Classic autonomic cardiac reflexes. Autonomic reflexes and centers for the regulation of autonomic functions
Parasympathetic nervous system consists of two sections: the brain (medulla oblongata and midbrain) and the sacral, and its ganglia are located either near the innervated organ or directly in it.
The parasympathetic nervous system also regulates the activity of almost all tissues and organs.
The mediator that transmits excitation of the parasympathetic nervous system is acetylcholine.
Excitation of parasympathetic centers is observed in a state of rest - during sleep, rest, after eating. In this case, the following vegetative reactions occur:
· bronchi dilate, breathing slows down;
· heart contractions slow down and weaken;
· blood pressure in the vessels decreases;
· skin vessels dilate;
· the vessels of the abdominal organs dilate and digestion processes intensify;
· the processes of urine formation intensify;
· the work of the endocrine glands and sweat glands slows down;
· the pupil of the eye narrows;
· skeletal muscles relax;
· inhibition of brain neurons occurs - drowsiness occurs;
· the amount of blood in the vessels decreases, a certain amount leaves the vessels to the liver and spleen.
Neurons of the sympathetic and parasympathetic system take part in the formation of certain autonomic reflexes. Autonomic reflexes manifest themselves in changes in the state of internal organs when the body position changes and when receptors are irritated.
Autonomic reflexes are of the following types:
· viscero-visceral reflexes;
· cutanovisceral reflexes;
· motor-visceral reflexes;
· eye-heart reflex.
Viscero-visceral reflexes – These are those reactions that are caused by irritation of the receptors of internal organs and are manifested by a change in the condition of the internal organs. For example, when blood vessels narrow, the amount of blood in the spleen increases.
Cutanovisceral reflexes– are expressed in the fact that when certain areas of the skin are irritated, vascular reactions and changes in the activity of certain internal organs occur. For example, acupressure of the skin affects the condition of internal organs. Or, applying cold to the skin causes blood vessels to constrict.
Motor-visceral reflexes- manifest themselves in changes in blood pressure and the number of heart contractions when changing body position. For example, if a person moves from a lying position to a sitting position, then his blood pressure will increase and the heart will contract more strongly.
Oculocardiac reflex- manifests itself in changes in heart function when the eyeball is irritated.
Viscero-visceral reflex. These are reflexes that arise as a result of irritation of the interoreceptors of internal organs and are manifested by changes in their functions. For example, with mechanical irritation of the peritoneum or abdominal organs, heart contractions slow down and weaken. Goltz reflex.
Viscero-somatic reflex. Excitation of vascular chemoreceptors by carbon dioxide promotes increased contractions of the intercostal respiratory muscles. When the mechanisms of autonomic regulation are disrupted, changes in visceral functions occur.
Viscero-sensory reflex. Zakharyin-Ged zones…
Viscero-dermal reflex. Irritation of the interoreceptors of internal organs leads to changes in sweating, the lumen of skin vessels, and skin sensitivity.
Somatovisceral reflex. The effect of an irritant on somatic receptors, for example skin receptors, leads to changes in the activity of internal organs. The Danini-Aschner reflex belongs to this group.
Dermo-visceral reflex. Acupuncture medicine.
Central mechanisms of regulation of autonomic functions.
The structures are localized in the central nervous system and provide either coordination of visceral reflexes and (or) coupling of visceral and motor reflexes when performing integral behavioral acts. They set the tone of the peripheral autonomic nerves, which ensures a constant tonic influence of the autonomic nervous system on the functions of the organ (increase or decrease).
Levels of autonomic regulation.
Spinal level.
It is represented by the bodies of preganglionic autonomic neurons, which are arranged in small cell nuclei of the spinal cord (intermedial nuclei of the lateral horns of the spinal cord). Conducting pathways carry effector signals from the brain to the preganglionic ones and afferent ones: from visceroreceptors to various parts of the brain.
Manifests itself in the form of phenomena:
In diseases of the internal organs, reflex tension of the striated abdominal muscles occurs and strictly corresponds to the localization of the pathological process. Irradiation of excitation occurs from spinal autonomic neurons to motor neurons of the same segment, which are located nearby.
If internal organs are damaged, there may be reddening of the skin area - a viscerocutaneous reflex.
