Autonomic reflexes, features of the reflex arc, classification and clinical significance. Types of autonomic reflexes Autonomic unconditioned reflex
VEGETATIVE REFLEXES
Autonomic neurons nervous system participate in the implementation of many reflex reactions called autonomic reflexes. The latter can be caused by irritation of both exteroreceptors and interoreceptors. During autonomic reflexes, impulses are transmitted from the central nervous system to peripheral organs via sympathetic or parasympathetic nerves.
The number of autonomic reflexes is very large. In medical practice, eiscero-esceral, eiscero-dermal and dermo-esceral reflexes are of great importance.
Viscero-visceral reflexes are reactions that are caused by irritation of receptors located in the internal organs and end with a change in the activity of the 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 organ irritation abdominal cavity and etc.
Viscerodermal 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, the topography of which varies depending on which organ is irritated.
Dermovisceral 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 a series medical procedures, for example, local warming or cooling of the skin for pain in the internal organs.
A number of autonomic reflexes are used in practical medicine to judge the state of the autonomic nervous system (autonomic functional tests). These include the oculocardiac reflex, or Aschner reflex (short-term decrease in heart rate when pressing on eyeballs), respiratory-cardiac reflex, or so-called respiratory arrhythmia (decrease in heart rate at the end of exhalation before the start of the next inhalation), orthostatic reaction (increased heart rate and increased blood pressure during the transition from a lying position to a standing position), etc.
To judge vascular reactions in the clinic, reflex changes in the state of blood vessels are often examined during mechanical irritation of the skin, which is caused by running a blunt object over it. For many healthy people in this case, a local narrowing of the arterioles occurs, manifested in the form of a short blanching of the irritated area of the skin (white dermographism). With higher sensitivity, a red stripe of dilated skin vessels appears, bordered by pale stripes of narrowed vessels (red dermographism), and with very high sensitivity, a stripe of skin thickening and swelling.
PARTICIPATION OF THE AUTONOMIC NERVOUS SYSTEM IN THE ADAPTIVE REACTIONS OF THE ORGANISM
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.
With any muscular work, an increase in heart rate and intensification occurs, a redistribution of blood flowing through various organs (constriction of the blood vessels of internal organs and dilation of the blood vessels of working muscles), an increase in the amount of circulating blood due to its release from blood depots, increased and deepening of breathing, mobilization of sugar from depot, etc. All these and many other adaptive reactions that contribute to muscle activity are formed by the higher parts of the central nervous system, the influence of which is realized through the autonomic nervous system.
The participation of the autonomic nervous system in maintaining constancy is important internal environment organism under various environmental changes and its internal state. An increase in air temperature is accompanied by reflex sweating, reflex dilation of peripheral vessels and increased heat transfer, which helps maintain body temperature at a constant level and prevents overheating. Severe blood loss is accompanied by increased heart rate, narrowing of blood vessels, release of blood deposited in the spleen into the general circulation. As a result of these changes in hemodynamics, blood pressure is maintained at a relatively high level and a more or less normal blood supply to the organs is ensured.
The participation of the autonomic nervous system in general reactions the organism as a whole and its adaptive significance in cases where there is a threat to the very existence of the organism, for example, in case of damage causing pain, suffocation, etc. In such situations, tension reactions arise - “stress” with a strong emotional coloring (rage, fear, anger, etc.). They are characterized by widespread cortical excitation cerebral hemispheres brain and the entire central nervous system, leading to intense muscle activity and causing a complex set of autonomic reactions and endocrine changes. All the forces of the body are mobilized to overcome the impending danger. The involvement of the autonomic nervous system is found when physiological analysis emotional reactions of a person, no matter what caused them. To illustrate, we point out the acceleration of the heart rate, dilatation of skin vessels, redness of the face with joy, paleness skin, sweating, appearance goose bumps, inhibition of gastric secretion and changes in intestinal peristalsis with fear, dilation of pupils with anger, etc.
Many physiological manifestations of emotional states are explained both by the direct influence of the autonomic nerves and by the action of adrenaline, the content of which in the blood during emotions increases due to increased release from the adrenal glands.
During some general reactions of the body, for example those caused by pain, as a result of excitation of the higher centers of the autonomic nervous system, the secretion of the hormone of the posterior lobe of the pituitary gland - vasopressin - increases, which leads to vasoconstriction and cessation of urine formation.
