Nervous system carries out the unification of parts of the body into a single whole (integration), ensures the regulation of various processes, coordination of functions various organs and tissues and the interaction of the body with the external environment. She perceives a variety of information coming from external environment and from internal organs, processes it and generates signals that provide responses adequate to existing stimuli. The activity of the nervous system is based on reflex arcs- chains of neurons that provide reactions working organs (target organs) in response to receptor stimulation. In reflex arcs, neurons connected to each other by synapses form three links: receptor (afferent), effector and located between them associative (intercalated).
Divisions of the nervous system
Anatomical division of departments nervous system:
(1)central nervous system(CNS) -
includes head And dorsal brain;
(2)peripheral nervous system - includes peripheral nerve ganglia (nodes), nerves And nerve endings(described in the section “Nervous tissue”).
Physiological division of the nervous system(depending on the nature of the innervation of organs and tissues):
(1)somatic (animal) nervous system - controls primarily the functions of voluntary movement;
(2)autonomic nervous system - regulates the activity of internal organs, blood vessels and glands.
The autonomic nervous system is divided into interacting with each other sympathetic And parasympathetic departments, which differ in the localization of peripheral nodes and centers in the brain, as well as the nature of the effect on internal organs.
The somatic and autonomic nervous system includes links located in the central nervous system and the peripheral nervous system. Functionally leading tissue organs of the nervous system is nerve tissue, including neurons and glia. Clusters of neurons in the central nervous system are usually called nuclei, and in the peripheral nervous system - ganglia (nodes). Bundles of nerve fibers in the central nervous system are called tracts, in the peripheral - nerves.
Nerves(nerve trunks) connect the nerve centers of the brain and spinal cord with receptors and working organs. They are formed by bundles myelin And unmyelinated nerve fibers, which are united by connective tissue components (shells): endoneurium, perineurium And epineurium(Fig. 114-118). Most nerves are mixed, that is, they include afferent and efferent nerve fibers.
Endoneurium - thin layers of loose fibrous connective tissue with small blood vessels surrounding individual nerve fibers and connecting them into a single bundle.
Perineurium - a sheath that covers each bundle of nerve fibers from the outside and extends the septa deeper into the bundle. It has a lamellar structure and is formed by concentric sheets of flattened fibroblast-like cells connected by tight junctions and gap junctions. Between the layers of cells in fluid-filled spaces are located the components of the basement membrane and longitudinally oriented collagen fibers.
Epineurium - the outer sheath of a nerve that binds together bundles of nerve fibers. It consists of dense fibrous connective tissue containing fat cells, blood and lymphatic vessels (see Fig. 114).
Nerve structures revealed using various staining methods. Various histological staining methods allow for more detailed and selective examination of individual components
nerve. So, osmation gives contrast staining of the myelin sheaths of nerve fibers (allowing us to assess their thickness and differentiate myelinated and unmyelinated fibers), however, the processes of neurons and connective tissue components of the nerve remain very weakly stained or unstained (see Fig. 114 and 115). When painting hematoxylin-eosin the myelin sheaths are not stained, the processes of neurons have a weak basophilic staining, but the nuclei of neurolemmocytes in the nerve fibers and all connective tissue components of the nerve are clearly visible (see Fig. 116 and 117). At silver nitrate staining the processes of neurons are brightly colored; the myelin sheaths remain unstained, the connective tissue components of the nerve are poorly identified, their structure cannot be traced (see Fig. 118).
Nerve ganglia (nodes)- structures formed by clusters of neurons outside the central nervous system - are divided into sensitive And autonomous(vegetative). Sensory ganglia contain pseudounipolar or bipolar (in the spiral and vestibular ganglia) afferent neurons and are located mainly along the dorsal roots of the spinal cord (sensitive ganglia of the spinal nerves) and some cranial nerves.
Sensory ganglia (nodes) of the spinal nerves have a spindle shape and are covered capsule made of dense fibrous connective tissue. Along the periphery of the ganglion there are dense clusters of bodies pseudounipolar neurons, A central part occupied by their processes and thin layers of endoneurium located between them, bearing vessels (Fig. 121).
Pseudounipolar sensory neurons characterized by a spherical body and a light nucleus with a clearly visible nucleolus (Fig. 122). The cytoplasm of neurons contains numerous mitochondria, cisterns of the granular endoplasmic reticulum, elements of the Golgi complex (see Fig. 101), and lysosomes. Each neuron is surrounded by a layer of adjacent flattened oligodendroglial cells or mantle gliocytes) with small round nuclei; outside the glial membrane there is a thin connective tissue capsule (see Fig. 122). A process extends from the body of the pseudounipolar neuron, dividing in a T-shape into peripheral (afferent, dendritic) and central (efferent, axonal) branches, which are covered with myelin sheaths. Peripheral process(afferent branch) ends with receptors,
central process(efferent branch) as part of the dorsal root enters the spinal cord (see Fig. 119).
Autonomic nerve ganglia formed by clusters of multipolar neurons on which numerous synapses form preganglionic fibers- processes of neurons whose bodies lie in the central nervous system (see Fig. 120).
Classification of autonomic ganglia. By location: ganglia can be located along the spine (paravertebral ganglia) or ahead of him (prevertebral ganglia), as well as in the wall of organs - the heart, bronchi, digestive tract, bladder, etc. (intramural ganglia- see, for example, fig. 203, 209, 213, 215) or near their surface.
Based on their functional characteristics, the autonomic nerve ganglia are divided into sympathetic and parasympathetic. These ganglia differ in their localization (sympathetic are para- and prevertebral, parasympathetic - intramural or near organs), as well as the localization of neurons giving preganglionic fibers, the nature of neurotransmitters and the direction of reactions mediated by their cells. Most internal organs have double autonomous innervation. Overall plan The structure of the sympathetic and parasympathetic nerve ganglia is similar.
Structure of autonomous ganglia. The autonomous ganglion is covered on the outside with connective tissue capsule and contains diffusely or grouply located bodies multipolar neurons, their processes in the form of unmyelinated or (less commonly) myelinated fibers and endoneurium (Fig. 123). The cell bodies of neurons are basophilic, irregularly shaped, and contain an eccentrically located nucleus; there are multicore and polyploid cells. Neurons are surrounded (usually incompletely) by sheaths of glial cells (satellite glial cells, or mantle gliocytes). Outside the glial membrane there is a thin connective tissue membrane (Fig. 124).
Intramural ganglia and the pathways associated with them, due to their high autonomy, complexity of organization and features of mediator exchange, some authors distinguish them as independent metasympathetic division autonomic nervous system. Three types of neurons are described in the intramural ganglia (see Fig. 120):
1) Long axonal efferent neurons (Dogel type I cells) with short dendrites and a long axon extending beyond the node
to the cells of the working organ, on which it forms motor or secretory endings.
2)Equal-processed afferent neurons (Dogel type II cells) contain long dendrites and an axon that extends beyond the boundaries of a given ganglion into neighboring ones and forms synapses on cells of types I and III. They are included as a receptor link in local reflex arcs, which close without the nerve impulse entering the central nervous system.
3)Association cells (Dogel type III cells)- local interneurons, connecting with their processes several cells of types I and II. The dendrites of these cells do not extend beyond the node, and the axons are sent to other nodes, forming synapses on type I cells.
Reflex arcs in the somatic (animal) and autonomous (vegetative) parts of the nervous system have a number of features (see Fig. 119 and 120). The main differences lie in the associative and effector links, since the receptor link is similar: it is formed by afferent pseudounipolar neurons, the bodies of which are located in sensory ganglia. The peripheral processes of these cells form sensory nerve endings, and the central ones enter the spinal cord as part of the dorsal roots.
