), involved in unconditioned reflexes, are closed in the segmental apparatus of the spinal cord, but can also be closed higher (for example, in the subcortical ganglia or in the cortex). Other parts of the nervous system are also involved in reflexes: the brain stem, cerebellum, and cerebral cortex.

The arcs of unconditioned reflexes are formed at the time of birth and remain throughout life. However, they can change under the influence of illness. Many unconditioned reflexes appear only at a certain age; Thus, the grasping reflex characteristic of newborns fades away at the age of 3-4 months.

There are monosynaptic (involving the transmission of impulses to the command neuron through one synaptic transmission) and polysynaptic (involving the transmission of impulses through chains of neurons) reflexes.

Neural organization of the simplest reflex

The simplest reflex of vertebrates is considered monosynoptic. If the arc of the spinal reflex is formed by two neurons, then the first of them is represented by the cell dorsal ganglion, and the second - a motor cell (motoneuron) anterior horn spinal cord. The long dendrite of the spinal ganglion goes to the periphery, forming a sensitive fiber of some kind nerve trunk, and ends with a receptor. The axon of a neuron of the spinal ganglion is part of the dorsal root of the spinal cord, reaches the motor neuron of the anterior horn and, through a synapse, connects with the body of the neuron or one of its dendrites. The axon of the motor neuron of the anterior horn is part of the anterior root, then the corresponding motor nerve and ends with a motor plaque in the muscle.

Pure monosynaptic reflexes do not exist. Even the knee reflex, which is a classic example of a monosynaptic reflex, is polysynaptic, since the sensory neuron not only switches to the motor neuron of the extensor muscle, but also sends out an axonal collateral that switches to the inhibitory interneuron of the antagonist muscle, the flexor muscle.

Conditional

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

The development of the doctrine of conditioned reflexes is associated primarily with the name of I.P. Pavlova. He showed that a new stimulus can initiate a reflex response if it is presented for some time together with an unconditioned stimulus. For example, if a dog is allowed to smell meat, it will secrete gastric juice(this is an unconditioned reflex). If you ring a bell at the same time as the meat, the dog’s nervous system associates this sound with food, and gastric juice will be released in response to the bell, even if the meat is not presented. Conditioned reflexes underlie acquired behavior. This is the most simple programs. The world around us is constantly changing, so only those who quickly and expediently respond to these changes can live successfully in it. As you purchase life experience A system of conditioned reflex connections is formed in the cerebral cortex. Such a system is called a dynamic stereotype. It underlies many habits and skills. For example, having learned to skate or bicycle, we subsequently no longer think about how we should move so as not to fall.

reflex arc nerve impulse

Swallowing, salivation, rapid breathing due to lack of oxygen - all these are reflexes. They exist huge variety. Moreover, they may differ for each individual person and animal. Read more about the concepts of reflex, reflex arc and types of reflexes further in the article.

What are reflexes

This may sound scary, but we do not have one hundred percent control over all our actions or the processes of our body. We are, of course, not talking about decisions to get married or go to university, but smaller, but very important actions. For example, about jerking our hand when accidentally touching a hot surface or trying to hold on to something when we slip. It is in such small reactions that reflexes appear, controlled by the nervous system.

Most of them are inherent in us at birth, others are acquired later. In a sense, we can be compared to a computer, into which, even during assembly, programs are installed in accordance with which it operates. Later, the user will be able to download new programs, add new action algorithms, but the basic settings will remain.

Reflexes are not limited to humans. They are characteristic of all multicellular organisms that have a CNS (central nervous system). Various types reflexes are carried out constantly. They contribute to the proper functioning of the body, its orientation in space, and help us quickly respond to danger. The absence of any basic reflexes is considered a disorder and can make life much more difficult.

Reflex arc

Reflex reactions occur instantly, sometimes you don’t have time to think about them. But despite all their apparent simplicity, they are extremely complex processes. Even the most basic action in the body involves several parts of the central nervous system.

The irritant acts on the receptors, the signal from them travels along the nerve fibers and goes directly to the brain. There, the impulse is processed and sent to the muscles and organs in the form of a direct instruction to action, for example, “raise your hand,” “blink,” etc. The entire path that the nerve impulse travels is called a reflex arc. IN full version it looks something like this:

Receptors are nerve endings that perceive a stimulus.
Afferent neuron - transmits a signal from receptors to the center of the central nervous system.
Interneuron - nerve center, is not involved in all types of reflexes.
Efferent neuron - transmits a signal from the center to the effector.
An effector is an organ that carries out a reaction.

The number of arc neurons may vary, depending on the complexity of the action. The information processing center can pass through either the brain or the spinal cord. The simplest involuntary reflexes are carried out by the spinal cord. These include changes in the size of the pupil when the lighting changes or withdrawal when pricked with a needle.

What types of reflexes are there?

