Reflexes Earlier we talked about how the simplest neural networks are organized. Thus, in Hydra, some branches of the nervous network are directed to receptor cells, and others to contractile cells. This organization of connections makes it possible to implement the simplest algorithm of behavior - reaction to

After a complete transverse section of the spinal cord, the flexion, or flexor, muscles are restored before others. spinal cord reflexes, occurring in response to painful skin irritation, such as an injection. With the flexion reflex, when it is completely restored, simultaneously with the contraction of the flexor muscles of the limb, it results in relaxation of the extensor muscles. At the same time, contraction of the extensor and relaxation of the flexor muscles of the opposite - contralateral - limb occurs. The flexion reflex can be caused by irritation of various areas of the skin; in this case, the nature of the response may be different, i.e., different muscle groups will participate in it. Features of the same reflex act, depending on the location of stimulation, are called local signs of the reflex.

In a spinal animal, one can also observe an extension reflex when light pressure is applied to the plantar paw pads, a scratching reflex when the lateral surface of the body is irritated, as well as a number of myotatic reflexes in response to stretching of a muscle when its tendon is struck. In some cases, due to the occurrence of the recoil phenomenon in response to strong irritation causing a flexion reflex, rhythmic movements of the limb occur. When hanging the body of a spinal dog, pressing on the sole of one of the paws causes reflex movements such as walking of all four paws (Philippson reflex). The centers of the spinal cord also carry out some reflexes of the internal organs: urination, defecation, vasomotor.

Since all of the above spinal cord reflexes persist after high transection of the spinal cord and its separation from the overlying parts of the central nervous system, then the natural conclusion is that the centers of all reflexes are located in the spinal cord below the site of transection. After removing most of the spinal cord by pushing it out of the spinal canal, from the upper thoracic to the lower lumbar segments, all spinal reflexes disappear. Certain reflexes also disappear after the destruction of certain parts of the spinal cord or after cutting the spinal roots corresponding to them.

In a person, some time after a break in the spinal cord, in addition to flexion reflexes, a rut reflex is clearly expressed, manifested in the extension of the leg in the knee joint when the tendon of the quadriceps femoris is struck, and the Achilles reflex, manifested in extension in the ankle joint when the Achilles tendon is struck. These reflexes in a “spinal” person are significantly enhanced. Some time after a complete break in the spinal cord, a person’s urination and defecation reflexes, which occur with a certain degree of stretching of the bladder and rectum, are restored. When the penis is irritated, a man may experience a reflex erection and ejaculation, i.e. swelling of the penis and ejaculation of semen.

All spinal reflexes in a person with a spinal cord interruption, due to widespread irradiation of excitation in the spinal cord, lose their normal limitation and localization. This shows that the coordination of reflex reactions is deeply disturbed due to the switching off of the inhibitory influences of the brain stem. In all likelihood, in humans, coordination in the spinal cord is less developed than in animals, due to the greater role of coordination processes occurring in the overlying parts of the central nervous system.

With local lesions of the human spinal cord, one can observe the disappearance of various reflexes depending on the location of the lesion. Thus, with damage to several thoracic segments of the spinal cord, loss of sweating and vasomotor reactions and loss of sensitivity of the skin in the corresponding metameres of the chest and abdomen, as well as motor paralysis of individual muscle groups, are observed. Such numerous observations indicate a relatively segmental location of the spinal centers. Noting the segmental localization of a number of spinal centers, it must be emphasized that the spinal cord has numerous intersegmental connections that ensure the functional unity of the entire spinal cord.

The most important human spinal reflexes studied in clinical practice, methods of inducing them, the nature of the observed reaction and the localization of spinal centers, i.e., groups of neurons involved in the implementation of these reflexes, are given in table.

The spinal cord also contains a number of effector centers related to the autonomic nervous system: the spinal center of the ocular muscles, vasomotor and sweating centers, centers for regulating the functions of the genitourinary organs and rectum, etc. The localization of these centers will be discussed in the chapter devoted to the regulation of autonomic functions.

Human spinal reflexes

Unconditioned reflexes, most often studied in the clinic and have topical diagnostic significance, are divided into superficial, exteroceptive(skin, reflexes from mucous membranes) and deep, proprioceptive(tendon, periosteal, joint reflexes).

Most reflexes that are important for self-preservation, maintaining body position, and quickly restoring balance are carried out on the basis of “fast-acting mechanisms” with a minimum number of involved neural circuits. Tendon reflexes are of great interest in clinical practice as a test of the functional state of the body in general and the locomotor system in particular, as well as for topical diagnostics in cases of spinal cord injuries.

Tendon reflexes. They are also called myotatic reflexes, as well as T-reflexes, since they are caused by stretching the muscles by hitting the tendon with a neurological hammer (from the Latin. Tendo- tendons).

