^ Nervous system: general morphofunctional characteristics; sources of development, classification.
The nervous system provides the regulation of all vital processes in the body and its interaction with the external environment. Anatomically, the nervous system is divided into central and peripheral. The first includes the brain and spinal cord, the second combines peripheral nerve nodes, trunks and endings.
From a physiological point of view, the nervous system is divided into somatic, innervating the entire body, except for internal organs, vessels and glands, and autonomous, or autonomic, regulating the activity of these organs.
The nervous system develops from the neural tube and the ganglionic plate. The brain and sense organs differentiate from the cranial part of the neural tube. The spinal cord, spinal and autonomic nodes, and chromaffin tissue of the body are formed from the trunk region of the neural tube and the ganglionic plate.
The mass of cells in the lateral sections of the neural tube increases especially rapidly, while its dorsal and ventral parts do not increase in volume and retain their ependymal character. The thickened lateral walls of the neural tube are divided by a longitudinal groove into the dorsal - alar and ventral - main plate. At this stage of development, three zones can be distinguished in the lateral walls of the neural tube: the ependyma lining the canal, the mantle layer, and the marginal veil. The gray matter of the spinal cord subsequently develops from the mantle layer, and its white matter develops from the marginal veil.
Simultaneously with the development of the spinal cord, spinal and peripheral vegetative nodes are laid. The starting material for them is the cellular elements of the ganglion plate, which differentiate into neuroblasts and glioblasts, from which neurons and mayial gliocytes of the spinal ganglia are formed. Part of the cells of the ganglionic plate migrates to the periphery to the localization of the autonomic nerve ganglia and chromaffin tissue.
^ Spinal cord: morphofunctional characteristics; structure of gray and white matter.
The gray matter on the cross section of the brain is presented in the form of the letter "H" or a butterfly. The protrusions of the gray matter are called horns. There are anterior, or ventral, posterior, or dorsal, and lateral, or lateral, horns.
The gray matter of the spinal cord consists of neuron bodies, non-myelinated and thin myelinated fibers, and neuroglia. The main component of gray matter, which distinguishes it from white, are multipolar neurons.
The white matter of the spinal cord is a collection of longitudinally oriented predominantly myelinated fibers. The bundles of nerve fibers that communicate between different parts of the nervous system are called the pathways of the spinal cord.
Among the neurons of the spinal cord, one can distinguish: neurites, radicular cells, internal, bundle.
In the posterior horns, there are: a spongy layer, a gelatinous substance, a proper nucleus of the posterior horn and a thoracic nucleus. The posterior horns are rich in diffusely located intercalary cells. In the middle of the posterior horn is its own nucleus of the posterior horn.
The thoracic nucleus (Clark's nucleus) consists of large intercalary neurons with highly branched dendrites.
Of the structures of the posterior horn, of particular interest are the gelatinous substance, which stretches continuously along the spinal cord in plates I-IV. Neurons produce enkephalin, an opioid-type peptide that inhibits pain effects. The gelatinous substance has an inhibitory effect on the functions of the spinal cord.
The largest neurons of the spinal cord are located in the anterior horns, which have a body diameter of 100-150 microns and form nuclei of considerable volume. This is the same as the neurons of the nuclei of the lateral horns, radicular cells. These nuclei are motor somatic centers. In the anterior horns, the medial and lateral groups of motor cells are most pronounced. The first innervates the muscles of the trunk and is well developed throughout the spinal cord. The second is located in the region of the cervical and lumbar thickenings and innervates the muscles of the limbs.
^ Brain: morphofunctional characteristics.
The brain is enclosed in a reliable shell of the skull. In addition, it is covered with shells of connective tissue - hard, arachnoid and soft.
In the brain, gray and white matter are distinguished, but the distribution of these two components is much more complicated here than in the spinal cord. Most of the gray matter of the brain is located on the surface of the cerebrum and in the cerebellum, forming their cortex. A smaller part forms numerous nuclei of the brain stem.
The brainstem consists of the medulla oblongata, the pons, the cerebellum, and the structures of the midbrain and diencephalon. All nuclei of the gray matter of the brainstem are composed of multipolar neurons. There are nuclei of cranial nerves and switching nuclei.
The medulla oblongata is characterized by the presence of nuclei of the hypoglossal, accessory, vagus, glossopharyngeal, vestibulocochlear nerves. In the central region of the medulla oblongata there is an important coordination apparatus of the brain - the reticular formation.
The bridge is divided into dorsal (tire) and ventral parts. The dorsal part contains fibers of the medulla oblongata, the nuclei of the V-VIII cranial nerves, the reticular formation of the bridge.
The midbrain consists of the roof of the midbrain (the quadrigemina), the tegmentum of the midbrain, the substantia nigra, and the legs of the brain. Substance nigra got its name from the fact that its small spindle-shaped neurons contain melanin.
In the diencephalon, the optic tubercle predominates in volume. Ventral to it is a hypothalamic (hypothalamic) region rich in small nuclei. Nerve impulses to the visual hillock from the brain go along the extrapyramidal motor pathway.
^ Cerebellum: structure and morphofunctional characteristics.
