Spinal ganglion. Nervous system

Department of Histology, Cytology and Embryology, SSMU Lecture topic: “Nervous system. Spinal ganglia. Spinal cord” The purpose of the lecture. To study the general plan of the structure of the nervous system, the features of embryonic development, tissue composition, the functional significance of various departments nervous system , to give the concept of the nerve centers of the nuclear and screen type. Content. Tissue composition and development of the organs of the nervous system. Somatic and autonomic parts of the nervous system. Organs of the central nervous system, their functional significance. The structure and localization of the spinal ganglia, cellular composition. Development, localization and structure of the spinal cord, structure of gray and white matter, gray matter nuclei, types of neurons in them, functional purpose. Structure and functions of the nervous system. The nervous system has integrating, coordinating, adaptive, regulatory and other functions that ensure the interaction of a living organism with the external environment and the development of an adequate response to changing conditions. Anatomically, the nervous system is divided into central (brain and spinal cord) and peripheral (nerve nodes, nerve trunks and endings). According to the functions performed in the nervous system, the following are distinguished: 1. the vegetative section, which provides communication between the central nervous system and the vessels, internal organs and glands, 2. somatic, which innervates all other parts of the body (for example, skeletal muscle tissue). The source of the development of the nervous system is the neuroectoderm. On the 3rd week of embryogenesis in the central part of the neroectodera, cell differentiation occurs, from which the neural tube is formed by neurulation and the neural crest, which is divided into 2 gangious plates. The brain and sensory organs form from the cranial part of the neural tube. The spinal cord, spinal and autonomic ganglia, as well as the chromaffin tissue of the body are formed from the trunk region and the ganglionic plate. Connective tissue layers and membranes develop from the mesenchyme. Sources of development of the nervous system Sources of development of the spinal cord The structure of the spinal ganglion 1. Posterior root; 2. pseudo-unipolar neurons; 2a. mantle gliocytes; 3. front spine; 4. nerve fibers; 5. layers of connective tissue of the spinal ganglion axons of pseudo-unipolar neurons contact with the bodies of neurons of the medulla oblongata or dorsal horns of the spinal cord. Dendrites go as part of sensory nerves to the periphery and end with receptors. Pseudo-unipolar neurons of the spinal ganglion 1. The dendrite goes as part of the sensitive part of the mixed spinal nerves to the periphery and ends with receptors. 2. The axon passes as part of the posterior roots to the medulla oblongata. 3. Pericaryon. 4. Nucleus with nucleolus. 5. Nerve fibers. Simple reflex arc Cross section of the spinal cord Structure of the spinal cord. The gray matter of the spinal cord is formed by clusters of neurons called nuclei, neuroglial cells, unmyelinated and thin myelinated nerve fibers. The protrusions of the gray matter are called horns or pillars, among them there are: 1. anterior (ventral), 2. lateral (lateral), 3. posterior (dorsal) large cells anterior spinal cord zigzag - Anterior and lateral horns INTERMEDIATE ZONE AND SIDE HORNS Here, the neurons are grouped into two or one nucleus (depending on the level of the spinal cord). Medial intermediate nucleus (located in the intermediate zone). As in the case of the thoracic nucleus. axons of neurons enter the lateral funiculus of the same side and rise to the cerebellum. Lateral intermediate nucleus (located in the lateral horns and is an element of the sympathetic nervous system; Neuronal axons leave the spinal cord through the anterior roots, separate from them in the form of white connecting branches and go to the sympathetic ganglia. B. ANTERIOR HORNS Several somatomotor nuclei; contain the largest cells of the spinal cord - motor neurons.Axons of motor neurons also leave the spinal cord through the anterior roots and then, as part of mixed nerves, go to the skeletal muscles.HORNS The posterior horns contain intercalary (associative) neurons that receive signals from sensory neurons of the spinal nodes.Her horn neurons form the following structures: 1. Spongy layer and gelatinous substance: located in the posterior part and on the periphery of the posterior horns; contain small neurons in the glial framework. The axons of these neurons go to the motor neurons of the anterior horns of the same segment of the spinal cord - the same side or opposite (in in the latter case, the cells are called k omissural, because their axons form a commissure, or commissure, lying in front of the spinal canal). diffuse intercalary neurons. 2. Proper nucleus of the posterior horn (located in the center of the horn) Axons of neurons pass to the opposite side into the lateral funiculus and go to the cerebellum or to the optic tubercle. 3. Thoracic nucleus (at the base of the horn) Axons of neurons enter the lateral funiculus of the same side and rise to the cerebellum. White matter of the spinal cord White matter of the spinal cord White matter consists of nerve fibers and neuroglial cells. The horns of the gray matter divide the white matter into three cords: 1. the posterior cords are located between the posterior septum and the posterior roots, 2. the lateral cords lie between the anterior and posterior roots, 3. the anterior cords are delimited by the anterior fissure and the anterior roots. Anterior to the gray commissure there is a section of white matter connecting the anterior cords - the white commissure. The pathways are formed by a chain of neurons connected in series by their processes; provide conduction of excitation from neuron to neuron (from nucleus to nucleus). Anterior horn of the spinal cord 1. Multipolar motor neuron of gray matter. 2. White matter. 3. Myelinated nerve fibers. 4. Connective tissue layers According to the nature of the relationship, neurons are divided into: 1 - internal cells, the processes of which end in synapses within the gray matter of the spinal cord; 2 - bundle cells, their axons pass in the white matter in separate bundles and connect the neurons of various segments of the spinal cord, as well as with the brain, forming pathways; 3 - radicular neurons, the axons of which go beyond the boundaries of the spinal cord and form the anterior roots of the spinal nerves (in the skin, on the muscles). Simple reflex arc In the anterior horns - motor neurons, by interconnection - radicular, forming 2 groups of motor nuclei: medial (muscles of the trunk) and lateral (muscles of the lower and upper extremities). In the lateral horns - associative neurons, according to the relationship - bundle neurons, forming 2 intermediate nuclei: medial and lateral. The axons of the lateral neurons leave the spinal cord as part of the anterior roots and go to the peripheral sympathetic ganglia. In the posterior horns - associative neurons (internal and fascicular) form 4 nuclei: spongy substance, gelatinous, nucleus proper of the posterior horn and Clark's thoracic nucleus. Thank you for attention!

The spinal ganglion has a fusiform shape, surrounded by a capsule of dense connective tissue. From the capsule, thin layers of connective tissue penetrate into the parenchyma of the node, in which the blood vessels are located.

Neurons spinal ganglion are characterized by a large spherical body and a light nucleus with a clearly visible nucleolus. Cells are arranged in groups, mainly along the periphery of the organ. The center of the spinal ganglion consists mainly of processes of neurons and thin layers of endoneurium that carry blood vessels. Dendrites nerve cells go as part of the sensitive part of the mixed spinal nerves to the periphery and end there with receptors. The axons collectively form the posterior roots that carry nerve impulses to the spinal cord or medulla oblongata.

In the spinal nodes of higher vertebrates and humans, bipolar neurons in the process of maturation become pseudo-unipolar. A single process departs from the body of a pseudounipolar neuron, which repeatedly wraps around the cell and often forms a tangle. This process divides in a T-shape into afferent (dendritic) and efferent (axonal) branches.

