The sequence of elements of the reflex arc of a conditioned reflex. General diagram of a reflex arc
Lesson. Reflex, reflex arc
Analysis of test work, 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 have high sensitivity to stimuli specific to them and convert their energy into the process of nervous excitation. Reflexes are carried out due to the presence in the nervous system reflectorny arcs, in other words, chains nerve cells, connecting sensory cells with muscles or glands involved in the reflex response. There are 5 elements in the reflex arc: 1 – receptors, 2 – sensitive neuron, 3 – nerve center, 4 – motor neuron, 5 – executive body.
The simplest reflex arcs are formed by just two neurons. The processes of sensory nerve cells form contacts directly on the executive neurons, which send their long processes to the muscles or glands.
An example of the simplest reflexes is the knee reflex, which is usually caused by a doctor examining a patient. To do this, the patient is asked to cross his legs and hit the tendon ligament just below with a rubber mallet. kneecap. The impact causes the muscle to become tense 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 vast majority of reflex arcs have a more complex structure. They are formed by a chain of sensitive, one or more intercalary and executive neurons. Touching a hot object with your hand creates painful sensation and causes the hand to be withdrawn. This occurs as a result of the flexion reflex.
In this case, pain signals enter the spinal cord and are transmitted to interneurons. These, in turn, excite executive neurons that send commands to the arm muscles. The muscles contract and the arm bends.
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. This is it nerve centerof this reflex. In other words, a nerve center is a combination of neurons designed to participate in the performance of a specific reflex act, and therefore to control the activity of an organ or organ system.
The reflex principle of the activity of the nervous system was initially attributed only to the functions spinal cord and only later extended to brain activity. 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 characteristic of an organism as the shape of the body, the number of fingers or the pattern on the wings of butterflies. To carry out an innate reflex, the body has ready-made reflex arcs. Therefore, their implementation does not require any special additional conditions, that's why they got the name bezusmental reflexes.
To implement the same discovered by I.P. Pavlov conditioned reflexes the body does not have ready nerve pathways. Conditioned reflexes are formed throughout life when they arise necessary conditions. The formation of conditioned reflexes underlies the body's learning of various skills and adaptations to a changing environment. The presence of a reflex arc is an indispensable condition for the implementation 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 arise in receptors located in the executive organs themselves. Through “feedback” he receives information about the features of the reflex. Such a device allows the nerve centers, if necessary, to make urgent changes in the work of the executive bodies.
Basic terms and concepts:
Reflex. Reflex arc. Nerve center. Unconditioned reflex. Conditionalreflex. Feedback.
Card on the board:
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 a reflex arc.
What types of reflex arcs do you know?
What are the parts of the reflex arc of a simple reflex?
How does the nervous system control the execution of the reflex?
What is "feedback"?
Cards for written work:
Reflex, reflex arc.
Examples of simple and complex reflex arcs.
What reflexes are called conditioned? Unconditional? Give examples.
Define or expand the concept: Reflex. Reflex arc. Simple reflex arc. Nerve center. Unconditioned reflex. Conditioned reflex. Feedback.
Computer testing:
**Test 1. Correct judgments:
A reflex is the body’s response to external or internal stimulation.
A reflex is the body’s response 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.
The basis of learning is the formation of conditioned reflexes.
The basis of learning is the formation of unconditioned reflexes.
**Test 4. Conditioned reflexes include:
The dog's reaction to the word "Face".
Pulling away the hand when touching a hot object.
The dog salivates when food enters the mouth.
The dog salivates 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 sensory neuron, a nerve center and a motor neuron that transmits excitation to an organ.
From receptors, a sensory neuron, a nerve center, a motor neuron that transmits excitation to an organ and feedback connections 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 a sensory neuron and a motor neuron.
From sensory, intercalary and motor neurons.
From sensory, intercalary, motor neurons and feedback connections, with the help of which the nerve center controls the reflex.
Test 8. The nerve center of the reflex consists of:
From a sensory neuron with receptors.
From a sensory neuron and a motor neuron.
From intercalary and executive neurons.
From sensory, intercalary, motor neurons and feedback connections, with the help of which the nerve center controls the reflex.
Test 9. Merit in creating the doctrine of reflex activity brain belongs to:
I.P. Pavlov.
I.M. Sechenov.
I.I. Mechnikov.
E. Jenner.
Test 10. Feedbacks:
Motor neurons.
Sensory neurons that perceive irritation.