The most common classification is the division of reflexes into conditioned and unconditioned, depending on how they were formed. But there are other groups, let’s look at them in the table:

Classification sign	Types of reflexes
By nature of education	Conditional Unconditional
According to biological significance	Defensive Approximate Digestive
By type of executive body	Motor (locomotor, flexor, etc.) Vegetative (excretory, cardiovascular, etc.)
By influence on the executive body	Exciting Brake
By type of receptor	Exteroceptive (olfactory, cutaneous, visual, auditory) Proprioceptive (joints, muscles) Interoceptive (endings of internal organs).

Unconditioned reflexes

Congenital reflexes are called unconditioned. They are transmitted genetically and do not change throughout life. Within them there are simple and complex species reflexes. Most often they are processed in spinal cord, but in some cases the cerebral cortex, cerebellum, brain stem or subcortical ganglia may be involved.

A striking example of unconditioned reactions is homeostasis - the process of maintaining internal environment. It manifests itself in the form of regulation of body temperature, blood clotting during cuts, increased breathing during increased quantity carbon dioxide.

Unconditioned reflexes are inherited and are always tied to a specific species. For example, all cats land strictly on their paws; this reaction manifests itself in them already in the first month of life.

Digestive, orientation, sexual, protective - these are simple reflexes. They manifest themselves in the form of swallowing, blinking, sneezing, salivation, etc. Complex unconditioned reflexes manifest themselves in the form separate forms behavior, they are called instincts.

Conditioned reflexes

Unconditioned reflexes alone are not enough in the course of life. In the course of our development and acquisition of life experience, conditioned reflexes often arise. They are acquired by each individual individually, are not hereditary and can be lost.

They are formed with the help of the higher parts of the brain on the basis of unconditioned reflexes and arise under certain conditions. For example, if you show an animal food, it will produce saliva. If you show him a signal (lamp light, sound) and repeat it every time food is served, the animal will get used to it. Next time, saliva will begin to be produced when the signal appears, even if the dog does not see the food. Such experiments were first carried out by the scientist Pavlov.

All types of conditioned reflexes are developed in response to certain stimuli and are necessarily reinforced by negative or positive experience. They underlie all our skills and habits. On the basis of conditioned reflexes, we learn to walk, ride a bicycle, and can acquire harmful addictions.

Excitation and inhibition

Each reflex is accompanied by excitation and inhibition. It would seem that these are absolutely opposite actions. The first stimulates the functioning of organs, the other is designed to inhibit it. However, they both simultaneously participate in the implementation of any types of reflexes.

Inhibition does not in any way interfere with the manifestation of the reaction. This nervous process It does not affect the main nerve center, but dulls the others. This happens so that the excited impulse reaches strictly for its intended purpose and does not spread to organs that perform the opposite action.

When bending the arm, inhibition controls the extensor muscles; when turning the head to the left, it inhibits the centers responsible for turning to the right. Lack of inhibition would lead to involuntary and ineffective actions that would only get in the way.

Animal reflexes

The unconditioned reflexes of many species are very similar to each other. All animals have a feeling of hunger or the ability to excrete digestive juice At the sight of food or suspicious sounds, many listen or begin to look around.

But some reactions to stimuli are the same only within a species. For example, hares run away when they see an enemy, while other animals try to hide. Porcupines, equipped with spines, always attack a suspicious creature, a bee stings, and opossums pretend to be dead and even imitate the smell of a corpse.

Animals can also acquire conditioned reflexes. Thanks to this, dogs are trained to guard the house and listen to the owner. Birds and rodents easily get used to people feeding them and do not run away at the sight of them. Cows are very dependent on their daily routine. If you violate their routine, they produce less milk.

Human reflexes

Like other species, many of our reflexes appear in the first months of life. One of the most important is sucking. With the smell of milk and the touch of the mother's breast or a bottle that imitates it, the baby begins to drink milk from it.

There is also a proboscis reflex - if you touch the baby’s lips with your hand, he sticks them out with a tube. If the baby is placed on his stomach, his head will necessarily turn to the side, and he himself will try to rise. With the Babinski reflex, stroking the baby's feet causes the toes to fan out.

Most of the very first reactions accompany us only for a few months or years. Then they disappear. Among the types of human reflexes that remain with him for life: swallowing, blinking, sneezing, olfactory and other reactions.

Historical information

Assumption about reflexive nature the activity of the higher parts of the brain was first developed by the scientist-physiologist I.M. Sechenov. Before him, physiologists and neurologists did not dare to raise the question of the possibility of physiological analysis mental processes, which were left to psychology to solve.

Further, the ideas of I.M. Sechenov were developed in the works of I.P. Pavlov, who discovered the ways of objective experimental research of the functions of the cortex, developed a method for developing conditioned reflexes and created the doctrine of higher nervous activity. Pavlov in his works introduced the division of reflexes into unconditioned ones, which are carried out by congenital, hereditarily fixed neural pathways, and conditional, which, according to Pavlov’s views, are carried out through neural connections formed in the process of individual life of a person or animal.

