The bodies of the central ganglia of the parasympathetic nervous system are located. Autonomic autonomic ganglia
4. Vegetative ganglia, their properties. The concept of the metasympathetic nervous system and its mediators.
A feature of the peripheral link of the autonomic nervous system is the presence of ganglia, which are a cluster of neurons.
Autonomic ganglia play an important role in the distribution and propagation of nerve influences on organs. It was noted that the number of nerve cells in the ganglia is several times higher than the number of preganglionic fibers.
The phenomenon of convergence is observed in the ganglia. Along with this, the phenomenon of spatial and temporal summation is revealed. The autonomic ganglia exhibit the same properties as the somatic nerve centers. Therefore, the ganglia of the autonomic nervous system are sometimes called peripheral nerve centers.
Metasympathetic The (intraorganic) nervous system (NNS) is a complex of nerve formations - neurons, the bodies of which form ganglia, and processes of nerve cells that extend beyond the ganglion. These structures are localized in the wall of the heart, intestines and other organs. The number of neurons in this system exceeds that in the spinal cord. The Ministry of Taxes and Taxes does not have a central department, i.e., it is relatively autonomous; its functional module includes a pacemaker, sensory cells, intercalary, tonic and effector neurons. These nerve formations ensure the autonomy of organs and the local regulation of the functions of smooth and cardiac muscles, secretory epithelium, the absorption apparatus, and small blood vessels. The role of the metasympathetic nervous system is especially important in regulating the functions of the intestine (above the rectum), where there are practically no central nervous influences. About 20 mediators and modulators were found in MHC synapses, among them acetylcholine, cholecystokinin, enkephalins, histamine, serotonin, somatostatin, ATP, substance P, catecholamines. Sympathetic and parasympathetic nerves can form synapses on metasympathetic neurons and influence their activity.
Ticket number 8
1. Reflex as the main principle of the activity of the central nervous system. The main stages of the doctrine of the reflex. Reverse afferentation, its significance for the organism.
Reflex(R.) is a natural reaction of the body to changes in the external or internal environment, occurring with the participation of the nervous system in response to irritation of the receptors. reflex arc- the reflex nerve pathway - consists of a sensitive nerve ending (or receptor cell), a sensitive nerve fiber with a ganglion, a central part (sensitive, intercalary, effector neurons of different levels of the central nervous system), an efferent nerve fiber and an effector. The founder reflex teachings The French philosopher, mathematician and physiologist Rene Descartes (1648) was a response to irritation realized by the nerve centers of the spinal cord. He formulated two important provisions of the reflex theory: 1) the activity of the organism under external influence is reflected (later it was called reflex: lat. reflexus - reflected); 2) the response to irritation is carried out with the help of the nervous system. The term “reflex” was first used by the Czech physiologist, anatomist and ophthalmologist I. Prochazka, and the expression “reflex arc” was used by the English neuropathologist and physiologist M. Hall. A new step in the development of the doctrine of the reflex was the book by I. M. Sechenov "Reflexes of the brain" (1863), the main idea of which was the statement: "All acts of conscious and unconscious life are reflexes." In other words, I. M. Sechenov used the reflex principle to explain the mechanisms of brain activity, including thought processes. The absence in a number of cases of a visible response to the action of stimuli, the scientist explained by the development of central inhibition, discovered by him a year earlier (1862). Thus, reflexes can have a "truncated end." I. P. Pavlov, not being a direct student of I. M. Sechenov, however, considered him his teacher and highly appreciated the value of I. M. Sechenov's book, calling it "a stroke of genius in Russian thought."
IP Pavlov devoted more than 30 years of his life to the study of the higher reflexes of the brain, using for this purpose the method of conditioned reflexes and, consequently, an objective approach to the study of brain functions. He developed a reflex theory based on three principles: 1) determinism, that is, the causation of various processes of brain activity; 2) analysis and synthesis of stimuli in the higher parts of the brain; 3) the timing of dynamics to the structure, i.e., the connection of brain functions with certain structures. A. Bernstein and P. K. Anokhin. Feedback ideas were used to explain the mechanisms of reflex activity by N. A. Bernshtein (1947), as a result, the term “reflex ring” appeared.
P. K. Anokhin (1949) called feedback reflexes "reverse afferentation". Its source is receptors localized in the effector organ (1) and in the sensory organs involved in evaluating the result of the reflex act (2). So, when performing any melody on musical instrument such receptors can be proprioceptors of the muscles and tendons of the hand (1), as well as receptors of the organ of hearing (2). Signals back afferentation are used to compare the result of a reflex act with its program.