Dendrites and axons of cells in the node and beyond are covered with myelin sheaths of neurolemmocytes. The body of each nerve cell in the spinal ganglion is surrounded by a layer of flattened oligodendroglia cells, here called mantle gliocytes, or ganglion gliocytes, or satellite cells. They are located around the body of the neuron and have small rounded nuclei. Outside, the glial sheath of the neuron is covered with a thin fibrous connective tissue sheath. The cells of this shell are distinguished by the oval shape of the nuclei.

Spinal ganglion neurons contain neurotransmitters such as acetylcholine, glutamic acid, substance P.

Autonomous (vegetative) nodes

Autonomic nerve nodes are located:

along the spine (paravertebral ganglia);

in front of the spine (prevertebral ganglia);

in the wall of organs - the heart, bronchi, digestive tract, Bladder(intramural ganglia);

near the surface of these organs.

Myelin preganglionic fibers containing processes of neurons of the central nervous system approach the vegetative nodes.

According to the functional feature and localization, the autonomic nerve nodes are divided into sympathetic and parasympathetic.

Majority internal organs has a double autonomic innervation, i.e. receives postganglionic fibers from cells located in both sympathetic and parasympathetic nodes. The responses mediated by their neurons often have the opposite direction (for example, sympathetic stimulation enhances cardiac activity, while parasympathetic stimulation inhibits it).

General plan of the building vegetative nodes is similar. Outside, the node is covered with a thin connective tissue capsule. Vegetative nodes contain multipolar neurons, which are characterized by an irregular shape, an eccentrically located nucleus. Often there are multinucleated and polyploid neurons.

Each neuron and its processes are surrounded by a sheath of glial satellite cells - mantle gliocytes. The outer surface of the glial membrane is covered with a basement membrane, outside of which there is a thin connective tissue membrane.

Intramural ganglions internal organs and the pathways associated with them due to their high autonomy, the complexity of the organization and the characteristics of the mediator exchange are sometimes distinguished into an independent metasympathetic department of the autonomic nervous system.

In intramural nodes, the Russian histologist Dogel A.S. three types of neurons are described:

1. long-axon efferent type I cells;

2. equal-length afferent cells of type II;

3. type III association cells.

Long-axon efferent neurons ( Type I Dogel cells) - numerous and large neurons with short dendrites and a long axon, which goes beyond the node to the working organ, where it forms motor or secretory endings.

Equidistant afferent neurons ( Type II Dogel cells) have long dendrites and an axon extending beyond the given node into neighboring ones. These cells are part of the local reflex arcs as a receptor link, which are closed without a nerve impulse entering the central nervous system.

Associative neurons ( Type III Dogel cells) are local intercalary neurons that connect several cells of type I and II with their processes.

The neurons of the autonomic nerve ganglia, like those of the spinal nodes, are of ectodermal origin and develop from neural crest cells.

peripheral nerves

Nerves, or nerve trunks, connect the nerve centers of the brain and spinal cord with receptors and working organs, or with nerve nodes. Nerves are formed by bundles of nerve fibers, which are united by connective tissue sheaths.

Most of the nerves are mixed, i.e. include afferent and efferent nerve fibers.

Nerve bundles contain both myelinated and unmyelinated fibers. The diameter of the fibers and the ratio between myelinated and unmyelinated nerve fibers in different nerves are not the same.

On the cross section of the nerve, sections of the axial cylinders of the nerve fibers and the glial membranes that dress them are visible. Some nerves contain single nerve cells and small ganglia.

Between the nerve fibers in the composition of the nerve bundle are thin layers of loose fibrous connective tissue - endoneurium. There are few cells in it, reticular fibers predominate, small blood vessels pass through.

Individual bundles of nerve fibers are surrounded perineurium. The perineurium consists of alternating layers of densely packed cells and thin collagen fibers oriented along the nerve.

The outer sheath of the nerve trunk epineurium- is a dense fibrous connective tissue rich in fibroblasts, macrophages and fat cells. Contains blood and lymphatic vessels, sensitive nerve endings.

48. Spinal cord.

The spinal cord consists of two symmetrical halves, separated from each other in front by a deep median fissure, and behind by a median sulcus. The spinal cord is characterized by a segmental structure; each segment is associated with a pair of anterior (ventral) and a pair of posterior (dorsal) roots.

In the spinal cord there are Gray matter located in the central part, and white matter lying on the periphery.

The white matter of the spinal cord is a collection of longitudinally oriented predominantly myelinated nerve fibers. Bundles of nerve fibers that communicate between different parts of the nervous system are called tracts, or pathways, of the spinal cord.

The outer border of the white matter of the spinal cord forms glial border membrane, consisting of fused flattened processes of astrocytes. This membrane is permeated by nerve fibers that make up the anterior and posterior roots.

Throughout the entire spinal cord in the center of the gray matter runs the central canal of the spinal cord, which communicates with the ventricles of the brain.

The gray matter on the transverse section has the appearance of a butterfly and includes front, or ventral, rear, or dorsal, and lateral, or lateral, horns. The gray matter contains the bodies, dendrites and (partly) axons of neurons, as well as glial cells. The main component of gray matter, which distinguishes it from white, are multipolar neurons. Between the bodies of neurons there is a neuropil - a network formed by nerve fibers and processes of glial cells.

As the spinal cord develops from the neural tube, neurons cluster into 10 layers, or Rexed's plates. At the same time, plates I-V correspond to the posterior horns, plates VI-VII correspond to the intermediate zone, plates VIII-IX correspond to the anterior horns, plate X corresponds to the zone near the central canal. This division into plates complements the organization of the structure of the gray matter of the spinal cord, based on the localization of the nuclei. On transverse sections, nuclear groups of neurons are more clearly visible, and on sagittal sections, the lamellar structure is better seen, where neurons are grouped into Rexed columns. Each column of neurons corresponds to a specific area on the periphery of the body.

Cells similar in size fine structure and functional significance, lie in the gray matter in groups called nuclei.

Among the neurons of the spinal cord, three types of cells can be distinguished:

radicular,

internal,

beam.

Axons of radicular cells leave the spinal cord as part of its anterior roots. The processes of internal cells end in synapses within the gray matter of the spinal cord. The axons of the beam cells pass through the white matter as separate bundles of fibers that carry nerve impulses from certain nuclei of the spinal cord to its other segments or to the corresponding parts of the brain, forming pathways. Separate areas of the gray matter of the spinal cord differ significantly from each other in the composition of neurons, nerve fibers and neuroglia.

AT posterior horns Distinguish between the spongy layer, the gelatinous substance, the nucleus proper of the posterior horn and the thoracic nucleus of Clark. Between the posterior and lateral horns, the gray matter juts into the white as strands, as a result of which its mesh-like loosening is formed, which is called the mesh formation, or reticular formation, of the spinal cord.

The posterior horns are rich in diffusely located intercalary cells. These are small multipolar associative and commissural cells, the axons of which terminate within the gray matter of the spinal cord of the same side (associative cells) or the opposite side (commissural cells).

The neurons of the spongy zone and the gelatinous substance communicate between the sensitive cells of the spinal ganglia and the motor cells of the anterior horns, closing the local reflex arcs.

Clark's nucleus neurons receive information from muscle, tendon, and joint receptors (proprioceptive sensitivity) along the thickest radicular fibers and transmit it to the cerebellum.

In the intermediate zone, there are centers of the autonomic (autonomous) nervous system - preganglionic cholinergic neurons of its sympathetic and parasympathetic divisions.