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 central nuclei. Three layers are distinguished in the cerebellar cortex: the outer one is the molecular layer, the middle one is the ganglionic layer, and the inner one is the granular one.
The ganglionic layer contains pear-shaped neurons. They have neurites, which, leaving the cerebellar cortex, form the initial link of its efferent inhibitory pathways.
The molecular layer contains two main types of neurons: basket and stellate. Basket neurons are located in the lower third of the molecular layer. These are irregularly shaped small cells about 10-20 microns in size. Their thin long dendrites branch mainly in a plane located transversely to the gyrus. The long neurites of the cells always run across the gyrus and parallel to the surface above the pear-shaped neurons. The activity of the neurites of the basket neurons causes inhibition of the piriform neurons.
The stellate neurons lie above the basket cells and are of two types. Small stellate neurons are equipped with thin short dendrites and weakly branched neurites that form synapses on the dendrites of pear-shaped cells. Large stellate neurons, unlike small ones, have long and highly branched dendrites and neurites.
Basket and stellate neurons of the molecular layer are a single system of intercalary neurons that transmit inhibitory nerve impulses to the dendrites and bodies of pear-shaped cells in a plane transverse to the convolutions. The granular layer is very rich in neurons. The first type of cells in this layer can be considered granular neurons, or granule cells. They have a small volume. The cell has 3-4 short dendrites. The dendrites of granule cells form characteristic structures called cerebellar glomeruli.
The second type of cells in the granular layer of the cerebellum are inhibitory large stellate neurons. There are two types of such cells: with short and long neurites.
The third type of cells are spindle-shaped horizontal cells. They are found predominantly between the granular and ganglionic layers. Afferent fibers entering the cerebellar cortex are represented by two types - mossy and so-called climbing fibers. Mossy fibers are part of the olivocerebellar and cerebellopontine tracts. They end in the glomeruli of the granular layer of the cerebellum, where they come into contact with the dendrites of the granule cells.
Climbing fibers enter the cerebellar cortex, apparently, along the dorsal-cerebellar and vestibulocerebellar pathways. Climbing fibers transmit excitation directly to piriform neurons.
The cerebellar cortex contains various glial elements. The granular layer contains fibrous and protoplasmic astrocytes. All layers in the cerebellum contain oligodendrocytes. The granular layer and white matter of the cerebellum are especially rich in these cells. Glial cells with dark nuclei lie in the ganglion layer between pear-shaped neurons. Microglia are found in large quantities in the molecular and ganglionic layers.
^ The subject and tasks of human embryology.
In embryogenesis, 3 sections are distinguished: pre-embryonic, embryonic and early post-embryonic.
Actual tasks of embryology are the study of the influence of various endogenous and exogenous factors of the microenvironment on the development and structure of germ cells, tissues, organs and systems.
^ Medical Embryology.
Medical embryology studies the patterns of development of the human embryo. Particular attention in the course of histology with embryology is drawn to the sources and mechanisms of tissue development, the metabolic and functional features of the mother-placenta-fetus system, which make it possible to establish the causes of deviations from the norm, which is of great importance for medical practice.
Knowledge of human embryology is necessary for all doctors, especially those working in the field of obstetrics. This helps in diagnosing disorders in the mother-fetus system, identifying the causes of deformities and diseases in children after birth.
Currently, knowledge of human embryology is used to uncover and eliminate the causes of infertility, the birth of "test-tube" children, transplantation of fetal organs, the development and use of contraceptives. In particular, the problems of culturing eggs, in vitro fertilization and implantation of embryos in the uterus have become topical.
The process of human embryonic development is the result of a long evolution and to a certain extent reflects the features of the development of other representatives of the animal world. Therefore, some of the early stages of human development are very similar to similar stages in the embryogenesis of lower organized chordates.
Human embryogenesis is a part of its ontogenesis, including the following main stages: I - fertilization, and the formation of a zygote; II - crushing and formation of the blastula (blastocyst); III - gastrulation - the formation of germ layers and a complex of axial organs; IV - histogenesis and organogenesis of germinal and extra-embryonic organs; V - systemogenesis.
Embryogenesis is closely related to progenesis (development and maturation of germ cells) and the early postembryonic period. Thus, the formation of tissues begins in the embryonic period and continues after the birth of a child.
^ Sex cells: the structure and functions of male and female germ cells, the main stages of their development.
The spermatozoon is covered with a cytolemma, which in the anterior section contains a receptor - glycosyltransferase, which ensures recognition of egg receptors.
The spermatozoon head includes a small dense nucleus with a haploid set of chromosomes containing nucleoprotamines and nucleohistones. The anterior half of the nucleus is covered with a flat sac that forms the cap of the spermatozoon. The acrosome is located in it (from the Greek asgop - top, soma - body). The acrosome contains a set of enzymes, among which an important place belongs to hyaluronidase and proteases. The human sperm nucleus contains 23 chromosomes, one of which is sexual (X or Y), the rest are autosomes. The tail section of the spermatozoon consists of an intermediate, main and terminal parts.