Under natural conditions of life, reflexes are usually
integrated into systems. Moreover, the system-forming factor is the overall result, which leads to the implementation of this set of reflexes. Thus, maintaining the optimal concentration of oxygen in the blood plasma is provided by cardiac, respiratory, motor and other reflexes that form a functional reflex system. The doctrine of functional systems of regulation of functions was developed by P. K. Anokhin (1949).
Details
ganglia represent clusters of multipolar (one axon and several dendrites) neurons(from a few cells to tens of thousands). Extraorganic (sympathetic) ganglia have a well-defined connective tissue capsule, as a continuation of the perineurium. The parasympathetic ganglia are usually located in the intramural nerve plexuses. The ganglia of the intramural plexuses, like other autonomic nodes, contain autonomic neurons of local reflex arcs. Multipolar neurons with a diameter of 20-35 μm are located diffusely, each neuron is surrounded by ganglion gliocytes.
In addition, described neuroendocrine, chemoreceptor, bipolar, and in some vertebrates, unipolar neurons. In the sympathetic ganglia there are small intensely fluorescent cells (MYF cells) with short processes and a large number of granular vesicles in the cytoplasm. They secrete catecholamines and have an inhibitory effect on the transmission of impulses from the preganglionic nerve fibers to the efferent sympathetic neuron. These cells are called interneurons.
Among the major multipolar neurons vegetative ganglia distinguish: motor (Dogel's cells of the 1st type), sensitive (Dogel's cells of the II-th type) and associative (Dogel's cells of the III-th type). Motor neurons have short dendrites with lamellar extensions ("receptive pads"). The axon of these cells is very long, goes beyond the ganglion as part of postganglionic thin non-myelinated nerve fibers and ends on smooth myocytes. internal organs. Cells of the 1st type are called long-axon neurons. Neurons of the II-th type are equidistant nerve cells. 2-4 processes depart from their body, among which it is difficult to distinguish an axon. Without branching, the processes go far from the body of the neuron. Their dendrites have sensitive nerve endings, and the axon terminates on the bodies of motor neurons in neighboring ganglia. Type II cells are sensitive neurons of local autonomic reflex arcs. Type III Dogel cells are similar in body shape to type II autonomic neurons, but their dendrites do not extend beyond the ganglion, and the neurite goes to other ganglia. Many researchers consider these cells to be varieties of sensitive neurons.
Thus, in the peripheral autonomic ganglia there are local reflex arcs consisting of sensory, motor, and possibly associative autonomic neurons.
Intramural autonomic ganglia in the wall of the digestive tract are distinguished by the fact that, in addition to motor cholinergic neurons, they contain inhibitory neurons. They are represented by adrenergic and purinergic nerve cells. In the latter, the mediator is a purine nucleotide. In the intramural autonomic ganglia, there are also peptidergic neurons that secrete vasointestinal peptide, somatostatin, and a number of other peptides, with the help of which neuroendocrine regulation and modulation of the activity of tissues and organs of the digestive system are carried out.
Acetylcholine- nicotinic (curare block, hexamethonium), muscarinic (atropine block) receptors. Receptor activation → EPSP generation. Rapid EPSP (N-cholinergic)→opening of ion channels. Slow EPSP (M-cholinergic) → suppression of M-current due to an increase in K-conductivity.
Neuropeptides- act as neuromodulators.
Enkephalins, substance P, luliberin, neurotensin, somatostatin - symptom. ganglia (+Ach)
Catecholamines(NA, dopamine) are small cell neurotransmitters with intense fluorescence.
Neuropeptide Y, somatostatin - symptom. postganglionic.
Sympathetic postganglionic cells: NA, ATP, neuropeptide U.
α1→inosotol triphosphate, diacylglycerol. α2→G-protein activation, ↓cAMP.
β→G-protein→AC→cAMP
Exceptions: mediator Ach, muscarinic receptors.
Parasymp. postganglionic: Ach, VIP, NO, somatostatin, ATP, opioid peptides.
M1 (high affinity for pirenzepine) - increased acid secretion by the cells of the glands of the stomach, M2 (low) - slow down the heart. rhythm, secretion of the lacrimal and salivary glands.
Miscellaneous action:
-Specific sec. mediators: M2 may act IP3, or it may induce AC, reducing cAMP.
- Action on K and Ca channels
- NO → guanylate cyclase → cGMP → cGMP-dependent protein kinase → smooth muscle relaxation is formed on the endothelium.