Associative link in the somatic arc it is represented by interneurons, the dendrites and bodies of which are located in dorsal horns of the spinal cord, and the axons are sent to front horns, transmitting impulses to the bodies and dendrites of efferent neurons. In an autonomous arc, dendrites and bodies interneurons located in lateral horns of the spinal cord, and the axons (preganglionic fibers) leave the spinal cord as part of the anterior roots, heading to one of the autonomous ganglia, where they end on the dendrites and bodies of efferent neurons.
Effector link in the somatic arch is formed by multipolar motor neurons, the bodies and dendrites of which lie in the anterior horns of the spinal cord, and the axons exit the spinal cord as part of the anterior roots, go to the sensory ganglion and then, as part of the mixed nerve, to the skeletal muscle, on the fibers of which their branches form neuromuscular synapses. In the autonomous arch, the effector link is formed by multipolar neurons, the bodies of which lie as part of the autonomous ganglia, and axons (postganglionic fibers) as part of the nerve trunks and their branches are directed to the cells of the working organs - smooth muscles, glands, heart.
Organs of the central nervous system Spinal cord
Spinal cord has the appearance of a rounded cord, expanded in the cervical and lumbosacral regions and penetrated by a central canal. It consists of two symmetrical halves, separated at the front anterior median fissure, behind - posterior median sulcus, and is characterized by a segmental structure; each segment has a pair associated with it anterior (motor, ventral) and a pair posterior (sensitive, dorsal) roots. In the spinal cord there are Gray matter, located in its central part, and white matter lying on the periphery (Fig. 125).
Gray matter on cross section has the appearance of a butterfly (see Fig. 125) and includes paired anterior (ventral), posterior (dorsal) And lateral (lateral) horns. The horns of the gray matter of both symmetrical parts of the spinal cord are connected to each other in the area anterior and posterior gray commissure. The gray matter contains the bodies, dendrites and (partially) axons of neurons, as well as glial cells. Between the cell bodies of neurons is neuropil- a network formed by nerve fibers and processes of glial cells. Neurons are located in the gray matter in the form of not always sharply demarcated clusters (nuclei).
The posterior horns contain several nuclei formed multipolar interneurons, on which the axons of the pseudounipolar cells of the sensory ganglia end (see Fig. 119), as well as the fibers of the descending tracts from the overlying (supraspinal) centers. The axons of interneurons a) end in the gray matter of the spinal cord on motor neurons located in the anterior horns (see Fig. 119); b) form intersegmental connections within the gray matter of the spinal cord; c) exit into the white matter of the spinal cord, where they form ascending and descending pathways (tracts).
The lateral horns, well defined at the level of the thoracic and sacral segments of the spinal cord, contain nuclei formed by bodies multipolar interneurons, which belong to the sympathetic and parasympathetic divisions of the autonomic nervous system (see Fig. 120). On the dendrites and bodies of these cells, axons end: a) pseudounipolar neurons carrying impulses from receptors located in the internal organs, b) neurons of the centers for the regulation of autonomic functions, the bodies of which are located in the medulla oblongata. The axons of autonomic neurons, leaving the spinal cord as part of the anterior roots, form a pregan-
glionic fibers going to the sympathetic and parasympathetic nodes.
The anterior horns contain multipolar motor neurons (motoneurons), united into nuclei, each of which usually extends into several segments. There are large α-motoneurons and smaller γ-motoneurons scattered among them. There are numerous synapses on the processes and bodies of motor neurons that exert excitatory and inhibitory effects on them. The following end on motor neurons: collaterals of the central processes of pseudounipolar cells of sensory ganglia; intercalary neurons, the bodies of which lie in the dorsal horns of the spinal cord; axons of local small interneurons (Renshaw cells) connected to collaterals of motor neuron axons; fibers of the descending pathways of the pyramidal and extrapyramidal systems, carrying impulses from the cerebral cortex and brainstem nuclei. The bodies of motor neurons contain large clumps of chromatophilic substance (see Fig. 100) and are surrounded by gliocytes (Fig. 126). Axons of motor neurons leave the spinal cord as part of anterior roots, are directed to the sensitive ganglion and then, as part of the mixed nerve, to the skeletal muscle, on the fibers of which they form neuromuscular junctions(see Fig. 119).
Central channel (see Fig. 128) runs in the center of the gray matter and is surrounded front And posterior gray commissures(see Fig. 125). It is filled with cerebrospinal fluid and is lined with a single layer of cubic or columnar ependymal cells, the apical surface of which is covered with microvilli and (partially) cilia, and the lateral surfaces are connected by complexes of intercellular junctions.
White matter of the spinal cord surrounds the gray (see Fig. 125) and is divided by the anterior and posterior roots into symmetrical rear, side And anterior cords. It consists of longitudinally running nerve fibers (mainly myelin), forming descending and ascending conducting paths (tracts). The latter are separated from each other by thin layers of connective tissue and astrocytes, which are also found inside the tracts (Fig. 127). Conducting tracts include two groups: propriospinal (they communicate between various departments spinal cord) and supraspinal tracts (provide communication between the spinal cord and brain structures - ascending and descending tracts).
Cerebellum
Cerebellum is part of the brain and is a center of balance that maintains
improving muscle tone and coordination of movements. It is formed by two hemispheres with a large number of grooves and convolutions on the surface and a narrow middle part (the vermis). Gray matter forms cerebellar cortex And kernels; the latter lie in its depths white matter.
Cerebellar cortex characterized by a highly ordered arrangement of neurons, nerve fibers and glial cells of all types. It is distinguished by a wealth of interneuron connections, which ensure the processing of various sensory information entering it. There are three layers in the cerebellar cortex (from the outside to the inside): 1) molecular layer; 2) layer of Purkinje cells (layer of piriform neurons); 3) granular layer(Fig. 129 and 130).
Molecular layer contains a relatively small number of small cells, it contains bodies basket-shaped And stellate neurons. Basket neurons located in the inner part of the molecular layer. Their short dendrites form connections with parallel fibers in the outer part of the molecular layer, and a long axon runs across the gyrus, giving off collaterals at certain intervals, which descend to the bodies of Purkinje cells and, branching, cover them like baskets, forming inhibitory axo-somatic synapses (see Fig. 130). Stellate neurons- small cells whose bodies lie above the bodies of basket neurons. Their dendrites form connections with parallel fibers, and axon branches form inhibitory synapses on the dendrites of Purkinje cells and can participate in the formation of a basket around their bodies.
Purkinje cell layer (pyriform neuron layer) contains the bodies of Purkinje cells lying in one row, braided by collaterals of axons of basket cells (“baskets”).
Purkinje cells (piriform neurons)- large cells with a pear-shaped body containing well-developed organelles. From it, 2-3 primary (stem) dendrites extend into the molecular layer, intensively branching with the formation of final (terminal) dendrites that reach the surface of the molecular layer (see Fig. 130). The dendrites contain numerous spines- contact zones of excitatory synapses formed by parallel fibers (axons of granule neurons) and inhibitory synapses formed by climbing fibers. The axon of a Purkinje cell extends from the base of its body, becomes covered with a myelin sheath, penetrates the granular layer and penetrates the white matter, being the only efferent pathway of its cortex.
Granular layer contains closely spaced bodies granular neurons, large stellate neurons(Golgi cells), as well as cerebellar glomeruli- special rounded complex synaptic contact zones between mossy fibers, dendrites of granule neurons and axons of large stellate neurons.