The importance of the sympathetic system is demonstrated by experiments with its removal. Both borderline sympathetic trunks and all sympathetic ganglia were removed from cats. In addition, one adrenal gland was removed and the second was denervated (to prevent sympathomimetic adrenaline from entering the bloodstream under certain influences). The operated animals were almost no different from normal ones under resting conditions. However, in different conditions requiring strain on the body, for example, during intense muscular work, overheating, cooling, blood loss, emotional arousal, significantly lower endurance and often death of sympathectomized animals were found.
They are divided into central and peripheral.
Central reflexes are carried out with the participation of neurons of the central nervous system - segmental and suprasegmental nerve centers.
Peripheral autonomic reflexes - with the participation of ganglion neurons located outside the central nervous system - in the autonomic ganglia.
1. Intraorgan reflexes, for example, intracardiac. They are carried out within the metasympathetic nervous system of the organ. They ensure the autonomous functioning of the organ after transection of the sympathetic and parasympathetic nerves.
2. Interorgan reflexes - carried out due to reflex arcs, which close at the level of the autonomic ganglion without connecting the segmental and suprasegmental centers. This 1) frees the central nervous system from processing redundant information and 2) after turning off the connection between the organ and the central nervous system (for example, injury spinal cord) provide autonomous functioning and relative reliability of regulation physiological functions organ.
3. Axon reflex - a reflex reaction within the branching of one axon without the participation of the neuron body due to the retrograde spread of excitation from one axon branch to another. For example, with mechanical or painful irritation of an area of skin, redness of this area may occur. Limits the effect of signals from the periphery to the center.
Depending on the location of the receptor link and the effector organ, reflexes are divided into viscero-visceral, viscero-somatic, somato-visceral, viscero-dermal, dermo-visceral and viscero-sensory.
1. Viscero-visceral reflexes arise when receptors that are located in the internal organs are excited. Information from them goes to the ganglion, is processed and returns along efferent pathways to the same organ where the receptors were excited or to another organ. For example, the Goltz reflex occurs with mechanical irritation of the peritoneum and is accompanied by a decrease in heart rate. Bainbridge reflex - stretching of the right atrium leads to increased release of vasopressin in the supraoptic nucleus of the hypothalamus and increased diuresis by the kidneys.
2. Viscero-somatic reflexes are accompanied by an integrated reaction of visceral and somatic organs due to the segmental innervation of certain organs - the heart, intestines, etc. For example, irritation of the anterior abdominal wall can lead to contraction of the abdominal muscles or contraction of the flexor muscles of the limbs. With cholecystitis and appendicitis, muscle tension in the corresponding areas occurs and the patient’s posture changes.
3. Somato-visceral - irritation of somatic receptors changes the activity of internal organs. For example, the Danini-Aschner reflex - pressure on the eyeballs causes a decrease in heart rate, which is used
emergency physicians to reduce tachycardia. Irritation of proprioceptors of muscles and tendons during the transition from a lying position to a standing position causes an increase in heart rate, blood pressure and respiratory rate (orthostatic reflex).
4. Viscero-dermal - occur when internal organs are irritated and manifest themselves in changes in sweating, electrical resistance of the skin, redness or pallor in the corresponding areas.
5. Dermo-visceral - when areas of the skin are irritated, vascular reactions and changes in the activity of internal organs occur. For example, stroking the skin of the abdomen clockwise increases intestinal motility. Based on these reflexes, the principles of acupuncture and manual therapy were developed.
6. Viscero-sensory reflexes arise when the functioning of internal organs changes and are expressed in a change in sensitivity - tactile - (hypersthesia) or pain (hyperalgesia). These reflexes are based on the presence of projection zones of internal organs onto the surface of the body - Hed's zones. For example, disturbances in the activity of the heart can lead to pain in the area of the left hand and little finger. Cholecystitis may be accompanied by pain in the heart and sternum.
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 are playing important role in the functional interaction of internal organs and their self-regulation. These reflexes include viscerocardial (reflex changes in cardiac activity upon irritation of the receptors of the stomach, intestines, bile and Bladder etc.), cardio-cardiac, gastrohepatic, etc.. Some patients with gastric damage experience gastrocardial syndrome, 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 the internal organs, are called referred pain, and the areas where it occurs are called Zakharyin-Ged zones; with diseases of the heart, liver, gallbladder, stomach, colon and other internal organs, patients often complain of pain in these areas, which makes diagnosis easier. 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
With the manifestation of segmental organization autonomic innervation internal organs are 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 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, flexion and adduction lower limbs 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 physical therapy for diseases of internal organs.