The autonomic ganglia are an accumulation of numerous multipolar nerve cells.
The size of the autonomic ganglia varies significantly. In this regard, there are large, medium-sized, small and very small (microganglia) ganglia.
It should be noted that in addition to the anatomically isolated ganglia, along the autonomic branches of the peripheral nerves, there are a large number of nerve cells similar to the nerve cells of the autonomic ganglion. These neurons, migrating here during embryogenesis, are localized along the nerves singly or form small groups - microganglia.
The vegetative ganglion is covered from the surface with a fibrous connective tissue capsule, from which numerous layers of connective tissue extend inside, forming the stroma of the node. Through these layers, blood vessels pass into the node, feeding it and forming a capillary network in it. In the capsule and stroma of the node, receptors are often found near the blood vessels - diffuse, bushy or encapsulated.
Multipolar nerve cells of the autonomic ganglion were first described by A.S. Dogel. At the same time, Dogel singled out 3 types of nervous autonomic ganglion cells, which are called Dogel cellsI, II, III type. The morphological and functional characteristics of Dogel cells differ significantly.
Dogel cellsItype according to their functional significance, they are effector (motor) neurons. These are more or less large nerve cells, with somewhat short dendrites that do not extend beyond this ganglion. The longer axon of these cells extends beyond the ganglion and goes to the working apparatus - smooth muscle cells, glandular cells, forming motor (or, respectively, secretory) nerve endings on them. The axons and dendrites of Type I Dogel cells are non-pulmonic. Dendrites often form lamellar extensions, on which (as well as on the cell body) synaptic endings are located, which are formed by branches of the preganglionic nerve fiber.
The bodies of neurons in the autonomic ganglion, in contrast to the spinal ganglion, are arranged randomly throughout the node and more loosely (i.e., more rarely). On preparations stained with hematoxylin or other general histological stains, the processes of nerve cells remain unidentified, and the cells have the same rounded, processless shape as in the spinal nodes. The body of each nerve cell (as in the spinal ganglion) is surrounded by a layer of flattened elements of oligodendroglia - a layer of satellites.
To the outside of the layer of satellites there is still a thin connective tissue capsule. Type I Dogel cells are the main cellular form of autonomic ganglia.
Dogel cellsIItype are also multipolar nerve cells, with several long dendrites and a neurite extending beyond a given ganglion into neighboring ganglia. The surface of the axon is covered with myelin. The dendrites of these cells begin as receptor apparatuses in smooth muscles. From a functional point of view, type II Dogel cells are sensitive. In contrast to the sensitive pseudo-unipolar nerve cells of the spinal ganglion, Type II Dogel cells apparently form a receptor (afferent) link of local reflex arcs that are closed without a nerve impulse entering the central nervous system.
Dogel cellsIIItype are local associative (inserted) elements that connect several cells of type II and II with their processes. Their dendrites are short, but longer than those of type I cells; they do not go beyond the limits of this ganglion, but form basket-shaped branches that wrap around the bodies of other cells of this ganglion. The neurite of a type III Dogel cell goes to another ganglion and there enters into a synaptic connection with type I cells. Consequently, type III cells are included as an associative link in local reflex arcs.
It should be noted that there is such a point of view that Type III Dogel cells have a receptor or effector nature.
The ratio of the number of cells of I and II types of Dogel in various vegetative ganglia is not the same. Parasympathetic ganglia, in contrast to the sympathetic ganglia, are characterized by the predominance of cells with short intracapsular dendrites, the absence or small amount of pigment in the cells. In addition, in the parasympathetic ganglia, as a rule, the bodies lie much more compactly than in the sympathetic ganglia. In addition, the sympathetic ganglia contain MYTH cells(small cells with intense fluorescence).
Through the vegetative ganglion there are three types of pathways: centripetal, centrifugal and peripheral (local) reflex.
Centripetal pathways are formed by sensory processes of pseudounipolar cells of the spinal ganglion, beginning with receptors in the innervated tissues, as well as inside the ganglion. These fibers transit through the autonomic ganglia.
Centrifugal pathways are represented by preganglionic fibers that branch many times in the vegetative node and form synapses on many cell bodies of effector neurons. For example, in the upper cervical ganglion, the ratio of the number of preganglionic fibers entering it to postganglionic fibers is 1:32. This phenomenon leads, upon excitation of the preganglionic fibers, to a sharp expansion of the area of excitation (heperalization of the effector). Due to this, a relatively small number of central autonomic neurons provide nerve impulses to all organs and tissues. So, for example, when an animal is irritated with preganglionic sympathetic fibers passing through the anterior roots of the IY thoracic segment, vasoconstriction of the skin of the head and neck, dilation of the coronary vessels, vasoconstriction of the skin of the forelimb, kidney and spleen vessels can be observed.