Sensory neurons located in the executive organs.
Interneurons.
Physiological definition of the concept "reflex arc"
A reflex arc is a schematic path of excitation movement from a receptor to an effector.
Anatomical definition of the concept "reflex arc"
The reflex arc is a collection nerve structures, ensuring the implementation of the reflex act.
Both of these definitions of the reflex arc are correct, but for some reason the anatomical definition is more often used, although the concept of a reflex arc refers to physiology, not anatomy.
Remember that the pattern of any reflex arc must begin with a stimulus, although the stimulus itself is not part of the reflex arc. The reflex arc ends with an effector organ, which gives a response. There are not many types of effectors.
Types of effectoro V:
1) striated muscles of the body (fast white and slow red),
2) vascular smooth muscles and internal organs,
3) exocrine glands (for example, salivary glands),
4) glands internal secretion(eg adrenal glands).
Accordingly, 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 secretion of secretions by glands.
Types of reflex arcs:
1. Elementary (simple)
reflex arc without conditioned reflex.
The simplest one contains only 5 elements: receptor - afferent ("bringing") neuron - intercalary neuron - efferent ("outgoing") neuron - effector. It is important to understand the meaning of each element of the arc. Receptor: converts stimulation into nervous excitement. Afferent neuron: Delivers sensory stimulation to the central nervous system, to the interneuron. Interneuron: converts incoming excitation and directs it along the right way. So, for example, an interneuron can receive sensory ("signal") excitation, and then transmit another excitation - motor ("control"). Efferent neuron: delivers control excitation to the effector organ. For example, motor excitation - on a muscle. The effector responds.
The figure on the right shows an elementary reflex arc using the example of the knee reflex, which is so simple that it does not even have interneurons.
2. Conceptual reflex arc diagram E.P. Sokolova. It contains not one schematic receptor, but many. It also contains predictors, detector neurons and command neurons. The excitability of command neurons is controlled by general and local modulators.
The figure on the left shows a slightly modified diagram of the conceptual reflex arc. Added stimuli (incentives) and explanations.
3. Multi-storey arc of unconditioned reflex E.A. Asratyan. This diagram shows that in fact there are parallel arcs for the same unconditioned reflex on 5 different floors of the nervous system: 1) in the spinal cord, 2) in the medulla oblongata, 3) in the middle, 4) in the intermediate and 5) in the cerebral hemispheres brain
Ezras Asratovich. Asratyan (a prominent Soviet neurophysiologist, a student of I.P. Pavlov, who elevated his teaching into dogma), studying the unconditioned reflexes of normal and decorticated (deprived of the cerebral cortex) animals, came to the conclusion that central part The arc of the unconditioned reflex is not single-line, but has a multi-level structure, that is, it consists of many branches that pass through various “floors” of the central nervous system: the spinal cord, medulla oblongata, stem sections, etc. (see Fig. ). The highest part of the arc passes through the cortex cerebral hemispheres brain, it is the cortical representation of this unconditioned reflex and personifies corticolization (control by the cortex) of the corresponding function.
Based on the location of the neurons involved in the reflex, reflexes can be divided into the following types:
spinal reflexes: neurons are located in the spinal cord,
· bulbar reflexes: carried out with the obligatory participation of neurons medulla oblongata,
Mesencephalic reflexes: carried out with the participation of midbrain neurons
diencephalic reflexes: they involve neurons of the diencephalon
· cortical reflexes: carried out with the participation of neurons in the cerebral cortex.
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 oblongata and spinal cord - always participate. On the other hand, with reflexes that are carried out by the dorsal or oblongata, middle or diencephalon, nerve impulses reach the higher parts of the central nervous system.
4. Double sided arc of the conditioned reflex E.A. Asratyan. It shows that during the development of a conditioned reflex, opposing temporary connections are formed and both stimuli used are simultaneously both conditioned and unconditioned.
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 by an air flow (the effector is the contracting muscle of the eyelid), the right one is the salivary unconditioned reflex to irritation of the tongue with acid (the effector is salivary gland secreting saliva). Due to the formation of temporary conditioned reflex connections in the cerebral cortex, effectors begin to respond to stimuli that are normally inadequate for them: blinking in response to acid in the mouth and salivation in response to blowing air into the eye.
5. Reflex ring N.A. Bernstein. This diagram shows how movement is reflexively adjusted depending on the achievement of the set goal.
