Examples of autonomic reflexes. Vegetative reflexes: their types and significance for the human body. Reflexes of the ganglia of the autonomic nervous system. Reflexes of the metasympathetic department
Reflex
one). by origin:
conditional (acquired);
spinal (spinal cord);
food;
defensive;
sexual;
indicative;
What are somatic and autonomic reflexes? How are their reflex arcs different?
Somatic reflex - the general name of reflexes, manifested by a change in the tone of skeletal muscles or their contraction during any impact on the body. For somatic reflexes, the effector organ is the skeletal muscles, that is, as a result of the reflex act, certain muscles or muscle groups are contracted and some kind of movement is carried out.
Vegetative reflexes caused by stimulation of both intero- and exteroreceptors. Among the numerous and varied vegetative reflexes, viscero-visceral, viscerodermal, dermatovisceral, visceromotor and motor-visceral are distinguished.
Vegetative and somatic reflex arcs are built according to the same plan and consist of sensitive, associative and efferent circuits. They may share sensory neurons. The differences lie in the fact that in the arc of the vegetative reflex, efferent vegetative cells lie in the ganglia outside the CNS.
What is a reflex arc and a reflex ring?
The material basis of the reflex is the "reflex arc". According to the definition of I.P. Pavlov, “ reflex arc - this is the anatomical substrate of the reflex, or in other words, the path of the excitation impulse from the receptor through the central nervous system to the working organ. The simplest reflex arc necessarily includes 5 components:
one). receptor;
2). afferent (centripetal) nerve;
3). nerve center;
four). efferent (centrifugal) nerve;
5). effector organ (working organ).
In the doctrine of reflex there is a concept - " reflex ring ". According to this concept, from the receptors of the executive organ (effector), the excitation impulse is sent back to the central nervous system, despite the fact that the reflex has already been carried out. This is necessary to evaluate and correct the response performed.
What are extero-, intero- and proprioreceptors?
exteroreceptors (receptors on the outer surface of the body);
interoreceptors or visceral (receptors of internal organs and tissues);
proprioceptors (receptors of skeletal muscles, tendons, ligaments);
Nerve centers and their properties
In complex multicellular organisms of humans and animals, a single nerve cell is not able to regulate any functions. All the main forms of CNS activity are provided by groups of nerve cells called the “nerve center”. Nerve center is a set of neurons in the brain necessary for the implementation of a certain function.
All nerve centers are united by their common properties. These properties are largely determined by the work of synapses between neurons in the nerve centers. The main properties of the nerve centers include: one-way conduction, delay in the conduction of excitation, summation, irradiation, transformation, aftereffect, inertia, tone, fatigue, plasticity.
One way conduction
In the nerve centers of the brain, excitation spreads only in one direction - from the afferent to the efferent neuron. This is due to the unilateral conduction of excitation through the synapse.
Excitation Delay
The rate of conduction of excitation through the nerve centers significantly slows down. The reason lies in the peculiarities of synaptic transmission of excitation from one neuron to another. At the same time, the following processes occur in the synapse, requiring a certain amount of time:
one). the release of the neurotransmitter by the nerve ending of the synapse in response to the excitation impulse that came to it;
2). diffusion of the mediator through the synaptic cleft;
3). emergence under the influence of a mediator of excitatory postsynaptic potential.
This decrease in the rate of conduction of excitation in the nerve centers was called the central delay. The more synapses along the path of excitation, the greater the delay. It takes 1.5-2 milliseconds to conduct excitation through one synapse.
Excitation Summation
This property of the nerve centers was discovered in 1863 by I. M. Sechenov. There are two types of summation of excitation in the nerve centers: temporal (successive) and spatial.
Temporary summation is understood as the emergence or intensification of a reflex under the action of weak and frequent stimuli, each of which individually, respectively, either does not cause a response or the response to it is very weak. So, if a single subthreshold irritation is applied to the frog's foot, the animal is calm, and if a whole series of such frequent irritations is applied, the frog pulls back the foot.
Spatial summation is observed in the case of simultaneous receipt of nerve impulses in the same neuron through different afferent pathways, i.e. with simultaneous stimulation of several receptors of the same "receptive field". Under the receptive field (reflexogenic zone) is meant a part of the body, when the receptors of which are irritated, a certain reflex act is manifested.
The summation mechanism lies in the fact that in response to a single afferent wave (weak stimulus) coming from receptors to brain neurons, or when one receptor of a particular receptive field is irritated, not enough mediator is released in the presynaptic part of the synapse to cause an excitatory postsynaptic potential to occur on the postsynaptic membrane (VPSP). In order for the EPSP value to reach a “critical level” (10 millivolts) and an action potential to arise, summation of many subthreshold EPSPs on the cell membrane is required.
Irradiation of excitation
Under the action of strong and prolonged irritations, a general excitation of the central nervous system is observed. This excitation spreading in a "broad wave" was called irradiation. Irradiation is possible due to the huge number of collaterals (additional detours) that exist between individual brain neurons.
Aftereffect
After the end of the action of the stimulus, the active state of the nerve cell (nerve center) persists for some time. This phenomenon was called aftereffect. The aftereffect mechanism is based on a prolonged trace depolarization of the neuron membrane, which usually occurs as a result of prolonged rhythmic stimulation. On the wave of depolarization, a series of new action potentials can arise, "supporting" the reflex act without irritation. But in this case, only a short-term aftereffect is observed. A more prolonged effect is explained by the possibility of long-term circulation of nerve impulses along closed annular pathways of neurons within the same nerve center. Sometimes such “lost” waves of excitation can enter the main path and thus “support” the reflex act, despite the fact that the action of the main irritation has long ended.
