A simple reflex arc begins. Reflex. reflex arc

The knee jerk is also known as the patellar reflex. The unconditioned reflex, which belongs to the group of stretch reflexes, is caused by a light blow to the tendon of the quadriceps femoris muscle under the patella. Upon impact, the tendon is stretched, which causes the muscle to bring the lower leg into extension.

reflex arc

A reflex is a response of the body's nervous system to an external stimulus. The reflex arc of the knee includes the elements:

• Receptors. Axon ends or bodies of epithelial cells. The nerve fiber signals towards the center. After receiving the irritation signal, excitation occurs. Receptors are located in the skin, organs. They are the building blocks of the sense organs.
• Nerve fibre. Conducts a signal to the center. The bodies of neurons are located near the brain, in the nerve plexuses in the spinal cord.
• Nerve center. The place from where the signal is transmitted from the afferent neurons to the efferent.
• Efferent fiber. It is a long process of a centrifugal neuron.
• effector. An organ that responds to receptor stimulation.

Stages of passage of a nerve impulse

In the mechanism of action of the knee jerk, one connection of neurons is characteristic. The impulse originates in the region of the proprioreceptors of the quadriceps femoris, which act as sensitive sensors. Then the impulse is transmitted to the lumbar region.

Closure of the reflex arc of the knee jerk occurs at the level of L2-L4, from where the impulse goes to motor neurons, which are located near the anterior horns of the spinal cord. After that, the motor fibers transmit the impulse to the quadriceps muscle, which extends the lower leg.

Scheme of the reflex arc of the knee jerk

The physiology of the knee jerk is as follows. When the stimulus acts, the sensory fibers fix the impulse. After that, it is transmitted to the efferent centers of the spinal cord, from where, after instantaneous processing of information, a return signal comes. When reaching the muscles, the signal causes them to contract, and the body part moves. If there is no reaction, then the patient is susceptible to the pathology of the tissue of the muscles, brain, parts of the nervous system.

The reason for the lack of a knee jerk may be the severe emotional state of the patient.

Description of techniques for testing the knee jerk

The neurologist checks the knee reflex by performing actions with the following patient positions:

• The patient is seated on a chair, while one of his legs is thrown over the other.
• The doctor holds the leg of the patient lying on the table at an obtuse angle.
• The patient sits on a chair, legs down.
• The patient is placed on the couch in the supine position, one leg is on the knee of the other.

The neurologist easily strikes the ligament of the patella with a neurological hammer, this action leads to extension of the lower leg. At this time, the patient must turn off conscious control of movements. To this end, the doctor may suggest that he perform mental operations. Assess the knee reflex by the magnitude of the deviation of the lower limb. Which way to check the knee reflex to apply, the doctor chooses.

Deviations

Normally, the knee joint reflex is characterized by an average degree of tendon reactions, which is called normoreflexia. In case of violations of the functions of the nervous system, a signal transmission failure is observed, which leads to the development of the following conditions:

hyperreflexia

The check fixes the maximum extension of the lower leg. A similar phenomenon is often the result of deviations, accompanied by irritation of the motor fibers:

• Intoxication.
• Polyneuritis.
• Radiculitis.

Hyperreflexia is also observed in healthy people of a neurotic warehouse.

Hyporeflexia

It is characterized by a weak reaction of the knee to the stimulus due to a failure in the conduction of the reflex arc. A sharp decrease in human weight, infectious diseases provoke the depletion of neurons and the failure of cell functions. The reason for the disappearance of the reaction is also the transferred anesthesia.

Brain pathologies can lead to the absence of a reflex

Areflexia

It is most often found in pathologies of the central nervous system. With areflexia, there is no reaction to the stimulus. The reason for its absence is often paralysis. Temporary areflexia appears if the femoral artery is clamped, during anesthesia, during an epileptic attack. A change in the strength of the knee reflex is evidence of a pathology of the nervous system.

Composite components of stretch reflexes

Tension reflexes are characterized by dynamic and static components. The statistical component has an effect during muscle stretching. The duration of the dynamic component is short-term, it occurs as a result of a change in the length of the muscle.

Types of muscle fibers

Muscle fibers involved in the knee jerk:

• Nuclear chain fibers. Due to their structure, they provide a static component. Thin long fibers are characterized by uniform stretching. With their extension, the endings of the neurons of the arc significantly increase the frequency of signals, which is the mechanism of the static component.
• Nuclear marsupial fibers. In the middle they have a bulge, around which the ends of the nerves are wrapped, carrying a signal about the onset of stretching. The middle of the fiber is able to quickly elongate when it is stretched. The sides of the fiber resist rapid stretching, but stretching still occurs when the fiber is stretched for a short time.