The intermediate part contains 2 central and 9 pairs of peripheral microtubules surrounded by a helical mitochondrion. Paired protrusions, or “handles”, consisting of another protein, dynein, depart from the microtubules. Dynein breaks down ATP.
The main part (pars principalis) of the tail resembles a cilium in structure with a characteristic set of microtubules in the axoneme (9 * 2) + 2, surrounded by circularly oriented fibrils that give elasticity, and a plasma membrane.
The terminal, or final, part of the spermatozoon contains single contractile filaments. The movements of the tail are whip-like, which is due to the successive contraction of microtubules from the first to the ninth pair.
In the study of sperm in clinical practice, various forms of spermatozoa are counted in stained smears, counting their percentage (spermogram).
According to the World Health Organization (WHO), the normal characteristics of human sperm are the following: concentration 20-200 million/ml, content more than 60% of normal forms. Along with normal forms, human sperm always contains abnormal ones - biflagellated, with defective head sizes (macro and microforms), with an amorphous head, with fused heads, immature forms (with remnants of the cytoplasm in the neck and tail), with flagellum defects.
Oocytes, or oocytes (from Latin ovum - egg), mature in an immeasurably smaller amount than spermatozoa. In a woman during the sexual cycle B4-28 days), as a rule, one egg matures. Thus, during the childbearing period, about 400 mature eggs are formed.
The release of an oocyte from the ovary is called ovulation. The oocyte that comes out of the ovary is surrounded by a crown of follicular cells, the number of which reaches 3-4 thousand. It is picked up by the fringes of the fallopian tube (oviduct) and moves along it. Here the maturation of the germ cell ends. The egg cell has a spherical shape, a larger cytoplasmic volume than that of a sperm cell, and does not have the ability to move independently.
The classification of eggs is based on the signs of the presence, quantity and distribution of the yolk (lecithos), which is a protein-lipid inclusion in the cytoplasm used to nourish the embryo.
There are yolkless (alecital), low yolk (oligolecital), medium yolk (mesolecithal), multiyolk (polylecital) eggs.
In humans, the presence of a small amount of yolk in the egg is due to the development of the embryo in the mother's body.
Structure. The human egg has a diameter of about 130 microns. Adjacent to the cytolemma is a shiny, or transparent, zone (zona pellucida - Zp) and then a layer of follicular cells. The nucleus of the female germ cell has a haploid set of chromosomes with an X-sex chromosome, a well-defined nucleolus, and there are many pore complexes in the karyolemma. During the period of oocyte growth, intensive processes of mRNA and rRNA synthesis take place in the nucleus.
In the cytoplasm, the protein synthesis apparatus (endoplasmic reticulum, ribosomes) and the Golgi apparatus are developed. The number of mitochondria is moderate, they are located near the yolk nucleus, where there is an intensive synthesis of the yolk, the cell center is absent. The Golgi apparatus in the early stages of development is located near the nucleus, and in the process of maturation of the egg, it shifts to the periphery of the cytoplasm. Here are the derivatives of this complex - cortical granules, the number of which reaches about 4000, and the size is 1 micron. They contain glycosaminoglycans and various enzymes (including proteolytic ones), participate in the cortical reaction, protecting the egg from polyspermy.
The transparent, or shiny, zone (zona pellucida - Zp) consists of glycoproteins and glycosaminoglycans. The shiny zone contains tens of millions of Zp3 glycoprotein molecules, each of which has more than 400 amino acid residues connected to many oligosaccharide branches. Follicular cells take part in the formation of this zone: the processes of follicular cells penetrate through the transparent zone, heading towards the cytolemma of the egg. The cytolemma of the egg has microvilli located between the processes of the follicular cells. Follicular cells perform trophic and protective functions.
The cerebellum is the central organ of 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.
There are 3 layers in the cerebellar cortex: 1) the outer molecular layer contains relatively few cells, but many fibers. It distinguishes between basket and stellate neurons, which are inhibitory. Star-shaped - slow down vertically, basket-shaped - send axons over long distances, which end on the bodies of pear-shaped cells. 2) The middle ganglionic layer is formed by one row of large pear-shaped cells, first described by the Czech scientist Jan Purkinje. The cells have a large body, 2-3 short dendrites extend from the top, which branch in a small layer. 1 axon departs from the base, which goes into the white matter to the cerebellar nuclei. 3) The inner granular layer is characterized by a large number of tightly lying cells. Among the neurons, granule cells, Golgi cells (stellate), and fusiform horizontal neurons are distinguished here. Granule cells are small cells that have short dendrites, the latter forming excitatory synapses with mossy fibers in the cerebellar glamelurs. The granule cells excite the mossy fibers, and the axons go into the molecular layer and transmit information to the piriform cells and all the fibers located there. It is the only excitatory neuron in the cerebellar cortex. Golgi cells lie under the bodies of pear-shaped neurons, axons go to the cerebellar glameruli, and can inhibit impulses from mossy fibers to granule cells.