AT anterior horns the largest neurons of the spinal cord are located, which form nuclei of considerable volume. This is the same as the neurons of the nuclei of the lateral horns, radicular cells, since their neurites make up the bulk of the fibers of the anterior roots. As part of the mixed spinal nerves, they enter the periphery and form motor endings in the skeletal muscles. Thus, the nuclei of the anterior horns are motor somatic centers.

Glia of the spinal cord

The main part of the glial backbone of the gray matter is protoplasmic and fibrous astrocytes. The processes of fibrous astrocytes extend beyond the gray matter and, together with elements of connective tissue, take part in the formation of partitions in the white matter and glial membranes around blood vessels and on the surface of the spinal cord.

Oligodendrogliocytes are part of the sheaths of nerve fibers, predominate in the white matter.

The ependymal glia lines the central canal of the spinal cord. Ependymocytes participate in the production of cerebrospinal fluid (CSF). A long process departs from the peripheral end of the ependymocyte, which is part of the outer boundary membrane of the spinal cord.

Directly under the ependymal layer is a subependymal (periventricular) boundary glial membrane formed by processes of astrocytes. This membrane is part of the so-called. hemato-liquor barrier.

Microglia enter the spinal cord as blood vessels grow into it and are distributed in the gray and white matter.

The connective tissue membranes of the spinal cord correspond to the membranes of the brain.

49. Brain. general characteristics hemispheres, structural features in the motor and sensory areas. The cerebral cortex. The concept of myeloarchitectonics and cytoarchitectonics. Blood-brain barrier, its structure and significance. Age-related changes in the cortex.

BRAIN - is the highest central organ for the regulation of all vital functions of the body, plays an exceptional role in mental or higher nervous activity.
The GM develops from the neural tube. The cranial part of the neural tube in embryogenesis is divided into three cerebral vesicles: anterior, middle and posterior. In the future, due to folds and bends, five sections of the GM are formed from these bubbles:
- medulla;
- back brain;
- midbrain;
- diencephalon;
- telencephalon.
Differentiation of neural tube cells in the cranial region during the development of GM proceeds in principle similarly to the development of the spinal cord: i.e. The cambium is a layer of ventricular (germenal) cells located on the border with the tube channel. Ventricular cells intensively divide and migrate to the overlying layers and differentiate in 2 directions:
1. Neuroblasts neurocytes. Complex relationships are established between neurocytes, nuclear and screen nerve centers are formed. Moreover, in contrast to the spinal cord, centers of the screen type predominate in the GM.
2. Glioblasts gliocytes.
Conducting pathways of the GM, numerous nuclei of the GM - their localization and functions you study in detail at the Department of Normal Human Anatomy, so in this lecture we will focus on the features of the histological structure of individual parts of the GM. LARGE HEMISPHERE CORK (KBPSh). Embryonic histogenesis of BPSP begins at the 2nd month of embryonic development. Given the importance of CBPS for humans, the timing of its formation and development is one of the most important critical periods. The impact of many adverse factors during these periods can lead to disorders and malformations of the brain.
So, on the 2nd month of embryogenesis, from the ventricular layer of the telencephalon wall, neuroblasts migrate vertically upwards along the radially located gliocyte fibers and form the innermost 6th layer of the cortex. Then follow the next waves of neuroblast migration, and the migrating neuroblasts pass through the previously formed layers and this contributes to the establishment of a large number of synaptic contacts between the cells. The six-layered structure of BPSC becomes clearly expressed at the 5th-8th months of embryogenesis, and heterochronously in different areas and zones of the cortex.
The cortex of the BPS is represented by a layer of gray matter 3-5 mm thick. In the cortex, there are up to 15 or more billion neurocytes, some authors admit up to 50 billion. All neurocytes of the cortex are multipolar in morphology. Among them, stellate, pyramidal, fusiform, arachnid and horizontal cells are distinguished by shape. Pyramidal neurocytes have a triangular or pyramidal body, body diameter 10-150 microns (small, medium, large and giant). An axon departs from the base of the pyramidal cell, which is involved in the formation of descending pyramidal pathways, associative and commissural bundles, i.e. pyramidal cells are efferent neurocytes of the cortex. Long dendrites extend from the top and side surfaces of the triangular body of neurocytes. Dendrites have spines - places of synaptic contacts. One cell of such spines can have up to 4-6 thousand.
Star-shaped neurocytes are star-shaped; dendrites extending from the body in all directions, short and without spines. Stellar cells are the main perceptive sensory elements of BPSC and their bulk is located in the 2nd and 4th layer of BPSC.
CBPS is subdivided into the frontal, temporal, occipital and parietal lobes. The lobes are divided into regions and cytoarchitectonic fields. Cytoarchitectonic fields are cortical centers screen type. In anatomy, you study in detail the localization of these fields (the center of smell, vision, hearing, etc.). These fields overlap, therefore, in case of violation of the functions, damage to any field, its function can be partially taken over by neighboring fields.
The neurocytes of the BPS cortex are characterized by a regular layered arrangement, which forms the cytoarchitectonics of the cortex.

In the cortex, it is customary to distinguish 6 layers:
1. Molecular layer (the most superficial) - consists mainly of tangential nerve fibers, there is a small amount of fusiform associative neurocytes.
2. Outer granular layer - a layer of small stellate and pyramidal cells. Their dendrites are located in the molecular layer, part of the axons are sent to the white matter, the other part of the axons rises to the molecular layer.
3. Pyramidal layer - consists of medium and large pyramidal cells. Axons go to the white matter and in the form of associative bundles are sent to other convolutions of the given hemisphere or in the form of commissural bundles to the opposite hemisphere.
4. Inner granular layer - consists of sensory stellate neurocytes that have associative connections with neurocytes of the upper and lower layers.
5. Ganglion layer - consists of large and giant pyramidal cells. The axons of these cells are sent to the white matter and form descending projection pyramidal pathways, as well as commissural bundles to the opposite hemisphere.
6. Layer of polymorphic cells - formed by neurocytes of the various shapes(hence the name). Axons of neurocytes are involved in the formation of descending projection pathways. Dendrites penetrate the entire thickness of the cortex and reach the molecular layer.
The structural and functional unit of the BPS cortex is a module or column. A module is a collection of neurocytes of all 6 layers located in one perpendicular space and closely interconnected with each other and with subcortical formations. In space, the module can be represented as a cylinder penetrating all 6 layers of the cortex, oriented with its long axis perpendicular to the surface of the cortex and having a diameter of about 300 μm. There are about 3 million modules in the human BSP cortex. Each module contains up to 2 thousand neurocytes. The input of impulses into the module occurs from the thalamus along the 2nd thalamocortical fibers and along the 1st corticocortical fiber from the cortex of the given or opposite hemisphere. Corticocortical fibers start from the pyramidal cells of the 3rd and 5th layers of the cortex of the given or opposite hemisphere, enter the module and penetrate it from the 6th to the 1st layer, giving off collaterals for synapses on each layer. Thalamocortical fibers - specific afferent fibers coming from the thalamus, permeate giving collaterals from the 6th to the 4th layer in the module. Due to the presence of a complex interconnection of neurocytes of all 6 layers, the information received is analyzed in the module. Output efferent pathways from the module begin with large and giant pyramidal cells of the 3rd, 5th and 6th layer. In addition to participating in the formation of the projection pyramidal pathways, each module establishes connections with 2-3 modules of the given and opposite hemispheres.
The white matter of the telencephalon consists of associative (connect the convolutions of one hemisphere), commissural (connect the convolutions of opposite hemispheres) and projection (connect the cortex to the underlying sections of the NS) nerve fibers.
The cortex of the BPS also contains a powerful neuroglial apparatus that performs a trophic, protective, and musculoskeletal function. Glia contains all known elements - astrocytes, oligodendrogliocytes and brain macrophages.

