The path of the reflex arc. Reflex arc: the most important element of the nervous system. Diagram of the reflex arc and ring

reflexes- this is the body's response to irritation of sensitive nerve formations - receptors, realized with the participation of the nervous system.

Types of reflexes conditional and unconditional

reflexes	Unconditioned reflexes	Conditioned reflexes
Characteristic	1. It's innate , hereditarily transmitted reactions of the body. 2. Are species-specificthose. formed in the process of evolution and characteristic of all representatives of this species. 3. They are relatively constant and persist throughout the life of the organism. 4. Arise on specific (adequate) stimulus for each reflex. 5. Reflex centers are at the level spinal cord and brain stem.	1. These are purchased in the process of life, reactions of the body that are not inherited by the offspring. 2. Are individual,those. emerging from " life experience" of each organism. 3. They are fickle and depend dependence on certain conditionscan be produced Zach replyat'sya or fade away. 4. May form on any perceived by the body stimulus. 5. Reflex centers prey are significantly incerebral cortex.
Examples	Nutritional, sexual, defensive, orienting, maintenance of homeostasis.	Salivation by smell, precise movements when writing and playing the piano.
Meaning	They help survival, this is "the application of the experience of ancestors in practice".	P help fitadapt to changing conditions external environment.

reflex arc

With the help of a reflex, excitation spreads along reflex arcs and the process of inhibition is carried out.

reflex arc- this is the path along which nerve impulses are conducted during the implementation of the reflex.

Reflex arc diagram

5 links of the reflex arc:

1. Receptor - perceives irritation and converts it into a nerve impulse.

2. Sensitive (centripetal) neuron - transmits excitation to the center.

3. Nerve center - excitation switches from sensory to motor neurons (there is an intercalary neuron in the three-neuron arc).

4. Motor (centrifugal) neuron - carries excitation from the central nervous system to the working organ.

5. Working body - reacts to the received irritation.

Information from the receptors of the working organ enters the nerve center to confirm the effectiveness of the reaction and, if necessary, coordinate it.

Scheme of the reflex arc of the knee jerk (a simple arc of two neurons)

When a reflex occurs, there is always a sequential spread of excitation from the formation of the perceiving action of the stimulus (from the receptor) towards the central nervous system (along the centripetal pathways) and then, after complex processes occurring within it, in the direction from the central nervous system (along the centrifugal pathways ) to the working body (to the effector).

An example of a reflex act

Using the activity of the salivary gland of a dog as an example, one can investigate the path along which excitation spreads during the implementation of a reflex act. The corresponding research is made in the conditions of vivisection (acute) experience.

The animal is immobilized in one way or another. A glass tube - a cannula - is inserted into the incision of the prepared duct of the gland. If the stimuli do not work, then the gland is at rest, and saliva is not released from the cannula. The experimenter immerses the tip of the animal's tongue in a weak acid solution. Saliva begins to flow from the cannula, indicating that the gland has come into an active state.

The acid excites the special apparatus of the sensory nerve endings located on the surface of the tongue, which perceive the chemical effect. The resulting excitation along the centripetal fibers of the sensory nerve (n. lingualis) spreads along the central part of the reflex arc (in the medulla oblongata) and through the centrifugal fibers of the secretory nerve (chorda tympani) reaches the salivary gland. If the sensitive nerve is cut, then immersion of the tip of the tongue in acid does not cause salivation, since the reflex arc will be interrupted at its centripetal link. If, on the other hand, stimulation of the central end of the cut nerve with an electric current is started, then a reflex separation of saliva can be called up again.

After transection of the nerves leading to the salivary gland, i.e. after violation of the integrity of the arc in its centrifugal part, irritation of the centripetal nerve ceases to cause an effect. Irritation by the current of the peripheral end of the cut central nerve, which goes directly to the gland, naturally causes salivation.

The formations that receive sites in the reflex reaction, in their totality, constituting a directed path for reflex excitation, are defined by the concept of "arc of the reflex". Separate links of the reflex arc are: receptor, effector (muscle or gland) and nerve cells with their processes.

Excitation that has come to the brain from any receptor through a complex system of pathways can go to any centrifugal pathway and reach any effector organ.

The central nervous system of animals and humans is characterized by a certain morphological and functional structure, due to which communication between any areas of the process is possible. All this is due to the occurrence of regularly repeating reflex reactions that ensure the regulation of body functions. When we later talk about reflex muscular acts, about vascular reflexes, about respiratory reflexes, about reflex excitation of the glands of the digestive tract ... We will keep in mind the relationships developed in the process of evolution, in which the excitation that has arisen in certain parts of the body reaches certain areas of the central nervous system. From here impulses are sent to certain organs and cause in them the corresponding activity.