Granular neurons- the most numerous neurons of the cerebellar cortex are small cells with short dendrites, shaped like a “bird’s foot”, on which rosettes of mossy fibers form numerous synaptic contacts in the cerebellar glomeruli. The axons of granule neurons are sent to the molecular layer, where they divide in a T-shape into two branches running parallel to the length of the gyrus (parallel fibers) and forming excitatory synapses on the dendrites of Purkinje cells, basket and stellate neurons, as well as large stellate neurons.
Large stellate neurons (Golgi cells) larger than granule neurons. Their axons within the cerebellar glomeruli form inhibitory synapses on the dendrites of granule neurons, and long dendrites rise into the molecular layer, where they branch and form connections with parallel fibers.
Afferent fibers of the cerebellar cortex include bryophytes And climbing fibers(see Fig. 130), which penetrate the cerebellar cortex from the spinal cord, medulla oblongata and a bridge.
Mossy fibers of the cerebellum end with extensions (sockets)- cerebellar glomeruli, forming synaptic contacts with the dendrites of granular neurons, on which the axons of large stellate neurons also end. The cerebellar glomeruli are not completely surrounded on the outside by flat processes of astrocytes.
Climbing fibers of the cerebellum penetrate the cortex from the white matter, passing through the granular layer to the layer of Purkinje cells and creeping along the bodies and dendrites of these cells, on which they terminate in excitatory synapses. Collateral branches of climbing fibers form synapses on other neurons of all types.
Efferent fibers of the cerebellar cortex are represented by axons of Purkinje cells, which in the form of myelin fibers are directed into the white matter and reach the deep nuclei of the cerebellum and vestibular nucleus, on the neurons of which they form inhibitory synapses (Purkinje cells are inhibitory neurons).
Cerebral cortex represents the highest and most complexly organized
a central nerve center whose activity ensures the regulation of various body functions and complex forms of behavior. The cortex is formed by a layer of gray matter covering the white matter on the surface of the gyri and in the depths of the sulci. Gray matter contains neurons, nerve fibers and neuroglial cells of all types. Based on differences in cell density and structure (cytoarchitectonics), fiber path (myeloarchitectonics) and the functional characteristics of various areas of the cortex, 52 vaguely demarcated fields are distinguished in it.
Cortical neurons- multipolar, of various sizes and shapes, includes more than 60 species, among which two main types are distinguished - pyramidal And non-pyramidal.
pyramidal cells - type of neurons specific to the cerebral cortex; according to various estimates, they make up 50-90% of all cortical neurons. From the apical pole of their cone-shaped (in sections - triangular) body, a long (apical) dendrite covered with spines extends to the surface of the cortex (Fig. 133), heading into the molecular plate of the cortex, where it branches. From the basal and lateral parts of the body, deep into the cortex and to the sides of the neuron body, several shorter lateral (lateral) dendrites diverge, which, branching, spread within the same layer where the cell body is located. A long and thin axon extends from the middle of the basal surface of the body, going into the white matter and giving collaterals. Distinguish giant, large, intermediate and small pyramidal cells. The main function of pyramidal cells is to provide connections within the cortex (intermediate and small cells) and form efferent pathways (giant and large cells).
Nonpyramidal cells are located in almost all layers of the cortex, perceiving incoming afferent signals, and their axons extend within the cortex itself, transmitting impulses to pyramidal neurons. These cells are very diverse and are predominantly varieties of stellate cells. The main function of nonpyramidal cells is the integration of neural circuits within the cortex.
Cytoarchitecture of the cerebral cortex. Cortical neurons are arranged in loosely demarcated layers (records), which are designated by Roman numerals and numbered from the outside inwards. In sections stained with hematoxylin-eosin, connections between neurons are not traced, since only
the bodies of neurons and the initial sections of their processes
(Fig. 131).
I - molecular plate located under the pia mater; contains a relatively small number of small horizontal neurons with long branching dendrites extending in a horizontal plane from the fusiform body. Their axons participate in the formation of the tangential plexus of fibers of this layer. In the molecular layer there are numerous dendrites and axons of cells of deeper layers that form interneuron connections.
II - outer granular plate formed by numerous small pyramidal and stellate cells, the dendrites of which branch and rise into the molecular plate, and the axons either go into the white matter or form arches and also go into the molecular plate.
III - external pyramidal plate characterized by a predominance pyramidal neurons, the sizes of which increase deep into the layer from small to large. The apical dendrites of pyramidal cells are directed to the molecular plate, and the lateral ones form synapses with the cells of this plate. The axons of these cells end within the gray matter or are directed into the white matter. In addition to pyramidal cells, the lamina contains a variety of nonpyramidal neurons. The plate performs predominantly associative functions, connecting cells both within given hemisphere, and with the opposite hemisphere.
IV - internal granular plate contains small pyramidal And stellate cells. The main part of the thalamic afferent fibers ends in this plate. The axons of the cells of this plate form connections with the cells of the above and underlying plates of the cortex.
V - internal pyramidal plate educated large pyramidal neurons, and in the area of the motor cortex (precentral gyrus) - giant pyramidal neurons(Betz cells). The apical dendrites of pyramidal neurons reach the molecular lamina, and the lateral dendrites extend within the same lamina. The axons of giant and large pyramidal neurons project to the nuclei of the brain and spinal cord, the longest of them, as part of the pyramidal tracts, reach the caudal segments of the spinal cord.
VI - multiform plate formed by neurons of various shapes, and its
the outer sections contain larger cells, while the inner sections contain smaller and sparsely located cells. The axons of these neurons extend into the white matter as part of the efferent pathways, and the dendrites penetrate to molecular plasticity.
Myeloarchitecture of the cerebral cortex. The nerve fibers of the cerebral cortex include three groups: 1) afferent; 2) associative And commissural; 3) efferent.
Afferent fibers come to the cortex from the lower parts of the brain in the form of bundles consisting of vertical stripes- radial rays (see Fig. 132).
Association and commissural fibers - intracortical fibers that connect different areas of the cortex within one or in different hemispheres, respectively. These fibers form bundles (stripes), which run parallel to the surface of the cortex in lamina I (tangential plate), in plate II (dysfibrotic plate, or ankylosing spondylitis strip), in plate IV (a strip of outer granular plate, or outer stripe of Baillarger) and in plate V (a strip of internal granular plate, or inner stripe of Baillarger) - see fig. 132. The last two systems are plexuses formed by the terminal sections of afferent fibers.
Efferent fibers connect the cortex with subcortical formations. These fibers run in a descending direction as part of the radial rays.
Types of structure of the cerebral cortex.
In certain areas of the cortex associated with the performance of different functions, the development of one or another of its layers predominates, on the basis of which they distinguish agranular And granular types of cortex.
Agranular type of bark is characteristic of its motor centers and is distinguished by the greatest development of plates III, V and VI of the cortex with weak development of plates II and IV (granular). Such areas of the cortex serve as sources of descending pathways.
Granular type of bark characteristic of areas where sensitive cortical centers are located. It is characterized by weak development of layers containing pyramidal cells, with significant expression of granular (II and IV) plates.
White matter of the brain is represented by bundles of nerve fibers that ascend to the gray matter of the cortex from the brain stem and descend to the brain stem from the cortical centers of the gray matter.