Myeloarchitectonics

Among the nerve fibers of the cerebral cortex, one can distinguish associative fibers that connect individual parts of the cortex of one hemisphere, commissural connecting the cortex of different hemispheres, and projection fibers, both afferent and efferent, that connect the cortex with the nuclei of the lower parts of the central nervous system. Projection fibers in the cortex of the hemispheres form radial rays ending in the III - pyramidal layer. In addition to the already described tangential plexus of the I - molecular layer, at the level of IV - the inner granular and V - ganglionic layers there are two tangential layers of myelinated nerve fibers - respectively, the outer strip of Bayarger and the inner strip of Bayarger. The last two systems are plexuses formed by the terminal sections of the afferent fibers.

AGE CHANGES IN THE NERVOUS SYSTEM
Changes in the CNS in early postnatal age are associated with the maturation of the nervous tissue. In newborns, cortical neurocytes are characterized by a high nuclear-cytoplasmic ratio. With age, this ratio decreases due to an increase in the mass of the cytoplasm; the number of synapses increases.
Changes in the central nervous system in old age are primarily associated with sclerotic changes in blood vessels, leading to a deterioration in trophism. The soft and arachnoid membrane thickens, calcium salts are deposited there. There is atrophy of the cortex of the BPS, especially in the frontal and parietal lobes. The number of neurocytes per unit volume of brain tissue decreases due to cell death. Neurocytes decrease in size, the content of the basophilic substance decreases in them (a decrease in the number of ribosomes and RNA), and the proportion of heterochromatin increases in the nuclei. The pigment lipofuscin accumulates in the cytoplasm. The pyramidal cells of the V layer of the cortex of the BPS, the pear-shaped cells of the ganglion layer of the cerebellum change faster than others.

The blood-brain barrier is a cellular structure that forms the interface between the blood of the circulatory system and the tissue of the central nervous system. The purpose of the hematoencephalic barrier is to maintain a constant composition of the intercellular fluid - the environment for the best implementation of the functions of neurons.

The blood-brain barrier consists of several interacting layers. On the side of the cavity of the blood capillary there is a layer of endothelial cells lying on the basement membrane. Endothelial cells interact with each other through a complex network of tight junctions. From the side of the nervous tissue, a layer of astrocytes adjoins the basement membrane. The bodies of astrocytes are elevated above the basement membrane, and their pseudopodia rest on the basement membrane in such a way that the legs of astrocytes form a narrow-loop three-dimensional network, and its cells form a complex cavity. The blood-brain barrier does not allow large molecules (including many drugs) to pass from the blood into the intercellular space of the central nervous system. Endothelial cells can carry out pinocytosis. They have systems of carriers for the transport of the main substrates, which are sources of energy necessary for the vital activity of neurons. Amino acids are the main sources of energy for neurons. Astrocytes contribute to the transport of substances from the blood to neurons, as well as the removal of excess of many metabolites from the interstitial fluid.

50. Cerebellum. Structure and functions. Neuronal composition of the cerebellar cortex. Interneuronal connections. Affer and effer fibers.

Cerebellum

The cerebellum is the central organ balance and coordination of movements. It is formed by two hemispheres with a large number of grooves and convolutions, and a narrow middle part - a worm.

The bulk of the gray matter in the cerebellum is located on the surface and forms its cortex. A smaller part of the gray matter lies deep in the white matter in the form of the central nuclei of the cerebellum.

The cerebellar cortex is nerve center screen type and is characterized by a high orderliness of the arrangement of neurons, nerve fibers and glial cells. There are three layers in the cerebellar cortex: molecular, ganglionic and granular.

Outer molecular layer contains relatively few cells. It distinguishes between basket and stellate neurons.

Average ganglion layer formed by one row of large pear-shaped cells, first described by the Czech scientist Jan Purkinje.

Interior granular layer characterized by a large number of tightly lying cells, as well as the presence of the so-called. glomeruli of the cerebellum. Among neurons, granule cells, Golgi cells, and fusiform horizontal neurons are distinguished here.

spinal ganglion

Peripheral nerves and trunks.

Peripheral nerves always go next to the vessels and form neurovascular bundles. All peripheral nerves are mixed, that is, they contain sensory and motor fibers. Myelinated fibers predominate, and there are a small number of unmyelinated fibers.

Sensitive nervousfibers contain dendrites of sensitive neurons, which are localized in the spinal ganglia and they begin on the periphery with receptors (sensitive nerve endings).

motor nervefibers contain axons of motor neurons that emerge from the spinal ganglion and end in neuromuscular synapses on skeletal muscle fibers.

Around each nerve fiber lies a thin plate of loose connective tissue - endoneurium which contains blood capillaries. A group of nerve fibers is surrounded by a more rigid connective tissue sheath, there are practically no vessels, and it is customary to call it perineurium. It acts as a case. Around everything peripheral nerve there is also a layer of loose connective tissue, which contains larger vessels and is commonly called epineurium.

Peripheral nerves regenerate well. The regeneration rate is about 1-2 mm per day.

Located along the spinal column. Covered with a connective tissue capsule. Partitions go inside from it. Vessels penetrate through them into the spinal node. Nerve fibers are located in the middle part of the node. Myelin fibers predominate.

In the peripheral part of the node, as a rule, pseudo-unipolar sensory nerve cells are located in groups. Οʜᴎ make up 1 sensitive link of the somatic reflex arc. They have a round body, a large nucleus, a wide cytoplasm, and well-developed organelles. Around the body is a layer of glial cells - mantle gliocytes. Οʜᴎ constantly support the vital activity of cells. Around them is a thin connective tissue sheath, which contains blood and lymphatic capillaries. This shell performs protective and trophic functions.

The dendrite is part of the peripheral nerve. On the periphery, it forms a sensitive nerve fiber, where it begins with a receptor. Another neuritic process, the axon, runs towards the spinal cord, forming the posterior root, which enters the spinal cord and terminates in the gray matter of the spinal cord. If you delete a node. Sensitivity will suffer, if you cross the back spine, the same result.

Spinal ganglion - concept and types. Classification and features of the category "Spinal Ganglion" 2017, 2018.

GANGLIA (ganglia ganglions) - clusters of nerve cells, surrounded by connective tissue and glial cells, located along the peripheral nerves.

Distinguish G. of vegetative and somatic nervous system. G. of the autonomic nervous system are divided into sympathetic and parasympathetic and contain the bodies of postganglionic neurons. G. of the somatic nervous system are represented by spinal nodes and G. sensitive and mixed cranial nerves containing the bodies of sensory neurons and giving rise to sensitive portions of the spinal and cranial nerves.