Innervated by afferent and efferent fibers of a certain segment of the spinal cord. This is due to the fact that at the segment level, with the arrival of pathological signals, sympathetic preganglionic neurons, which would normally have a vasoconstrictor effect, are reflexively inhibited. Inhibition of sympathetic neurons leads to redness of the skin area; the phenomenon of increased skin sensitivity (hyperesthesia) and increased pain sensitivity (hyperalgesia) appears in a limited area of the skin. With angina pectoris, ischemic heart disease – pain in the heart, under the left shoulder blade and in the skin of the left arm.
Associated with the segmental level - afferent autonomic neurons from the affected organ in this segment converge with afferent neurons from the dermis at the level of segment 1 and switch to common afferent neurons of the spinothalamic tract, and the spinothalamic tract carries pain information to the thalamus and cerebral cortex. The pain center in the cortex attributes the sensation of pain to the skin and internal organs.
The phenomenon of referred pain is used for diagnosis and reflects the autonomic principle of regulation.
Stem level.
The autonomic centers of the medulla oblongata, pons and midbrain are active. There is no segmental structure; there is an accumulation of gray matter nuclei, the localization of which is difficult to determine.
Localization of centers.
1. Circulatory (medulla oblongata) – regulation of blood circulation.
Vasomotor
Regulation of cardiac activity.
Parasympathetic fibers travel as part of the vagus nerve to the circulatory organs and provide involuntary regulation of blood pressure levels.
Regulation of complex motor processes. Changing the position of the body in space - orthostatic test.
2. Urination (bridge).
3. Salivation.
4. Center that regulates the activity of the glands of the stomach and intestines.
5. Tear secretion.
Hypothalamic level.
3 departments, their excitement leads to changes in functions.
- front.
Centers for parasympathetic regulation of visceral functions. Excitation of these nuclei leads to constriction of the pupils, a decrease in blood pressure and cardiac activity, and an increase in the secretion of gastrointestinal glands.
- rear.
Sympathetic regulation. Opposite effects: pupil dilation, increased blood pressure.
- average.
Regulation of metabolism. Centers of innate forms of behavior associated with feelings of hunger and thirst. The thermoregulation center is located in the hypothalamus. At the level of the diencephalon, the regulatory influences of visceral and behavioral functions converge.
Cerebral cortex.
Frontal lobes: centers that provide voluntary regulation of breathing. Conditioned reflex effect on blood circulation, digestion, endocrine mechanisms.
Spinal cord (SC).
SM has segmental structure. 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1-3 coccygeal segments. Moreover, the division into segments is functional.
Each segment forms anterior and posterior roots. The posterior ones are sensitive, i.e. afferent, anterior - motor, efferent. This pattern is called Bell-Magendie law .
The roots of each segment innervate 3 body metamere, but as a result of overlap, each metamer is innervated by three segments. This applies to a greater extent to sensory innervation, and in motor it is typical for the intercostal muscles.
Morphologically, the cell bodies of spinal cord neurons form its gray matter. Functionally, all its neurons are divided into motor neurons (3%) , insert (97%), neurons somatic And autonomic nervous system.
Motor neurons, are divided into alpha, beta and gamma motor neurons. The cell bodies of motor neurons are located in the anterior horns of the spinal cord, their axons innervate skeletal muscles. α-motoneurons are phasic and tonic. β-motoneurons are small and innervate the tonic muscles.
Gamma motor neurons regulate the tension of muscle spindles, i.e. intrafusal fibers. Thus, they are involved in the regulation of skeletal muscle tone. Therefore, when the anterior roots are cut, muscle tone disappears.
Interneurons provide communication between the centers of the spinal cord and the overlying parts of the central nervous system. There are: own spinal(own reflexes of the spinal cord) somatic and vegetative; projection (receive ascending and descending signals).
Vegetative neurons of the sympathetic department of the autonomic nervous system are located in the lateral horns of the thoracic segments, and the parasympathetic ones in the sacral region.
Functions:
1. Wired (providing communication in both directions)
2. Actually reflex (segmental).
There are complex relationships between them: the subordination of segmental activity to suprasegmental centers of various functional levels.