Afferent pathways enter the cerebellar cortex through 2 types of fibers: 1) liana-shaped (climbing) - they rise from the white matter through the granular and ganglionic layers. They reach the molecular layer, form synapses with the dendrites of pear-shaped cells and excite them. 2) Bryophytes - from the white matter they enter the granular layer. Here they form synapses with the dendrites of granular cells, and the axons of granular cells go into the molecular layer, forming synapses with the dendrites of pear-shaped neurons, which form inhibitory nuclei.
The cerebral cortex. Development, neural composition and layered organization. The concept of cyto- and myeloarchitectonics. Blood-brain barrier. Structural and functional unit of the cortex.
The cerebral cortex is the highest and most complexly organized nerve center of the screen type, whose activity ensures the regulation of various body functions and complex forms of behavior. The cortex is made up of a layer of gray matter. Gray matter contains nerve cells, nerve fibers, and neuroglial cells.
Among the multipolar neurons of the cortex, pyramidal, stellate, fusiform, arachnid, horizontal, "candelabra" cells, cells with a double bouquet of dendrites, and some other types of neurons are distinguished.
Pyramidal neurons constitute the main and most specific form for the cortex of the hemispheres. They have an elongated cone-shaped body, the apex of which faces the surface of the cortex. Dendrites extend from the apex and lateral surfaces of the body. Axons originate from the base of the pyramidal cells.
Pyramidal cells of different layers of the cortex differ in size and have different functional significance. Small cells are intercalary neurons. The axons of the large pyramids take part in the formation of motor pyramidal pathways.
The neurons of the cortex are located in unsharply demarcated layers, which are designated by Roman numerals and numbered from outside to inside. Each layer is characterized by the predominance of any one type of cell. There are six main layers in the cerebral cortex:
I - The molecular layer of the cortex contains a small number of small associative horizontal Cajal cells. Their axons run parallel to the surface of the brain as part of the tangential plexus of nerve fibers of the molecular layer. However, the bulk of the fibers of this plexus is represented by branching of the dendrites of the underlying layers.
II - The outer granular layer is formed by numerous small pyramidal and stellate neurons. The dendrites of these cells rise into the molecular layer, and the axons either go into the white matter, or, forming arcs, also enter the tangential plexus of fibers of the molecular layer.
III - The widest layer of the cerebral cortex is pyramidal. It contains pyramidal neurons, and spindle cells. The apical dendrites of the pyramids go into the molecular layer, the lateral dendrites form synapses with adjacent cells of this layer. The axon of the pyramidal cell always departs from its base. In small cells, it remains within the cortex; in large cells, it forms a myelin fiber that goes to the white matter of the brain. Axons of small polygonal cells are sent to the molecular layer. The pyramidal layer performs mainly associative functions.
IV - The inner granular layer in some areas of the cortex is very strongly developed (for example, in the visual and auditory cortex), while in others it may be almost absent (for example, in the precentral gyrus). This layer is formed by small stellate neurons. It consists of a large number of horizontal fibers.
V - The ganglionic layer of the cortex is formed by large pyramids, and the region of the motor cortex (precentral gyrus) contains giant pyramids, which were first described by the Kyiv anatomist V. A. Bets. The apical dendrites of the pyramids reach the 1st layer. The axons of the pyramids are projected to the motor nuclei of the brain and spinal cord. The longest axons of Betz cells in the pyramidal pathways reach the caudal segments of the spinal cord.
VI - The layer of polymorphic cells is formed by neurons of various shapes (fusiform, stellate). The axons of these cells go into the white matter as part of the efferent pathways, and the dendrites reach the molecular layer.
Cytoarchitectonics - features of the location of neurons in different parts of the cerebral cortex.
Among the nerve fibers of the cerebral cortex, one can single out associative fibers that connect individual parts of the cortex of one hemisphere, commissural fibers that connect 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.
autonomic nervous system. General structural characteristics and main functions. The structure of sympathetic and parasympathetic reflex arcs. Differences between vegetative reflex arcs and somatic ones.
It is a system of tissues and organs built from nervous tissue. It highlights:
Central region: brain and spinal cord
Peripheral: autonomic and sensory ganglia, peripheral nerves, nerve endings.
There is also a division into:
Somatic (animal, cerebrospinal) department;
Vegetative (autonomous) department: sympathetic and parasympathetic parts.
The nervous system is formed by the following embryonic sources: neural tube, neural crest (ganglion plate) and embryonic placodes. The tissue elements of the membranes are mesenchymal derivatives. At the stage of neuropore closure, the anterior end of the tube expands significantly, the side walls thicken, forming the beginnings of three cerebral vesicles. The bladder lying cranially forms the forebrain, the middle bladder forms the midbrain, and the posterior (rhomboid) brain develops from the third bladder, which passes into the anlage of the spinal cord. Soon after this, the neural tube bends almost at a right angle, and through the narrowing furrows, the first bladder is divided into the final and intermediate sections, and the third cerebral bladder into the medulla oblongata and posterior sections of the brain. Derivatives of the middle and posterior cerebral vesicles form the brainstem and are ancient formations; they retain the segmental principle of structure, which disappears in the derivatives of the diencephalon and telencephalon. In the latter, integrative functions are concentrated. This is how five parts of the brain are formed: the final and diencephalon, middle, medulla oblongata and hindbrain (in humans, this occurs approximately at the end of the 4th week of embryonic development). The telencephalon forms the two hemispheres of the cerebrum.