Embryology

The rudiment of the spinal and autonomic nodes is the ganglionic plate. It is formed in the embryo in those parts of the neural tube that border on the ectoderm. In the human embryo on the 14th-16th day of development, the ganglionic plate is located on the dorsal surface of the closed neural tube. Then it splits along its entire length, both of its halves move ventrally and lie in the form of neural folds between the neural tube and the superficial ectoderm. In the future, according to the segments of the dorsal side of the embryo, foci of proliferation of cellular elements appear in the neural folds; these areas thicken, separate and turn into spinal nodes. From the ganglion plate also develop sensory ganglia Y, VII-X pairs of cranial nerves, similar to the spinal ganglia. The germinal nerve cells, the neuroblasts that form the spinal ganglia, are bipolar cells, that is, they have two processes extending from opposite poles of the cell. The bipolar form of sensory neurons in adult mammals and humans is retained only in the sensory cells of the vestibulocochlear nerve, vestibular and spiral ganglia. In the rest, both spinal and cranial sensory nodes, the processes of bipolar nerve cells in the process of their growth and development approach and merge in most cases into one common process (processus communis). On this basis, sensitive neurocytes (neurons) are called pseudounipolar (neurocytus pseudounipolaris), less often protoneurons, emphasizing the antiquity of their origin. Spinal nodes and nodes in. n. With. differ in the nature of the development and structure of neurons. Development and morphology of the autonomic ganglia - see Autonomic nervous system.

Anatomy

Basic information about G.'s anatomy is given in the table.

Histology

The spinal ganglia are covered on the outside with a connective tissue sheath, which passes into the sheath of the posterior roots. The stroma of nodes is formed by connecting fabric with circulatory and limf, vessels. Each nerve cell (neurocytus ganglii spinalis) is separated from the surrounding connective tissue by a capsule shell; much less often in one capsule there is a colony of nerve cells tightly adjacent to each other. The outer layer of the capsule is formed by fibrous connective tissue containing reticulin and precollagen fibers. The inner surface of the capsule is lined with flat endothelial cells. Between the capsule and the body of the nerve cell there are small stellate or spindle-shaped cellular elements called gliocytes (gliocytus ganglii spinalis) or satellites, trabantes, mantle cells. They are elements of neuroglia, similar to lemmocytes (Schwann cells) of peripheral nerves or oligodendrogliocytes of c. n. With. A common process departs from the body of a mature cell, starting with an axon tubercle (colliculus axonis); then it forms several curls (glomerulus processus subcapsularis), located near the cell body under the capsule and called the initial glomerulus. In different neurons (large, medium and small), the glomerulus has a different structural complexity, expressed in an unequal number of curls. Upon exiting the capsule, the axon is covered with a pulpy membrane and, at a certain distance from the cell body, was divided into two branches, forming a T- or Y-shaped figure at the site of division. One of these branches leaves the peripheral nerve and is a sensory fiber that forms a receptor in the corresponding organ, while the other enters the spinal cord through the posterior root. The body of a sensitive neuron - pyrenophore (part of the cytoplasm containing the nucleus) - has a spherical, oval or pear-shaped shape. There are large neurons ranging in size from 52 to 110 nm, medium - from 32 to 50 nm, small - from 12 to 30 nm. Neurons of medium size make up 40-45% of all cells, small - 35-40%, and large - 15-20%. The neurons in the ganglia of different spinal nerves are different in size. So, in the cervical and lumbar nodes, the neurons are larger than in others. There is an opinion that the size of the cell body depends on the length of the peripheral process and the area of ​​the area innervated by it; there is also a nek-swarm correspondence between the size of the body surface of animals and the size of sensitive neurons. For example, among fish, the largest neurons were found in the moon-fish (Mola mola), which has a large body surface. In addition, atypical neurons are found in the spinal nodes of humans and mammals. These include "fenestrated" Cajal cells, characterized by the presence of loop-like structures on the periphery of the cell body and axon (Fig. 1), in the loops of which there is always a significant number of satellites; "hairy" cells [C. Ramon y Cajal, de Castro (F. de Castro) and others], equipped with additional short processes extending from the cell body and ending under the capsule; cells with long processes, equipped with flask-shaped thickenings. The listed forms of neurons and their numerous varieties are not typical for healthy young people.

Age and past diseases affect the structure of the spinal ganglia - they appear in them much more than in healthy ones, the number of various atypical neurons, especially with additional processes equipped with flask-shaped thickenings, as, for example, in rheumatic heart disease (Fig. 2), angina pectoris, etc. Clinical observations, as well as experimental studies Animals have shown that sensitive neurons of the spinal ganglions react much faster with the intensive growth of additional processes to various endogenous and exogenous hazards than motor somatic or autonomic neurons. This ability of sensory neurons is sometimes significantly expressed. In cases hron, irritations again formed shoots can twist (in the form of winding) around a body of own or next neuron, reminding a cocoon. Sensory neurons of the spinal nodes, like other types of nerve cells, have a nucleus, various organelles and inclusions in the cytoplasm (see Nerve cell). Thus, a distinctive property of sensitive neurons of the spinal cord and nodes of cranial nerves is their bright morphol, reactivity, which is expressed in the variability of their structural components. This is ensured by a high level of protein synthesis and various active substances and testifies to their functional mobility.

Physiology

In physiology, the term "ganglia" is used to refer to several types of functionally different nerve formations.

In invertebrates G. play the same role as c. n. With. in vertebrates, being the highest centers of coordination of somatic and vegetative functions. In the evolutionary series from worms to cephalopods and arthropods, G., processing all information about the state of the environment and the internal environment, reach a high degree of organization. This circumstance, as well as the simplicity of anatomical preparation, the relatively large size of the bodies of nerve cells, the possibility of introducing several microelectrodes into the soma of neurons under direct visual control at the same time, made G. invertebrates a common object of neurophysiol and experiments. On neurons roundworms, octapods, decapods, gastropods, and cephalopods, electrophoresis, direct measurement of ion activity, and voltage clamping are used to study the mechanisms of potential generation and the process of synaptic transmission of excitation and inhibition, which are often impossible on most mammalian neurons. Despite the evolutionary differences, the main electrophysiol, constants and neurophysiol, the mechanisms of the work of neurons are largely the same in invertebrates and higher vertebrates. Therefore G.'s researches, invertebrates have obshchefiziol. meaning.

In vertebrates, somatosensory cranial and spinal cords are functionally the same type. They contain the bodies and proximal parts of the processes of afferent neurons that transmit impulses from peripheral receptors to c. n. With. In somato-sensory G. there are no synaptic switches, efferent neurons and fibers. So, the neurons of the spinal G. in a toad are characterized by the following basic electrophysiol parameters: specific resistance - 2.25 kOhm / cm 2 for depolarizing and 4.03 kOhm / cm 2 for hyperpolarizing current and a specific capacity of 1.07 μF / cm 2. The total input resistance of neurons in somatosensory G. is significantly lower than the corresponding parameter of axons; therefore, with high-frequency afferent impulses (up to 100 impulses per 1 second), the conduction of excitation can be blocked at the level of the cell body. In this case, action potentials, although not recorded from the cell body, continue to be conducted from the peripheral nerve to the posterior root and persist even after the extirpation of the nerve cell bodies, provided that the T-shaped axon branches are intact. Consequently, excitation of the soma of neurons of somatosensory G. for the transmission of impulses from peripheral receptors to the spinal cord is not necessary. This feature first appears in the evolutionary series in tailless amphibians.