Reflex from the forearm flexor tendon. It is caused by a blow with a neurological hammer on the tendon of the biceps brachii muscle in the elbow bend (Fig. 4.13, 4.14). In this case, the forearms of the subject are supported by the left hand of the one who carries out the research. Components of the reflex arc: musculocutaneous nerve, V and VI cervical segments of the spinal cord. The answer is muscle contraction and flexion. elbow joint.

Reflex from the triceps tendon. Caused by a hammer blow on the triceps brachii tendon above the olecranon process (see Fig. 4.13, 4.14). In this case, the arm of the person being examined should be bent at a right or obtuse angle and supported by the left hand of the one doing the research. The resulting reaction is muscle contraction and extension of the arm at the elbow joint. Components of the reflex arc: radial nerve, VII-VIII segments of the cervical spinal cord.

Rice. 4.13. Reflexes from the upper limbs

1 - reflex from the biceps tendon;

2 - reflex from the triceps tendon;

3 - metacarpal radial reflex

Rice. 4.14. The most important proprioceptive reflexes (according to P. Duus, 1995):

1 - reflex from the forearm flexor tendon

2 - reflex from the tendon of the triceps brachii muscle;

3 - knee reflex;

4 - reflex from the Achilles tendon

Knee reflex. Occurs when a hammer hits the ligament below the kneecap (see Fig. 4.14, Fig. 4.15]. The subject sits on a chair, placing his legs so that the shins are at an obtuse angle to the thighs, and the soles touch the floor. Another way is for the subject to sit on a chair and crosses his legs. It is convenient to study the knee reflex when the subject lies on his back with his legs half-bent at the hip joints, and the one doing the research brings his left hand under his legs in the area of ​​the popliteal fossa for maximum relaxation of the thigh muscles and applies the right hand. hand blow with a hammer. The reflex consists of contraction of the quadriceps muscle of the thigh and extension of the leg at the knee joint.

Components of the reflex arc: femoral nerve, III and IV lumbar segments of the spinal cord.

Achilles tendon reflex. Caused by a hammer hitting the Achilles tendon (see Fig. 4.14,4.15). The study can be carried out by placing the person being examined on his knees on a couch or on a chair so that the feet hang freely and the hands rest against the wall or the back of the chair. Can

Rice. 4.15. Reflexes from the lower extremities

1 - knee reflex; 2 - Jendraszek's maneuver; 3 - reflex from the Achilles tendon; 4 - plantar reflex

to examine when the subject lies on his stomach - in this case, the one who carries out the research, grasping the toes of both feet of the subject with his left hand and bending his leg at a right angle at the ankle and knee joints, strikes with a hammer with his right hand. The reaction is plantar flexion of the foot. Components of the reflex arc: tibial nerve, I-II sacral segments of the spinal cord.

Skin reflexes

Superficial abdominal reflexes. A quick stroke across the skin of the abdomen in the direction from the outside to the midline (below the costal arches - upper, at the level of the navel - middle and above the inguinal fold - lower abdominal reflexes) causes contraction of the muscles of the abdominal wall. Elements of reflex arcs: intercostal nerves, thoracic segments of the spinal cord (VII-VIII for the upper, IX-X for the middle, XI-XII for the lower abdominal reflexes).

Plantar reflex caused by applying a blunt object to the skin of the outer edge of the sole, resulting in flexion of the toes (see Fig. 4.15). The plantar reflex is evoked better when the subject lies on his back and his legs are slightly bent. Research can be carried out with the subject kneeling on a couch or chair. Elements of the reflex arc: hydnic nerve, V lumbar - I sacral segments of the spinal cord.

Periosteal reflex

Metacarpal radial reflex. Caused by a hammer blow on the styloid process of the radius (see Fig. 4.13). The response is flexion of the arm at the elbow joint, pronation of the hand and flexion of the fingers. When studying the reflex, the arm should be bent at a right angle at the elbow joint, the hand should be slightly pronated. In this case, the hands can lie on the hips of the subject, sitting, or restrain the left hand of the one who is examining. Components of the reflex arc: nerves - median, radial, musculocutaneous; V-VIII cervical segments of the spinal cord, innervating the pronator muscles, brachioradialis muscle, finger flexors, biceps brachii muscle.

H-stretch reflex (Hofmann) is caused in a person by electrical irritation in the popliteal fossa (voltage up to 30 V) - an effect on the tibial nerve. Effector - soleus muscle. Electromyographic registration (Fig. 4.16).

Intersegmental reflexes - participate in locomotion (cross pendulum). Caused in a supine position by strong compression of the Achilles tendon or flexion of the foot of one of the limbs. It turns out that the motor program for the act of walking is genetically fixed.

