The spinal ganglion has a fusiform shape, surrounded by a capsule of dense connective tissue. Thin layers of connective tissue penetrate from the capsule into the parenchyma of the node, in which they are located blood vessels.
Neurons The spinal ganglion is characterized by a large spherical body and a light nucleus with a clearly visible nucleolus. Cells are located in groups, mainly along the periphery of the organ. The center of the spinal ganglion consists mainly of neuronal processes and thin layers of endoneurium bearing vessels. Dendrites nerve cells They 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 dorsal roots, which carry nerve impulses to spinal cord or medulla oblongata.
In the spinal ganglia of higher vertebrates and humans, bipolar neurons become pseudounipolar. One process extends from the body of the pseudounipolar neuron, which wraps around the cell many times and often forms a ball. This process divides in a T-shape into afferent (dendritic) and efferent (axonal) branches.
The dendrites and axons of cells in the node and beyond are covered with myelin sheaths made of neurolemmocytes. The body of each nerve cell in the spinal ganglion is surrounded by a layer of flattened oligodendroglial cells, which are called mantle gliocytes, or ganglion gliocytes, or satellite cells. They are located around the body of the neuron and have small round nuclei. On the outside, the glial membrane of the neuron is covered with a thin fibrous connective tissue membrane. The cells of this membrane are distinguished by the oval shape of their nuclei.
Neurons of the spinal ganglia 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 their functional characteristics and localization, the autonomic nerve ganglia are divided into sympathetic And parasympathetic.
Majority internal organs has double autonomic innervation, i.e. receives postganglionic fibers from cells located in both the sympathetic and parasympathetic nodes. The reactions mediated by their neurons often have opposite directions (for example, sympathetic stimulation increases cardiac activity, and parasympathetic stimulation inhibits it).
General plan of the building vegetative nodes are similar. On the outside, the node is covered with a thin connective tissue capsule. Autonomic ganglia contain multipolar neurons, which are characterized by an irregularly shaped, eccentrically located nucleus. Multinucleated and polyploid neurons are common.
Each neuron and its processes are surrounded by a shell 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 nerve ganglia internal organs and associated pathways, due to their high autonomy, complexity of organization and characteristics of mediator exchange, are sometimes distinguished as independent metasympathetic department of the autonomic nervous system.
In intramural nodes by Russian histologist A.S. Dogel. Three types of neurons have been described:
1. long axonal efferent cells of type I;
2. equilateral afferent cells of type II;
3. type III association cells.
Long axon efferent neurons ( Dogel cells type I) - numerous and large neurons with short dendrites and a long axon, which is directed beyond the node to the working organ, where it forms motor or secretory endings.
Equilateral afferent neurons ( Dogel cells type II) have long dendrites and an axon extending beyond a given node to neighboring ones. These cells are included as a receptor link in the local reflex arcs, which close without the nerve impulse entering the central nervous system.
Association neurons ( Dogel cells type III) are local interneurons, connecting with their processes several cells of type I and II.
The neurons of the autonomic nerve ganglia, like the spinal ganglia, are of ectodermal origin and develop from neural crest cells.
Peripheral nerves
Nerves, or nerve trunks, connect nerve centers the brain and spinal cord with receptors and working organs, or with nerve ganglia. Nerves are formed by bundles of nerve fibers, which are united by connective tissue membranes.
Most nerves are mixed, i.e. include afferent and efferent nerve fibers.
Nerve fiber bundles contain both myelinated and unmyelinated fibers. The diameter of the fibers and the ratio between myelinated and unmyelinated nerve fibers are not the same in different nerves.
A cross section of a nerve shows sections of the axial cylinders of nerve fibers and the glial sheaths covering them. Some nerves contain single nerve cells and small ganglia.
Between the nerve fibers in the nerve bundle there are thin layers of loose fibrous connective tissue - endoneurium. There are few cells in it, reticular fibers predominate, and 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.
Outer sheath of the nerve trunk - epineurium- is a dense fibrous connective tissue rich in fibroblasts, macrophages and fat cells. Contains blood vessels and lymphatic vessels, sensory nerve endings.
48. Spinal cord.
The spinal cord consists of two symmetrical halves, delimited from each other in front by the deep median fissure, and behind by the 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. The bundles of nerve fibers that communicate between different parts of the nervous system are called tracts, or pathways, of the spinal cord.