ORGANS OF THE NERVOUS SYSTEM
Organs of the peripheral nervous system
Rice. 114. Nerve (nerve trunk). Cross section
Coloring: osmation
1 - nerve fibers; 2 - endoneurium; 3 - perineurium; 4 - epineurium: 4.1 - adipose tissue, 4.2 - blood vessel
Rice. 115. Nerve section (nerve trunk)
Coloring: osmation
1- myelin fiber: 1.1 - neuron process, 1.2 - myelin sheath;
2- unmyelinated fiber; 3 - endoneurium; 4 - perineurium
Rice. 116. Nerve trunk (nerve). Cross section
Staining: hematoxylin-eosin
1 - nerve fibers; 2 - endoneurium: 2.1 - blood vessel; 3 - perineurium; 4 - epineurium: 4.1 - fat cells, 4.2 - blood vessels
Rice. 117. Section of the nerve trunk (nerve)
Staining: hematoxylin-eosin
1 - myelin fiber: 1.1 - neuron process, 1.2 - myelin sheath, 1.3 - neurolemmocyte nucleus; 2 - unmyelinated fiber; 3 - endoneurium: 3.1 - blood vessel; 4 - perineurium; 5 - epineurium
Rice. 118. Section of the nerve trunk (nerve)
1 - myelin fiber: 1.1 - neuron process, 1.2 - myelin sheath; 2 - unmyelinated fiber; 3 - endoneurium: 3.1 - blood vessel; 4 - perineurium
Rice. 119. Somatic reflex arc
1.Receptor link educated afferent (sensitive) pseudounipolar neurons, whose bodies (1.1) are located in the sensory nodes of the spinal nerve (1.2). The peripheral processes (1.3) of these cells form sensory nerve endings (1.4) in the skin or skeletal muscle. The central processes (1.5) enter the spinal cord as part of dorsal roots(1.6) and are directed to dorsal horns of gray matter, forming synapses on the bodies and dendrites of interneurons (three-neuron reflex arcs, A), or pass into the anterior horns to motor neurons (two-neuron reflex arcs, B).
2.Associative link presented (2.1), the dendrites and bodies of which lie in the dorsal horns. Their axons (2.2) are directed to front horns, transmitting nerve impulses to the bodies and dendrites of effector neurons.
3.Efferent link educated multipolar motor neurons(3.1). The cell bodies and dendrites of these neurons lie in the anterior horns, forming the motor nuclei. Axons (3.2) of motor neurons exit the spinal cord as part of anterior roots(3.3) and then, as part of the mixed nerve (4), are directed to the skeletal muscle, where the axon branches form neuromuscular synapses (3.4)
Rice. 120. Autonomous (vegetative) reflex arc
1.Receptor link educated afferent (sensitive) pseudounipolar neuron mi, whose bodies (1.1) lie in the sensory nodes of the spinal nerve (1.2). The peripheral processes (1.3) of these cells form sensitive nerve endings (1.4) in the tissues of the internal organs. The central processes (1.5) enter the spinal cord as part of the backs of them roots(1.6) and are directed to lateral horns of gray matter, forming synapses on the bodies and dendrites of interneurons.
2.Associative link presented multipolar interneurons(2.1), the dendrites and bodies of which are located in the lateral horns of the spinal cord. The axons of these neurons are preganglionic fibers (2.2). They leave the spinal cord as part of anterior roots(2.3), heading to one of the autonomic ganglia, where they end on the bodies and dendrites of their neurons.
3.Efferent link educated multipolar or bipolar neurons, whose bodies (3.1) lie in the autonomic ganglia (3.2). The axons of these cells are postganglionic fibers (3.3). As part of the nerve trunks and their branches, they are directed to the cells of the working organs - smooth muscles, glands, heart, forming endings on them (3.4). In the autonomic ganglia, in addition to the “long-axonal” efferent neurons - Dogel type I (DI) cells, there are “equal-processed” afferent neurons - Dogel type II (DII) cells, which are included as a receptor link in the local reflex arcs, and type III associative cells Dogel (DIII) - small interneurons
Rice. 121. Sensory ganglion of the spinal nerve
Staining: hematoxylin-eosin
1 - posterior root; 2 - sensory ganglion of the spinal nerve: 2.1 - connective tissue capsule, 2.2 - bodies of pseudounipolar sensory neurons, 2.3 - nerve fibers; 3 - anterior root; 4 - spinal nerve
Rice. 122. Pseudounipolar neuron of the sensory ganglion of the spinal nerve and its tissue microenvironment
Staining: hematoxylin-eosin
1 - body of pseudounipolar sensory neuron: 1.1 - nucleus, 1.2 - cytoplasm; 2 - satellite glial cells; 3 - connective tissue capsule around the neuron body
Rice. 123. Autonomous (vegetative) ganglion from the solar plexus
1 - preganglionic nerve fibers; 2 - autonomous ganglion: 2.1 - connective tissue capsule, 2.2 - bodies of multipolar autonomic neurons, 2.3 - nerve fibers, 2.4 - blood vessels; 3 - postganglionic fibers
Rice. 124. Multipolar neuron of the autonomic ganglion and its tissue microenvironment
Stain: iron hematoxylin
1 - body of a multipolar neuron: 1.1 - nucleus, 1.2 - cytoplasm; 2 - beginning of processes; 3 - gliocytes; 4 - connective tissue membrane
Organs of the central nervous system
Rice. 125. Spinal cord (cross section)
Color: silver nitrate
1 - gray matter: 1.1 - anterior (ventral) horn, 1.2 - posterior (dorsal) horn, 1.3 - lateral (lateral) horn; 2 - anterior and posterior gray commissures: 2.1 - central canal; 3 - anterior median fissure; 4 - posterior median groove; 5 - white matter (tracts): 5.1 - dorsal funiculus, 5.2 - lateral funiculus, 5.3 - ventral funiculus; 6 - soft membrane of the spinal cord
Rice. 126. Spinal cord.
Area of gray matter (anterior horns)
Staining: hematoxylin-eosin
1- bodies of multipolar motor neurons;
2- gliocytes; 3 - neuropil; 4 - blood vessels
Rice. 127. Spinal cord. White matter area
Staining: hematoxylin-eosin
1 - myelinated nerve fibers; 2 - nuclei of oligodendrocytes; 3 - astrocytes; 4 - blood vessel
Rice. 128. Spinal cord. Central channel
Staining: hematoxylin-eosin
1 - ependymocytes: 1.1 - cilia; 2 - blood vessel
Rice. 129. Cerebellum. Bark
(cut perpendicular to the course of the convolutions)
Staining: hematoxylin-eosin
1 - soft shell of the brain; 2 - gray matter (cortex): 2.1 - molecular layer, 2.2 - layer of Purkinje cells (piriform neurons), 2.3 - granular layer; 3 - white matter
Rice. 130. Cerebellum. Area of cortex
Color: silver nitrate
1 - molecular layer: 1.1 - dendrites of Purkinje cells, 1.2 - afferent (climbing) fibers, 1.3 - neurons of the molecular layer; 2 - layer of Purkinje cells (pyriform neurons): 2.1 - bodies of piriform neurons (Purkinje cells), 2.2 - “baskets” formed by collaterals of axons of basket neurons; 3 - granular layer: 3.1 - bodies of granular neurons, 3.2 - axons of Purkinje cells; 4 - white matter
Rice. 131. Cerebral hemisphere. Bark. Cytoarchitecture
Staining: hematoxylin-eosin
1 - soft membrane of the brain; 2 - gray matter: plates (layers) of the cortex are indicated by Roman numerals: I - molecular lamina, II - external granular lamina, III - external pyramidal lamina, IV - internal granular lamina, V - internal pyramidal lamina, VI - multiform lamina; 3 - white matter
Rice. 132. Cerebral hemisphere. Bark.