Short aftereffects (lasting about an hour) underlie the so-called. short-term (operative) memory.
inertia
In the nerve centers, traces of previous excitations may persist for a longer time than occurs during aftereffect. So, in the brain they do not disappear within a few days, but in the cerebral cortex they remain for decades. This property of the nerve centers is called inertia. Even IP Pavlov believed that this property underlies the mechanisms of memory. A similar point of view is shared by modern physiological science. According to the biochemical theory of memory (Hiden), in the process of memorization, structural changes occur in the molecules of ribonucleic acid (RNA) contained in nerve cells that conduct certain waves of excitation. This leads to the synthesis of "altered" proteins that form the biochemical basis of memory. Unlike the aftereffect, inertia provides the so-called. long term memory.
Fatigue
Fatigue of the nerve centers is characterized by a weakening or complete cessation of the reflex reaction with prolonged stimulation of the afferent pathways of the reflex arc. The reason for the fatigue of the nerve centers is a violation of the transmission of excitation in interneuronal synapses. This leads to a sharp decrease in the stocks of the mediator in the endings of the axon and a decrease in the sensitivity of the receptors of the postsynaptic membrane to it.
Tone
The tone of the nerve centers is the state of their insignificant constant excitation in which they are. The tone is maintained by a continuous rare flow of afferent impulses from numerous peripheral receptors, which leads to the release of a small amount of the mediator into the synaptic cleft.
Plastic
Plasticity is the ability of nerve centers to change or rebuild their function if necessary.
Coordination of nervous processes
The central nervous system constantly receives many excitatory impulses coming from numerous extero-, intero- and proprioreceptors. The CNS responds to these excitations strictly selectively. This is ensured by one of the most important functions of the brain - the coordination of reflex processes.
Coordination of reflex processes - this is the interaction of neurons, synapses, nerve centers and the processes of excitation and inhibition occurring in them, due to which the coordinated activity of various organs, systems of vital activity and the body as a whole is ensured.
Coordination of nervous processes is possible due to the following phenomena:
Dominant
Dominant - this is a temporary, persistent excitation that dominates in any nerve center of the brain, subordinating all other centers to itself and thereby determining the specific and expedient nature of the body's response to external and internal irritations. The dominant principle was formulated by the Russian scientist A. A. Ukhtomsky.
The dominant focus of excitation is characterized by the following main properties: increased excitability, the ability to sum up excitations, persistence of excitation, and inertia. The center that dominates in the central nervous system is able to attract (attract) nerve impulses to itself from other nerve centers that are less excited at the moment. Due to these impulses, not addressed to him, his excitation is even more intensified, and the activity of other centers is suppressed.
Dominants can be of exogenous and endogenous origin.
Exogenous dominant occurs under the influence of environmental factors. For example, a dog during training can be distracted from work by the appearance of some stronger stimulus: a cat, a loud shot, an explosion, etc.
Endogenous dominant is created by factors of the internal environment of the organism. These can be hormones, physiologically active substances, metabolic products, etc. So, with a decrease in the content of nutrients (especially glucose) in the blood, the food center is excited and a feeling of hunger appears. From now on, the behavior of a person or animal will be focused solely on finding food and saturation.
The most persistent dominants in humans and animals are food, sexual and defensive.
Feedback
Important for the normal functioning of the brain is the principle of coordination - feedback (reverse afferentation). Any reflex act does not end immediately after the "command" received in the form of a stream of impulses from the brain to the effector organ. So, despite the fact that the working organ has fulfilled this “command”, reverse waves of excitation (secondary afferentation) go from its receptors to the central nervous system, signaling the degree and quality of the implementation by the organ of the “task” of the center. This enables the center to "compare" the actual result with what was planned, and, if necessary, correct the reflex act. Thus, secondary afferent impulses perform a function that in technology is called feedback.
Convergence
One of the conditions for the normal coordination of reflex processes is the principle of convergence and the principle of a common final path, discovered by the English physiologist Charles Sherrington. The essence of this discovery is that impulses coming to the CNS through different afferent pathways can converge (converge) on the same intermediate and efferent neurons. This is facilitated, as noted earlier, by the fact that the number of afferent neurons is 4-5 times greater than that of efferent ones. Connected with convergence, for example, is the mechanism of spatial summation of excitation in the nerve centers.
To explain the above phenomenon, Ch. Sherrington proposed an illustration in the form of a "funnel", which went down in history as "Sherrington's funnel". Impulses enter the brain through the wide part of it, and exit through the narrow part.
Common final path
The principle of a common final path should be understood as follows. The reflex act can be caused by stimulation of a large number of different receptors, i.e. the same efferent neuron can be part of many reflex arcs. For example, by turning the head, as the final reflex act, stimulation of various receptors (visual, auditory, tactile, etc.) ends.
In 1896, N. E. Vvedensky, and somewhat later - C. Sherrington, discovered reciprocal (conjugate) innervation as a principle of coordination. An example is the work of antagonist nerve centers. According to this principle, the excitation of one center is accompanied by reciprocal (conjugate) inhibition of another. Reciprocal innervation is based on translational postsynaptic inhibition.
Reciprocal inhibition
It underlies the functioning of antagonist muscles and ensures muscle relaxation at the moment of contraction of the antagonist muscle. The afferent fiber that conducts excitation from muscle proprioceptors (for example, flexors) in the spinal cord is divided into two branches: one of them forms a synapse on the motor neuron that innervates the flexor muscle, and the other on the intercalary, inhibitory, forming an inhibitory synapse on the motor neuron that innervates extensor muscle. As a result, excitation coming along the afferent fiber causes excitation of the motor neuron innervating the flexor and inhibition of the motor neuron of the extensor muscle.
Induction
The name of the next principle of coordination of reflex processes - induction - was borrowed by physiologists from physicists (induction - “guidance”). There are two types of induction: simultaneous and sequential. Simultaneous induction is understood as the induction by one process (excitation or inhibition), which takes place in any nerve center, of a process of the opposite sign - in another center. Simultaneous induction is based on reciprocal inhibition in antagonist centers.
Sequential induction is called contrasting changes in the state of the same nerve center after the cessation of excitatory or inhibitory stimulation. This induction can be positive or negative. The first is accompanied by an increase in excitation in the center after the cessation of inhibition, the second, on the contrary, by an increase in inhibition after the cessation of excitation.