Vegetative G. of vertebrates in the functional plan is usually divided into sympathetic and parasympathetic. In all autonomic G. there is a synaptic switch from preganglionic fibers to postganglionic neurons. In the vast majority of cases, synaptic transmission is carried out chemically. by using acetylcholine (see Mediators). In the parasympathetic ciliary G. of birds, electrical transmission of impulses was found using the so-called. connection potentials, or connection potentials. Electrical transmission of excitation through the same synapse is possible in two directions; in the process of ontogenesis, it is formed later than chemical. The functional significance of electrical transmission is not yet clear. In sympathetic G. of amphibians, a small number of synapses with chem. transmission of a non-cholinergic nature. In response to a strong single stimulation of the preganglionic fibers of the sympathetic G., in the postganglionic nerve, first of all, an early negative wave (O-wave) occurs, caused by excitatory postsynaptic potentials (EPSP) during the activation of n-cholinergic receptors of postganglionic neurons. The inhibitory postsynaptic potential (IPSP), which occurs in postganglionic neurons under the action of catecholamines secreted by chromaffin cells in response to the activation of their m-cholinergic receptors, forms a positive wave following the 0-wave (P-wave). The late negative wave (PO-wave) reflects the EPSP of postganglionic neurons when their m-cholinergic receptors are activated. The process is completed by a long-term negative late wave (DPO-wave), which occurs as a result of the summation of EPSPs of a non-cholinergic nature in postganglionic neurons. Under normal conditions, at the height of the O-wave, when the EPSP reaches a value of 8-25 mV, a propagating excitation potential arises with an amplitude of 55-96 mV, a duration of 1.5-3.0 ms, accompanied by a wave of trace hyperpolarization. The latter essentially masks the P and PO waves. At the height of trace hyperpolarization, excitability decreases (refractory period), so usually the frequency of discharges of postganglionic neurons does not exceed 20-30 impulses per 1 sec. According to the main electrophysiol. to characteristics neurons of vegetative G. are identical to the majority of neurons of c. n. With. Neurophysiol. a feature of autonomic G.'s neurons is the absence of true spontaneous activity during deafferentation. Among the pre- and postganglionic neurons, neurons of groups B and C predominate according to the classification of Gasser - Erlanger, based on electrophysiol, characteristics of nerve fibers (see Fig. ). Preganglionic fibers branch extensively, so irritation of one preganglionic branch leads to the appearance of EPSP in many neurons of several G. (multiplication phenomenon). In turn, on each postganglionic neuron, the terminals of many preganglionic neurons terminate, differing in the threshold of irritation and the speed of conduction (the phenomenon of convergence). Conventionally, the ratio of the number of postganglionic neurons to the number of preganglionic nerve fibers can be considered a measure of convergence. In all vegetative G. it is greater than one (with the exception of the ciliary ganglion of birds). In the evolutionary series, this ratio increases, reaching a value of 100:1 in the sympathetic human G.. Multiplication and convergence, which provide spatial summation) of nerve impulses, in combination with temporal summation, are the basis of the integrating function of G. in the processing of centrifugal and peripheral impulses. Afferent pathways pass through all autonomic G., the bodies of neurons of which lie in the spinal G. For the lower mesenteric G., the celiac plexus, and some intramural parasympathetic G., the existence of true peripheral reflexes has been proven. Afferent fibers that conduct excitation at a low speed (approx. 0.3 m/sec) enter the G. as part of the postganglionic nerves and terminate on the postganglionic neurons. In vegetative G. the terminations of afferent fibers are found. The latter inform c. n. With. about what is happening in G. functional-chemical. changes.

Pathology

In a wedge, practice most often meets ganglionitis (see), called also sympatho-ganglionitis, - the disease connected with defeat of ganglions of a sympathetic trunk. The defeat of several nodes is defined as polyganglionic, or truncite (see).

Spinal ganglia are often involved in the pathological process in radiculitis (see).

Brief anatomical description of the nerve ganglia (nodes)

Bibliography Brodsky V. Ya. Cell trophism, M., 1966, bibliogr.; Dogel A.S. The structure of the spinal nodes and cells in mammals, Zapiski imp. Acad. Sciences, vol. 5, no. 4, p. 1, 1897; Milokhin A. A. Sensitive innervation of autonomic neurons, new ideas about the structural organization of the autonomic ganglion, L., 1967; bibliography; Roskin G. I., Zhirnova A. A. and Shornikova M. V. Comparative histochemistry of sensitive cells of spinal ganglia and motor cells of the spinal cord, Dokl. Academy of Sciences of the USSR, new, ser., v. 96, JSfc 4, p. 821, 1953; Skok V. I. Physiology of autonomic ganglia, L., 1970, bibliogr.; Sokolov B. M. General gangliology, Perm, 1943, bibliogr.; Yarygin H. E. and Yarygin V. N. Pathological and adaptive changes in the neuron, M., 1973; de Castro F. Sensory ganglia of the cranial and spinal nerves, normal and pathological, in: Cytol a. cell. path, of the nervous system, ed. by W. Penfield, v. 1, p. 91, N. Y., 1932, bibliogr.; Clara M. Das Nervensystem des Menschen, Lpz., 1959.

E. A. Vorobieva, E. P. Kononova; A. V. Kibyakov, V. N. Uranov (phys.), E. K. Plechkova (embr., gist.).

The nervous system is divided into central and peripheral. CNS includes the brain and spinal cord peripheral- peripheral nerve ganglia, nerve trunks and nerve endings. On a functional basis, the nervous system is divided into somatic and autonomic. somatic nervous system innervates the whole body, except for internal organs, glands of external and internal secretion and of cardio-vascular system.Autonomic nervous the system innervates everything except the body.

Development. The source of the development of the nervous system is the neural tube and the neural crest (ganglion plate). From the anterior end of the neural tube and neural crest, the brain and head ganglions develop, and from the caudal end, the spinal cord develops. From the neural crest, neurons and neuroglia of the spinal ganglia and peripheral ganglions of the autonomic nervous system are formed.

As a result of the proliferation of neural tube cells, its lateral surfaces thicken, in which 3 layers are formed: 1) ependymal, 2) mantle (mantle), 3) marginal veil. At this time, dorsal (wing) and ventral plates and anterior, posterior and lateral columns are distinguished in the neural tube.

From ependymal layer ependymoglial epithelium develops, lining the central canal, from raincoat- gray matter edge veil- white matter of the spinal cord.

Anterior column neuroblasts differentiate into motor neurons, whose axons form anterior roots. The neuroblasts of the posterior columns differentiate into associative-efferent neurons, the axons of which exit into the white matter and go to the brain.

Neural crest neuroblasts migrate to the sites of localization of the autonomic nerve and spinal ganglia and differentiate into neurocytes of these structures. The axons of the sensory neurons of the spinal ganglia form the posterior roots of the spinal cord, in which they are sent to its gray and white matter.

Nerve trunks. They consist of nerve myelinated and non-myelinated afferent and efferent fibers; nerves may contain individual neurons and individual nerve ganglia. The nerves have layers of connective tissue. The layer of loose connective tissue that surrounds each nerve fiber is called endoneurium; surrounding bundle of nerve fibers perineurium, which consists of 5-6 layers of collagen fibers; between these layers there are slit-like cavities lined with neuroepithelium in which fluid circulates. The entire nerve is surrounded by a layer of connective tissue called epineurium. The perineurium and epineurium contain blood vessels and nerves.