In the implementation of the reflex acts discussed above, the “centers” of the dorsal, oblongata, middle, diencephalon. 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 so-called peripheral, or local, visceral reflexes.Back in the last century, N. Sokovnin proved that it is possible to cause 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. These data coincide with the data morphological studies about 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 various departments The central nervous system in their provision, the mediator mechanism of impulse transmission at the synapses of the autonomic nervous system.
Details
Fine sympathetic and parasympathetic system
are constantly active, and their basal levels of activity are known as sympathetic tone and parasympathetic tone, respectively.
The meaning of tone is that it allows a single nervous system to both increase and decrease the activity of the organ being stimulated. For example, sympathetic tone normally keeps almost all systemic arterioles constricted to approximately half their maximum diameter. When the degree of sympathetic stimulation increases above normal, these vessels may constrict even more; on the contrary, when stimulation decreases below normal, arterioles may dilate. In the absence of a constant background tone, sympathetic stimulation would lead only to vasoconstriction and never to their dilation.
Another interesting example of tone is the background parasympathetic tone in the gastrointestinal tract. Surgical removal parasympathetic supply to most of the intestine by cutting vagus nerves can cause severe and prolonged atony of the stomach and intestines. As a result, much of the normal forward movement of contents is blocked, with subsequent development of severe constipation. This example demonstrates the importance of having normal parasympathetic tone. digestive tract for its function. Tone may decrease, which inhibits motor skills gastrointestinal tract, or increase, contributing to increased activity of the digestive tract.
Tone associated with the basal secretion of adrenaline and norepinephrine by the adrenal medulla. At rest, the adrenal medulla normally secretes approximately 0.2 mcg/kg/min of epinephrine and approximately 0.05 mcg/kg/min of norepinephrine. These quantities are significant as they are sufficient to support almost normal level blood pressure, even if all direct sympathetic pathways to the cardiovascular system are removed. Consequently, much of the overall tone of the sympathetic nervous system results from basal secretion of epinephrine or norepinephrine in addition to the tone resulting from direct sympathetic stimulation.
Reflexes of the autonomic nervous system.
Many visceral functions of the body are regulated by autonomic reflexes.
Cardiovascular autonomic reflexes.
Some reflexes in the cardiovascular system help regulate arterial pressure blood and heart rate. One of them is the baroreceptor reflex. In the walls of some large arteries, including internal carotid arteries and the aortic arch, stretch receptors called baroreceptors are localized. When they are stretched under the influence high pressure the signals are transmitted to the brain stem, where they inhibit sympathetic impulses to the heart and blood vessels and excite the parasympathetic pathway; this allows blood pressure to return to normal.
Gastrointestinal autonomic reflexes.
The most top part The digestive tract and rectum are regulated mainly by autonomic reflexes. For example, the smell of tasty food or its entry into the mouth initiates signals sent from the nose and mouth to the nuclei of the vagus and glossopharyngeal nerves, as well as to the salivary nuclei of the brain stem. They, in turn, conduct signals through the parasympathetic nerves to secretory glands oral cavity and stomach, causing the secretion of digestive juices, sometimes even before food enters the mouth.
When, at the other end of the alimentary canal, fecal matter fills the rectum, sensory impulses initiated by its distension are sent to the sacral spinal cord, and a reflex signal is carried back through the sacral parasympathetic fibers to the distal parts of the colon; this leads to strong peristaltic contractions causing defecation.
Other autonomic reflexes. Bladder emptying is regulated in the same way as rectal emptying. Stretching of the bladder causes the appearance of impulses going to the sacral part of the spinal cord, and this, in turn, causes a reflex contraction of the bladder and relaxation of the sphincters urinary tract, thus promoting urination.
Sexual reflexes.
Also important are sexual reflexes, which are initiated by both mental stimuli from the brain and stimuli from the genitals. Impulses from these sources converge at the level of the sacral spinal cord, which in men leads first to erection, which is mainly a parasympathetic function, and then to ejaculation, partly a function of the sympathetic system.