In the embryonic histo- and organogenesis of the nervous system, the development of different parts of the brain occurs at different rates (heterochronously). Earlier, the caudal parts of the central nervous system (spinal cord, brain stem) are formed; the time of the final formation of brain structures varies greatly. In a number of parts of the brain, this occurs after birth (cerebellum, hippocampus, olfactory bulb); in each part of the brain there are spatio-temporal gradients in the formation of neuronal populations that form a unique structure of the nerve center.
The spinal cord is a part of the central nervous system, in the structure of which the features of the embryonic stages of development of the brain of vertebrates are most clearly preserved: the tubular nature of the structure and segmentation. In the lateral sections of the neural tube, the mass of cells rapidly increases, while its dorsal and ventral parts do not increase in volume and retain their ependymal character. The thickened lateral walls of the neural tube are divided by a longitudinal groove into the dorsal - alar, and ventral - the main plate. At this stage of development, three zones can be distinguished in the lateral walls of the neural tube: ependyma lining the central canal, intermediate (cloak layer) and marginal (marginal veil). The gray matter of the spinal cord subsequently develops from the mantle layer, and its white matter develops from the marginal veil. The neuroblasts of the anterior columns differentiate into motor neurons (motor neurons) of the nuclei of the anterior horns. Their axons exit the spinal cord and form the anterior roots of the spinal nerves. In the posterior columns and the intermediate zone, various nuclei of intercalary (associative) cells develop. Their axons, entering the white matter of the spinal cord, are part of various conducting bundles. The posterior horns include the central processes of the sensory neurons of the spinal nodes.
Simultaneously with the development of the spinal cord, the spinal and peripheral nodes of the autonomic nervous system are laid. The starting material for them is the stem cell elements of the neural crest, which, through divergent differentiation, develop in the neuroblastic and glioblastic directions. Part of the neural crest cells migrate to the periphery to the localization sites of the nodes of the autonomic nervous system, paraganglia, neuroendocrine cells of the APUD series, and chromaffin tissue.
Peripheral nervous system.
The peripheral nervous system combines peripheral nerve nodes, trunks and endings.
Nerve ganglia (nodes) - structures formed by clusters of neurons outside the central nervous system - are divided into sensitive and autonomous (vegetative). Sensory ganglia contain pseudo-unipolar or bipolar (in the spiral and vestibular ganglia) afferent neurons and are located mainly along the posterior roots of the spinal cord (sensory nodes of the spinal nerves) and some cranial nerves. The sensory ganglia of the spinal nerves are fusiform and covered with a capsule of dense fibrous connective tissue. On the periphery of the ganglion there are dense clusters of bodies of pseudo-unipolar neurons, and the central part is occupied by their processes and thin layers of endoneurium located between them, carrying vessels. Autonomic nerve ganglia are formed by clusters of multipolar neurons, on which numerous synapses form preganglionic fibers - processes of neurons whose bodies lie in the CNS.
Nerve. Building and regeneration. Spinal ganglia. Morphofunctional characteristics.
Nerves (nerve trunks) connect the nerve centers of the brain and spinal cord with receptors and working organs. They are formed by bundles of myelinated and non-myelinated fibers, which are united by connective tissue components (shells): endoneurium, perineurium and epineurium. Most of the nerves are mixed, i.e. include afferent and efferent fibers.
Endoneurium - thin layers of loose fibrous connective tissue with small blood vessels, surrounding individual nerve fibers and linking them into a single bundle. The perineurium is a sheath that covers each bundle of nerve fibers from the outside and extends the partitions deep into the bundle. It has a lamellar structure and images in concentric layers of flattened fibroblast-like cells connected by dense and gap joints. Between the layers of cells in the spaces filled with liquid, there are components of the basement membrane and longitudinally oriented collagen fibers. Epineurium is the outer sheath of the nerve that binds bundles of nerve fibers together. It consists of dense fibrous connective tissue containing fat cells, blood and lymph vessels.
Spinal cord. Morphofunctional characteristics. Development. Structure of gray and white matter. neural composition.
The spinal cord consists of two symmetrical halves, delimited from each other in front by a deep median fissure, and behind by a connective tissue septum. The inner part of the organ is darker - this is its gray matter. On the periphery of the spinal cord is a lighter white matter. The gray matter of the spinal cord consists of neuron bodies, non-myelinated and thin myelinated fibers, and neuroglia. The main component of gray matter, which distinguishes it from white, are multipolar neurons. The protrusions of the gray matter are called horns. There are anterior, or ventral, posterior, or dorsal, and lateral, or lateral, horns. During the development of the spinal cord, neurons are formed from the neural tube, grouped in 10 layers, or in plates. Characteristic of a person
the following architectonics of the indicated plates: plates I-V correspond to the posterior horns, plates VI-VII - to the intermediate zone, plates VIII-IX - to the anterior horns, plate X - to the zone of the near-central canal. The gray matter of the brain consists of three types of multipolar neurons. The first type of neurons is phylogenetically older and is characterized by a few long, straight and weakly branching dendrites (isodendritic type). The second type of neurons has a large number of strongly branching dendrites that intertwine, forming "tangles" (idiodendritic type). The third type of neurons, in terms of the degree of development of dendrites, occupies an intermediate position between the first and second types. The white matter of the spinal cord is a collection of longitudinally oriented predominantly myelinated fibers. The bundles of nerve fibers that communicate between different parts of the nervous system are called the pathways of the spinal cord.