Sensitive nerve nodes. There are sensitive spinal (ganglion spinalis), or spinal, ganglia in the head region.

spinal ganglia. They are located along the posterior roots of the spinal cord. Anatomically and functionally closely related to the posterior and anterior roots and the spinal nerve.

Outside, the ganglia are covered with a capsule (capsula fibrosa), which consists of dense connective tissue, from which connective tissue layers extend into the depth of the node, forming its stroma. The composition of the spinal ganglia includes sensitive pseudo-unipolar neurons, from which one common process departs, several times braiding the round body of the neuron, which then divides into an axon and a dendrite.

The bodies of neurons are located on the periphery of the ganglion. They are surrounded by glial cells (gliocyti ganglii) that form the glial sheath around the neuron. Outside of the glial sheath around the body of each neuron there is a connective tissue sheath.

The processes of pseudounipolar neurons are located closer to the center of the ganglion. Dendrites neurons are sent as part of the spinal nerves to the periphery and end with receptors.

spinal nerves consist of dendrites of pseudounipolar neurons of the spinal ganglion (sensory nerve fibers) and the anterior roots of the spinal cord (motor nerve fibers) that have joined them.

In this way, spinal nerve is mixed. Most nerves human body are branches of the spinal nerves.

Axons of pseudounipolar neurons as part of the posterior roots are sent to the spinal cord. Some of these axons enter the gray matter of the spinal cord and end in synapses on its neurons. Some of them form thin fibers that carry substance P and glutamic acid, i.e. mediators. Thin fibers conduct sensitive impulses from the skin (skin sensitivity) and internal organs (visceral sensitivity). Other, thicker fibers conduct impulses from tendons, joints, and skeletal muscles (proprioceptive sensitivity).

The second part of the axons of the pseudounipolar neurons of the spinal ganglia enters the white matter and forms the delicate (thin) and wedge-shaped bundles, in which it goes to the medulla oblongata and ends on the neurons of the nucleus of the tender bundle and the nucleus of the wedge-shaped bundle, respectively.

Spinal cord(Medulla spinalis). The spinal cord is located in the spinal canal. The transverse section shows that the spinal cord consists of 2 symmetrical halves (right and left). The boundary between these halves passes through the posterior connective tissue septa (commissure), the central canal, and the anterior notch of the spinal cord.

The cross section also shows that the spinal cord consists of gray and white matter. Gray matter(substantia grisea) is located in the central part and resembles a butterfly or the letter H in shape. In the gray matter there are posterior horns (cornu posterior), anterior horns (cornu anterior) and lateral horns (cornu lateralis). Between the anterior and posterior horns is the intermediate zone (zona intermedia), in the center of the gray matter is the central canal of the spinal cord.

From a histological point of view, gray matter consists of neurons, their sheathed processes, i.e., nerve fibers, and neuroglia. All gray matter neurons are multipolar. Among them, cells with weakly branched dendrites (isodendritic neurons), with strongly branched dendrites (idiodendritic neurons) and intermediate cells with moderately branched dendrites are distinguished.

Conventionally, the gray matter is divided into 10 Rexed plates. The posterior horns are presented I-V plates, the intermediate zone - with plates VI-VII, the anterior horns - with plates VIII-IX, the space around the central canal - with plate X.

gelatinous substance localized in I-IV plates. In the neurons of this substance, enkephalin (pain mediator) is produced. Neurons of plates I and III synthesize metenkephalin and neurotensin, which are able to inhibit pain impulses that come with thin radicular fibers (axons of spinal ganglion neurons) carrying substance P. GABA is produced in the neurons of plate IV (a mediator that inhibits the passage of an impulse through the synapse). The gelatinous neurocytes suppress sensory impulses coming from the skin (skin sensitivity) and partly from the internal organs (visceral sensitivity), and partly from the joints, muscles and tendons (proprioceptive sensitivity).

Neurons associated with the conduction of various sensory impulses are concentrated in certain plates of the spinal cord.

Skin and visceral sensitivity are associated with the gelatinous substance (plates I-IV). Partially sensitive, partly proprioceptive impulses pass through the own nucleus of the posterior horn (IV plate), and proprioceptive impulses pass through the thoracic nucleus, or Clark's nucleus (V plate), and the medial intermediate nucleus (VI-VII plates).

Gray matter neurons of the spinal cord represented by: 1) beam neurons (neurocytes fasciculatus); 2) radicular neurons (neurocytus radiculatus); 3) internal neurons (neurocytus internus). Beam and radicular neurons are formed into nuclei. In addition, some of the bundle neurons are diffusely scattered in the gray matter.

Internal neurons are concentrated in the spongy and gelatinous substance of the posterior horns and in the Cajal nucleus located in the anterior horns (VIII plate), and diffusely scattered in the posterior horns and the intermediate zone. On the internal neurons, the axons of the pseudounipolar cells of the spinal ganglia end in synapses.

Spongy substance of the posterior horn(substantia spongiosa cornu posterior) consists mainly of an interweaving of glial fibers, in the loops of which internal neurons are located. Some scientists call the spongy substance of the posterior horn the dorsomarginal nucleus (nucleus dorsomarginalis) and believe that the axons of some part of this nucleus join the spinothalamic pathway. At the same time, it is generally accepted that the axons of the internal cells of the spongy substance connect the axons of the pseudounipolar neurons of the spinal ganglia with the neurons of their own half of the spinal cord (associative neurons) or with the neurons of the opposite half (commissural neurons).

Gelatinous substance of the posterior horn(substantia gelatinosa cornu posterior) is represented by glial fibers, between which there are internal neurons. All neurons, concentrated in the spongy and gelatinous substance and scattered diffusely, are associative, or intercalary, in function. These neurons are divided into associative and commissural. Associative neurons are those that connect the axons of the sensory neurons of the spinal ganglia with the dendrites of the neurons of their half of the spinal cord. Commissural - these are neurons that connect the axons of the neurons of the spinal ganglia with the dendrites of the neurons of the opposite half of the spinal cord. The internal neurons of the Cajal nucleus connect the axons of the pseudounipolar cells of the spinal ganglia with the neurons of the motor nuclei of the anterior horns.

Nuclei nervous system - these are clusters of nerve cells similar in structure and function. Almost every nucleus of the spinal cord begins in the brain and ends at the caudal end of the spinal cord (stretches in the form of a column).

Nuclei composed of bundles neurons: 1) own nucleus of the posterior horn (nucleus proprius cornu posterior); 2) thoracic nucleus (nucleus thoracicus); 3) medial intermediate nucleus (nucleus intermediomedialis). All neurons of these nuclei are multipolar. They are called bundled because their axons, leaving the gray matter of the spinal cord, form bundles (ascending paths) connecting the spinal cord with the brain. By function, these neurons are associative-afferent.

Proprietary nucleus of the posterior horn is located in its middle part. Part of the axons from this nucleus goes to the anterior gray commissure, passes to the opposite half, enters the white matter and forms the anterior (ventral) spinal cerebellar tract (tractus spinocerrebellaris ventralis). As part of this pathway, axons in the form of climbing nerve fibers enter the cerebellar cortex. The 2nd part of the axons of the neurons of its own nucleus forms the spinothalamic pathway (tractus spinothalamicus), which carries impulses to the visual mounds.