Spinal cord
The spinal cord is the oldest part of the central nervous system of vertebrates. It is located in the spinal canal, covered with meninges and surrounded on all sides by cerebrospinal fluid (CSF).
On the transverse section of the spinal cord, white and gray matter are distinguished. Gray matter, shaped like a butterfly, is represented by the bodies of nerve cells and has a so-called. "horns" - dorsal and ventral. The white matter is formed by the processes of neurons. Two pairs of roots depart from each segment of the spinal cord - dorsal and ventral (in humans - posterior and anterior, respectively), which, when combined, form peripheral spinal nerves. The dorsal roots are "responsible" for sensitivity, and the ventral roots are responsible for motor acts.
The spinal cord performs two important functions - reflex and conduction.
reflex activity the spinal cord is determined by the presence in it of certain nerve centers responsible for specific reflex acts.
The most important centers of this part of the brain are locomotor. They control and coordinate the work of the skeletal muscles of the body, maintain their tone and are responsible for the organization of elementary motor acts.
Special motor neurons located in the spinal cord innervate the respiratory muscles (in the region of 3-5 cervical vertebrae - the diaphragm, in the thoracic region - the intercostal muscles).
The centers of defecation and genitourinary reflexes are localized in the sacral spinal cord. Part of the parasympathetic and all sympathetic fibers depart from the spinal cord.
Conductor function spinal cord is to conduct impulses. This is provided by the white matter of the brain. The pathways of this department of the central nervous system are divided into ascending and descending. The first ones conduct excitations entering the CNS from numerous receptors to the brain, the second ones, on the contrary, from the brain to the spinal cord and effector organs.
The ascending pathways (tracts) of the spinal cord include: bundles of Gaulle and Burdach, lateral and ventral spinal thalamic tracts, dorsal and ventral spinal cerebellar tracts (respectively, bundles of Flexig and Gowers).
The descending tracts of the spinal cord include: corticospinal (pyramidal) tract, rubro-spinal (extrapyramidal) tract of Monakov, vestibulo-spinal tracts, reticulo-spinal tract.
The hypothalamus and its functions
The hypothalamus (hypothalamus) is the oldest formation of the brain, located under the visual tubercles. It is formed by 32 pairs of nuclei, the most important of which are: supraoptic, paraventricular, gray tubercle and mastoid body. The hypothalamus is connected with all parts of the central nervous system and is an intermediate link between the cerebral cortex and the autonomic nervous system. In the hypothalamus there are nerve centers involved in the regulation of various metabolisms (protein, carbohydrate, fat, water-salt) and a thermoregulation center.
The hypothalamus forms a close morpho-functional relationship with the pituitary gland - the "king" of all endocrine glands. The resulting so-called. The "hypothalamic-pituitary system" combines the nervous and humoral mechanisms of regulation of functions in the body. Many emotional and behavioral responses are associated with the hypothalamus.
The concept of reflexes. Classification of reflexes
The functional activity of the central nervous system, in essence, is a reflex activity. It is based on the "reflex".
Reflex - This is the body's response to irritation with the participation of the central nervous system.
Reflexes are very diverse. They can be classified according to a number of characteristics into several groups:
one). by origin:
unconditional (congenital, inherited);
conditional (acquired);
2). depending on the location of the receptors:
exteroceptive (receptors on the outer surface of the body);
Interoreceptive or visceral (receptors of internal organs and tissues);
proprioceptive (receptors of skeletal muscles, tendons, ligaments);
3). according to the location in the central nervous system of the nerve centers "involved" in the implementation of the reflex:
spinal (spinal cord);
bulbar (medulla oblongata);
mesencephalic (midbrain);
diencephalic (midbrain);
cortical (cortex of the cerebral hemispheres);
four). biological significance for the body
food;
defensive;
sexual;
indicative;
locomotor (motion function);
tonic (posture formation, balance maintenance);
5). by the nature of the response
motor or motor (work of skeletal or smooth muscles);
secretory (secretion);
vasomotor (narrowing or expansion of blood vessels);
6). at the site of irritation and the corresponding response:
cutano-visceral (carried out from the skin to the internal organs);
viscero-cutaneous (from the internal organs to the skin);
viscero-visceral (from one internal organ to another).
The neurons of the autonomic nervous system are involved in the implementation of many reflex reactions, called vegetative reflexes. The latter can be caused by irritation of both intero- and exteroreceptors. The criterion for crediting the reflex to the autonomic one 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
A lot of vegetative ganglia perform the function of those placed on the periphery reflex centers. They have all the structures needed to perform a reflex switch. The intramural ganglia and nerve plexuses found in empty organs are no exception. These ganglia are part of the efferent pathway of the parasympathetic nervous system. But at the same time, nerve cells from internal organ receptors come to them, there are also intercalary neurons, therefore, already in the ganglion itself, the transfer of influences from the receptor neuron to the efferent one is possible. Weighty arguments in favor of the presence of receptor neurons in the peripheral nerve ganglia revealed 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 a 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, they should be reborn.
The structure of the intramural ganglia resembles typical nerve centers. Each neuron is surrounded by a large number neuroglial cells. In addition, there are structures here that selectively pass only certain substances from the blood to the neuron, which in their function resemble the BBB. Thus, ganglion neurons, like brain neurons, are protected from direct exposure to substances circulating in the blood.
Among the structures of the metasympathetic division of the autonomic nervous system is pacemaker cells, that they have the ability to spontaneous depolarization, which provides the rhythm of activity, the contraction of all the unstoppable muscle cells of the organ. This activity is corrected by impulses of one's own afferentation depending on the state of the organ and its separate parts.
"Local" peripheral reflexes, which are performed by intramural vegetative ganglia, which regulate the work of the heart, intestinal motility, carry out the interconnection of various sections of the stomach and some other organs. The neurons included in these ganglia, their processes, synapses and endings form intraorganic reflex structures that regulate the work of the organ by internal organ peripheral reflexes.