Charles S. Sherrington (Nobel Prize in Physiology or Medicine, 1932) made a great contribution to the formation of the doctrine of reflexes. He discovered coordination, mutual inhibition and facilitation of reflexes.

The meaning of the doctrine of reflexes

The doctrine of reflexes has given a lot to understanding the very essence of nervous activity. However, the reflex principle itself could not explain many forms of goal-directed behavior. Currently, the concept of reflex mechanisms has been supplemented by the idea of the role of needs in the organization of behavior; it has become generally accepted that the behavior of animal organisms, including humans, is active in nature and is determined not so much by the irritations that arise, but by the plans and intentions that arise under influenced by certain needs. These new ideas were expressed in physiological concepts " functional system"P.K. Anokhin or "physiological activity" N.A. Bernstein. The essence of these concepts boils down to the fact that the brain can not only adequately respond to external stimuli, but also foresee the future, actively make plans for its behavior and implement them in action. The idea of an “acceptor of action”, or a “model of the required future”, allows us to talk about “ahead of reality”.

General mechanism of reflex formation

Neurons and the pathways of nerve impulses during a reflex act form a so-called reflex arc:

Stimulus - receptor-affector - CNS neuron - effector - reaction.

Classification

Based on a number of characteristics, reflexes can be divided into groups

By type of education: conditioned and unconditioned reflexes
By type of receptor: exteroceptive (skin, visual, auditory, olfactory), interoceptive (from receptors of internal organs) and proprioceptive (from receptors of muscles, tendons, joints)
By effector: somatic or motor (skeletal muscle reflexes), for example flexor, extensor, locomotor, statokinetic, etc.; vegetative internal organs - digestive, cardiovascular, excretory, secretory, etc.
According to biological significance: defensive, or protective, digestive, sexual, orientation.
According to the degree of complexity of neural organization reflex arcs distinguish between monosynaptic, the arcs of which consist of afferent and efferent neurons (for example, knee), and polysynaptic, the arcs of which also contain 1 or more interneurons and have 2 or more synaptic switches (for example, flexor).
According to the nature of the influences on the activity of the effector: excitatory - causing and enhancing (facilitating) its activity, inhibitory - weakening and suppressing it (for example, reflex increase heart rate sympathetic nerve and its slowdown or cardiac arrest - wandering).
By anatomical location The central part of the reflex arcs distinguishes between spinal reflexes and cerebral reflexes. Neurons located in the spinal cord are involved in the implementation of spinal reflexes. An example of the simplest spinal reflex is the withdrawal of a hand from a sharp pin. Brain reflexes are carried out with the participation of brain neurons. Among them there are bulbar, carried out with the participation of neurons of the medulla oblongata; mesencephalic - with the participation of midbrain neurons; cortical - with the participation of neurons in the cerebral cortex.

Unconditional

Unconditioned reflexes are hereditarily transmitted (innate) reactions of the body, inherent to the entire species. They perform a protective function, as well as the function of maintaining homeostasis (adaptation to environmental conditions).

Unconditioned reflexes are inherited, unchangeable reactions of the body to certain influences of the external or internal environment, regardless of the conditions for the occurrence and course of reactions. Unconditioned reflexes ensure the body's adaptation to constant environmental conditions. The main types of unconditioned reflexes: food, protective, orientation, sexual.

An example of a defensive reflex is the reflexive withdrawal of the hand from a hot object. Homeostasis is maintained, for example, by a reflex increase in breathing when there is an excess of carbon dioxide in the blood. Almost every part of the body and every organ is involved in reflex reactions.

Pathological reflexes

Pathological reflexes are a neurological term that refers to reflex reactions that are unusual for a healthy adult. In some cases, more early stages phylo- or ontogeny.

There is an opinion that mental dependence on something is caused by the formation of a conditioned reflex. For example, mental dependence on drugs is due to the fact that taking a certain substance associated with a pleasant state (a conditioned reflex is formed that persists throughout almost the entire life).

Notes

Literature

Skoromets A. A., Skoromets A. P., Skoromets T. A. Propaedeutics of clinical neurology. St. Petersburg: Politekhnika, 2004
Chief editor member Academy of Medical Sciences of the USSR Kositsky G.I., “Human Physiology.” Ed. "Medicine", 1985.
Dictionary of physiological terms / resp. ed. Gazenko O.G.. - M.: “Science”, 1987. - 32,000 copies.
Fundamental and clinical physiology: Textbook for higher students educational institutions/ ed. Kamkin A.G., Kamensky A.A.. - M.: Publishing Center "Academy", 2004. - 1072 p. - 5,000 copies. -