Myeloarchitecture
(scheme)
1 - tangential plate; 2 - dysfibrous plate (Bechterev's strip); 3 - radial rays; 4 - strip of the outer granular plate (outer strip of Baillarger); 5 - strip of internal granular plate (internal strip of Baillarger)
Rice. 133. Large pyramidal neuron of the cerebral hemisphere
Color: silver nitrate
1 - large pyramidal neuron: 1.1 - neuron body (perikaryon), 1.2 - dendrites, 1.3 - axon;
2- gliocytes; 3 - neuropil
In addition to the parasympathetic and sympathetic divisions, physiologists distinguish the metasympathetic division of the autonomic nervous system. This term refers to a complex of microganglionic formations located in the walls of internal organs that have motor activity (heart, intestines, ureters, etc.) and ensure their autonomy. The function of nerve nodes is to transmit central (sympathetic, parasympathetic) influences to tissues, and, in addition, they ensure the integration of information arriving along local reflex arcs. Metasympathetic structures are independent formations capable of functioning with complete decentralization. Several (5-7) of the nearby nodes related to them are combined into a single functional module, the main units of which are oscillator cells that ensure the autonomy of the system, interneurons, motor neurons, and sensory cells. Individual functional modules form a plexus, thanks to which, for example, a peristaltic wave is organized in the intestine.
The functions of the metasympathetic division of the autonomic nervous system do not directly depend on the activity of the sympathetic or parasympathetic
nervous systems, but can be modified under their influence. For example, activation of the parasympathetic influence increases intestinal motility, and the sympathetic influence weakens it.
- Numerous small accumulations of nerve cells that are part of extensive nerve plexuses in the walls of internal organs (gastrointestinal tract, heart, etc.) are sometimes attributed to the parasympathetic division of the autonomic nervous system on the grounds that morphological studies easily reveal synaptic contacts between these cells and fibers vagus nerve.
- The metasympathetic nervous system, intramural nerve plexuses are found in the heart and all hollow organs, but are more deeply studied using the example of the innervation of the stomach and intestines. In these parts of the gastrointestinal tract, the intragastric and enteric nervous system is represented so abundantly that the number of neurons (108 units) is comparable to the spinal cord. This gives rise to the figurative name of its “abdominal brain.”
- Based on their responses to a long-term impulse of depolarizing current, all enteric neurons of the intermuscular plexus can be divided into two types: the first is type S and the second is type AN. Neurons of type S respond to this stimulation with a long series of spikes, and neurons of type AN - with only one or two spikes, which are accompanied by a strong and long-lasting (4-20 s) trace hyperpolarization, which is absent in type S. The spike in type S neurons is caused by sodium, and in neurons of the AN type - sodium and calcium conductivity of the membrane.
- PM - longitudinal muscle, MS - intermuscular plexus, KM - orbicularis muscle, PS - submucosal plexus, S - mucous membrane; Neurons containing or releasing acetylcholine [A X], serotonin (5-hydroxytryptamine (5-HT)) and various peptides (causing excitatory (+) or inhibitory MChR - muscarinic cholinergic receptors, a-A R - alpha adrenergic receptors are indicated.
The metasympathetic nervous system (MNS) as a whole consists of nerve ganglia and plexuses located deep within the internal organs. The MNS differs from other parts of the nervous system in a number of features:
1. Innervates only internal organs endowed with their own motor activity;
2. Does not have direct contacts with the reflex arcs of the somatic nervous system; receives synaptic inputs only from the sympathetic and parasympathetic systems;
3. Along with the afferent pathways common to the entire autonomic system, it also has its own sensitive link;
4. Does not exhibit effects that are opposite to the action of other parts of the ANS, which is typical for the sympathetic and parasympathetic systems;
5. Has significantly greater autonomy than other parts of the ANS.
All the main characteristics of the structure and functioning of the metasympathetic nervous system are expressed in the gastrointestinal tract, and, in addition, it is in the gastrointestinal tract that this system has been studied most fully compared to all other organs. Therefore, the gastrointestinal tract is the most suitable object for familiarization with the MNS.
The gastrointestinal tract includes a variety of effector formations - smooth muscle, epithelium of mucous membranes, glands, blood and lymph vessels, elements immune system, endocrine cells. Regulation and coordination of the activity of all these structures is carried out by the local enteric metasympathetic nervous system, with the participation of the sympathetic and parasympathetic divisions of the autonomic nervous system and visceral afferents formed by neurons of the spinal ganglia. Most of the simplest functions of the gastrointestinal tract are not impaired when extraorgan (parasympathetic and sympathetic) nerve pathways are ruptured.
The cell bodies of most neurons of the enteric metasympathetic nervous system lie in the nerve plexuses (in the ganglia and inside the nerve trunks).
In humans, in the walls of the esophagus, stomach and intestines there are three interconnected plexuses: subserosal, intermuscular(Auerbach) and submucosal(Meisner). Subserosal the plexus is most represented at the bottom and in the greater curvature of the stomach and consists of small, densely located clusters of neurons and nerve fibers. In the intestine, the elements of this plexus are concentrated mainly under the muscle bands of the colon. The most massive of all the nerve plexuses of the gastrointestinal tract is intermuscular, located between the circular and longitudinal layers of the muscularis propria. In the wall of the stomach, this plexus looks like a multilayer network, and its density increases from the bottom to the pyloric part. In the area of the pylorus, the plexus contains a huge mass of nodes that form extensive cellular fields. Large (up to 60 neurons), medium and small (2-8 neurons) nodes are located along the nerve trunks and in places of their branching. The number of neurons per 1 cm2 reaches 2000. The intermuscular plexus is also highly developed in the wall of the small intestine. Here the ganglia are mostly small, containing 5-20 neurons.
Submucosal The plexus is a narrowly looped network of nerve bundles and microganglia containing 5-15 (rarely up to 30) neurons. It has superficial and deep parts. The branches of this plexus approach the bases excretory ducts glands and form the interglandular plexus. Thin fibers end on epithelial cells. The structure of the submucosal plexus along the length of the digestive tract changes slightly, only in the esophagus it is poorly developed. According to scanning electron microscopy, the superficial submucosal plexus in all parts of the small intestine is located directly under the muscular layer of the mucosa and sends out numerous bundles with a diameter of 1-20 μm to this layer. Individual nodes are also connected by the same bundles, the diameter of which is 20-400, sometimes up to 800 microns. The nodes are covered with a continuous layer of fibroblasts and collagen fibers, after removal of which the contours of neurons are visible, and numerous thin processes are visible on their surface. However, neurons as a whole are not detected, since they are surrounded by processes of glial cells.
The trunks of non-organ nerves (sympathetic, parasympathetic) enter all parts of the intermuscular and submucosal plexuses (Fig. 10). The size of neurons and nodes, their number in plexuses varies greatly in different parts of the gastrointestinal tract. Thus, in a middle-aged person, in the lower third of the esophagus in the intermuscular plexus there are large nodes, up to 960 microns in diameter, containing 50-60 (sometimes up to 85 neurons), while the nodes of the submucosal plexus of the esophagus contain only 10-15 neurons.
In the nodes of the enteric metasympathetic system, along with differentiated neurons with a diameter of 30-58 microns, there are small poorly differentiated cells.
The famous Russian histologist A.S. Dogel, as a result of studies of neurons in the intramural nodes of the digestive tract, identified three types of cells. (Fig. 11) Type I includes medium-sized cells with a rounded perikaryon, a well-defined, long axon and numerous (up to 20) short dendrites with a wide base. They differ from other neurons of the node in their tinctorial properties: they are weakly impregnated with silver nitrate, but are well stained with methylene blue. On preparations impregnated with silver, they have a dark large nucleus and light cytoplasm. Dendrites do not extend beyond the node, branch strongly, forming a dense plexus, and enter into numerous contacts with other neurons. These cells are efferent; their axons leave the node and end in varicose terminals on bundles of smooth myocytes and glands. Type I Dogel cells terminate preganglionic parasympathetic fibers from the dorsal nucleus of the vagus nerve, as well as sympathetic preganglionic fibers from the interlateral nucleus of the spinal cord.