Influence of parasympathetic nerve centers on metasympathetic reflexes.
The impulses coming to the organ by the preganglionic fibers of the parasympathetic nerves interact with the 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 of regulation are found, preganglionic parasympathetic fibers can exert (depending on the functional state of the organ that is innervated) both exciting, so and inhibitory effect.
The opposite influences of the 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 the current regulation of physiological processes and ensuring the full maintenance of the constancy of the internal environment of the body. The number of intramural neurons per 1 cm2 of the intestinal surface can reach 20,000. As a result, 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, the impulses coming to the organ by the preganglionic fibers of the parasympathetic nerves interact with the impulses that carry out the processes of internal organ reflex regulation. Depending on the current state of physiological processes in this organ or system, they can turn on or off, enhance or weaken one or another function of the organ, exercising 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 intraorganic and extraorganic (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, is of great physiological importance. As a result this The central nervous system is freed from the need to process redundant information coming from internal organs. In addition, peripheral reflexes increase the reliability of the regulation of the physiological functions of these organs. Such regulation, being basic, aimed at maintaining homeostasis. At the same time, if necessary, it can be easily corrected by the highest levels of the autonomic nervous system and humoral mechanisms. In addition, this regulation can be carried out even after the connection of organs with the central nervous system is turned off.
spinal reflexes
At the level of the spinal cord, the reflex arcs of many autonomic reflexes are closed (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 division of the sympathetic nervous system has signs of a segmental (metameric) organization. This is expressed in the fact that a clear switching of sensitive inputs to efferent ones occurs within a particular segment. Although overlap zones of adjacent segments also occur, in this case the response to irritation of adjacent roots is less pronounced. The most indicative in this regard are the reflexes of the cardiovascular system and excretory organs (cardio-cardiac, gastrointestinal, evacuatory 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 launched from the receptors of one, and end with the effectors of another part of the nervous system.
Spinal centers of regulation of vegetative functions.
At the level of the last cervical and two upper thoracic segments of the spinal cord, there are neurons that innervate three unsightly muscles of the eye: the muscle that dilates the pupil, the orbital part of the orbicular muscle of the eye, and one of the muscles of the upper eyelid.
The upper thoracic segments of the spinal cord contain neurons that are part of the center that regulates the functioning of the heart and the state of blood vessels (see Section 3). There are neurons that innervate the bronchi.
All thoracic and upper lumbar segments of the spinal cord contain neurons that innervate the sweat glands. Defeats of individual segments
Rice. 58.(on the legs): afferent pathways of each nerve of the somatic nervous system (1). autonomic nerve (2), somatic reflex (3), autonomic reflex (4)
cops causes a cessation of sweating in areas of the body that have lost sympathetic innervation.
In the sacral spinal cord there are spinal centers for urination, defecation, erection and ejaculation reflexes. The destruction of these centers causes impotence, urinary and fecal incontinence. Violations of urination and defecation occurs due to paralysis of the muscles-patterns of the bladder and rectum.
Vegetative reflexes can be divided into: viscero-visceral, viscerodermal and dermatosceral.
Viscero-visceral reflexes are caused by irritation of receptors located in the internal organs, and end with a change in the activity of the internal organs as well. 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 filling of the spleen due to an increase or decrease in pressure in the aorta, carotid sinus or pulmonary vessels, reflex cardiac arrest with irritation of the abdominal organs, etc.
Viscerodermal reflexes arise when internal organs are irritated and manifest themselves in a change in sweating, electrical resistance (electrical conductivity) of the skin and skin sensitivity in limited areas of the body surface, the topography of which is diverse depending on which organ is irritated.
Dermatovisceral reflexes are expressed in the fact that when some areas of the skin are irritated, vascular reactions occur and a change in the activity of certain internal organs.
Many of these autonomic reflexes are used in practical medicine, moreover, their application is multifaceted.
An example of the use of the dermatosceral reflex in the clinic is the use of heating pads or, conversely, ice packs to influence the pathological focus in the internal organs. The therapeutic effect of different types of acupunctures 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 soreness with a light touch or even without an irritant (reflected pain in the Ged-Zakharyin zones) (Fig. 59). Such a reflex can begin with interoceptors, and skeletal muscles can become an efector: during a "fire" in the abdominal cavity,
Rice. 59. 1-section of the lungs and bronchi; 2 - region of the heart; FROM- part of the intestines; 4,5 - area of the bladder; b- area of the kidneys; 7,9 - area of the liver; 8 - part of the stomach and pancreas; 10 - part of the urinary and genital organs
the tone of the flexor muscles is felt (the person curls up), the muscles of certain sections of the abdominal wall are tensed.
spinal shock.
These reflexes of the spinal cord in the whole organism are coordinated by the higher sections of the central nervous system. This is clearly manifested after the rupture of the connection between the brain and spinal cord. As a result of such damage, as in the somatic nervous system, spinal shock- temporary disappearance of autonomic reflexes of the spinal cord. Disappeared reflexes gradually, within 1-6 months. are restored, and even such complex ones as emptying the bladder and colon, sexual.
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
The vegetative centers of the brain stem are involved in the regulation of the functions of the cardiovascular, digestive systems, which carry out evacuation reflexes, control the reproductive organs, controlling their innervation by autonomic nerves. Here, the spinal centers responsible for individual autonomic functions are combined into functional complexes.
The medulla oblongata contains the boulevard section of the vasomotor center, which regulates the function of the heart and the state of the vessels. It also contains centers that stimulate lacrimation and secretion of the salivary and gastric glands, the pancreas, cause the release of bile from the gallbladder and bile duct, stimulate the motility of the stomach and small intestine.
In the middle of the brain (in the anterior tubercles of the chotyrigump plate) contains the nerve centers of the pupillary reflex and accommodation of the eye. In the anterior part of the midbrain is one of the centers that are involved in the emptying of the bladder. These centers belong to the parasympathetic department. But in the whole organism, in order to perform a reflex function, many of them (this is especially pronounced in the example of the vasomotor center) closely interact with other parts of the central nervous system. Thus, the vasomotor center of the medulla oblongata functions together with the sympathetic department of the thoracic region, and evacuation reflexes are carried out when the centers of the brainstem interact with the crescent centers of the parasympathetic nervous system. (These reflections are discussed in more detail in the presentation of the relevant sections.)