The outer boundary of the white matter of the spinal cord is formed by limiting glial membrane, consisting of fused flattened processes of astrocytes. This membrane is pierced by the nerve fibers that make up the anterior and posterior roots.
Throughout the entire spinal cord, in the center of the gray matter there passes the central canal of the spinal cord, which communicates with the ventricles of the brain.
Gray matter in cross 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 (partially) axons of neurons, as well as glial cells. The main component of gray matter, distinguishing it from white matter, are multipolar neurons. Between the neuron bodies 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 are grouped into 10 layers, or plates of Rexed. In this case, plates I-V correspond to the posterior horns, plates VI-VII - the intermediate zone, plates VIII-IX - the anterior horns, plate X - 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 visible, 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 cores.
Among the neurons of the spinal cord, three types of cells can be distinguished:
radicular,
· internal,
· bundled.
The axons of the root cells leave the spinal cord as part of its anterior roots. The processes of the internal cells end at synapses within the gray matter of the spinal cord. The axons of tuft cells pass through the white matter in 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. Individual areas of the gray matter of the spinal cord differ significantly from each other in the composition of neurons, nerve fibers and neuroglia.
IN hind horns distinguish between spongy layer, gelatinous substance, and nucleus proper posterior horn and Clark's thoracic core. Between the posterior and lateral horns, the gray matter protrudes into the white matter in strands, as a result of which its network-like loosening is formed, called the reticular formation, or reticular formation, of the spinal cord.
The posterior horns are rich in diffusely located intercalary cells. These are small multipolar association and commissural cells, the axons of which end within the gray matter of the spinal cord on the same side (association cells) or the opposite side (commissural cells).
Neurons of the spongy zone and gelatinous substance communicate between the sensory cells of the spinal ganglia and the motor cells of the anterior horns, closing 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 (autonomic) nervous system - preganglionic cholinergic neurons of its sympathetic and parasympathetic divisions.
IN front horns The largest neurons of the spinal cord are located, which form nuclei of significant volume. This is the same as the neurons of the nuclei of the lateral horns, the root 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 represent motor somatic centers.
Spinal cord glia
The main part of the glial skeleton of gray matter consists of 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 septa 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 and predominate in the white matter.
Ependymal glia line the central canal of the spinal cord. Ependymocytes participate in the development cerebrospinal fluid(cerebrospinal fluid). A long process extends from the peripheral end of the ependymocyte, which is part of the outer limiting membrane of the spinal cord.
Directly below the ependymal layer is the subependymal (periventricular) limiting glial membrane, formed by the processes of astrocytes. This membrane is part of the so-called. blood-cerebrospinal fluid 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 of the hemispheres, structural features in the motor and sensitive areas. Cerebral cortex. The concept of myeloarchitectonics and cytoarchitectonics. Blood-brain barrier, its structure and significance. Adult changes in the cortex.
BRAIN - is the highest central organ for regulating all vital functions of the body, plays an exceptional role in mental or higher nervous activity.
The GM develops from the neural tube. During embryogenesis, the cranial section of the neural tube is divided into three brain vesicles: anterior, middle and posterior. Subsequently, due to folds and bends, five sections of the GM are formed from these bubbles:
- medulla;
- hindbrain;
- midbrain;
- diencephalon;
- telencephalon.
The differentiation of neural tube cells in the cranial region during the development of the brain proceeds in principle similar to the development of the spinal cord: i.e. The cambium is a layer of ventricular (germenative) cells located at the border with the tube canal. Ventricular cells intensively divide and migrate to the overlying layers and differentiate in 2 directions:
1. Neuroblasts are neurocytes. Complex relationships are established between neurocytes, and nuclear and screen nerve centers are formed. Moreover, unlike the spinal cord, screen-type centers predominate in the brain.
2. Glioblasts are gliocytes.
The conductive pathways of the brain, numerous nuclei of the brain - their localization and functions are studied in detail at the department normal anatomy human, so in this lecture we will focus on the features histological structure individual parts of GM. CORTEX OF THE LARGE HEMISPHERES (CLCH). Embryonic histogenesis of CPPS begins at the 2nd month embryonic development. Considering the importance of the CBPS for humans, the timing of its establishment and development is one of the important critical periods. Exposure to many unfavorable factors during these periods can lead to disorders and malformations of the brain.