Other functions of autonomic control include regulation of pancreatic secretion, gallbladder emptying, kidney urine output, sweating, and blood glucose concentration.
The role of adrenaline and norepinephrine in the autonomic nervous system.
Sympathetic stimulation of the adrenal medulla causes the release of large quantity adrenaline and norepinephrine into the circulating blood, and these two hormones, in turn, are carried by the blood to all tissues of the body. On average, about 80% of the secretion is adrenaline and 20% is norepinephrine, although the relative proportion may vary markedly under different physiological conditions.
Circulating adrenaline and norepinephrine have almost the same effect on different organs, which occurs with direct sympathetic stimulation, except that the effects last 5-10 times longer because both substances are removed from the blood slowly - within 2-4 minutes.
Circulating norepinephrine causes narrowing of almost all blood vessels in the body; it also increases the activity of the heart, inhibits the activity of the gastrointestinal tract, dilates the pupils of the eyes, etc.
Epinephrine produces the same effects as norepinephrine, but there are some differences. Firstly, adrenaline due to more pronounced stimulation of beta receptors has a stronger effect on the heart than norepinephrine. Secondly, adrenaline causes only a slight contraction blood vessels in the muscles compared to the much stronger constriction caused by norepinephrine. Since muscle vessels make up the majority of the body's blood vessels, this distinction is especially important because norepinephrine significantly increases total peripheral resistance and increases blood pressure, while adrenaline increases blood pressure to a lesser extent, but increases cardiac output more.
Third difference between the effects of adrenaline and norepinephrine is associated with their effects on tissue metabolism. Epinephrine has a 5-10 times longer metabolic effect than norepinephrine. Indeed, adrenaline secreted by the adrenal medulla can increase the metabolic rate of the entire body to more than 100% above normal, thereby increasing the body's activity and excitability. It also increases the rate of other metabolic events, such as glycogenolysis in the liver and muscles and the release of glucose into the blood.
Neurons of the autonomic nervous system are involved in many reflex reactions, called autonomic reflexes. The latter can be caused by irritation of both intero- and exteroceptors. The criterion for classifying a reflex as vegetative is the receipt of impulses to the efferent peripheral organ with the central nervous system by sympathetic or parasympathetic nerves.
Reflexes of the ganglia of the autonomic nervous system. Reflexes of the metasympathetic department
Many autonomic ganglia perform the function of being located in the periphery reflex centers. They have all the structures necessary to perform reflex switching. The intramural ganglia and nerve plexuses present in empty organs are no exception. These ganglia are part of the efferent pathway of the parasympathetic nervous system. But at the same time they are approached nerve cells from internal organ receptors, there are also interneurons here, therefore, already in the ganglion itself it is possible to transmit influences from the receptor neuron to the efferent one. Strong arguments in favor of the presence of receptor neurons in the peripheral nerve ganglia have been revealed by the facts of the preservation of afferent, intercalary and efferent neurons and nerve fibers coming from them, as well as local internal organ reflex regulation in the transplanted heart. If these receptors, nerve cells and nerve fibers belonged to neurons whose bodies are located in the central nervous system, that is, outside the transplanted heart, their degeneration should occur.
The structure of the intramural ganglia resembles typical nerve centers. Each neuron is surrounded by a large number neuroglia cells. In addition, there are structures that selectively allow only certain substances from the blood to reach the neuron, which in their function resemble the BBB. Thus, ganglion neurons, like brain neurons, are protected from the direct effects of substances circulating in the blood
Among the structures of the metasympathetic division of the autonomic nervous system is pacemaker cells, that have the ability to spontaneous depolarization, which ensures the rhythm of activity and the reduction of all disturbances muscle cells organ. This activity is corrected by impulses of its own afferentation depending on the state of the organ and its individual parts.
"Local" peripheral reflexes that perform intramural autonomic ganglia, regulating the functioning of the heart, intestinal motility, and interconnection of various parts of the stomach and some other organs. The neurons entering these ganglia, their processes, synapses and endings form intraorgan reflex structures that regulate the functioning of the organ with internal peripheral reflexes.
The influence of parasympathetic nerve centers on metasympathetic reflexes.
Impulses entering the organ by preganglionic fibers of the parasympathetic nerves interact with impulses that carry out the processes of internal organ reflex regulation. The nature of the organ's response determines the result of this interaction. Therefore, the effect of irritation of preganglionic fibers is not unambiguous. On organs in which intramural reflex mechanisms regulation, preganglionic parasympathetic fibers can have (depending on functional state organ that is innervated) as exciting, so and inhibitory influence.