Reflex regulation of functions by the nerve centers of the trunk is carried out with the direct participation of interneuronal mechanisms that are responsible for the intercentral interaction of various parts of the central nervous system: sympathetic, parasympathetic autonomic and somatic nervous systems. A good example is the respiratory-cardiac reflex, or the so-called respiratory arrhythmia: a slowdown in heart rate at the end of exhalation before the start of the next breath.
Naturally, all reflexes of the brain stem 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. So, for example, some reflexes that close here make it possible to determine the state of the autonomic nervous system (vegetative functional tests). These include: a) peripheral reflex, or the Danin-Ashner reflex (short-term slowing of the heartbeat with pressure on the eyeballs); b) orthostatic response(increased heart rate and increased blood pressure during the change from lying to standing position), etc.
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, there is a slowdown and weakening of heart contractions. Goltz reflex.
Viscero-somatic reflex. Excitation of vascular chemoreceptors by carbon dioxide enhances contractions of the intercostal respiratory muscles. When the mechanisms of autonomic regulation are violated, changes in visceral functions occur.
Viscero-sensory reflex. Zakharyin-Ged zones…
Viscero-dermal reflex. Irritation of the interoreceptors of the internal organs leads to a change in sweating, the lumen of skin vessels, and skin sensitivity.
Somatovisceral reflex. The action of the stimulus on somatic receptors, such as skin receptors, leads to a change in the activity of internal organs. This group includes the Danini-Ashner reflex.
Dermovisceral reflex. Acupuncture medicine.
Central mechanisms of regulation of vegetative functions.
The structures are localized in the CNS and provide either the coordination of viscerovisceral reflexes and (or) the conjugation of visceral reflexes with motor ones, when performing holistic behavioral acts. They set the tone of the peripheral autonomic nerves, due to which a constant tonic effect of the autonomic nervous system on the functions of the organ (increase or decrease) is ensured.
Levels of autonomic regulation.
spinal level.
It is represented by the bodies of preganglionic autonomic neurons, which are grouped into small cell nuclei of the spinal cord (intermedial-lateral nuclei of the lateral horns of the spinal cord). Conducting pathways - carry effector signals from the brain to preganglionic and afferent: from visceroreceptors to various parts of the brain.
Manifested in the form of phenomena:
In diseases of the internal organs, a reflex tension of the striated abdominal muscles occurs and strictly corresponds to the localization of the pathological process. There is an irradiation of excitation from the spinal autonomic neurons to the motoneurons of the same segment, which are nearby.
With damage to the internal organs, there may be reddening of the skin area - the viscerocutaneous reflex.
It is innervated by afferent and efferent fibers of a certain segment of the spinal cord. This is due to the fact that at the level of the segment, with the receipt of pathological signals, sympathetic preganglionic neurons are reflexively inhibited, which would normally have a vasoconstrictive effect. Inhibition of sympathetic neurons leads to reddening 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, coronary artery disease - pain in the heart, under the left shoulder blade and in the skin of the left hand.
Associated with the segmental level - afferent autonomic neurons from the affected organ to 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 center of pain sensitivity in the cortex attributes the sensation of pain to the skin and internal organ.
The phenomenon of reflected pain is used for diagnosis and reflects the vegetative principle of regulation.
stem level.
The autonomic centers of the medulla oblongata, pons varolii and midbrain are active. There is no segmental structure, there is an accumulation of nuclei of gray matter, the localization of which is difficult to determine.
Center localization.
1. Circulatory (medulla oblongata) - regulation of blood circulation.
Vasomotor
Regulation of cardiac activity.
Parasympathetic fibers go as part of the vagus nerve to the circulatory organs and provide involuntary regulation of blood pressure.
Regulation of complex motor processes. Changing the position of the body in space is an orthostatic test.
2. Urination (bridge).
3. Salivation.
4. The center that regulates the activity of the glands of the stomach and intestines.
5. Tearing.
hypothalamic level.
3 departments, their excitation leads to a change in functions.
- front.
Centers of parasympathetic regulation of visceral functions. The excitation of these nuclei leads to a narrowing of the pupils, a decrease in blood pressure and cardiac activity, and an increase in the secretion of the glands of the gastrointestinal tract.
- rear.
sympathetic regulation. Opposite effects: dilation of the pupil, increased blood pressure.
- average.
regulation of metabolism. Centers of innate forms of behavior associated with hunger, thirst. The thermoregulatory center is located in the hypothalamus. At the level of the diencephalon, the regulatory influences of visceral and behavioral functions converge.
The cerebral cortex.
Frontal lobes: centers that provide voluntary regulation of breathing. Conditioned reflex effect on blood circulation, digestion, endocrine mechanisms.
Spinal cord (SM).
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 rear 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 the overlap, each metamere 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 neuron bodies of the spinal cord form its gray matter. Functionally, all its neurons are divided into motor neurons (3%) , insert (97%), neurons somatic and autonomic nervous system.
Motoneurons, divided into alpha, beta and gamma motor neurons. The bodies of motor neurons are located in the anterior horns of the spinal cord, their axons innervate skeletal muscles. α-motor neurons are phasic and tonic. β-motor neurons are small, they 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 transection of the anterior roots, muscle tone disappears.
interneurons provide communication between the centers of the spinal cord and the overlying parts of the central nervous system. Distinguish: own spinal(own reflexes of the spinal cord) somatic and vegetative; projection (receive signals, ascending and descending).
Vegetative the neurons of the sympathetic division of the autonomic nervous system are located in the lateral horns of the thoracic segments, and the parasympathetic in the sacral division.