6. Functional system PC. Anokhina. This diagram shows the management of complex behavioral acts aimed at achieving a useful planned result. The main features of this model: an acceptor of the result of an action and feedbacks between elements.
7. Double arc of the conditioned salivary reflex. This diagram shows that any conditioned reflex must consist of two reflex arcs formed by two different unconditioned reflexes, because Each stimulus (conditioned and unconditioned) generates its own unconditioned reflex.
All activity of the nervous system is of a reflex nature, i.e. consists of huge amount various reflexes different levels complexity. Reflex- this is the body’s response to any external or internal influence involving the nervous system. Reflex- this is an adaptive reaction of the body, providing a subtle, precise and perfect balance of the body with the state of external or internal environment. "If you turn off all receptors, then a person should fall asleep dead asleep and never wake up" (I.M. Sechenov). Thus, the nervous system works on the principle of reflection: stimulus - response. Authors reflex theory are outstanding domestic physiologists I.P. Pavlov and I.M. Sechenov.
For any reflex to occur, a special anatomical education- reflex arc. A reflex arc is a chain of neurons along which a nerve impulse passes from the receptor (perceiving part) to the organ that responds to irritation.
The reflex arc consists of 5 links:
1. receptor, perceiving external or internal influences; receptors convert the influencing energy into the energy of a nerve impulse; receptors have very high sensitivity and specificity (certain receptors perceive only certain type energy)
2. sensitive (centripetal, afferent) a neuron formed by a sensory neuron through which the nerve impulse enters the central nervous system
3. interneuron, lying in the central nervous system, along which the nerve impulse switches to the motor neuron
4. motor neuron (centrifugal, efferent), along which the nerve impulse is conducted to the working organ that responds to irritation
5. nerve endings- effectors, transmitting a nerve impulse to a working organ (muscle, gland, etc.)
The reflex arcs of some reflexes do not have interneurons, for example the knee reflex.
Each reflex has:
- reflex time - the time from the application of irritation to the response to it
- receptive field - a certain reflex occurs only when a certain receptor zone is irritated
- nerve center - a specific localization of each reflex in the central nervous system.
The nervous activity of the human body consists of transmitting impulses. One of the results of such transfers is reflexes. In order for a certain reflex to be performed by the body, a connection must be established from receiving the signal to the response to the stimulus.
A reflex is a reaction of a part of the body to changes in the external or internal environment as a result of influence on receptors. They can be located on the surface of the skin, generating exteroceptive reflexes, as well as on internal organs and blood vessels, which underlies the interorecessive or myostatic reflex.
Responses to stimuli are, by their nature, conditional and unconditional. The second group includes reflexes, the arc of which has already been formed at the time of birth. In the first, it is created under the influence of external factors.
What does the reflex arc consist of?
The arc itself represents the entire path of a nerve impulse from the moment a person comes into contact with the stimulus to the manifestation of a response. The reflex arc contains various types neurons: receptor, effector and intercalary.
The reflex arc of the human body works like this:
- receptors perceive irritation. Most often, such receptors are the processes of centripetal-type nerve fibers or neurons.
- the sensitive fiber transmits excitation to the central nervous system. The structure of the sensitive neuron is such that its body is located outside the nervous system; they lie in a chain in the nodes along the spine and at the base of the brain.
- switching from fiber sensitive type The motor part occurs in the spinal cord. The brain is responsible for the formation of more complex reflexes.
- the motor fiber carries excitation to the reacting organ. This fiber is an element of a motor neuron.
The effector is actually the reacting organ itself, responding to irritation. The reflex reaction can be contractile, motor or excretory.
Polysynaptic arcs
Polysynaptic is a three-neuron arc in which a nerve center is located between the receptor and the effector. This arc is clearly illustrated by withdrawing the hand in response to pain.
Polysynaptic arcs have a special structure. Such a circuit necessarily passes through the brain. Depending on the location of the neurons processing the signal, there are:
- spinal;
- bulbar;
- mesencephalic;
- cortical.
If the reflex is processed in upper parts central nervous system, then neurons also take part in its processing lower sections. Parts of the brain stem and spinal cord are also involved in the formation of high-level reflexes.
Whatever the reflex, if the continuity of the reflex arc is disrupted, then the reflex disappears. Most often, such a rupture occurs as a result of injury or illness.
In complex reflexes to react to a stimulus, the links of the chain include various organs, which can change the behavior of the body and its systems.