Brain. Sources of development. General morphofunctional characteristics of the cerebral hemispheres. Neuronal organization of the cerebral hemispheres. Cyto- and myeloarchitectonics of the cerebral cortex. Age-related changes in the cortex.
In the brain, gray and white matter are distinguished, but the distribution of these two components is much more complicated here than in the spinal cord. Most of the gray matter of the brain is located on the surface of the cerebrum and in the cerebellum, forming their cortex. A smaller part forms numerous nuclei of the brain stem.
Structure. The cerebral cortex is represented by a layer of gray matter. It is most strongly developed in the anterior central gyrus. The abundance of furrows and convolutions significantly increases the area of the gray matter of the brain .. Its various parts, which differ from each other in some features of the location and structure of cells (cytoarchitectonics), the location of fibers (myeloarchitectonics) and functional significance, are called fields. They are places of higher analysis and synthesis of nerve impulses. sharply defined
there are no boundaries between them. The cortex is characterized by the arrangement of cells and fibers in layers. The development of the human cerebral cortex (neocortex) in embryogenesis occurs from the ventricular germinal zone of the telencephalon, where poorly specialized proliferating cells are located. Neocortical neurocytes differentiate from these cells. In this case, the cells lose their ability to divide and migrate to the emerging cortical plate. First, the neurocytes of future layers I and VI enter the cortical plate, i.e. the most superficial and deep layers of the cortex. Then neurons of layers V, IV, III and II are built into it in the direction from the inside and outwards. This process is carried out due to the formation of cells in small areas of the ventricular zone at different periods of embryogenesis (heterochronous). In each of these areas, groups of neurons are formed, sequentially lining up along one or more fibers.
radial glia in the form of a column.
Cytoarchitectonics of the cerebral cortex. Multipolar neurons of the cortex are very diverse in shape. Among them are pyramidal, stellate, fusiform, arachnid and horizontal neurons. The neurons of the cortex are located in unsharply demarcated layers. Each layer is characterized by the predominance of any one type of cell. In the motor zone of the cortex, 6 main layers are distinguished: I - molecular, II - external granular, III - nuramid neurons, IV - internal granular, V - ganglionic, VI - layer of polymorphic cells. The molecular layer of the cortex contains a small number of small spindle-shaped associative cells. Their neurites run parallel to the surface of the brain as part of the tangential plexus of the nerve fibers of the molecular layer. The outer granular layer is formed by small neurons that have a rounded, angular and pyramidal shape, and stellate neurocytes. The dendrites of these cells rise into the molecular layer. Neurites either go into the white matter, or, forming arcs, also enter the tangential plexus of fibers of the molecular layer. The widest layer of the cerebral cortex is the pyramidal. From the top of the pyramidal cell, the main dendrite departs, which is located in the molecular layer. The neurite of the pyramidal cell always departs from its base. The inner granular layer is formed by small stellate neurons. It consists of a large number of horizontal fibers. The ganglionic layer of the cortex is formed by large pyramids, and the region of the precentral gyrus contains giant pyramids.
The layer of polymorphic cells is formed by neurons of various shapes.
Myeloarchitectonics of the cortex. Among the nerve fibers of the cerebral cortex, one can single out associative fibers that connect individual parts of the cortex of one hemisphere, commissural fibers that connect 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.
Age changes. At the 1st year of life, typification of the shape of pyramidal and stellate neurons, their increase, the development of dendritic and axon arborizations, and intraensemble connections along the vertical are observed. By the age of 3, “nested” groups of neurons, more clearly formed vertical dendritic bundles and bundles of radiant fibers are revealed in the ensembles. By the age of 5-6, neuronal polymorphism increases; the system of intra-ensemble connections along the horizontal becomes more complicated due to the growth in length and branching of the lateral and basal dendrites of pyramidal neurons and the development of the lateral terminals of their apical dendrites. By the age of 9-10, cell groups increase, the structure of short-axon neurons becomes much more complicated, and the network of axon collaterals of all forms of interneurons expands. By the age of 12-14, specialized forms of pyramidal neurons are clearly marked in ensembles; all types of interneurons reach a high level of differentiation. By the age of 18, the ensemble organization of the cortex, in terms of the main parameters of its architectonics, reaches the level of that in adults.
Cerebellum. Structure and morphofunctional characteristics. Neuronal composition of the cerebellar cortex, gliocytes. Interneuron connections.