From this it follows that if the fibers are subjected to rapid stretching, the middle will take on the lion's share of the stretch, while stretching the side parts, the middle will contract. The nerve ending first gives intense signals, then the frequency flow of impulses decreases due to the stretching of the lateral parts, and the middle again becomes shorter.

Stretching the tendon as a prerequisite for the manifestation of the knee jerk

You can conduct an experiment to reveal the features of the reflexes of the spinal cord. It is known that stretching the tendon leads to extension of the lower limb at the knee. During the demonstration, the reflex will weaken if the leg is clamped by the subject. To distract him, they offer to squeeze his hands into the lock.

During the experiment, a blow is made with a medical hammer on the tendon. If the blow does not stretch the tendon, there will be no reaction. From this we can draw conclusions: the knee reflex occurs only if there is a tendon stretch, when impulses enter the spinal cord, after which they enter the spinal cord through motor neurons.

Should deviations be treated?

Hyperreflexia, hyporeflexia are not independent diseases, they only signal damage to the central nervous system. It is possible to eliminate violations of the function of each link of the knee reflex in the following ways:

• In case of infection of the brain, antibiotic treatment is carried out.
• If mental disorders appear, psychic blockers are used.
• When diagnosing radiculitis, they are treated with anti-inflammatory steroids.
• With paralysis of the legs caused by hemorrhage, post-stroke therapy is performed.
• In the presence of intoxication, cleansing of the body is indicated.

It is important to establish the cause of the violation of the knee jerk to match the sequence of treatment of the disease that caused the pathology. The study of the causes after the designation of violations of the knee jerk includes hardware studies and laboratory diagnostics.

When nerve fibers are torn, resulting in paralysis, surgical stitching is performed

A special method of treating disorders of the knee reflex is massage, as well as therapeutic exercises. Useful activities in the pool. If knee sensitivity fails, constant monitoring is required, as the risk of hidden pathologies is increased. Maintaining a healthy lifestyle, eliminating stressful situations contribute to obtaining a positive result in the treatment of disorders of the knee joint, which persists for life.

Reflex arc diagram

NERVOUS SYSTEM

Meaning:

1. Maintaining a constant composition of the internal environment of the body ( homeostasis)
2. Coordination of the work of cells, tissues, organs, organ systems
3. The connection of the organism with the external environment
4. Provides conscious behavior, thinking, speech.

Features of the structure of the nervous tissue:

Neuron A nerve cell that receives, transmits and stores information.

Gray matter - accumulation tel neurons and short processes - dendrites.

White matter - accumulation of long processes of neurons - axons covered with white

fatty myelin sheath.

Types of neurons

1. sensitive (centripetal) - transmit impulses from the sense organs to the spinal cord or brain. Their bodies are located in the nerve nodes.
2. Motor (centrifugal)) - transmit impulses from the central nervous system to the muscles and internal organs.
3. Insertion- communicate between sensory and motor neurons. Located in the CNS.

Nerves - bundles of neuronal processes extending beyond the CNS (types: sensitive

ny, motor, mixed).

Nerves (ganglia) - accumulation of neuron bodies outside the CNS

The structure of the nervous system

REFLEX

Reflex - response to stimuli from the external or internal environment, carried out with the participation of the nervous system.

reflex arc - path along which a nerve impulse travels.

Reflex arc diagram

instincts - complex unconditioned reflexes.

Braking - weakening or inhibition of the work of nerve cells, leading to the disappearance of the reflex (temporary or permanent).

SPINAL CORD

Appearance: a white cord, 1 cm in diameter and 40 - 45 cm long, is located inside the spinal canal. 31 pairs of mixed spinal nerves depart from it (according to the number of vertebrae). On the anterior and posterior sides of the sulcus, which divide the spinal cord into left and right parts.

Internal structure:B center channel with cerebrospinal fluid. Gray matter inside in the form of a butterfly, white matter outside. In the anterior part of the gray matter are motor neurons, and in the back of the intercalary. Each spinal nerve has two roots: anterior - motor, posterior sensory and has a nerve node.

Functions:reflex- participation in motor reactions; ANS centers (regulation)

Conductor– conduction of nerve impulses in the GM – brain connection

with other parts of the CNS.

BRAIN

The reflex arc consists of:

• receptor - a nerve link that perceives irritation;
• afferent link - centripetal nerve fiber - processes of receptor neurons that transmit impulses from sensory nerve endings to the central nervous system;
• the central link is the nerve center (an optional element, for example, for an axon reflex);
• efferent link - carry out transmission from the nerve center to the effector;
• effector - an executive body whose activity changes as a result of a reflex.