The structure of the arc of the blink reflex is also interesting. This reflex, due to its complexity, makes it possible to study the movement of excitation along an arc, which is difficult to study in other cases. The reflex arc of this reflex begins with the activation of excitatory and inhibitory neurons simultaneously. Depending on the nature of the damage, different parts of the arc are activated. The onset of the blink reflex can be triggered by trigeminal nerve- response to touch, auditory - response to a sharp sound, visual - response to a change in light or visible danger.
The reflex has early and late components. The late component is responsible for generating the response delay. As an experiment, touch the skin of the eyelid with your finger. The eye closes with lightning speed. When the skin is touched again, the reaction is slower. After the brain processes the information received, conscious inhibition of the acquired reflex occurs. Thanks to this inhibition, for example, women very quickly learn to paint their eyelids, overcoming the natural desire of the eyelid to cover the cornea of the eye.
Other variants of polysynaptic arcs are also amenable to research, but they are often too complex and not very clear to study.
No matter what heights science has reached, the blinking and knee reflexes remain the basic reflexes for studying human reactions. Study and measurement of the speed of impulse passage in the trigeminal and facial nerves are the basis for assessing the state of the brain stem during various pathologies and pain.
Monosynaptic reflex arc
An arc that consists of only two neurons, which is quite enough for an impulse, is called monosynaptic. A classic example of a monosynaptic arc is the knee jerk reflex. That's why detailed diagram reflex arc of the knee is located in all medical textbooks. The peculiarity of the composition of such an arc is that it does not involve the brain. The knee reflex is an unconditioned muscle reflex. In humans and other vertebrates, such muscle reflexes are responsible for survival.
It is not surprising that it is the knee reflex that is checked by a neurologist as one of the indicators of the state of the somatic nervous system. When a hammer hits a tendon, the muscle is stretched, after the irritation passes through the centripetal fiber to spinal node, signal through the motor neuron into the centrifugal fiber. Skin receptors do not take part in this experiment, however, the result is very noticeable and the strength of the reaction is easy to differentiate.
The autonomic reflex arc breaks into pieces, forming a synapse, whereas in the somatic system the path covered by the impulse from the receptor to the acting skeletal muscle, is not interrupted by anything.
Reflexes. Reflex arc.
A reflex is a reaction of the body in response to irritation of receptors, occurring with the participation of the nervous system. When an adequate stimulus acts on the receptor of a sensory neuron, a volley of impulses appears in it, triggering a response action called a reflex act (reflex). Reflexes underlie most of the vital functions of our body. The reflex act is carried out by the so-called. reflex arc; this term refers to the route of transmission nerve impulses from the point of initial stimulation on the body to the organ that performs the response action.
Reflex arc composition:
1) receptors that perceive irritation
2) sensitive reflex nerve fibers
3) neurons and synapses, transmitting impulses to effector neurons
4) effector (motor) nerve fibers
5) executive body
I. Types of reflex arcs by structure:
1. Simple. The reflex arc that causes contraction of a skeletal muscle consists of at least two neurons: a sensory neuron, whose body is located in the ganglion, and the axon forms a synapse with neurons of the spinal cord or brain stem, and a motor (lower or peripheral, motor neuron), whose body is located in gray matter, and the axon ends at the motor end plate on skeletal muscle fibers.
2. Difficult. The reflex arc between the sensory and motor neurons may also include a third, intermediate, neuron located in the gray matter. The arcs of many reflexes contain two or more interneurons.
Examples of reflex arcs:
Reflex actions are carried out involuntarily, many of them are not realized.
1. Knee reflex (simple arc), for example, caused by tapping the quadriceps tendon in the knee area. This is a two-neuron reflex, its reflex arc consists of muscle spindles (muscle receptors), a sensory neuron, a peripheral motor neuron and a muscle.
2. Another example is (complex arc) reflexive withdrawal of the hand from a hot object: The arc of this reflex includes a sensory neuron, one or more interneurons in the gray matter of the spinal cord, a peripheral motor neuron, and a muscle.
Complex reflexes.
Many reflex acts have significantly more complex mechanism. The so-called intersegmental reflexes are made up of combinations of simpler reflexes, in the implementation of which many segments of the spinal cord take part. Thanks to such reflexes, for example, those that are closed in the brain include movements associated with maintaining balance. Visceral reflexes, i.e. reflex reactions of internal organs, mediated by the autonomic nervous system; they provide emptying bladder and many processes in the digestive system.
