The term "metasympathetic nervous system" was introduced by A. D. Nozdrachev. This is a separate system of interconnected neurons that regulates all the work of internal organs. This is an extremely developed nervous network, which is also subject to the principle of the hierarchy of vegetative ganglia.
The metasympathetic division of the nervous system is an important and integral part of the entire network. The nerve plexuses of the metasympathetic network lie inside the hollow organs, more precisely in their muscle walls. Therefore, the system is sometimes called the intraorgan.
The metasympathetic autonomic nervous system has its own structural features and can work separately from brain signals. This became clear during experiments, when after perfusion the heart continued to contract; the excised ureter remained dynamic. But how is each module innervated and how is it interconnected with the central nervous system?
Metesympathetic nervous system. What is it?
Until recently, only 2 parts of the nervous system were isolated - sympathetic and parasympathetic. The first, as you know, is responsible for mobilizing the body, and the second for relaxation and rest. But when scientists noticed that each organ has its own rhythm of movement and its separately functioning microganglia, they decided to single out another system - the metasympathetic one.
This is a completely independent formation, which has at its disposal reflex arcs. Each ganglion network has its own hollow organ: in the kidneys, stomach, uterus, intestines, and prostate, men also have their own nerve plexuses. Moreover, some networks are still poorly understood, so you can only make assumptions about how complex they are organized.
The entire autonomic nervous system (sympathetic, parasympathetic, metasympathetic departments) is designed to control homeostasis, that is, the constancy of the internal environment. If there are no failures in the autonomic nervous system, then the metabolism is perfectly adjusted, the lymphatic system and the circulatory system are working properly.
After damage to the spinal central nerve canal, all internal organs, such as the bladder, intestines, after the shock experienced, are gradually restored. The organs are rebuilt and again begin to work fully in 5-6 months. This is due to another metasympathetic nervous system embedded in their muscle walls.
Localization
The main rhythm leading cells of the intraorgan system are located in the submucous membranes and intramuscular structures. Higher autonomic centers that control all reflexes of the MHC are localized in the diencephalon. Namely, in the striatum and hypothalamus.
MHC value
In medicine, the study of ganglionic nodes of internal organs is important for the study of diseases associated with impaired organ development. One such abnormality is Hirschsprung's disease. MHC is responsible for the nutrition of organ cells and blood circulation in the internal muscle layers of organs.
Another important detail. Due to the fact that in the intraorgan system there are reflex arcs, it has the ability to work without constant "guidance" of the central nervous system. What is a reflex arc? This is a chain of neurons that allows you to quickly transmit a pain signal and get an immediate response to irritation of the receptors.
Features of the metasympathetic system
What is the most prominent for the MHC? What properties distinguish it from the sympathetic and parasympathetic systems? Scientific evidence has confirmed the assumption that the system:
- It has its own sensory link and afferent path.
- Innervates exclusively the muscles of the internal organs.
- It receives signals from the sympathetic and parasympathetic systems through incoming synapses.
- It does not have a direct connection with the efferent link of the somatic reflex.
- Those internal organs in which the metasympathetic nervous system (MNS) is impaired lose their coordinated motor function.
- The network has its neurotransmitters.
As you can see, the entire nervous system is subordinate to the hierarchy. "Senior" departments regulate the work of subordinate relations. The intraorgan network is βlowerβ, but not the simplest.
Vegetative ganglia
Ganglia are nerve nodes. Vegetative ganglia help distribute electrical signals efficiently. One or several preganglionic nerve fibers that transmit signals from the "superior" system approaches one ganglion. And postganglionic neurons departing from the ganglion, transmitting excitation or inhibition further down the network. This universal system allows you to fully control all processes in the body.
In the ganglia of the exciting nervous network, the presynaptic fiber regulates up to 30 nerve cells connected to the ganglion. And in the parasympathetic - only 3 or 4 neurons.
Vegetative nodes are found in all tissues and organs, as well as in the glands of internal and external secretion. The neurons of the MHC network are extremely diverse, but each consists of an axon, nucleus, and dendrite.
Dendrite - from Latin - woody. From the name it is clear that this part of the neuron transmits signals along a highly branched network of small fibers. In the enteral system, for example, each neuron has a lot of dendrites.
Some fibers have a myelin sheath, which improves conductivity and accelerates the signal.
Types of MHC
There are several systems. They are divided depending on the location of the microganglia:
- cardiometasympathetic system;
- vesiculometasympathetic;
- enterometasympathetic;
- urethrometasympathetic;
- ganglionic system of the uterus.