Rice. 11. Scheme of interneuron connections of the enteric part of the MNS.
1 – sensitive neuron; 2 – interneuron; 3 – efferent neuron; 4 – postganglionic sympathetic neuron and its fiber; 5 – preganglionic sympathetic neuron and its fiber; 6 – preganglionic parasympathetic neuron and its fiber; 7 – axon of a sensitive neuron, transmitting ascending signals to the central nervous system.
Type II cells are larger, their perikarya are oval or round in shape with a smooth surface; when impregnated with silver, they have dark cytoplasm and a light nucleus with a dark nucleolus. Up to five long processes of equal diameter extend from the cell body. Among them, it is morphologically difficult to distinguish between axon and dendrites. The processes, as a rule, leave the node. Type II cells are sensory neurons. Their dendrites form a variety of receptor endings on smooth myocytes, ganglia and other elements. Axons form synapses on cells I, closing a local reflex arc. In addition, they give off collaterals that end in synapses on the neurons of the prevertebral sympathetic ganglia, through which sensitive impulses from the collecting afferent neurons of the gastrointestinal tract reach the central nervous system.
Rice. 11. Fragment of the autonomic ganglion of the MNS. Impregnation with silver nitrate.
1 – Dogel cell type I; 2 – its axon; 3 – Dogel cell type II; 4 – nuclei of gliocytes; 5 – nerve fibers
Type III cells are local interneurons. Their perikarya are oval or irregular in shape, with a long axon and a large number of short dendrites of varying lengths extending from them. Dendrites do not extend beyond the node and form synapses with type II cells. The axon travels to other nodes and makes synaptic contacts with type I cells.
Type III cells are rare and poorly studied. As for Dogel cells of types I and II, they are contained in significant quantities in the intramural ganglia of all organs that have a metasympathetic nervous system.
A study of the intramural nervous apparatus of allogeneically transplanted hearts of 1 - 2 month old puppies into recipients of the same age showed that after 1 - 5 days the receptor endings and preganglionic fibers of central origin die, and their own intracardiac nerve elements are preserved and look quite normal. After one month, most of the neurons in the nodes are represented by differentiated multipolar cells. After 20–30 days, receptor apparatuses formed by type II Dogel cells appear.
In humans, the enteric nervous system has about 108 neurons, about the same number as the spinal cord. Of course, the diversity of enteral MHC neurons is not limited to those described in late XIX centuries three types according to A.S. Dogel. Currently, more than 10 main types of neurons have been identified based on a combination of ultrastructural, immunochemical, physiological and other criteria. In this case, associative and efferent neurons can have an excitatory, tonic or inhibitory effect on other nerve or efferent (smooth muscle, secretory) cells. One of the main types of synaptic transmission in the MNS, along with adrenergic and cholinergic, is also purinergic.
Important morphological features of the nodes of the enteric part of the MNS, as well as other vegetative nodes, include the fact that all processes of their neurons, without exception, are myelin-free conductors (Fig. 12), which have low speeds of transmission of nerve impulses. The intramural metasympathetic ganglia, especially the enteric ganglia, differ from other autonomic ganglia in a number of ultrastructural features. They are surrounded by a thin layer of glial cells.
Human metasympathetic nervous system
The capsule of perineurium and epineurium, characteristic of extraorgan nodes, is absent in them. The nodes also do not contain fibroblasts or bundles of collagen fibers; they are found only outside the basement membrane of the gliocyte capsule. The perikarya of nerve cells and their numerous processes are enclosed in a dense neuropal, like in the central nervous system. In many places, their perikarya lie close to each other and are not separated by processes of glial cells.
The intercellular spaces between neurons are 20 nm. The nodes contain numerous gliocytes with a rounded nucleus rich in heterochromatin; their cytoplasm contains mitochondria, polysomes, other main organelles and bundles of gliofilaments. In addition, the nodes are usually equipped with sensitive nerve endings. (Fig. 13).
Rice. 12. Ultrastructure of unmyelinated nerve fiber. Drawing from the electron diffraction pattern with modifications.
1 – cytoplasm of a Schwann cell; 2 – Schwann cell nucleus; 3 – nerve fibers (axial cylinders); 4 – Schwann cell membrane; 5 – mesaxons.
Rice. 13. Sensitive nerve endings in the intestinal plexus ganglion. Impregnation according to Bielschowsky - Gross.
The results of studying the structure and functions of the metasympathetic nervous system are of undoubted practical importance. Thus, Hirschsprung's disease is one of the common diseases of the gastrointestinal tract. In newborns, it is observed with a frequency of 1: 2000 – 3000, and also occurs in adults. The cause of the disease is the absence and insufficiency of development of nerve ganglia in the intermuscular and submucosal nerve plexuses of many segments of the colon. These segments of the intestine are spasmed, and the overlying ones are sharply expanded due to a violation of the patency of the chyme. These manifestations of Hirschsprung's disease are further evidence that normal intestinal tone and motility are regulated by the enteric metasympathetic nervous system. In atypical cases, the absence of nodes (aganglionosis) is observed not only in the colon, but also in jejunum, stomach and esophagus, which is accompanied by certain dysfunctions of these organs. In addition to agangliosis, this disease causes changes in the existing nodes: a decrease in the number of neurons, dystrophic disorders in their perikarya, abnormal tortuosity and hyperimpregnation of nerve fibers.
In the heart, as in the gastrointestinal tract, the metasympathetic nervous system is crucial in regulating the coordinated functioning of all elements of the organ.
Metasympathetic nervous systemMNSNumerous small accumulations of nerve cells that are part of extensive nerve plexuses in the walls of internal organs (gastrointestinal tract, heart, etc.) are sometimes attributed to the parasympathetic division of the autonomic nervous system on the grounds that morphological studies easily reveal synaptic contacts between these cells and fibers of the vagus nerve.
MNS
The intramural nervous system is formed as a result of the migration of proneuroblasts along the sympathetic and parasympathetic nerve trunks.
Autonomic innervation of the heart: Metasympathetic intramural nervous systemLocalization of enteral NSThe metasympathetic nervous system, intramural nerve plexuses are found in the heart and all hollow organs, but are more deeply studied using the example of the innervation of the stomach and intestines. In these parts of the gastrointestinal tract, the intragastric and enteric nervous system is represented so abundantly that the number of neurons (108 units) is comparable to the spinal cord. This gives rise to the figurative name of its “abdominal brain.”
Physiological and histochemical studies can identify neurons that secrete as putative transmitters
Based on their responses to a long-term impulse of depolarizing current, all enteric neurons of the intermuscular plexus can be divided into two types: the first is type S and the second is type AN. Neurons of type S respond to this stimulation with a long series of spikes, and neurons of type AN - with only one or two spikes, which are accompanied by a strong and long-lasting (4-20 s) trace hyperpolarization, which is absent in type S. The spike in type S neurons is caused by sodium, and in neurons of the AN type - sodium and calcium conductivity of the membrane. PM - longitudinal muscle, MS - intermuscular plexus, KM - orbicularis muscle, PS - submucosal plexus, S - mucous membrane; neurons containing or releasing acetylcholine are indicated [A X), serotonin (5-hydroxytryptamine (5-HT)) and various peptides (causing excitatory (+) or inhibitory MHR - muscarinic cholinergic receptors, a-A R- alpha adrenergic receptors. |
Human metasympathetic nervous system
Autonomic (autonomic) nervous system,systema nervo-sutn autonomicum,- part of the nervous system that innervates the heart, blood and lymph vessels, viscera and other organs. This system coordinates the work of all internal organs, regulates metabolic and trophic processes, and maintains the constancy of the internal environment of the body.