Basic reflexes of the spinal cord
n Stretch reflexes (myotatic)- mainly extensor - posture reflexes, pushing (jumping, running) reflexes (knee)
n Flexion jerk reflexes
n Rhythmic reflexes ( carding, walking)
n Positional reflexes ( cervical tonic reflexes of Magnus position - inclination and position, 7th cervical vertebra)
n Autonomic reflexes
The conductor function is to ensure communication between peripheral receptors, centers of the spinal cord with the overlying parts of the central nervous system, as well as its nerve centers with each other. It is carried out through conductive pathways. All spinal cord tracts are divided into own or propriospinal , ascending and descending .
Propriospinal pathways connect nerve centers of different segments of the spinal cord. Their function is to coordinate muscle tone and movements of various metameres of the body.
Towards the ascending paths include several tracts. The Gaulle and Burdach bundles conduct nerve impulses from the proprioceptors of muscles and tendons to the corresponding nuclei of the medulla oblongata, and then to the thalamus and somatosensory areas of the cortex. Thanks to these pathways, the body posture is assessed and corrected. Govers' and Flexig's bundles transmit excitation from proprioceptors and mechanoreceptors of the skin to the cerebellum. Due to this, perception and unconscious coordination of the posture is ensured. The spinothalamic tracts conduct signals from pain, temperature, and tactile skin receptors to the thalamus, and then the somatosensory code areas. They ensure the perception of appropriate signals and the formation of sensitivity.
Descending, paths are also formed by several tracts. The corticospinal tracts extend from the pyramidal and extrapyramidal neurons of the cortex to the α-motonerons of the spinal cord. Due to them, voluntary movements are regulated. The rubrospinal tract carries signals from the red nucleus of the midbrain to the gamma motor neurons of the flexor muscles. The vestibulospinal tract transmits signals from the vestibular nuclei of the medulla oblongata, primarily Deiters' nucleus, to the gamma motor neurons of the extensor muscles. Due to these two pathways, the tone of the corresponding muscles is regulated during changes in body position.
At spinal cord injury: during a fracture (transection and compression of the gray matter), a phenomenon is observed spinal shock. This is a complete shutdown of autonomic, somatic reflexes below the level of the damage segment. Up to 6 months Normal autonomic reflexes stop: urination, defecation, sexual functions. With spinal shock, there is reddening of the skin below the injury site. The skin is dry, sweating is reduced.
Mechanism of spinal shock. Normal somatic and autonomic regulation is carried out under constant control from the reticular formation of the brain stem. The reticular formation of the brain stem has an activating effect on the spinal centers and the tone of autonomic neurons. When cutting, the tonic effect stops. Sympathetic vasomotor neurons are inhibited - redness of the skin. Normally, sympathetic neurons have a vasoconstrictor effect.
After 6 months reflexes are disinhibited and their activity increases. Hyperreflexia. Redness turns into pallor due to increased constriction of skin vessels. Sweating increases. Normally, while maintaining the integrity of the central nervous system, the reticular formation has an activating and inhibitory effect on the autonomic spinal centers.
They are built according to the same plan and consist of sensitive, associative and efferent circuits. They may share sensory neurons. The differences are that in the arc of the autonomic reflex, the efferent autonomic cells lie in ganglia outside the central nervous system.
Autonomic reflexes are caused by stimulation of both inter and exteroceptors. Among the numerous and varied autonomic reflexes, viscero-visceral, viscerodermal, dermatovisceral, visceromotor and motor-visceral are distinguished.