The opposite influences of parasympathetic fibers are by no means “paradoxical”. This is a natural manifestation of multidirectional influences necessary to ensure the normal function of organs and tissues. The parasympathetic department is a system capable of carrying out ongoing regulation physiological processes and ensure full maintenance of the constancy of the internal environment of the body. The number of intramural neurons per 1 cm2 of intestinal surface can reach 20,000. As a consequence, only one part of the metasympathetic system, which is located in the intestines, contains approximately the same number of neurons as the entire spinal cord.
Thus, impulses arriving to the organ by preganglionic fibers of the parasympathetic nerves interact with impulses that carry out the processes of internal organ reflex regulation. Depending on the current state physiological processes in this organ or system, they can turn on or off, strengthen or weaken this or that function of the organ, carrying out a variety of regulatory influences necessary to maintain normal current activity and homeostasis.
Physiological significance of "local" reflexes.
Efferent intramural neurons are the common final pathway for impulses of intraorgan and extraorgan (central) origin. The presence of “local” mechanisms of nervous regulation of the functions of internal organs, which is carried out with the help of peripheral reflexes by the ganglia of the autonomic nervous system, internal and external organs, has a large physiological significance. As a result this The central nervous system is freed from the need to process excess information coming from internal organs. In addition, peripheral reflexes increase the reliability of regulation of the physiological functions of these organs. Such regulation, being basic, aimed at maintaining homeostasis. At the same time, it can be easily adjusted if necessary higher levels autonomic nervous system and humoral mechanisms. In addition, this regulation can also occur after the connection between organs and the central nervous system is turned off.
Spinal reflexes
At the level of the spinal cord, the reflex arcs of many autonomic reflexes close (Fig. 58).
The nature of the reflex response is largely determined by the presence of nerve centers of the sympathetic (thoracolumbar) and parasympathetic (sacral) divisions of the autonomic nervous system. The spinal section of the sympathetic nervous system has signs of a segmental (metameric) organization. This is expressed in the fact that a clear switching of sensory inputs to efferent ones occurs within a specific segment. Although there are also zones of overlap of adjacent segments, in this case the response to irritation of adjacent roots is less pronounced. The most indicative reflexes in this regard of cardio-vascular system and excretory organs (cardiocardiac, gastrointestinal, evacuation reflexes).
The interneuronal apparatus of the spinal cord ensures the interaction of reflex pathways both within the autonomic nervous system and between it and the somatic nervous system. As a result, a wide involvement of various internal organs in the reflex response is ensured. It is also important that the reflex can be started from the receptors of one, and end with the effectors of another part of the nervous system.
Spinal centers for the regulation of autonomic functions.
At the level of the last cervical and two upper thoracic segments of the spinal cord there are neurons that innervate the three muscles of the eye: the muscle that dilates the pupil, the orbital part orbicularis muscle eyes and one of the muscles of the upper eyelid.
In the upper thoracic segments The spinal cord contains neurons that make up the center, which regulates the functioning of the heart and the condition of the blood vessels (see section 3). There are neurons that innervate the bronchi.
In all thoracic and upper lumbar segments of the spinal cord there are neurons that innervate the sweat glands. Defeats of individual segments
Rice. 58.(along the legs): afferent pathways of each nerve of the somatic nervous system (1). autonomic nerve (2), somatic reflex (3), autonomic reflex (4)
cops causes the cessation of sweating in areas of the body that have lost sympathetic innervation.
IN sacral region The spinal cord contains the spinal centers for the reflexes of urination, defecation, erection and ejaculation. The destruction of these centers causes impotence, urinary and fecal incontinence. Disorders of urination and defecation occur due to paralysis of the closing muscles of the bladder and rectum.
Autonomic reflexes can be divided into: Viscero-visceral, viscerodermal And dermatovisceral.
Viscero-visceral reflexes are caused by irritation of receptors located in internal organs and end with a change in the activity of internal organs. In addition, these reflexes can begin and end in the organs of one functional system(for example, cardiovascular) or be intersystemic. Viscero-visceral reflexes include reflex changes in cardiac activity, vascular tone, blood supply to the spleen due to an increase or decrease in pressure in the aorta, carotid sinus or pulmonary vessels, reflex cardiac arrest due to irritation of the abdominal organs, etc.