Distinguish:

• monosynaptic, two-neuron reflex arcs;
• polysynaptic reflex arcs (include three or more neurons).

The simplest reflex arc in humans is formed by two neurons - sensory and motor (motor neuron). An example of the simplest reflex is the knee reflex. In other cases, three (or more) neurons are included in the reflex arc - sensory, intercalary and motor. In a simplified form, this is the reflex that occurs when a finger is pricked with a pin. This is a spinal reflex, its arc passes not through the brain, but through the spinal cord. The processes of sensory neurons enter the spinal cord as part of the posterior root, and the processes of motor neurons exit the spinal cord as part of the anterior root. The bodies of sensory neurons are located in the spinal node of the posterior root (in the dorsal ganglion), and the intercalary and motor neurons are located in the gray matter of the spinal cord.

The simple reflex arc described above allows a person to automatically (involuntarily) adapt to changes in the environment, for example, withdraw his hand from a painful stimulus, change the size of the pupil depending on the lighting conditions. It also helps to regulate the processes occurring inside the body. All this contributes to maintaining the constancy of the internal environment, that is, maintaining homeostasis.

In many cases, a sensory neuron transmits information (usually through several interneurons) to the brain. The brain processes incoming sensory information and stores it for later use. Along with this, the brain can send motor nerve impulses along the descending path directly to the spinal motor neurons; spinal motor neurons initiate the response

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.

Physiological definition of the concept of "reflex arc"

The reflex arc is a schematic path for the movement of excitation from the receptor to the effector.

Anatomical definition of the concept of "reflex arc"

The reflex arc is a set of nervous structures that ensure the implementation of the reflex act.

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

Remember that the circuit 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 so many types of effectors.

Types of effector in:

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

2) smooth muscles of blood vessels and internal organs,

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

4) endocrine glands (for example, 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 vessels, or the secretion of glands.

Types of reflex arcs:

1. Elementary (simple) reflex arc of the unconditioned reflex.
The simplest one contains only 5 elements: receptor - afferent ("bringing") neuron - intercalary neuron - efferent ("carrying out") neuron - effector. It is important to understand the meaning of each arc element. Receptor: converts irritation into nervous excitation. Afferent neuron: delivers sensory stimulation to the central nervous system, to the intercalary neuron. Intercalary neuron: transforms the incoming excitation 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 excitation to the effector organ. For example, motor excitation - on a muscle. The effector carries out the response.

The figure on the right shows an elementary reflex arc using the example of a knee jerk, which is so simple that it does not even have intercalary neurons.

2. Conceptual scheme of the reflex arc E.P. Sokolov. 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 (stimuli) and explanations.

3. Multi-storey the arc of the unconditioned reflex E.A. Hasratyan. This diagram shows that in fact there are parallel arcs for the same unconditioned reflex on 5 different levels 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 raised his teachings into a dogma), studying the unconditioned reflexes of normal and decorticated (devoid of the cerebral cortex) animals, came to the conclusion that the central part of the arc of the unconditioned reflex is not unilinear, but has a multilevel 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 figure). The highest part of the arc passes through the cerebral cortex, it is the cortical representation of this unconditioned reflex and represents corticolization (control by the cortex) of the corresponding function.

According to 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 of the medulla oblongata,

mesencephalic reflexes: carried out with the participation of midbrain neurons

diencephalic reflexes: they involve the neurons of the diencephalon

Cortical reflexes: carried out with the participation of neurons of the cerebral cortex.

In the 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 and spinal cord always participate. On the other hand, with reflexes that are carried out by the spinal or medulla oblongata, middle or diencephalon, nerve impulses reach the higher parts of the central nervous system.

4. double sided the arc of the conditioned reflex E.A. Hasratyan. It shows that during the development of a conditioned reflex, counter temporary connections are formed and both used stimuli 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 an unconditioned blinking reflex to eye irritation with an air flow (effector is a contracting eyelid muscle), the right one is a salivary unconditioned reilex to tongue irritation with acid (effector is a salivary gland that secretes saliva). Due to the formation of temporary conditioned reflex connections in the cerebral cortex, effectors begin to give responses to irritants that are not normally adequate for them: blinking in response to acid in the mouth and salivation in response to blowing air into the eye.

5. reflex ring ON THE. Bernstein. This diagram shows how the movement is reflexively adjusted depending on the achievement of the goal.

6. Functional system PC. Anokhin. This diagram shows the management of complex behavioral acts aimed at achieving a useful planned result. The main features of this model are: an acceptor of the result of an action and feedbacks between elements.

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