It is known that parasympathetic and sympathetic systems interact with the system of organ ganglia and adjust their work when necessary. And also many organs have intersecting reflexes. For example, the Goltz reflex.
Metasympathetic nervous system. Physiology
What neurons does this nervous system consist of? What is the structure of the metasympathetic nervous system? Let us consider in more detail the system of neurons. In the structure of nerve fibers of each hollow organ there is a rhythm leader, which controls motor activity (vibration), there are intercalary, tonic and effector neurons. And of course, there are sensory mats.
The key unit of the entire module is the oscillator cell, or pacemaker. This cell transmits its signals (action potentials) to the motor neuron. The axon of each motor neuron is in contact with muscle cells.
The function of the oscillator cell is very significant. Cells are protected from external influences, such as from the influence of ganglion blockers or neurotransmitters.
Thanks to the work of the network of neurons, the work of the muscles that absorb the useful substances of the apparatus and the mechanism of blood supply to the organ is controlled.
MHC mediators
Neurotransmitters are substances that help transmit impulses from one neuron to another. The mediators of the metasympathetic nervous system are as follows:
- histamine;
- serotonin;
- adenosine triphosphoric acid;
- acetylcholine;
- somatostanin;
- catecholamines.
In total, about 20 mediators and modulators in the neural network were found in laboratory conditions. A mediator such as acetylcholine, belonging to the catecholamine group, is a mediator of the sympathetic system, that is, it helps to transmit an excitation signal. An excess of catecholamines in the body leads to overexcitation of the central nervous system. Often, heart failure begins due to constant stress and emissions of norepinephrine. Therefore, the body urgently needs a restoring parasympathetic system.
Mediators such as the pituitary peptide and ATP are designed to transmit an impulse of relaxation and recovery. Parasympathetic centers are located in the autonomic nuclei of the cranial nerves.
Cardiometasympathetic system
The metasympathetic autonomic nervous system, as mentioned, consists of several sections. The ganglionic system of the heart is already quite well studied, so you can consider how it works.
The protection of the heart occurs due to cycles of reflexes that have a βbaseβ in the intramural ganglia.
Thanks to the work of G. Kositsky, we know about one very interesting reflex. Stretching of the right atrium always affects the work of the right ventricle. It works harder. The same thing happens on the left side of the heart.
With aortic distension, contractility of both ventricles decreases reflexively. These effects occur due to the metasympathetic nervous system. The Goletz reflex is manifested when, upon hitting the abdomen, the heart can stop contracting for a while. The reaction is associated with the activation of the abdominal nerve, with its afferent part.
The frequency of contractions of the heart is reduced with other influences. Ashner-Dagnini reflex is a reaction of the heart when pressing on the eyes. Cardiac arrest also occurs when the vagus nerve is irritated. But with subsequent irritation of the nerve, this effect disappears.
Heart reflexes are designed to maintain arterial blood flow at a single constant level. The autonomy of the nervous intracardial system proves the ability of the heart to take root after transplantation. Although all cardiac underlying nerves are cut, the organ continues to contract.
Enterometasympathetic system
The enteric nervous system is a unique mechanism where thousands of neurons are fully coordinated with each other. This mechanism, created by nature, is rightfully considered the second human brain. Since even with damage to the vagus nerve, which is associated with the brain, the system continues to perform all its functions, namely: digesting food and absorbing nutrients.
But it turns out that the food tract is not only responsible for the digestion of food, but, according to the latest data, and for the emotional background of a person. It has been established that 50% of dopamine, the hormone of joy, and about 80% of serotonin are produced in the intestines. And this is even more than is produced in the brain. Therefore, the intestines can be safely called the emotional brain.
In the enteric vegetative metasympathetic system, several types of neurons are distinguished:
- primary afferent sensory;
- ascending and descending interneurons;
- motor neurons.
Motoneurons, in turn, are divided into moving muscles that excite and inhibit.
Peristaltic reflex of the intestines and MHC
The small and large intestines also have an autonomous metasympathetic division of the autonomic nervous system. It is known that on each villus of the large intestine there are 65 sensory neurons; each millimeter of tissue contains 2500 different nerve cells.
Sensory neurons are combined with motor neurons through various interneurons in the enteral system. It is enough to be activated by one neuron so that further tension and relaxation of the muscles of the intestine start up along the chain. This is called the peristaltic reflex, which promotes food through the intestines. The autonomic system of the intestine is also completely independent of the central nervous system, which is vital if, in the event of a stroke, for example, part of the brain ceases to function.