Viscero-visceral reflexes
Viscero-visceral reflexes are caused by irritation of interoreceptors (visceroreceptors) located in the internal organs. They play an important role in the functional interaction of internal organs and their self-regulation. These reflexes include viscerocardial (reflex changes in cardiac activity when irritating receptors of the stomach, intestines, gall and bladder, etc.), cardiocardiac, gastrohepatic, etc. Some patients with damage to the stomach experience gastrocardial syndrome, one one of the manifestations of which is disruption of the heart, up to the appearance of angina attacks caused by insufficient coronary circulation.Viscerodermal reflexes
Viscerodermal reflexes occur when the receptors of the visceral organs are irritated and are manifested by impaired skin sensitivity, sweating, and elasticity of the skin in limited areas of the skin surface (dermatome). Such reflexes can be observed in the clinic. Thus, with diseases of the internal organs, tactile (hyperesthesia) and pain (hyperalgesia) sensitivity increases in limited areas of the skin. It is possible that painful and non-painful cutaneous afferent fibers and visceral afferents belonging to a specific segment of the spinal cord are converted on the same neurons of the sympothalamic pathway. Similar skin reactions (hypersensitivity) appear in diseases of internal organs, are called referred pain, and the areas where it occurs are called Zakharyin-Ged zones; in diseases of the heart, liver, gallbladder, stomach, colon and other internal organs, patients often complain for pain in these areas, which facilitates diagnosis. For example, patients with angina pectoris note pain in the region of the heart, which radiates to the left shoulder blade and left arm, patients with stomach ulcers - in the epigastric region on the left, etc.Dermatovisceral reflexes
Dermatovisceral reflexes manifest themselves in the fact that irritation of certain areas of the skin is accompanied by vascular reactions and dysfunction of certain internal organs. This is the basis for the use of a number of therapeutic procedures (physiotherapy, reflexology). Thus, damage to the skin (by heating or cooling) through the sympathetic centers leads to redness of the skin, inhibition of the activity of internal organs, which are innervated from the segments of the same name.Visceromotor and motor-visceral reflexes
The manifestation of the segmental organization of the autonomic innervation of internal organs is also associated with visceromotor reflexes, in which excitation of the receptors of internal organs leads to a reduction or inhibition of the current activity of skeletal muscles.There are " corrective" And " launchers» influence from the receptor fields of internal organs on skeletal muscles. The former lead to changes in skeletal muscle contractions, which occur under the influence of other afferent stimuli, enhancing or suppressing them. The latter independently activate contractions of skeletal muscles. Both types of influences are associated with an increase in signals received by the afferent pathways of the autonomic reflex arc. Visceromotor reflexes are often observed in diseases of internal organs. For example, with cholecystitis or appendicitis, muscle tension occurs in the area corresponding to the localization of the pathological process. This protective tension of the abdominal muscles (Defense) is associated with the excitatory effect of visceral afferent fibers on motor neurons. Protective visceromotor reflexes also include the so-called forced postures that a person takes in case of diseases of the internal organs (for example, bending and bringing the lower extremities to the stomach).
At the same time, tension in the skeletal muscles can also affect the activity of internal organs that are innervated by afferents and efferents of the spinal cord segment of the same name (motor-visceral or somatovisceral reflexes). This is the basis, in particular, for the use of certain complexes of physical therapy for diseases of internal organs.
The “centers” of the spinal cord, medulla oblongata, midbrain, and diencephalon participate in the implementation of the reflex acts discussed above. They can also be activated by impulses from the corresponding zones of the cerebral cortex. Based on afferent signals from internal organs, any conditioned interoreceptive reflexes can be produced.
Axon reflex
In addition to the above-mentioned autonomic reflexes, the arcs of which close at different levels of the central nervous system, there are the so-called peripheral, or local, visceral reflexes.Back in the last century, N. Sokovnin proved that it is possible to cause a contraction of the bladder when irritating the pelvic nerve, provided that all connections of the inferior brischial ganglion from the central nervous system are interrupted. This phenomenon is called the preganglionic axon reflex - excitation first spreads by preganglionic fibers in the antidromic direction (i.e., in the central nervous system), and then through branches (collaterals) of the same axon goes in the orthodromic (i.e., to the periphery) to the ganglion neurons .
At the same time, I. P. Razenkova (1959) and I. A. Bulygin (1973) obtained data indicating the possibility of direct switching in the autonomic ganglia of excitation from afferent fibers to ganglionic neurons, that is, the real reflex function of the autonomic ganglia, the possibility of true peripheral reflexes. Such data coincide with the data of morphological studies on the presence of special nerve cells (type II Dogel cells) in the autonomic ganglia.
There are at least three types of local reflex arcs at the ganglion level:
- enteral, when all the arc chains are located in the ganglia of the intermuscular or submucosal plexuses,
- short arcs of Ghana at the lionary level with closure in the prevertebral ganglia (solar plexus, caudal mesenteric ganglion),
- long arcs with closure in the paravertebral ganglia of the sympathetic trunk. The shorter the autonomic reflex arc and its lower level, the higher the degree of functional autonomy.