Cerebellum. It is the central organ of balance and coordination of movements. It is connected to the brainstem by afferent and efferent conducting bundles, which together form three pairs of cerebellar peduncles. There are many convolutions and grooves on the surface of the cerebellum, which significantly increase its area. Furrows and convolutions are created on the cut
characteristic for the cerebellum picture of the "tree of life". 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 central nuclei. In the center of each gyrus there is a thin layer
white matter, covered with a layer of gray matter - the bark. Three layers are distinguished in the cerebellar cortex: the outer one is the molecular layer, the middle one is the ganglionic layer, or the layer of pear-shaped neurons, and the inner one is granular. The ganglionic layer contains pear-shaped neurons. They have neurites, which, leaving the cerebellar cortex, form the initial link of its efferent
brake paths. From the pear-shaped body, 2-3 dendrites extend into the molecular layer, which penetrate the entire thickness of the molecular layer. From the base of the bodies of these cells, neurites depart, passing through the granular layer of the cerebellar cortex into the white matter and ending on the cells of the cerebellar nuclei. The molecular layer contains two main types of neurons: basket and stellate. Basket neurons are located in the lower third of the molecular layer. Their thin long dendrites branch mainly in a plane located transversely to the gyrus. The long neurites of the cells always run across the gyrus and parallel to the surface above the pear-shaped neurons. The stellate neurons lie above the basket cells and are of two types. Small stellate neurons are equipped with thin short dendrites and weakly branched neurites that form synapses. Large stellate neurons have long and highly branched dendrites and neurites. grainy layer. The first type of cells in this layer can be considered granular neurons, or granule cells. The cell has 3-4 short dendrites,
ending in the same layer with terminal branches in the form of a bird's paw. The neurites of the granule cells pass into the molecular layer and in it are divided into two branches, oriented parallel to the surface of the cortex along the gyri of the cerebellum. The second type of cells in the granular layer of the cerebellum are inhibitory large stellate neurons. There are two types of such cells: with short and long neurites. Neurons with short neurites lie near the ganglionic layer. Their branched dendrites spread in the molecular layer and form synapses with parallel fibers - axons of granule cells. Neurites are sent to the granular layer to the glomeruli of the cerebellum and end in synapses at the terminal branches of the dendrites of the granule cells.
A few stellate neurons with long neurites have dendrites and neurites abundantly branching in the granular layer, extending into the white matter. The third type of cells are spindle-shaped horizontal cells. They have a small elongated body, from which long horizontal dendrites extend in both directions, ending in the ganglionic and granular layers. The neurites of these cells give collaterals to the granular layer and go to
white matter. Gliocytes. The cerebellar cortex contains various glial elements. The granular layer contains fibrous and protoplasmic astrocytes. The peduncles of fibrous astrocyte processes form perivascular membranes. All layers in the cerebellum contain oligodendrocytes. The granular layer and white matter of the cerebellum are especially rich in these cells. Glial cells with dark nuclei lie in the ganglion layer between pear-shaped neurons. The processes of these cells are sent to the surface of the cortex and form glial fibers of the molecular layer of the cerebellum. Interneuronal connections. Afferent fibers entering the cerebellar cortex are represented by two types - mossy and so-called climbing fibers. Mossy fibers go as part of the olive-cerebellar and cerebellopontine tracts and indirectly through the granule cells have an exciting effect on the pear-shaped cells.
Climbing fibers enter the cerebellar cortex, apparently, along the dorsal-cerebellar and vestibulocerebellar pathways. They cross the granular layer, adjoin pear-shaped neurons and spread along their dendrites, ending on their surface with synapses. Climbing fibers transmit excitation directly to piriform neurons.
Autonomic (vegetative) nervous system. General morphofunctional characteristics. Departments. Structure of extramural and intramural ganglia.
The ANS is divided into sympathetic and parasympathetic. Both systems simultaneously take part in the innervation of organs and have the opposite effect on them. It consists of the central sections, represented by the nuclei of the gray matter of the brain and spinal cord, and the peripheral ones: nerve trunks, nodes (ganglia) and plexuses.
Due to their high autonomy, the complexity of organization, and the characteristics of mediator metabolism, the intramural ganglia and the pathways associated with them are distinguished into an independent metasympathetic department of the autonomous NS. There are three types of neurons:
Long-axon efferent neurons (Dogel type I cells) with short dendrites and a long axon extending beyond the node to the cells of the working organ, on which it forms motor or secretory endings.
Equally outgrowth afferent neurons (type II Dogel cells) contain long dendrites and an axon that extends beyond this ganglion into neighboring ones and forms synapses on type I and III cells. They are part of the local reflex arcs as a receptor link, which are closed without a nerve impulse entering the central nervous system.
Associative cells (type III Dogel cells) are local intercalary neurons that connect several cells of types I and II with their processes. The dendrites of these cells do not go beyond the node, and the axons go to other nodes, forming synapses on type I cells.
The spinal cord is the most ancient formation of the central nervous system; it first appears in the lancelet
A characteristic feature of the organization of the spinal cord is the periodicity of its structure in the form of segments with inputs in the form of posterior roots, a cell mass of neurons (gray matter) and outputs in the form of anterior roots.
The human spinal cord has 31-33 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1-3 coccygeal.