So, in the 2nd month of embryogenesis, from the ventricular layer of the telencephalon wall, neuroblasts migrate vertically upward along the radially located fibers of gliocytes 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 cells. The six-layer structure of the CBPS becomes clearly defined in the 5th-8th months of embryogenesis, and heterochronously in different areas and zones of the cortex.
The BPS cortex is represented by a layer of gray matter 3-5 mm thick. In the cortex there are up to 15 billion or more neurocytes, some authors suggest up to 50 billion. All cortical neurocytes are multipolar in morphology. Among them, stellate, pyramidal, spindle-shaped, arachnid and horizontal cells are distinguished by shape. Pyramidal neurocytes have a triangular or pyramidal body, body diameter 10-150 µm (small, medium, large and giant). An axon departs from the base of the pyramidal cell and is involved in the formation of descending pyramidal tracts, associative and commissural bundles, i.e. pyramidal cells are efferent neurocytes of the cortex. Long dendrites extend from the apex and lateral surfaces of the triangular body of neurocytes. Dendrites have spines - sites of synaptic contacts. One cell can have up to 4-6 thousand such spines.
Stellate neurocytes are shaped like a star; dendrites extend from the body in all directions, are short and without spines. Stellate cells are the main perceptive sensory elements of the CBPS and their bulk is located in the 2nd and 4th layers of the CBPS.
The CBPS is divided into the frontal, temporal, occipital and parietal lobes. The lobes are divided into regions and cytoarchitectonic fields. Cytoarchitectonic fields are cortical centers of the screen type. In anatomy, you study in detail the localization of these fields (center of smell, vision, hearing, etc.). These fields overlap, therefore, if functions are disrupted or damaged, neighboring fields can partially take over its function.
The neurocytes of the BPS cortex are characterized by a regular layer-by-layer arrangement, which forms the cytoarchitectonics of the cortex.
It is customary to distinguish 6 layers in the cortex:
1. Molecular layer (the most superficial) - consists mainly of tangential nerve fibers, there is a small number of spindle-shaped associative neurocytes.
2. The outer granular layer is a layer of small stellate and pyramidal cells. Their dendrites are located in the molecular layer, some of the axons are directed into the white matter, the other part of the axons rises into the molecular layer.
3. Pyramidal layer - consists of medium and large pyramidal cells. Axons go into the white matter and in the form of association bundles are sent to other convolutions given hemisphere or in the form of commissural bundles in the opposite hemisphere.
4. Inner granular layer - consists of sensory stellate neurocytes that have associative connections with neurocytes of the above and underlying layers.
5. Ganglion layer - consists of large and giant pyramidal cells. The axons of these cells are directed into the white matter and form descending projection pyramidal tracts, as well as commissural bundles in the opposite hemisphere.
6. Layer of polymorphic cells - formed by neurocytes of 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 from 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 BPS cortex. Each module contains up to 2 thousand neurocytes. Impulses enter the module from the thalamus along 2 thalamocortical fibers and through 1 corticocortical fiber from the cortex of the given or opposite hemisphere. Corticocortical fibers begin 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 layers, giving collaterals to synapses on each layer. Thalamocortical fibers - specific afferent fibers coming from the thalamus, penetrate giving collaterals from the 6th to 4th layers in the module. Due to the presence of a complex relationship between neurocytes of all 6 layers, the received information is analyzed in the module. The output efferent pathways from the module begin with large and giant pyramidal cells of the 3rd, 5th and 6th layers. In addition to participating in the formation of projection pyramidal pathways, each module establishes connections with 2-3 modules of the given and opposite hemisphere.
The white matter of the telencephalon consists of associative (connect the convolutions of one hemisphere), commissural (connect the convolutions of the opposite hemispheres) and projection (connect the cortex with the underlying sections of the NS) nerve fibers.
The BPS cortex also contains a powerful neuroglial apparatus that performs trophic, protective, and musculoskeletal functions. Glia contain all known elements - astrocytes, oligodendrogliocytes and brain macrophages.