Thick radicular fibers (axons of neurons of the spinal ganglia) approach the proper nucleus of the posterior horn, transmitting proprioceptive sensitivity (impulses from muscles, tendons, joints), and thin radicular fibers that carry impulses from the skin (skin sensitivity) and internal organs (visceral sensitivity).

Thoracic nucleus, or Clark's nucleus, located in the medial part of the base of the posterior horn. The thickest nerve fibers, formed by axons of neurons of the spinal ganglia, approach the nerve cells of Clark's nucleus. Through these fibers, proprioceptive sensitivity (impulses from tendons, joints, skeletal muscles) is transmitted to the thoracic nucleus. The axons of the neurons of this nucleus extend into the white matter of their half and form the posterior, or dorsal, spinal tract (tractus spinocerebellaris dorsalis). The axons of the neurons of the thoracic nucleus in the form of climbing fibers reach the cerebellar cortex.

Medial intermediate nucleus located in the intermediate zone near the central canal of the spinal cord. The axons of the bundle neurons of this nucleus join the spinal tract of their half of the spinal cord. In addition, the medial intermediate nucleus contains neurons containing cholecystokinin, vasoactive intestinal peptide (VIP), and somatostatin; their axons go to the lateral-intermediate nucleus. Thin radicular fibers (axons of neurons of the spinal ganglia) approach the neurons of the medial intermediate nucleus, carrying mediators: glutamic acid and substance P. Sensitive impulses from the internal organs (visceral sensitivity) are transmitted through these fibers to the neurons of the medial intermediate nucleus. In addition, thick radicular fibers carrying proprioceptive sensitivity approach the medial nucleus of the intermediate zone.

Thus, the axons of the bundle neurons of all 3 nuclei are sent to the cerebellar cortex, and from the own nucleus of the posterior horn they are also directed to the visual tubercle.

From radicular neurons are formed: 1) nuclei of the anterior horn, including 5 nuclei; 2) lateral-intermediate nucleus (nucleus intermediolateralis).

Lateral-intermediate nucleus belongs to the autonomic nervous system and is associative-efferent in function, consists of large radicular neurons. The part of the nucleus located at the level of the 1st thoracic (Th 1) to the 2nd lumbar (L 2) segments, inclusive, belongs to the sympathetic nervous system. The part of the nucleus located cranial to Th l and caudal to the 1st sacral (S 1) segments belongs to the parasympathetic nervous system. The axons of the neurons of the sympathetic division of the lateral-intermediate nucleus leave the spinal cord as part of the anterior roots, then separate from them and go to the peripheral sympathetic ganglia. The axons of the neurons that make up the parasympathetic division are sent to the intramural ganglia. The neurons of the lateral intermediate nucleus are characterized by high activity of acetylcholinesterase and choline acetyltransferase, which cause the breakdown of mediators.

These neurons are called radicular because their axons leave the spinal cord as part of the anterior roots in the form of preganglionic myelinated cholinergic nerve fibers. Thin radicular fibers (axons of neurons of the spinal ganglia) carrying glutamic acid as a mediator, fibers from the medial nucleus of the intermediate zone, fibers from the internal neurons of the spinal cord approach the lateral nucleus of the intermediate zone.

Radicular neurons The anterior horns are located in 5 nuclei: lateral anterior, lateral posterior, medial anterior, medial posterior, and central. The axons of the radicular neurons of these nuclei leave the spinal cord as part of the anterior roots of the spinal cord, which connect with the dendrites of the sensory neurons of the spinal ganglia, resulting in the formation of the spinal nerve. As part of this nerve, the axons of the radicular neurons of the anterior horn are sent to the fibers of the skeletal muscle tissue and end with neuromuscular endings (motor plaques). All 5 nuclei of the anterior horns are motor.

The radicular neurons of the anterior horn are the largest in the spinal cord. They are called radicular because their axons take part in the formation of the anterior roots of the spinal cord. These neurons belong to the somatic nervous system. The axons of the internal neurons of the spongy substance, the gelatinous substance, the nucleus of Cajal, neurons diffusely scattered in the gray matter of the spinal cord, pseudounipolar cells of the spinal ganglia, scattered bundle neurons, and fibers of the descending pathways coming from the brain approach them. Due to this, about 1000 synapses are formed on the body and dendrites of motor neurons.

In the anterior horn, medial and lateral groups of nuclei are distinguished. Lateral nuclei consisting of radicular neurons, are located only in the region of the cervical and lumbosacral thickenings of the spinal cord. From the neurons of these nuclei, axons are sent to the muscles of the upper and lower extremities. Medial nuclei innervate the muscles of the body.

Thus, in the gray matter of the spinal cord, 9 main nuclei are distinguished, 3 of which consist of bundle neurons (the nucleus proper of the posterior horn, the thoracic nucleus and the medial intermediate nucleus), 6 of the radicular neurons (5 nuclei of the anterior horn and 1 lateral intermediate nucleus).

Small (scattered) bundle neurons scattered in the gray matter of the spinal cord. Their axons leave the gray matter of the spinal cord and form their own pathways. Leaving the gray matter, the axons of these neurons divide into descending and ascending branches, which come into contact with the motor neurons of the anterior horns at different levels of the spinal cord. Thus, if an impulse hits only one small fascicular cell, then it immediately spreads to many motor neurons located in different segments of the spinal cord.

White matter of the spinal cord(substantia alba). It is represented by myelinated and non-myelinated nerve fibers that form pathways. The white matter of each half of the spinal cord is divided into 3 cords:

1) anterior cord (funiculus anterior), limited by the anterior notch and anterior roots;

2) lateral funiculus (funiculus lateralis), limited by the anterior and posterior roots of the spinal cord;

3) posterior cord (funiculus dorsalis), limited by the posterior connective tissue septum and posterior roots.

In the anterior cords there are descending paths connecting the brain with the spinal cord; in the back cords - ascending pathways connecting the spinal cord with the brain; in the lateral cords both descending and ascending paths.

Main ascending paths 5:

1) gentle bundle (fasciculus gracilis) and 2) wedge-shaped bundle (fasciculus cuneatus) are formed by axons of sensory neurons of the spinal ganglia, pass in the posterior funiculus and end in the medulla oblongata on the nuclei of the same name (nucleus gracilis and nucleus cuneatus);

3) anterior spinal tract (tractus spinocerebellaris ventralis),

4) the posterior spinal cerebellar tract (tractus spinocerebellaris dorsalis) and 5) the spinal thalamic tract (tractus spinothalamicus) pass through the lateral funiculus.

Anterior spinal tract formed by the axons of the nerve cells of the nucleus proper of the posterior horn and the medial nucleus of the intermediate zone, located in the lateral funiculus of the white matter of the spinal cord.

Posterior spinal tract formed by axons of neurocytes of the thoracic nucleus, located in the lateral funiculus of the same half of the spinal cord.

Spinothalamic pathway formed by the axons of the nerve cells of the posterior horn's own nucleus, located in the lateral funiculus.

pyramid paths are the main descending paths. There are 2 such paths: anterior pyramidal and lateral pyramidal. The pyramidal tracts branch off from the great pyramids of the cerebral cortex. Part of the axons of the large pyramids do not cross and form the anterior (ventral) pyramidal turbidity. Part of the axons of the pyramidal neurons crosses in the medulla oblongata and forms the lateral pyramidal pathways. The pyramidal pathways terminate at the motor nuclei of the anterior horns of the gray matter of the spinal cord.