The continuation of these pathways are postganglionic fibers reaching the innervated tissues.
Peripheral (local) reflex pathways begin in the tissues with branchings of the processes of their own sensitive neurons of the autonomic ganglia (i.e., Type II Dogel cells). The neurites of these cells end on Type I Dogel cells, whose postganglionic fibers are part of the centrifugal pathways.
The morphological substrate of the reflex activity of the autonomic nervous system is the reflex arc. For the reflex arc of the autonomic nervous system, all three links are characteristic - receptor (afferent), autonomic (associative) and effector (motor), but their localization is different than in the somatic.
It is interesting to note that many morphologists and physiologists point to the absence of their own afferent (receptor) link in its composition as a distinctive feature of the autonomic nervous system, i.e. they believe that the sensitive innervation of the internal organs, blood vessels, etc. carried out by the dendrites of the pseudounipolar cells of the spinal ganglion, i.e. somatic nervous system.
It is more correct to consider that the spinal nodes contain neurons that innervate the skeletal muscles, skin (ie neurons of the somatic nervous system), and neurons innervating all internal organs, blood vessels (ie autonomic neurons).
In a word, the affective link, as in the somatic (animal) nervous system, in the autonomic nervous system is represented by a cell lying in the spinal ganglion.
The body of the neuron of the associative link is located, in contrast to the somatic reflex neural arch, not in the region of the posterior horn, but in the lateral horns gray matter, and the axon of these cells extends beyond the brain and ends in one of the autonomic ganglia.
Finally, the greatest differences between the animal and autonomic reflex arcs are observed in the efferent link. Thus, the body of an efferent neuron in the somatic nervous system is located in the gray matter of the spinal or cerebral ganglion, and only its axon goes to the periphery as part of one or another cranial or spinal nerve. In the autonomic system, the bodies of effector neurons are located on the periphery: they are either scattered along the course of some nerves or form clusters - autonomic ganglia.
Thus, due to such localization of effector neurons, the autonomic nervous system is characterized by the presence of at least one break in the efferent pathway that passes in the autonomic ganglion, i.e. here the neurites of the intercalary neurons contact with the effector neurons, forming synapses on their bodies and dendrites. Therefore, the autonomic ganglia are peripheral nerve centers. In this they are fundamentally different from the spinal ganglia, which are not nerve centers, because. they do not have synapses and there is no switching of nerve impulses.
Thus, the spinal nodes are mixed formations, animal-vegetative.
A feature of the reflex arc of the sympathetic nervous system is the presence of short preganglionic fibers and very long postganglionic fibers.
A feature of the reflex arc of the parasympathetic nervous system is, on the contrary, the presence of very long preganglionic and very short postganglionic fibers.
The main functional differences between the sympathetic and parasympathetic systems are as follows. mediator, i.e. Sympathin (a substance identical to the hormone of the adrenal medulla - noadrenaline) is a substance that is formed in the region of synapses and carries out chemical impulse transmission in sympathetic nerve endings.
The mediator in the parasympathetic nerve endings is the “vagus substance” (a substance identical to acetylcholine). However, this difference concerns only postganglionic fibers. Synapses formed by preganglionic fibers in both the sympathetic and parasympathetic systems are cholinergic, i.e. as a mediator, they form a choline-like substance.
These chemical substances - mediators and by themselves, even without irritation of the autonomic nerve fibers, cause effects in the working organs similar to the action of the corresponding autonomic nerve fibers. So, noadrenaline, when injected into the blood, accelerates the heartbeat, but slows down the peristalsis of the intestinal tract, and acetylcholine, on the contrary. Noadrenaline causes narrowing, and acetylcholine - the expansion of the lumen of the vessels.
Cholinergic and synapses formed by the fibers of the somatic nervous system.
The activity of the autonomic nervous system is under the control of the cerebral cortex, as well as the subcortical autonomic centers of the striatum and, finally, the autonomic centers of the diencephalon (the nucleus of the hypothalamus).
In conclusion, it should be noted that the doctrine of the autonomic nervous system was also greatly contributed by Soviet scientists B.I. Lavrentiev, A.A. Zavarzin, D.I. Golub, awarded state prizes.