The autonomic (autonomic) nervous system is divided into central and peripheral sections. The central department includes: 1) parasympathetic nuclei III, VII, IX and X pairs cranial nerves, lying in the brain stem (mesencephalon, ports, medulla oblongala); 2) vegetative (sympathetic) core forming a lateral intermediate column, columna intermediolateralis (autonomica), VIII cervical, all thoracic and two upper lumbar segments of the spinal cord (Cvni, Thi - Lu); 3) sacral parasympathetic nuclei,nuclei parasym-pathici sacrales, located in the gray matter of the three sacral segments of the spinal cord (Sn-Siv).
The peripheral department includes: 1) autonomic (autonomic) nerves, branches and nerve fibers,pa., rr. et neurofibrae autonomici (viscerates), emerging from the brain and spinal cord; 2) vegetative (autonomous, visceral) plexuses,plexus autonomici (viscerates); 3) nodes of the vegetative (autonomous, visceral) plexuses,ganglia plexum autono-micorum (viscerdlium); 4) sympathetic trunk,truncus sympathicus(right and left), with its nodes, internodal and connecting branches and sympathetic nerves; 5) end nodes,ganglia termindlia, parasympathetic part of the autonomic nervous system.
Neurons of the nuclei of the central part of the autonomic nervous system are the first efferent neurons on the way from the central nervous system (spinal cord and brain) to the innervated organ. The nerve fibers formed by the processes of these neurons are called prenodal (preganglionic) fibers, since they go to the nodes of the peripheral part of the autonomic nervous system and end with synapses on the cells of these nodes. Autonomic nodes are part of the sympathetic trunks and large autonomic plexuses abdominal cavity and pelvis. Preganglionic fibers leave the brain as part of the roots of the corresponding cranial nerves and the anterior roots of the spinal nerves. The nodes of the peripheral part of the autonomic nervous system contain the bodies of second (effector) neurons lying on the way to the innervated organs. The processes of these second neurons of the efferent pathway, carrying the nerve impulse from the autonomic ganglia to the working organs, are post-nodal (postganglionic) nerve fibers.
In the reflex arc In the autonomic part of the nervous system, the efferent link consists not of one neuron, but of two. In general, a simple autonomic reflex arc is represented by three neurons. The first link of the reflex arc is a sensory neuron, the body of which is located in the spinal ganglia and in the sensory ganglia of the cranial nerves. The second link of the reflex arc is efferent, since it carries impulses from the spinal cord or brain to the working organ. This efferent pathway of the autonomic reflex arc is represented by two neurons. The first of these neurons, the second in a simple autonomic reflex arc, is located in the autonomic nuclei of the central nervous system. It can be called intercalary, since it is located between the sensitive (afferent) link of the reflex arc and the second (efferent) neuron of the efferent pathway. The effector neuron is the third neuron of the autonomic reflex arc. The bodies of effector (third) neurons lie in the peripheral nodes of the autonomic nervous system.
The metasympathetic nervous system is a set of microganglionic formations located in the wall of various organs, characterized by motor activity - the metasympathetic nervous system of the myocardium, gastrointestinal tract, blood vessels, bladder, ureters. Microglia include 3 types of neurons: sensory, motor, intercalary.
The meaning of the metasympathetic nervous system.
The metasympathetic nervous system forms local reflex reactions and includes all components of reflex arcs. Thanks to the metasympathetic nervous system, internal organs can work without the participation of the central nervous system. An isolated heart was taken to study the metasympathetic nervous system. An air balloon was inserted into the right atrium - stretching the atrium - leading to an increase in heart rate. The inner surface of the heart was treated with an anesthetic and the experiment was repeated - the work of the heart did not change. Thus, there are reflex arcs inside the heart. The metasympathetic nervous system ensures the transfer of excitation from the extraorgan nervous system to the organ tissue - thus the metasympathetic nervous system is an intermediary between the sympathetic nervous system (parasympathetic nervous system) and organ tissue. The parasympathetic nervous system synapses more often with the metasympathetic nervous system than the sympathetic nervous system.
The metasympathetic nervous system regulates organ blood flow.
TICKET No. 33
- Elbow joint: structure, movements, muscles that move it. Blood supply, innervation.
- External female genitalia. Blood supply, innervation.
- Vegetative nodes of the head.
Parasympathetic branch of the autonomic nervous system
To the parasympathetic branch of the autonomic nervous system there are parasympathetic nuclei formed by parasympathetic neurons (the central part of the parasympathetic branch of the autonomic system), nodes and parasympathetic nerve fibers.
The parasympathetic branch of the autonomic nervous system has the following characteristics:
1). and pelvic spinal nerves). Parasympathetic fibers that emerge from the brain and spinal cord go to the nerve nodes;
2) nerve nodes lie close to the organ or in the innervated organ (enter the warehouse of vegetative plexuses);
3) preganglionic fibers are long, so they go from the central nervous system to the organ;
4) the postganglionic fiber is short, as it is located directly in the organ.
Functions of parasympathetic innervation. The parasympathetic nervous system innervates the eyes, muscles, ventricles, trachea and bronchi, legions, all organs, heart, cervical nerves, ducts and other internal organs, as well as blood vessels . The transmission of impulses from postganglionic fibers to the organ is influenced by the mediator acetylcholine.
A large proportion of empty internal organs (heart, bronchi, sechovy mikhur, grass tract, uterus, ruminant mikhur,
In the order of sympathetic and parasympathetic innervation, there is a powerful muscular mechanism of regulatory action - metasympathetic to the nervous system.
The site of localization of the metasympathetic nervous system is the intramural ganglia, which lie in the walls of empty organs and are isolated from excess tissue with special barriers.
The metasympathetic nervous system consists of a sensitive neuron, an interneuron, an effector neuron and a mediator channel. The bodies of neurons of the metasympathetic nervous system carry no synapses, and in the adolescents of these neurons there are a large number of bulbs with mediators. The metasympathetic nervous system innervates only internal organs.
Functions of the metasympathetic nervous system. The metasympathetic nervous system programs and coordinates the urinary, secretory and stimulant activity of organs, the activity of local endocrine elements and local blood flow. This means the ability of organs to rhythmically move with a musical frequency and amplitude without an influx of sound under the influx of metabolic changes in the organ itself.
The transmission of excitation in neurons that become ganglia of the metasympathetic system is influenced by acetylcholine and norepinephrine.
In the synapses of postganglionic fibers, various substances are seen - acetylcholine, norepinephrine, ATP, adenosine, etc.
Autonomic ganglia can be divided, depending on their location, into three groups:
- vertebrates (vertebral),
- prevertebral (prevertebral),
- intra-organ.
Vertebral ganglia belong to the sympathetic nervous system. They are located on both sides of the spine, forming two border trunks (they are also called sympathetic chains). The vertebral ganglia are connected to the spinal cord by fibers that form white and gray connecting branches. Along the white connecting branches - rami comroimicantes albi - preganglionic fibers of the sympathetic nervous system go to the nodes.
The fibers of post-ganglionic sympathetic neurons are sent from the nodes to the peripheral organs either along independent nerve pathways or as part of somatic nerves. In the latter case, they go from the nodes of the border trunks to the somatic nerves in the form of thin gray connecting branches - rami commiinicantes grisei (their gray color depends on the fact that postganglionic sympathetic fibers do not have pulpy membranes). The course of these fibers can be seen in rice. 258.