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, push (jump, run) reflexes (knee)
n Flexion jerk reflexes
n Rhythmic reflexes ( scratching, striding)
n Positional reflexes ( cervical tonic reflexes of the position of Magnus - inclination and position, 7th cervical vertebra)
n Vegetative reflexes
The conductor function is to ensure the connection of peripheral receptors, centers of the spinal cord with the overlying parts of the central nervous system, as well as its nerve centers among themselves. It is carried out by conducting paths. All tracts of the spinal cord are divided into own or propriospinal , ascending and descending .
Propriospinal paths connect the nerve centers of different segments of the spinal cord. Their function is to coordinate muscle tone, movements of various body metameres.
To ascenders paths include several tracts. The Gaulle and Burdach bundles conduct nerve impulses from the proprioreceptors of the muscles and tendons to the corresponding nuclei of the medulla oblongata, and then to the thalamus and somatosensory cortical zones. Thanks to these pathways, the body posture is assessed and corrected. The Gowers and Flexig bundles transmit excitation from proprioreceptors, mechanoreceptors of the skin to the cerebellum. Due to this, the perception and unconscious coordination of the posture is ensured. Spinothalamic tracts conduct signals from pain, temperature, tactile skin receptors to the thalamus, and then somatosensory codes. They provide the perception of the corresponding signals and the formation of sensitivity.
descending, the paths are also formed by several tracts. Corticospinal pathways run from the pyramidal and extrapyramidal cortical neurons to the α-motoronerons of the spinal cord. Due to them, the regulation of voluntary movements is carried out. The rubrospinal pathway conducts signals from the red nucleus of the midbrain to the gamma motor neurons of the flexor muscles. The vestibulospinal pathway transmits signals from the vestibular nuclei of the medulla oblongata, primarily the nucleus of Deiters, to the gamma motor neurons of the extensor muscles. Due to these two ways, the tone of the corresponding muscles is regulated during changes in the position of the body.
At spinal cord injury: with 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 vegetative reflexes stop: urination, defecation, sexual functions. In 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, the tone of autonomic neurons. When transected, the tonic influence stops. Sympathetic vasomotor neurons are inhibited - reddening of the skin. Normally, sympathetic neurons have a vasoconstrictive effect.
In 6 months reflexes are disinhibited and their activity increases. Hyperreflexia. Redness turns into blanching due to increased narrowing of the skin vessels. Increases sweating. Normally, while maintaining the integrity of the CNS, the reticular formation has an activating and retarding effect on the autonomic spinal centers.
Vegetative reflexes are caused by stimulation of both intero and exteroreceptors. Among the numerous and varied vegetative reflexes, viscero-visceral, viscerodermal, dermatovisceral, visceromotor and motor-visceral are distinguished.
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 cardio-cardiac, gastrohepatic, etc. Some patients with gastric lesions have gastrocardial syndrome, one of the manifestations of which is a violation of the heart, up to the appearance of angina attacks due to insufficient coronary circulation.
Viscerodermal reflexes occur when receptors of visceral organs are irritated and are manifested by a violation of skin sensitivity, sweating, skin elasticity in limited areas of the skin surface (dermatome). Such reflexes can be observed in the clinic. So, in diseases of the internal organs, tactile (hyperesthesia) and pain (hyperalgesia) sensitivity increase in limited areas of the skin. Possibly, pain and non-pain skin-afferent fibers and visceral afferents belonging to a certain segment of the spinal cord convert on the same neurons of the sympotalamic pathway.
Dermatovisceral reflexes are manifested 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 medical procedures (physio-, reflexology). So, damage to skin thermoreceptors (by heating or cooling) through sympathetic centers leads to reddening of skin areas, 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 the segmental organization of the autonomic innervation of the internal organs, visceromotor reflexes are also associated, in which the excitation of the receptors of the internal organs leads to a reduction or inhibition of the current activity of the skeletal muscles.
There are "corrective" and "starting" influences from the receptor fields of the internal organs on the skeletal muscles. The former lead to changes in skeletal muscle contractions that occur with the influence of other afferent stimuli, intensifying or suppressing them. The latter independently activate contractions of skeletal muscles. Both types of influences are associated with the amplification of signals coming through the afferent pathways of the autonomic reflex arc. Visceromotor reflexes are often observed in diseases of the internal organs. For example, with cholecystitis or appendicitis, muscle tension occurs in the area of the pat. process. Protective visceromotor reflexes also include the so-called forced postures that a person takes in diseases of the internal organs (for example, bending and bringing the lower extremities to the stomach).
6. Levels of regulation of vegetative functions. The hypothalamus as the highest subcortical center for the regulation of vegetative functions.
In the system of regulation of vegetative functions, several levels are distinguished that interact with each other and the subordination of the lower levels by the higher located departments is observed.
The coordination of the activity of all three parts of the autonomic nervous system is carried out by segmental and suprasegmental centers (apparatuses) with the participation of the cerebral cortex.
Segment centers due to the peculiarities of their organization and patterns of functioning, they are truly autonomous. In the central nervous system, they are located in the spinal cord and in the brain stem (separate nuclei of the cranial nerves), and on the periphery they form a complex system of plexuses, ganglia, and fibers.
suprasegmental centers located in the brain mainly at the limbic-reticular level. These integrative centers provide holistic forms of behavior, adaptation to changing conditions of the external and internal environment.
All these complex mechanisms of regulation of the activity of visceral functions are conditionally united by a multi-level hierarchical structure. Its basic (first) level is intraorganic reflexes. The second structural level is the extramural paravertebral ganglia of the mesenteric and celiac plexuses. Both first levels have a pronounced autonomy. The third structural level is represented by the centers of the spinal and brain stem. The highest level of regulation (fourth) is represented by the hypothalamus, the reticular formation, the limbic system, and the cerebellum. The new KBP closes the pyramid of the hierarchy.
spinal level. At the level of the last cervical and two upper thoracic segments of the spinal cord is the spinociliary center. Its fibers terminate at the muscles of the eye. When these neurons are stimulated, pupil dilation (mydriasis), expansion of the palpebral fissure and protrusion of the eye (exophthalmos) are observed. With the defeat of this department, Bernard-Horner syndrome is noted - pupil constriction (miosis), narrowing of the palpebral fissure and retraction of the eye (endophthalmos).