Literature:
Zhabotinsky Yu.M. Normal and pathological morphology of the autonomic ganglia. M., 1953
Zavarzin A.A. Essay on the evolutionary histology of the nervous system. M-L, 1941
A.G. Knorre, I.D.Lev. autonomic nervous system. L., 1977, p.120
Kolosov N.G. Innervation of the human digestive tract. M-L, 1962
Kolosov N.G. vegetative node. L., 1972
Kolosov N.G., Khabarova A.L. Structural organization autonomic ganglia. L., Science, 1978.-72s.
Kochetkov A.G., Kuznetsov B.G., Konovalova N.V. autonomic nervous system. N-Novgorod, 1993.-92s.
Melman E.P. Functional morphology of the innervation of the digestive organs. M., 1970
Yarygin N.E. and Yarygin V.N. Pathological and adaptive changes in the neuron. M., 1973.
They are called nuclei. They act as connecting links of the structures of the nervous system, carry out the primary processing of impulses, and are responsible for the functions of visceral organs.
The human body performs two types of functions - and vegetative. Somatic means the perception of external stimuli and the reaction to them with the help of skeletal muscles. These reactions can be controlled by the human mind, and the central nervous system is responsible for their implementation.
Vegetative functions - digestion, metabolism, hematopoiesis, blood circulation, respiration, sweating and more, controls, which does not depend on human consciousness. In addition to regulating the work of visceral organs, the autonomic system provides trophism to the muscles and the central nervous system.
The ganglia responsible for somatic functions represent the spinal nodes and nodes of the cranial nerves. Vegetative, depending on the location of the centers in the central nervous system, are divided into: parasympathetic and sympathetic.
The former are located in the walls of the organ, and the sympathetic ones are located remotely in a structure called the border trunk.
The structure of the ganglion
Depending on the morphological features, the size of the ganglia ranges from a few micrometers to several centimeters. In fact, this is an accumulation of nerve and glial cells, covered with a connective sheath.
The connective tissue element is permeated with lymphatic and blood vessels. Each neurocyte (or group of neurocytes) is surrounded by a capsular membrane lined on the inside with endothelium and on the outside with connective tissue fibers. Inside the capsule there is a nerve cell and glial structures that provide the vital activity of the neuron.
A single axon leaves the neuron, covered with a myelin sheath, which branches into two parts. One of them is part of the peripheral nerve and forms a receptor, and the second is sent to the central nervous system.
Vegetative centers are located in the trunk and spinal cord. Parasympathetic centers are localized in the cranial and sacral regions, and sympathetic centers are located in the thoracolumbar region.
Ganglia of the autonomic nervous system
The sympathetic system includes two types of nodes: vertebral and prevertebral.
Vertebral are located on both sides of the spinal column, forming border trunks. They are connected to the spinal cord by nerve fibers that give rise to white and gray connecting branches. The nerve fibers emerging from the node are directed to the visceral organs.
Prevertebral located at a greater distance from the spine, while they are also remote from the organs for which they are responsible. An example of prevertebral nodes are the cervical, mesenteric clusters of neurons, the solar plexus.
Parasympathetic the department is formed by ganglia located on the organs, or in close proximity to them.
Intraorganic nerve plexuses placed on the organ or in its wall. Large intraorgan plexuses are located in the heart muscle, in the muscular layer of the intestinal wall, in the parenchyma of the glandular organs.
The ganglia of the autonomic and central nervous systems have the following properties:
- carrying out a signal in one direction;
- the fibers included in the knot overlap the zones of influence of each other;
- spatial summation (the sum of impulses is able to generate a potential in the neurocyte);
- occlusion (stimulation of the nerves causes a smaller response than the stimulation of each separately).
The synoptic delay in the autonomic ganglia is greater than in similar structures of the CNS, and the postsynaptic potential is long. A wave of excitation in ganglionic neurocytes is replaced by depression. These factors lead to a relatively low pulse rate compared to the CNS.
What are the functions of the ganglia
The main purpose of autonomic nodes is the distribution and transmission of nerve impulses, as well as the generation of local reflexes. Each ganglion, depending on the location and characteristics of the trophism, is responsible for the functions of a certain part of the body.
Ganglia are characterized by autonomy from the central nervous system, which allows them to regulate the activity of organs without the participation of the brain and spinal cord.
The structure of the intramural nodes contains cells - pacemakers, capable of setting the frequency of contractions of the smooth muscles of the intestine.
The feature is associated with an interruption, heading to the internal organs, of the CNS fibers at the peripheral nodes of the autonomic system, where they form synapses. In this case, axons leaving the ganglion have a direct effect on the internal organ.