The course of excitation in the arc of the unconditioned reflex

We have considered here the course of excitation in the arc, simplifying and schematizing the relationships and not taking into account the most complex processes that occur in the central part of the arc. In reality, the reflex act is almost never limited to a simple transfer of excitation from the centripetal part of the arc to a non-centrifugal one, as shown in the diagram. Excitation spreads much wider and involves various body systems in the reaction. Thus, for example, the ingestion of food substances into the mouth causes not only the secretory activity of the animal, on which we have focused our attention, but also motor activity, which captures a significant number of muscle effectors.

Conditioned reflex

Each excitation that enters the central nervous system reaches its highest section, the cerebral cortex, and can become the basis for the formation of a temporary connection. In this case, we can talk about a friend of the conditioned reflex and build diagrams that reflect the fundamental side of the course of excitation during the reflex activity of the cerebral cortex. However, consideration of such schemes should be attributed to the section of the course devoted to the special physiology of the cerebral hemispheres.

Here we only want to emphasize that no matter how complex the activity of the central nervous system, we will always find in it elements characteristic of a simple reflex arc. This makes it possible to establish an evolutionary link between the primitive nervous system of lower animals and the human central nervous system. The centripetal and centrifugal parts of the reflex arc retain a fundamental similarity in the phylogenetic series of animals. In the process of evolution, it was mainly the central part of the reflex pathway that changed, which can be called the central nervous system in the narrowed sense of the word.

Briefly about the reflex arc

Normal physiology: lecture notes Svetlana Sergeevna Firsova

3. Reflex arc, its components, types, functions

The activity of the body is a natural reflex reaction to a stimulus. Reflex- the reaction of the body to irritation of receptors, which is carried out with the participation of the central nervous system. The structural basis of the reflex is the reflex arc.

reflex arc- a chain of nerve cells connected in series, which ensures the implementation of a reaction, a response to irritation.

The reflex arc consists of six components: receptors, afferent (sensory) pathway, reflex center, efferent (motor, secretory) pathway, effector (working organ), feedback.

Reflex arcs can be of two types:

1) simple - monosynaptic reflex arcs (reflex arc of the tendon reflex), consisting of 2 neurons (receptor (afferent) and effector), there is 1 synapse between them;

2) complex - polysynaptic reflex arcs. They include 3 neurons (there may be more) - receptor, one or more intercalary and effector.

The idea of a reflex arc as an expedient response of the body dictates the need to supplement the reflex arc with one more link - a feedback loop. This component establishes a connection between the realized result of the reflex reaction and the nerve center that issues executive commands. With the help of this component, the open reflex arc is transformed into a closed one.

Features of a simple monosynaptic reflex arc:

1) geographically close receptor and effector;

2) the reflex arc is two-neuron, monosynaptic;

3) nerve fibers of group A? (70-120 m/s);

4) short reflex time;

5) muscles that contract as a single muscle contraction.

Features of a complex monosynaptic reflex arc:

1) territorially separated receptor and effector;

2) the receptor arc is three-neuronal (maybe more neurons);

3) the presence of nerve fibers of groups C and B;

4) muscle contraction by the type of tetanus.

Features of the autonomic reflex:

1) the intercalary neuron is located in the lateral horns;

2) from the lateral horns begins the preganglionic nerve path, after the ganglion - postganglionic;

3) the efferent path of the reflex of the autonomic neural arch is interrupted by the autonomic ganglion, in which the efferent neuron lies.

The difference between the sympathetic neural arch and the parasympathetic one: in the sympathetic neural arch, the preganglionic path is short, since the autonomic ganglion lies closer to the spinal cord, and the postganglionic path is long.

In the parasympathetic arch, the opposite is true: the preganglionic path is long, since the ganglion lies close to the organ or in the organ itself, and the postganglionic path is short.

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The structural basis of reflex activity is made up of neural circuits of receptor, intercalary and effector neurons. They form the path along which nerve impulses pass from the receptor to the executive organ during the implementation of any reflex. This path is called reflex arc. It consists of:

stimulus-perceiving receptors;
afferent nerve fibers - processes of receptor neurons that carry excitation to the central nervous system;
and , transmitting impulses to effector neurons;
efferent nerve fibers that conduct impulses from the central nervous system to the periphery;
an executive body whose activity changes as a result of a reflex.

the simplest reflex arc can be schematically represented as formed by only two neurons: receptor and effector, between which there is one synapse. Such a reflex arc is called two-neuron and monosynaptic ( rice. 170, A).

There are polysynaptic reflex arcs in which the receptor neuron is connected to several intercalary ones, each of which forms synapses on different ones in the same effector neuron. Then it is easy to imagine reflex arcs, in the formation of which several receptor neurons are involved, connected to the same or different intercalary neurons. Polysynaptic reflex arcs, even presented as diagrams, can be quite complex ( rice. 171).