The five upper segments of the thoracic spinal cord send impulses to the heart and bronchi. The defeat of individual segments of the thoracic and upper lumbar causes the disappearance of vascular tone, sweating.
In the sacral region, centers are localized, with the participation of which the reflexes of the genitourinary system and defecation are regulated. With a rupture of the spinal cord above the sacral region, these functions may disappear.
in the medulla oblongata the vasomotor center is located, which coordinates the activity of the sympathetic nerves located in the thoracolumbar region of the spinal cord. Also in the medulla oblongata are centers that inhibit the functions of the heart and activate the glands of the gastrointestinal tract, regulating the acts of sucking, swallowing, sneezing, coughing, vomiting, and lacrimation. These influences are transmitted to the executive organs along the fibers of the vagus, glossopharyngeal and facial nerves.
In the midbrain the center of the pupillary reflex and accommodation of the eye is localized. These departments obey the higher structures.
Hypothalamus is the highest center of regulation of vegetative functions, which are responsible for the state of the internal environment of the body. It is an important integrative center of autonomic, somatic and endocrine functions.
The hypothalamus is the central part of the diencephalon. It lies ventral to the thalamus. The lower border of the thalamus is the midbrain, and the upper border is the end plate, anterior commissure and optic chiasm. It has about 48 pairs of cores. The following sections are distinguished in the hypothalamus: 1) preoptic, 2) anterior group, 3) middle group, 4) external group, 5) posterior group. Among the nuclei, specific and nonspecific are distinguished. Specific nuclei are connected to the pituitary gland and are capable of neurocrinia, i.e. synthesis and release of a number of hormones.
The nuclei of the hypothalamus are neither sympathetic nor parasympathetic, although it is generally accepted that in the posterior nuclei of the hypothalamus there are groups of neurons connected mainly to the sympathetic system, and in its anterior nuclei there are neurons that regulate the functions of the parasympathetic system. The hypothalamus regulates the functions of both parts of the autonomic nervous system, depending on the nature and level of afferentation entering its nuclei. It forms bilateral (afferent and efferent) connections with various parts of the brain - the upper parts of the brain stem, the central gray matter of the midbrain, with the structures of the limbic system of the thalamus, the reticular formation, the subcortical nuclei and the cortex. Afferent signals enter the hypothalamus from the surface of the body and internal organs, as well as from some parts of the brain. In the medial region of the hypothalamus, there are special neurons (osmo-, gluco-, thermoreceptors) that control important parameters of the blood (water-electrolyte composition of plasma, blood temperature, etc.) and cerebrospinal fluid, that is, they “monitor” the state of the internal environment of the body. Through the nervous mechanisms, the medial section of the hypothalamus controls the activity of the neurohypophysis, and through the humoral mechanisms - the adenohypophysis.
The hypothalamus regulates water and electrolyte metabolism, body temperature, the functions of the endocrine glands, puberty, the activity of the cardiovascular, respiratory systems, digestive organs, and kidneys. It is involved in the formation of nutritional, sexual protection, in the regulation of the sleep cycle - cheerfulness like that. Therefore, any action on the hypothalamus is accompanied by a complex of reactions of many body systems, which is expressed in visceral, somatic and mental effects.
In case of damage to the hypothalamus (tumors, traumatic or inflammatory lesions), there are disorders of energy and water balances, thermoregulation, functions of the cardiovascular system, digestive organs, endocrine disorders, emotional reactions.
The vegetative functions of the body are significantly influenced by the limbic structures of the brain.
The structure of the hypothalamus . The hypothalamus belongs to the phylogenetically ancient formations of the brain and is already well developed in lower vertebrates. It forms the floor of the third ventricle and lies between the optic chiasm and the posterior margin of the mammillary bodies. The hypothalamus consists of a gray tubercle, a median eminence, a funnel, and the posterior or nervous lobe of the pituitary gland. In front, it borders on the preoptic region, which some authors also include in the hypothalamus system.
PHYSIOLOGY OF HIGHER NERVOUS ACTIVITY
1. Conditioned reflex as a form of human adaptation to changing conditions of existence. Differences between conditioned and unconditioned reflexes. Patterns of formation and manifestation of conditioned reflexes.
The adaptation of animals and humans to the changing conditions of existence in the external environment is ensured by the activity of the nervous system and is realized through reflex activity. In the process of evolution, hereditarily fixed reactions (unconditioned reflexes) arose, which unite and coordinate the functions of various organs, carry out the adaptation of the body. In humans and higher animals, in the process of individual life, qualitatively new reflex reactions arise, which IP Pavlov called conditioned reflexes, considering them the most perfect form of adaptation.
While relatively simple forms of nervous activity determine the reflex regulation of homeostasis and vegetative functions of the body, higher nervous activity (HNA) provides complex individual forms of behavior in changing living conditions. GNI is implemented due to the dominant influence of the cortex on all underlying structures of the central nervous system. The main processes that dynamically replace each other in the central nervous system are the processes of excitation and inhibition. Depending on their ratio, strength and localization, the control influences of the cortex are built. the functional unit of GNI is the conditioned reflex.
Reflexes are conditional and unconditional. An unconditioned reflex is a reflex that is inherited, passed down from generation to generation. In humans, by the time of birth, the almost reflex arc of unconditioned reflexes is fully formed, with the exception of sexual reflexes. Unconditioned reflexes are species-specific, that is, they are characteristic of individuals of a given species.
Conditioned reflexes (UR) are an individually acquired reaction of the body to a previously indifferent stimulus (an irritant is any material agent, external or internal, conscious or unconscious, acting as a condition for subsequent states of the body. Signal stimulus (aka indifferent) - an irritant that has not previously caused corresponding reaction, but under certain conditions for the formation of a conditioned reflex, which begins to cause it), reproducing an unconditioned reflex. SD are formed during life, associated with the accumulation of life experience. They are individual for each person or animal. Able to fade if not reinforced. Quenched conditioned reflexes do not disappear completely, that is, they are capable of recovery.