The data discussed in this section indicate that the nervous regulation of the body’s autonomic functions differs significantly from the nervous regulation of its somatic functions. This concerns the structure of the arcs of autonomic reflexes, the role of various parts of the central nervous system in their provision, and the mediator mechanism of impulse transmission at the synapses of the autonomic nervous system.
(sympathetic and parasympathetic) can be conditionally divided into skin-vascular reflexes, visceral reflexes, pupillary reflexes.
Skin-vascular reflexes.
Reflex dermographism is determined by passing a sharp object over the skin. A red stripe forms. The arc (innervation of the vasodilators) closes at the level, therefore, when the segmental apparatus of the spinal cord is damaged, loss of this reflex occurs.
The pilomotor reflex, or goose bump reflex, is caused by rapid cooling of the skin, cold water, or pinch stimulation. In response, a contraction of the smooth hair muscles on the side of the irritation occurs.
Cough reflex- a complex reflex in which the IX and X pairs and nerves of the nasal mucosa take part. The abdominal muscles, diaphragmatic, intercostal muscles, laryngeal muscles, etc. take part in its implementation.
Gag reflex- a complex reflex in which the IX and X pairs of cranial nerves and the lower part of the medulla oblongata take part. The gag reflex is carried out by contraction of the abdominal muscles, intercostal muscles, and antiperistaltic movements of the stomach. At the same time, the fundus of the stomach expands, relaxes, the cardiac part opens, and the prepyloric part contracts.
Neurons of the autonomic nervous system are involved in many reflex reactions called autonomic reflexes. They can be caused by irritation of both exteroreceptors and interoreceptors. With autonomic reflexes, impulses are transmitted from the central nervous system to peripheral organs through sympathetic or parasympathetic nerves.
Number of different autonomic reflexes very large. In medical practice the following are of great importance:
- viscero-visceral,
- viscero-cutaneous,
- cutaneous-visceral reflexes.
They differ depending on the location of the receptors, the irritation of which causes the reflex, and the effectors (working organs) involved in the implementation of the final reaction.
Viscero-visceral reflexes- these are reactions that are caused by irritation of receptors located in internal organs and end with a change in the activity of internal organs. Viscero-visceral reflexes include: reflex changes in cardiac activity, vascular tone, blood supply to the spleen as a result of an increase or decrease in pressure in the aorta, carotid sinus or pulmonary vessels; reflex cardiac arrest due to irritation of the abdominal organs; reflex contraction of the smooth muscles of the bladder and relaxation of the sphincter with increased intravesical pressure and many others.
Viscero-cutaneous reflexes occur when internal organs are irritated and manifest themselves in changes in sweating, electrical resistance (electrical conductivity) of the skin and skin sensitivity in limited areas of the body surface. Thus, in some diseases associated with damaged internal organs, there is an increase in skin sensitivity and a decrease in electrical resistance in some areas of the skin, the topography of which is different depending on which organ is affected.
Cutaneous-visceral reflexes are expressed in the fact that when certain areas of the skin are irritated, vascular reactions and changes in the activity of certain internal organs occur. This is the basis for the use of some medical procedures, for example local warming or cooling of the skin for pain in the internal organs.
Row autonomic reflexes used in practical medicine to judge the state of the autonomic nervous system (autonomic functional tests). These include:
- Aschner's ocular-heart reflex (short-term decrease in heart rate when pressing on the eyeballs),
- respiratory-cardiac reflex, or so-called respiratory arrhythmia (decrease in heart rate at the end of exhalation before the next inhalation),
- orthostatic reaction (increased heart rate and increased blood pressure when moving from a lying position to a standing position) and others.
. Reflex changes in the activity of organs innervated by autonomic nerves are constant components of all complex acts of behavior - all unconditioned and conditioned reflex reactions of the body. A variety of acts of behavior, manifested in muscular activity and active movements, are always accompanied by changes in the functions of internal organs, i.e., circulatory, respiratory, digestive, excretory, and internal secretion organs.