Morphological boundaries between segments of the spinal cord do not exist. Each segment innervates three metameres of the body through its roots and also receives information from three metameres of the body. As a result, each metamere of the body is innervated by three segments and transmits signals to three segments of the spinal cord.
The posterior roots are afferent, sensory, centripetal, and the anterior roots are efferent, motor, centrifugal (Bell-Magendie law).
Afferent inputs to the spinal cord are organized by the axons of the spinal ganglia, which lie outside the spinal cord, and by the axons of the sympathetic and parasympathetic divisions of the autonomic nervous system.
The first group of afferent inputs of the spinal cord is formed by sensory fibers coming from muscle receptors, tendon receptors, periosteum, and joint membranes. This group of receptors forms the beginning of the so-called proprioceptive sensitivity.
The second group of afferent inputs of the spinal cord starts from skin receptors: pain, temperature, tactile, pressure.
The third group of afferent inputs of the spinal cord is represented by fibers from visceral organs, this is the viscero-receptive system.
Efferent (motor) neurons are located in the anterior horns of the spinal cord, and their fibers innervate the entire skeletal muscles.
Features of the neural organization of the spinal cord
The neurons of the spinal cord form its gray matter in the form of symmetrically located two anterior and two posterior horns. the nuclei, elongated along the length of the spinal cord, and on the transverse section are located in the shape of the letter H. In the thoracic region, the spinal cord has, in addition to those mentioned, also lateral horns.
The posterior horns perform mainly sensory functions; signals are transmitted from them to the overlying centers, to the structures of the opposite side, or to the anterior horns of the spinal cord.
In the anterior horns are neurons that give their axons to the muscles. All descending pathways of the central nervous system that cause motor responses end at the neurons of the anterior horns. In this regard, Sherrington called them "the common final path".
In the lateral horns, starting from the 1st thoracic segment of the spinal cord and up to the first lumbar segments, there are neurons of the sympathetic, and in the sacral - of the parasympathetic division of the autonomic nervous system.
The human spinal cord contains about 13 million neurons, of which 3% are motor neurons, and 97% are intercalary. Functionally, spinal cord neurons can be divided into 4 main groups:
1) motor neurons, or motor, - cells of the anterior horns, the axons of which form the anterior roots;
2) interneurons - neurons that receive information from the spinal ganglia and are located in the posterior horns. These neurons respond to pain, temperature, tactile, vibrational, proprioceptive stimuli;
3) sympathetic, parasympathetic neurons are located mainly in the lateral horns. The axons of these neurons exit the spinal cord as part of the anterior roots;
4) associative cells - neurons of the spinal cord's own apparatus, establishing connections within and between segments.
In the middle zone of the gray matter (between the posterior and anterior horns) of the spinal cord there is an intermediate nucleus (Cajal nucleus) with cells whose axons go up or down by 1-2 segments and give collaterals to the neurons of the ipsi- and contralateral side, forming a network. There is a similar network at the top of the posterior horn of the spinal cord - this network forms the so-called gelatinous substance (Roland's gelatinous substance) and performs the functions of the reticular formation of the spinal cord. , between the cells of its anterior and posterior horns.
Motoneurons. The axon of a motor neuron innervates hundreds of muscle fibers with its terminals, forming a motor neuron unit. Several motor neurons can innervate one muscle, in which case they form the so-called motor neuron pool. The excitability of motor neurons is different, therefore, with different intensity of irritation, a different number of fibers of one muscle is involved in contraction. With the optimal strength of irritation, all fibers of this muscle are reduced; in this case, the maximum contraction develops. Motor neurons can generate impulses with a frequency of up to 200 per second.
Interneurons. These intermediate neurons, generating impulses with a frequency of up to 1000 per second, are background-active and have up to 500 synapses on their dendrites. The function of interneurons is to organize connections between the structures of the spinal cord and ensure the influence of ascending and descending pathways on the cells of individual segments of the spinal cord. A very important function of interneurons is the inhibition of neuron activity, which ensures the preservation of the direction of the excitation pathway. Excitation of interneurons associated with motor cells has an inhibitory effect on antagonist muscles.
The neurons of the sympathetic division of the autonomic nervous system are located in the lateral horns of the thoracic spinal cord, have a rare impulse frequency (3-5 per second), parasympathetic neurons are localized in the sacral spinal cord.
With irritation or lesions of the posterior roots, girdle pains are observed at the level of the metamer of the affected segment, sensitivity decreases, reflexes disappear or weaken. If an isolated lesion of the posterior horn occurs, pain and temperature sensitivity on the side of the injury is lost, while tactile and proprioceptive sensations are preserved, since axons of temperature and pain sensitivity go from the posterior root to the posterior horn, and axons of tactile and proprioceptive - directly to the posterior column and along the conductive paths rise up.
The defeat of the anterior horn and the anterior root of the spinal cord leads to paralysis of the muscles, which lose their tone, atrophy, and the reflexes associated with the affected segment disappear.
The defeat of the lateral horns of the spinal cord is accompanied by the disappearance of skin vascular reflexes, impaired sweating, trophic changes in the skin and nails. Bilateral damage to the parasympathetic department at the level of the sacrum leads to impaired defecation and urination.