In the ganglia of the border trunk, most of the sympathetic preganglionic nerve fibers are interrupted; a smaller part of them passes through the border trunk without interruption and is interrupted in the precertebral ganglia.
Prevertebral ganglia are located at a greater distance from the spine than the ganglia of the border trunk; at the same time, they are located at some distance from the organs they innervate. The prevertebral ganglia include the ciliary ganglion, the upper and middle cervical sympathetic nodes, the solar plexus, the upper and lower 6th mesenteric ganglia. In all of them, with the exception of the ciliary ganglion, sympathetic preganglionic fibers are interrupted, passing through the nodes of the border trunk without interruption. In the ciliary ganglion, the parasympathetic preganglionic fibers innervating the eye muscles are interrupted.
TO intraorgan ganglia include the rich nerve cells plexuses located in internal organs. Such plexuses (intramural plexuses) are found in muscle walls many internal organs, such as the heart, bronchi, middle and lower third of the esophagus, stomach, intestines, gall bladder, bladder, as well as in the glands of external and internal secretion. On the cells of these nerve plexuses, as shown by histological studies by B.I. Lavrentyev and others, parasympathetic fibers are interrupted.
. Autonomic ganglia play a significant role in the distribution and propagation of nerve impulses passing through them. The number of nerve cells in the ganglia is several times greater (in the superior cervical spmpathic ganglion 32 times, in the ciliary ganglion 2 times) greater than the number of preganglionic fibers coming to the ganglion. Each of these fibers forms synapses on many ganglion cells.
The autonomic nervous system, which regulates the visceral functions of the body, is divided into sympathetic and parasympathetic, providing different influence on the organs of our body innervated together. Both the sympathetic and parasympathetic systems have central divisions that have a nuclear organization (nuclei of the gray matter of the brain and spinal cord), and peripheral(nerve trunks, ganglia, plexuses). The central sections of the parasympathetic nervous system include the autonomic nuclei of the 3, 7, 9, 10 pairs of cranial nerves and the intermediate lateral nuclei of the cruciate spinal cord, and the sympathetic nervous system includes the radicular neurons of the intermediate lateral nuclei of the gray matter of the thoracolumbar spine.
The central sections of the autonomic nervous system have a nuclear organization and consist of multipolar associative neurocytes of autonomic reflex arcs. The autonomic reflex arc, in contrast to the somatic one, is characterized by the two-part nature of its efferent link. The first preganglionic neuron of the efferent link of the autonomic reflex arc is located in the central part of the autonomic nervous system, and the second in the peripheral autonomic ganglion. The axons of the autonomic neurons of the central sections, called preganglionic fibers (in both the sympathetic and parasympathetic links, usually myelin and cholinergic) go as part of the anterior roots of the spinal cord or cranial nerves and give synapses on the neurons of one of the peripheral autonomic ganglia. Axons of neurons of the peripheral autonomic ganglia, called postganglionic fibers, end with effector nerve endings on smooth myocytes in internal organs, vessels, and glands. Postganglionic nerve fibers (usually unmyelinated) in the sympathetic nervous system are adrenergic, and in the parasympathetic nervous system they are cholinergic. Peripheral nodes of the autonomic nervous system, consisting of multipolar neurons, can be located outside the organs - sympathetic paravertebral and prevertebral ganglia, parasympathetic ganglia of the head, as well as in the wall of organs - intramural ganglia in the wall of the digestive tube and other organs. The ganglia of the intramural plexuses contain, in addition to efferent neurons (like other autonomic ganglia), sensory and intercalary cells of local reflex arcs. Three main types of cells are distinguished in the intramural nerve plexuses. Long axonal efferent neurons are cells of the first type, having short dendrites and a long axon leaving the ganglion. Equal-processed, afferent neurons - cells of the second type, contain long dendrites and therefore their axons cannot be distinguished morphologically. The axons of these neurocytes (shown experimentally) form synapses on cells of the first type. Cells of the third type are associative, they send out their processes to neighboring ganglia, ending on the dendrites of their neurons. The gastrointestinal tract contains several intramural plexuses: submucosal, muscular (the largest) and subserosal. In the muscular plexus, cholinergic neurons were found that excite motor activity, inhibitory neurons - adrenergic and purinergic (non-adrenergic) with large electron-dense granules. In addition, there are peptidergic neurons that secrete hormones. Postganglionic fibers of intramural plexus neurons in the muscular tissue of organs form terminal plexuses containing varicose axons. The latter contain synaptic vesicles - small and light in cholinergic myoneural synapses and small granular in adrenergic ones.
In the autonomic nervous system distinguish between central and peripheral parts. The central sections of the sympathetic nervous system are represented by the nuclei of the lateral horns of the thoracolumbar spinal cord. In the parasympathetic nervous system, the central divisions include the nuclei of the midbrain and medulla oblongata, as well as the nuclei of the lateral horns of the sacral spinal cord. Parasympathetic fibers of the craniobulbar region emerge as part of the III, VII, IX and X pairs of cranial nerves.
Peripheral parts of the autonomic nervous system formed by nerve trunks, ganglia and plexuses.
Autonomic reflex arcs begin with a sensory neuron, the body of which lies in the spinal ganglion, as in the somatic reflex arcs. Association neurons located in the lateral horns of the spinal cord. Here, nerve impulses are switched to intermediate preganglionic neurons, the processes of which leave the central nuclei and reach the autonomic ganglia, where they transmit impulses to the motor neuron. In this regard, preganglionic and postganglionic nerve fibers are distinguished. The first of them leave the central nervous system as part of the ventral roots of the spinal nerves and cranial nerves. Both in the sympathetic and parasympathetic systems preganglionic nerve fibers belong to cholinergic neurons. The axons of neurons located in the autonomic ganglia are called postganglionic. They do not form direct contacts with effector cells. Their terminal departments along the way, they form expansions - varicosities, which contain mediator bubbles. In the area of varicose veins there is no glial membrane and the neurotransmitter is released in environment, affects effector cells (for example, gland cells, smooth myocytes, etc.).
In peripheral ganglia sympathetic nervous system, as a rule, there are adrenergic efferent neurons (with the exception of neurons that have synaptic connections with sweat glands, where sympathetic neurons are cholinergic). In parasympathetic ganglia, efferent neurons are always cholinergic.
Ganglia are clusters of multipolar neurons (from several cells to tens of thousands). Extraorgan (sympathetic) ganglia have a well-defined connective tissue capsule as a continuation of the perineurium. Parasympathetic ganglia are usually located in the intramural nerve plexuses. The ganglia of the intramural plexuses, like other autonomic ganglia, 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, neuroendocrine, chemoreceptor, bipolar, and in some vertebrates, unipolar neurons have been described. Sympathetic ganglia contain small, intensely fluorescent cells (MYF cells) with short processes and a large number of granular vesicles in the cytoplasm. They release catecholamines and have an inhibitory effect on the transmission of impulses from preganglionic nerve fibers to the efferent sympathetic neuron. These cells are called interneurons.
Among large multipolar neurons Autonomic ganglia are distinguished: motor (type I Dogel cells), sensitive (type II Dogel cells) and associative (type III Dogel cells). 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 unmyelinated nerve fibers and ends on the smooth myocytes of the internal organs. Type I cells are called long axon neurons. Type II neurons are equilateral nerve cells. 2-4 processes extend from their body, among which it is difficult to distinguish an axon. Without branching, the processes extend far from the neuron body. Their dendrites have sensory nerve endings, and the axon ends 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 is directed to other ganglia. Many researchers consider these cells to be a type of sensory neuron.
Thus, in 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 differ in that in their composition, in addition to motor cholinergic neurons, there are 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 is carried out.