General properties of conditioned reflexes. Despite certain differences, conditioned reflexes are characterized by the following general properties (features):
All conditioned reflexes are one of the forms of adaptive reactions of the body to changing environmental conditions.
· SD are acquired and canceled in the course of the individual life of each individual.
All URs are formed with the participation of the central nervous system.
UR are formed on the basis of unconditioned reflexes; without reinforcement, conditioned reflexes are weakened and suppressed over time.
All types of conditioned reflex activity are signal warning character. That is, they precede, prevent the subsequent occurrence of BR. Prepare the body for any biologically purposeful activity. SD is a reaction to a future event. SDs are formed due to the plasticity of the NS.
The biological role of SD is to expand the range of adaptive capabilities of the organism. SD complements BR and allows fine and flexible adaptation to a wide variety of environmental conditions.
Differences between conditioned reflexes and unconditioned
1. Unconditioned reactions are congenital, hereditary reactions, they are formed on the basis of hereditary factors and most of them begin to function immediately after birth. Conditioned reflexes are acquired reactions in the process of individual life.
2. Unconditioned reflexes are specific, i.e., these reflexes are characteristic of all representatives of a given species. Conditioned reflexes are individual, in some animals some conditioned reflexes can be developed, in others others.
3. Unconditioned reflexes are constant, they persist throughout the life of the organism. Conditioned reflexes are fickle, they can arise, gain a foothold and disappear.
4. Unconditioned reflexes are carried out at the expense of the lower parts of the central nervous system (subcortical nuclei, brain stem, spinal cord). Conditioned reflexes are predominantly a function of the higher parts of the central nervous system - the cerebral cortex.
5. Unconditioned reflexes are always carried out in response to adequate stimuli acting on a certain receptive field, that is, they are structurally fixed. Conditioned reflexes can be formed to any stimuli, from any receptive field.
6. Unconditioned reflexes are reactions to direct stimuli (food, being in the oral cavity, causes salivation). Conditioned reflex - a reaction to the properties (signs) of the stimulus (the smell of food, the type of food cause salivation). Conditional reactions are always signal in nature. They signal the upcoming action of the stimulus and the body meets the impact of the unconditioned stimulus, when all the responses are already turned on, ensuring the body is balanced by the factors that cause this unconditioned reflex. So, for example, food, getting into the oral cavity, meets saliva there, which is released conditioned reflex (by the type of food, by its smell); muscular work begins when the conditioned reflexes developed for it have already caused a redistribution of blood, an increase in respiration and blood circulation, etc. This is the manifestation of the higher adaptive nature of conditioned reflexes.
7. Conditioned reflexes are developed on the basis of unconditioned ones.
8. A conditioned reflex is a complex multicomponent reaction.
9. Conditioned reflexes can be developed in life and in laboratory conditions.
A conditioned reflex is a multicomponent adaptive reaction that has a signal character, carried out by the higher parts of the central nervous system through the formation of temporary connections between the signal stimulus and the signaled reaction.
In the zone of cortical representation of the conditioned stimulus and cortical (or subcortical) representation of the unconditioned stimulus, two foci of excitation are formed. The focus of excitation, caused by an unconditioned stimulus of the external or internal environment of the body, as a stronger (dominant) one, attracts excitation from the focus of a weaker excitation caused by a conditioned stimulus. After several repeated presentations of the conditioned and unconditioned stimuli between these two zones, a stable path of movement of excitation is "blazed": from the focus caused by the conditioned stimulus to the focus caused by the unconditioned stimulus. As a result, the isolated presentation of only the conditioned stimulus now leads to the response evoked by the previously unconditioned stimulus.
Intercalary and associative neurons of the cerebral cortex act as the main cellular elements of the central mechanism for the formation of a conditioned reflex.
For the formation of a conditioned reflex, the following rules must be observed: 1) an indifferent stimulus (which should become a conditioned, signal) must have sufficient strength to excite certain receptors; 2) it is necessary that the indifferent stimulus be reinforced by an unconditioned stimulus, and the indifferent stimulus must either somewhat precede or be presented simultaneously with the unconditioned one; 3) it is necessary that the stimulus used as a conditioned one be weaker than the unconditioned one. To develop a conditioned reflex, it is also necessary to have a normal physiological state of the cortical and subcortical structures that form the central representation of the corresponding conditioned and unconditioned stimuli, the absence of strong extraneous stimuli, and the absence of significant pathological processes in the body.
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 the excitation of the parasympathetic nervous system is acetylcholine.
Excitation of parasympathetic centers is observed at 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;
the blood pressure in the vessels decreases;
skin vessels dilate
the vessels of the abdominal organs expand and the processes of digestion increase;
the processes of urination are intensified;
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 of it leaves the vessels to the liver and spleen.
The neurons of the sympathetic and parasympathetic systems take part in the formation of certain autonomic reflexes. Vegetative reflexes are manifested in a change in the state of the internal organs when the position of the body changes and when the receptors are stimulated.
Vegetative reflexes are of the following types:
· viscero-visceral reflexes;
· cutano-visceral reflexes;
· motor-visceral reflexes;
· eye-heart reflex.
Viscero-visceral reflexes – these are the reactions that are caused by irritation of the receptors of the internal organs and are manifested by a change in the state of the internal organs as well. For example, when blood vessels narrow, the amount of blood in the spleen increases.
Cutano-visceral reflexes- are expressed in the fact that when some 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 the internal organs. Or, applying cold to the skin causes constriction of the blood vessels.
Motor-visceral reflexes- Manifested in a change in blood pressure and the number of heartbeats with a change in body position. For example, if a person moves from a lying position to a sitting position, then the value of his blood pressure will become greater, and the heart will contract more strongly.
Eye-heart reflex- manifested in a change in the work of the heart when the eyeball is irritated.