Each nerve fiber entering the sympathetic ganglion innervates up to thirty postganglionic neurocytes. This makes it possible to multiply the signal and propagate the excitation impulse coming out of the ganglion.
In the parasympathetic nodes, one fiber innervates no more than four neurocytes, and the impulse is transmitted locally.
Ganglia - reflex centers
The ganglia of the nervous system take part in the reflex arc, which allows you to adjust the activity of organs and tissues without the participation of the brain. At the end of the nineteenth century, the Russian histologist Dogel, as a result of experiments on the study of nerve plexuses in the gastrointestinal tract, identified three types of neurons - motor, intercalary and receptor, as well as synapses between them.
The presence of receptor nerve cells also confirms the possibility of heart muscle transplantation from a donor to a recipient. If the regulation of the heart rhythm was carried out through the central nervous system, after a heart transplant, the nerve cells would undergo degeneration. Neurons and synapses in the transplanted organ continue to function, which indicates their autonomy.
At the end of the twentieth century, the mechanisms of peripheral reflexes that make prevertebral and intramural vegetative nodes were experimentally established. The ability to create a reflex arc is inherent in some nodes.
Local reflexes allow you to unload the central nervous system, make the regulation of important functions more reliable, and are able to continue the autonomous operation of internal organs in the event of an interruption in communication with the central nervous system.
Vegetative nodes receive and process information about the work of organs, after which they send it to the brain. This causes a reflex arc in both the autonomic and somatic systems, which triggers not only reflexes, but also conscious behavioral responses.
autonomic nervous system maintains homeostasis. The ANS governs visceral functions such as circulation, digestion, and excretion, mostly without conditioned or conscious control. The ANS also modulates the function of the endocrine glands that regulate metabolism. The ANS has sensory and motor components and is divided into the sympathetic and parasympathetic systems. The first neurons of the sympathetic system are located in the intermediate horns of the thoracolumbar region of the spinal cord; the synapse with the second set of neurons is located in the para- or prevertebral sympathetic ganglion. In the parasympathetic system, the first neurons are located either in the cranial nerve, in the autonomic nuclei, or in the intermediate horn of the sacral spinal cord; the synapse with the second set of neurons is either in the autonomic ganglion (in the case of cranial nerves) or in the effector tissue itself. The ANS has three main components:
afferent (centripetal, sensitive);
central unifying;
efferent.
Afferent component carries information from neuronal physiological receptors located at the ends of the centripetal nerves to the spinal cord and higher areas of the central nervous system. Most of this information is processed within the hypothalamus and other underlying areas of the brain. Once processed, the appropriate signal is sent from the CNS down the efferent nerves to the executive organs (see Figures 8.1, 8.9), so named because they respond to activity in the CNS.
Based on differences in anatomy and mediators, the efferent part of the ANS is divided into three systems:
parasympathetic (cholinergic);
sympathetic (adrenergic);
non-adrenergic non-cholinergic (NANKh).
Acetylcholine- a neurotransmitter of the cholinergic system. - a neurotransmitter released from the presynaptic ending in the autonomic ganglion and from the endings of the nerves in the executive organ. Receptors for acetylcholine are cholinergic receptors, which are divided into muscarinic and nicotinic.
Norepinephrine- a neurotransmitter of the adrenergic system. Another important component of the ANS is the adrenergic system. It is still unknown which neurotransmitter was originally used in this system - epinephrine or norepinephrine. It is now known that, with the exception of the adrenal glands, which secrete epinephrine (adrenaline), the neurotransmitter in the adrenergic system is norepinephrine.
Acetylcholine- ganglionic mediator for cholinergic and adrenergic systems. The efferent nerves for both the cholinergic and adrenergic systems originate from their respective parts of the brainstem and spinal cord. Efferent nerves form a synapse in a ganglion located outside the organ, where ACh is the main neurotransmitter:
In the adrenergic system, the ganglia are found in a chain near the spinal cord known as the paravertebral sympathetic chain;
in the cholinergic system, the ganglion is usually located within or near the effector organ.
In spite of clear anatomical difference, both types of ganglia use ACh as the main ganglionic neurotransmitter that activates nicotinic receptors.
neurotransmitters can modulate their own release. Neurotransmitters can modulate their own release. Neurotransmitters can activate presynaptic receptors on the neuron, which inhibits the release of the neurotransmitters themselves.
Educational video of the anatomy of the autonomic nervous system (ANS)
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