Receptive fields of equal reflexes located on the surface of the skin can go one after another. As a result, irritation applied to a certain area of the skin, depending on its strength and the state of the central nervous system, can cause either one or the other reflex.

Reflex arc circuits should be thought of as consisting of rows of receptor, intercalary, and effector neurons. It follows that the simplest reflex arc can only conditionally be called "monosynaptic", since it includes not one synapse between two neurons, but one row of parallel synapses connecting a group of receptor neurons with a group of effector neurons that cause the same response. neurons.

monosynaptic reflex arcs are very rare. An example of them is the arc of the muscle stretch reflex, or myotatic reflex. Receptors - muscle spindles, - irritation of which causes these reflexes, are located in skeletal muscles, bodies of receptor nerve cells - in social ganglia, bodies of effector cells - in the anterior horns of the spinal cord. Stretching the muscle causes a discharge of nerve impulses in the receptors. The latter are sent along the processes of receptor neurons to the spinal cord and directly (without the participation of intercalary neurons) are transmitted to motor neurons, from which the discharge of impulses is directed to the end plates located in the same muscle. As a result, stretching the back causes its reflex shortening. Since in such a reflex arc the excitation passes through only one interneuronal synapse, such "monosynaptic" reflexes are carried out faster than others, in which the reflex arcs include a greater number of neurons and synapses.

Polysynaptic reflex arcs include several serially connected rows of neurons and synapses between them. An example of such a reflex can be a limb withdrawal reflex in animals and humans in response to pain irritation of the skin of an arm or leg. This reflex is multineuronal even when it is artificially caused by stimulation of only one receptor.

The idea of a reflex arc should be considered as a diagram convenient for analysis, in which neurons are shown that are necessarily involved in a particular reflex act. At the same time, it must be taken into account that nerve impulses, with any reflex, are capable of spreading widely in the central nervous system along numerous conducting paths. So, in animals, with the integrity of the entire central nervous system, the excitation that occurs in response to pain irritation also spreads to the subcortical nuclei and the cerebral cortex, and from there returns to the spinal cord along efferent pathways. It is precisely due to the fact that the neurons of the subcortical nuclei and the cortex participate in the protective reaction to strong pain stimulation that a sensation of pain occurs, accompanied by a number of vegetative reactions - changes in the pulse rate, frequency and depth of breathing, vascular tone, etc.

Similarly, in the implementation of food reflexes (chewing, salivation, swallowing, secretion of digestive juices) or respiratory and vasomotor reflexes, neurons located at different levels of the central nervous system participate - in the spinal cord and medulla oblongata, in the nuclei of the optic tubercles, in the cerebral cortex. Even with the simplest reflex reactions - tendon-muscle proprioceptive reflexes, for which the participation of two neurons is sufficient, excitation spreads widely throughout the central nervous system. Thus, a blow to the tendon causes a change in the electrical activity of the cerebral cortex.

Consequently, the nerve impulse during the spinal reflex can reach the higher parts of the central nervous system, which can to some extent participate in the reflex reaction.

The degree of involvement of nerve cells in the reaction to the stimulus of various parts of the central nervous system depends on the strength of the applied irritation, the duration of its action and the state of the central nervous system.

Lesson. Reflex, reflex arc

Test work analysis, computer testing, oral repetition (20 min)

1. Reflex, reflex arc

A reflex is the body's response to irritation of sensitive formations - receptors, carried out with the participation of the nervous system. Receptors are highly sensitive to stimuli specific to them and convert their energy into a process of nervous excitation. Reflexes are carried out due to the presence in the nervous system reflectorarcs, in other words, chains of nerve cells connecting sensory cells with muscles or glands involved in the reflex reaction. In the reflex arc, 5 elements are distinguished: 1 - receptors, 2 - sensitive neuron, 3 - nerve center, 4 - motor neuron, 5 - executive organ.

Most simple reflex arcs are formed by only two neurons. The processes of sensitive nerve cells form contacts directly on the executive neurons, sending their long processes to the muscles or glands.

An example of the simplest reflexes is the knee jerk, which is usually caused by a doctor examining a patient. To do this, the patient is asked to cross his legs and hit with a rubber mallet on the tendon ligament just below the kneecap. From the impact, the muscle is stretched and excitation occurs in its receptors, which is transmitted directly to the executive neuron, which sends a wave of excitation to the same muscle. The muscle contracts and the leg extends. The reflex arc of this reflex consists of only two neurons. The executive neuron is located in the spinal cord.

The overwhelming majority of reflex arcs has a more complex structure. They are formed by a chain of sensitive, one or more intercalary and executive neurons. Touching a hand to a hot object creates pain and causes hand withdrawal. This occurs as a result of the flexion reflex.