Rice. 4.16. Evoking and recording H-reflexes and T-reflexes in humans

A - Scheme of the experimental setup. A hammer with a contact switch causes the T-reflex in the triceps surae muscle. Closing the contact at the moment the hammer hits triggers the reversal of the oscilloscope beam and electromyographic recording of the response occurs. To induce the H-reflex, the tibial nerve is irritated through the skin with rectangular current pulses lasting 1 ms. The stimulus and deflection of the oscilloscope beam are synchronized.

B - N-responses and M-responses with increasing stimulus intensity.

B - Graph of the dependence of the amplitude of H-responses and M-responses (ordinate) on stimulus intensity (abscissa) (according to R. Schmidt, G. Tevs, 1985)

Reflex – a complex formation consisting of nerve endings, dendrites, sensory neurons, glia, and special tissue cells, which together ensure the transformation of the influence of external or internal environmental factors into a nerve impulse.

Receptive field of reflex– a surface with receptors, the irritation of which causes a reflex reaction.

According to the anatomical location of the central part of the reflex souls, they are distinguished:

Spinal reflexes

Brain reflexes

Neutrons located in the spinal cord are involved in the implementation of spinal reflexes. An example would be dropping your hand.

Spinal reflexes:

1. Myotatic – muscle stretch reflexes.

2. Reflexes from receptors

3. Visceromotor - a reflex to irritation of the afferent nerves of internal organs.

4. Reflexes of the autonomic nervous system - ensure the reaction of internal organs to irritation of visceral, muscle and skin receptors.

Examples of reflexes: knee, Achilles, plantar, abdominal, flexion and extension reflexes of the forearm.

The phenomenon of spinal shock, its mechanism.

Spinal shock- caused by injury or rupture of the spinal cord. It is expressed in a sharp drop in excitability and inhibition of the activity of all reflex centers of the spinal cord located below the site of transection (injury).

Cause of shock consists mainly in turning off the regulatory influences of the overlying parts of the central nervous system (reticular formation, cortex big brain etc.). During shock, hyperpolarization of the postsynaptic membrane of spinal cord motor neurons is observed, which is the basis of inhibition. Obviously, under natural conditions, the higher parts of the central nervous system excite and tone the centers of the spinal cord. After a traumatic rupture of the spinal cord at the level of the II-XII thoracic segments (as happens in a car accident), complete paralysis of both upper and lower extremities occurs, which is characterized by the disappearance of all voluntary movements innervated by the segments lying below the level of injury, as well as temporary impairment of reflexes, arch which connects in these segments. At the same time, tactile, temperature, proprioceptive and pain sensitivity is completely lost due to the rupture of the ascending pathways.

Involuntary motor reflexes are gradually (over weeks and months) restored (first bending, later extension). During this period, the reflexes even intensify (stage of hyperreflexia) along with an increase in muscle tone and the appearance of pathological reflexes (for example, the Babinski reflex).

The concept of genetically determined neural networks.

1. Hierarchical networks. Found in major sensory and motor pathways. In sensory systems it is ascending in nature; it includes various cellular levels, through which information flows to higher centers. Motor systems are organized according to a descending hierarchy.
Hierarchical systems provide very precise information transfer. As a result of convergence or divergence, information is filtered and signals are amplified.

2. Local networks . Their neurons keep the flow of information within a single hierarchical level. They can have an excitatory or inhibitory effect on neurons. The combination of these features with divergence and convergence results in an even more accurate transfer of information.

Most motor reflexes are carried out with the participation of spinal cord motor neurons.

Actually muscle reflexes (tonic reflexes) occur when the stretch receptors of muscle fibers and tendon receptors are irritated. They manifest themselves in prolonged muscle tension when they are stretched.

Defensive reflexes are represented by a large group of flexion reflexes that protect the body from the damaging effects of excessively strong and life-threatening stimuli.

Rhythmic reflexes manifest themselves in the correct alternation of opposite movements (flexion and extension), combined with tonic contraction of certain muscle groups (motor reactions of scratching and stepping).

Position reflexes (postural) are aimed at long-term maintenance of contraction of muscle groups that give the body posture and position in space.

The consequence of a transverse section between the medulla oblongata and the spinal cord is spinal shock. It is manifested by a sharp drop in excitability and inhibition of the reflex functions of all nerve centers located below the site of transection.

Lecture No. 7. Physiology of the brain.

Plan:

Medulla oblongata.

Hindbrain.

Midbrain.

Diencephalon.

Reticular formation.

Bark.

Bioelectrical activity of the brain.

The direct continuation of the spinal cord is the medulla oblongata. The medulla oblongata and the pons (pons) together with the midbrain and diencephalon form brain stem. The brainstem contains large number nuclei, ascending and descending pathways. The reticular formation located in the brain stem has important functional significance.

In the medulla oblongata there is no clear segmental distribution of gray and white matter. The accumulation of nerve cells leads to the formation of nuclei, which are the centers of more or less complex reflexes. Of the 12 pairs of cranial nerves connecting the brain with the periphery of the body, eight pairs (V-XII) originate in the medulla oblongata. The medulla oblongata performs two functions- reflex and conductive.