Myeloarchitecture
Among the nerve fibers of the cerebral cortex we can distinguish associative fibers connecting individual areas 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 cerebral cortex form radial rays ending in the third pyramidal layer. In addition to the already described tangential plexus of the I - molecular layer, at the level of IV - internal granular and V - ganglion layers there are two tangential layers of myelin nerve fibers - respectively, the outer strip of Baillarger and the internal strip of Baillarger. The last two systems are plexuses formed by the terminal sections of afferent fibers.
AGE CHANGES IN THE NERVOUS SYSTEM
Changes in the central nervous system in early postnatal age are associated with the maturation of 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 associated primarily with sclerotic changes in blood vessels, leading to deterioration of trophism. The soft and arachnoid, calcium salts are deposited there. There is atrophy of the BPS cortex, 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 basophilic substance decreases in them (decrease in the number of ribosomes and RNA), and the proportion of heterochromatin in the nuclei increases. The pigment lipofuscin accumulates in the cytoplasm. The pyramidal cells of the V layer of the BPS cortex and the pyriform 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 blood-brain 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 vascular capillary there is a layer of endothelial cells lying on the basement membrane. Endothelial cells communicate with each other through a complex network of tight junctions. On the nervous tissue side, a layer of astrocytes adjoins the basement membrane. The bodies of astrocytes are raised above the basement membrane, and their pseudopodia rest on the basement membrane so that the astrocyte legs form a narrowly looped three-dimensional network, and its cells form a complex cavity. The blood-brain barrier prevents the passage of large molecules (including many medications) from the blood into the intercellular space of the central nervous system. Endothelial cells can perform pinocytosis. They have carrier systems for the transport of basic substrates, which are sources of energy necessary for the life of neurons. For neurons, amino acids are the main sources of energy. 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 central authority balance and coordination of movements. It is formed by two hemispheres with a large number of grooves and convolutions, and a narrow middle part - the vermis.
The bulk of the gray matter in the cerebellum is located on the surface and forms its cortex. A smaller portion of the gray matter lies deep in the white matter in the form of the central cerebellar nuclei.
The cerebellar cortex is a nerve center of the screen type and is characterized by a highly ordered arrangement of neurons, nerve fibers and glial cells. The cerebellar cortex has three layers: 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 densely lying cells, as well as the presence of the so-called. cerebellar glomeruli. Among the neurons, granule cells, Golgi cells, and fusiform horizontal neurons are distinguished.
Spinal ganglion (g. spinale, PNA, BNA, JNA, LNH; synonym: G. intervertebral, G. spinal, spinal ganglion) common name sensory G. spinal nerves lying in the corresponding intervertebral foramina and giving fibers to the spinal nerves and dorsal roots.
Large medical dictionary. 2000 .
See what “spinal ganglion” is in other dictionaries:
I Ganglion (Greek ganglion node, tumor-like formation) is a cystic formation in the tissues adjacent to the tendon sheaths, joint capsules, less often to the periosteum or nerve trunks. The occurrence of G. is associated with constant mechanical... ... Medical encyclopedia
- (g. intervertebrale) see Ganglion of the spinal cord ... Large medical dictionary
- (g. spinale) see Ganglion of the spinal cord... Large medical dictionary
Large medical dictionary
1. Any structure (in neurology, anatomy ed.) containing a cluster of nerve cell bodies, as well as a number of synapses. In the sympathetic nervous system, chains of ganglia form sympathetic trunks (and nodes of large autonomic plexuses in the abdominal ... ... Medical terms
GANGLION, NODE- (ganglion, plural ganglia) 1. Any structure (in neurology, anatomy ed.) containing a cluster of nerve cell bodies, as well as a number of synapses. In the sympathetic nervous system, chains of ganglia form sympathetic trunks (and nodes of large autonomic... ... Dictionary in medicine
- (ganglion spinale) see Ganglion of the spinal cord... Medical encyclopedia
Spinal cord- (medulla spinalis) (Fig. 254, 258, 260, 275) is a cord of brain tissue located in the spinal canal. Its length in an adult reaches 41-45 cm, and its width is 1-1.5 cm. The upper part of the spinal cord smoothly passes into... ... Atlas of Human Anatomy
- (medulla spinalis), a phylogenetically ancient part of the central nervous system of vertebrates, located in the spinal canal. It first appears in skullless animals (the trunk brain of the lancelet), evolves in connection with the improvement of motor skills and the transition from... ... Biological encyclopedic dictionary
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