In this case, pain signals enter the spinal cord and are transmitted to intercalary neurons. Those, in turn, excite executive neurons that send commands to the muscles of the arm. The muscles contract and the arm flexes.

Part of the reflex arc of any reflex is always located in a certain area of the central nervous system and consists of intercalary and executive neurons. That's what it is nerve center this reflex. In other words, a nerve center is an association of neurons designed to participate in the performance of a certain reflex act, and therefore to control the activity of any organ or organ system.

The reflex principle of the activity of the nervous system was originally attributed only to the functions of the spinal cord and only later extended to the activity of the brain. The credit for this belongs to the great Russian

physiologist I.M. Sechenov who managed to understand that all acts of conscious and unconscious activity are reflexes. The knee and flexion reflexes described above belong to the category congenital. A person has a strictly defined set of innate reflexes. Their presence is the same obligatory species feature of an organism as the shape of the body, the number of fingers or the pattern on the wings of butterflies. For the implementation of the innate reflex, the body has ready-made reflex arcs. Therefore, no special additional conditions are required for their implementation, which is why they are called bezuscatching reflexes.

For the implementation opened by I.P. Pavlov conditioned reflexes the body does not have ready-made neural pathways. Conditioned reflexes are formed during life, when the necessary conditions for this arise. The formation of conditioned reflexes underlies the training of the body in various skills and adaptations to a changing environment. The presence of a reflex arc is an indispensable condition for the realization of a reflex, but it does not guarantee the accuracy of its implementation. However, the nerve center of this reflex has the ability to control the accuracy of the execution of its commands. These signals originate in receptors located in the executive organs themselves. He receives information about the features of the implementation of the reflex through "feedback". Such a device allows the nerve centers, if necessary, to make urgent changes in the work of the executive organs.

Basic terms and concepts:

Reflex. Reflex arc. Nerve center. Unconditioned reflex. Conditionalreflex. Feedback.

Board card:

Orally: What is a reflex?

What reflexes are called unconditioned?

Give examples of innate reflexes.

What reflexes are called conditioned?

Give examples of conditioned reflexes.

List the elements of the reflex arc.

What types of reflex arcs do you know?

What are the links of the reflex arc of a simple reflex?

How is the control of the nervous system for the implementation of the reflex?

What is "feedback"?

Cards for writing work:

Reflex, reflex arc.

Examples of simple and complex reflex arcs.

What reflexes are called conditioned? Unconditional? Give examples.

Give a definition or expand the concept: Reflex. Reflex arc. A simple reflex arc. Nerve center. Unconditioned reflex. Conditioned reflex. Feedback.

Computer testing:

**Test 1. Correct judgments:

A reflex is the body's response to an external or internal stimulus.

A reflex is a response of the body to irritation, carried out with the participation of the nervous system.

The movement of the amoeba towards food is a reflex.

The movement of the hydra towards food is a reflex.

**Test 2. Unconditioned reflexes include:

knee reflex.

**Test 3. Correct judgments:

Conditioned reflexes have ready-made reflex arcs already at birth.

The doctrine of conditioned reflexes was created by I.M. Sechenov.

Education is based on the formation of conditioned reflexes.

Education is based on the formation of unconditioned reflexes.

**Test 4. Conditioned reflexes include:

The reaction of the dog to the word "Face".

Withdrawal of the hand when touching a hot object.

Salivation in a dog when food enters the mouth.

Salivation in dogs at the sight of food.

Test 5. The reflex arc consists of:

From receptors and a sensitive neuron that transmits excitation to the nerve center.

From receptors, a sensitive neuron, a nerve center that analyzes information.

From receptors, a sensitive neuron, a nerve center and a motor neuron that transmits excitation to an organ.

From receptors, a sensitive neuron, a nerve center, a motor neuron that transmits excitation to an organ and feedbacks, with the help of which the nerve center controls the reflex.

Test 6. A simple reflex arc consists of:

Test 7. A complex reflex arc consists of:

From a sensitive neuron that transmits excitation to the nerve center.

From sensory neuron and motor neuron.

From sensory, intercalary and motor neurons.

From sensitive, intercalary, motor neurons and feedbacks, with the help of which the nerve center controls the reflex.

Test 8. The nerve center of the reflex consists of:

From a sensitive neuron with receptors.

From sensory neuron and motor neuron.

From intercalary and executive neurons.

From sensitive, intercalary, motor neurons and feedbacks, with the help of which the nerve center controls the reflex.

Test 9. The merit in creating the doctrine of the reflex activity of the brain belongs to:

I.P. Pavlov.

I.M. Sechenov.

I.I. Mechnikov.

E. Jenner.

Test 10. Feedbacks:

motor neurons.

Sensitive neurons that perceive stimulation.

Sensory neurons located in the executive organs.

Intercalary neurons.