Viscerodermal 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, the topography of which varies depending on which organ is irritated.
Dermatovisceral reflexes are expressed in the fact that when certain areas of the skin are irritated, vascular reactions occur and changes in the activity of certain internal organs.
Many of these autonomic reflexes are used in practical medicine, and their application is multifaceted.
An example of the use of the dermatovisceral reflex in the clinic is the use of heating pads or, conversely, ice packs to influence the pathological focus in the internal organs. Therapeutic effect different types acupuncture is also based on similar reflexes. Viscerodermal reflexes are often used in the diagnosis of pathology of internal organs. Thus, the development of a pathological focus in any internal organ can increase the sensitivity of certain areas of the skin, which is manifested by their pain with a light touch or even without an irritant (referred pain in the Ged-Zakharyin zones) (Fig. 59). Such a reflex can begin with interoceptors, and skeletal muscles can become an effector: during a “fire” in the abdominal cavity, the
Rice. 59. 1-section of the lungs and bronchi; 2 -heart area; WITH- part of the intestines; 4,5 - area of the bladder; b- kidney area; 7,9 - area of the liver; 8 - area of the stomach and pancreas; 10 - area of the urinary and genital organs
The tone of the flexor muscles is felt (the person curls up into a ball), the muscles of certain parts of the abdominal wall tense.
Spinal shock.
These reflexes of the spinal cord in the whole organism are coordinated by the higher parts of the central nervous system. This clearly manifests itself after the connection between the brain and spinal cord is broken. As a result of such damage, as in the somatic nervous system, there appears spinal shock- temporary disappearance of autonomic reflexes of the spinal cord. Reflexes disappeared gradually, over 1-6 months. are restored, even such complex ones as emptying the bladder, colon, and genitals.
Restoration of spinal reflexes after spinal shock may be associated with the activation of former or the formation of new synapses on intercalary preganglionic and motor neurons.
In this situation, the parasympathetic (vagal) reflex arcs are not damaged.
Brain stem reflexes
Autonomic centers of the brain stem are involved in the regulation of cardiovascular, digestive systems that carry out evacuation reflexes, control reproductive organs, controlling the innervation of their autonomic nerves. Here the spinal centers responsible for individual autonomic functions are united into functional complexes.
The medulla oblongata contains the boulevard section of the vasomotor center, which regulates the function of the heart and the condition of the blood vessels. It also contains centers that stimulate lacrimation and secretion of the salivary and gastric glands, pancreas, cause the release of bile from the gallbladder and bile duct, and stimulate the motility of the stomach and small intestine.
In the middle of the brain (in the anterior tubercles of the chotirid hump plate) there are nerve centers pupillary reflex and accommodation of the eye. In the anterior part of the midbrain is located one of the centers that are involved in emptying the bladder. These centers belong to the parasympathetic department. But in the whole organism, in order to perform the reflex function, many of them (this is especially clearly demonstrated in the example of the vasomotor center) closely interact with other parts of the central nervous system. So, the vasomotor center medulla oblongata functions together with the sympathetic section of the thoracic region, and evacuation reflexes are carried out through the interaction of the centers of the trunk with the Krijo centers of the parasympathetic nervous system. (These reflexes are discussed in more detail when presenting the relevant sections.)
Reflex regulation of functions by the nerve centers of the trunk is carried out with the direct participation of interneuron mechanisms that are responsible for the intercentral interaction of various parts of the central nervous system: sympathetic, parasympathetic, autonomic and somatic nervous systems. A clear example is the respiratory-cardiac reflex, or the so-called respiratory arrhythmia: a slowdown in heart rate at the end of exhalation before the next inhalation begins.
Naturally, all brain stem reflexes are under the control of the higher parts of the central nervous system. For example, the above evacuation reflexes are controlled by the cerebral cortex.
In medical practice, autonomic reflexes of the brain stem are used. For example, some reflexes that close here make it possible to determine the state of the autonomic nervous system (autonomic functional tests). These include: a) osocervical reflex, or the Danin-Aschner reflex (short-term slowing of the heartbeat when pressing on the eyeballs); b) orthostatic reaction(increased heart rate and increased blood pressure during a change from a lying position to a standing position), etc.