Reflex function of the medulla oblongata. Due to the activity of the medulla oblongata, the following occurs:

1) protective reflexes (blinking, tearing, sneezing, cough and gag reflexes);

2) setting reflexes, providing muscle tone necessary to maintain posture and perform work acts;

3) labyrinthine reflexes, which contribute to the correct distribution of muscle tone between individual muscle groups and the establishment of one or another body posture;

4) reflexes associated with the functions of the respiratory, circulatory, and digestive systems.

Conducting function of the medulla oblongata. The ascending tracts from the spinal cord to the brain and the descending tracts connecting the cortex pass through the medulla oblongata cerebral hemispheres with the spinal cord.

Reflex centers of the medulla oblongata. The medulla oblongata contains a number of vital centers: respiratory, cardiovascular and nutritional centers. The medulla oblongata regulates the functioning of the spinal cord.

The hindbrain consists of the pons and cerebellum.

The cerebellum is an unpaired formation; located behind the medulla oblongata and the pons, covered above by the occipital lobes of the cerebral hemispheres.

Movement disorders after removal of the cerebellum:

- atony- disappearance or weakening of muscle tone;

- asthenia- decreased strength of muscle contractions;

- astasia- loss of the ability to perform tetanic contractions,

Ataxia is a violation of movement coordination.

The whole complex of movement disorders with damage to the cerebellum is called cerebellar ataxia.

Midbrain.

The formations of the midbrain include the cerebral peduncles, nuclei of the III (oculomotor) and IV (trochlear) pairs of cranial nerves, the plate of the roof (quadrigeminal), red nuclei and substantia nigra. The ascending and descending nerve pathways pass through the cerebral peduncles.

The anterior tubercles of the roof plate receive impulses from the retina of the eyes. Posterior tubercles of the roof plate - from the nuclei of the auditory nerves

Red kernels participate in the regulation of muscle tone and in the manifestation of adjustment reflexes, ensuring the maintenance of the correct position of the body in space. When the hindbrain is separated from the midbrain, the tone of the extensor muscles increases, the animal's limbs tense and stretch, and the head is thrown back.

Black matter also regulates muscle tone and maintaining posture, is involved in the regulation of the acts of chewing, swallowing, blood pressure and breathing, i.e. the activity of the substantia nigra is closely related to the work of the medulla oblongata.

Thus, the midbrain regulates muscle tone, which is a necessary condition for coordinated movements.

Tonic reflexes are divided into two groups: static and statokinetic. Static reflexes occur when the position of the body, especially the head, changes in space. Statokinetic reflexes appear when the body moves in space, when the speed of movement changes (rotational or linear).

Due to the midbrain, the reflex activity of the body expands (orienting reflexes to sound and visual stimuli appear).

Diencephalon.

The diencephalon is part of the anterior part of the brain stem. The main formations of the diencephalon are visual cortex (thalamus) and subtubercular region (hypothalamus).

Visual tuberosities- massive paired formation, they occupy the bulk of the diencephalon. Through the visual hillocks, information from all receptors in our body, with the exception of the olfactory ones, arrives to the cerebral cortex.

If the visual tuberosities are damaged, a person experiences a complete loss of sensitivity or a decrease in sensitivity by opposite side, the contraction of facial muscles that accompanies emotions disappears, sleep disorders, decreased hearing, vision, etc. may occur.

Hypothalamic (subthalamic) region participates in regulation various types metabolism (proteins, fats, carbohydrates, salts, water), regulates heat generation and heat transfer, sleep and wakefulness. In the nuclei of the hypothalamus, a number of hormones are formed, which are then deposited in the posterior lobe of the pituitary gland. The anterior parts of the hypothalamus are the highest centers of the parasympathetic nervous system, the posterior parts of the sympathetic nervous system. The hypothalamus is involved in the regulation of many autonomic functions of the body.

Basal ganglia.

The subcortical, or basal, nuclei include three paired formations: the caudate nucleus and the shell of the lentiform nucleus (or striatum) and the globus pallidus. The basal ganglia are located inside the cerebral hemispheres, in their lower part, between the frontal lobes and the diencephalon.

Striatum regulates complex motor functions, unconditioned reflex reactions of a chain nature: running, swimming, jumping. In addition, the striatum, through the hypothalamus, regulates the autonomic functions of the body, and also, together with the nuclei of the diencephalon, ensures the implementation of complex unconditioned reflexes of a chain nature - instincts.

Pale ball is the center of complex motor reflex reactions (walking, running), forms complex facial reactions, and participates in ensuring the correct distribution of muscle tone. When the globus pallidus is affected, movements lose their smoothness, become clumsy, and constrained.