Source of development of the spinal nodes. Embryology of the organs of the nervous system

Private histology.

1. Spinal nodes has a spindle shape and is covered with a capsule of dense fibrous connective tissue. On its periphery there are dense accumulations of the bodies of pseudounipolar neurons, and the central part is occupied by their processes and thin layers of egdoneurium located between them, carrying vessels.

Pseudounipolar neurons characterized by a spherical body and a light nucleus with a clearly visible nucleolus. I single out large and small cells, which probably differ in the types of impulses carried out. The cytoplasm of neurons contains numerous mitochondria, GREP cisterns, elements of the Golgi complex, and lysosomes. The neurons of the spinal nodes contain neurotransmitters such as acetylcholine, glutamic acid, selfstatin, cholecystokinin, gastrin.
2. Dorsal brain located in the spinal canal and has the form of a rounded cord, expanded in the cervical and lumbar regions and penetrated by the central canal. It consists of two symmetrical halves, separated anteriorly by a median fissure and posteriorly by a median sulcus, and is characterized by a segmental structure.

Gray substance on a transverse section it looks like a butterfly and includes paired anterior, posterior and lateral horns. The gray horns of both symmetrical parts of the spinal cord are connected to each other in the region of the central gray commissure (commissure). In the gray part there are bodies, dendrites and partially axon neurons, as well as glial cells. Between the bodies of neurons there is a neuropil network formed by nerve fibers and processes of glial cells.

white matter the spinal cord is surrounded by gray and is divided by the anterior and posterior roots into symmetrical dorsal, lateral and ventral cords. It consists of longitudinally running nerve fibers that form descending and ascending pathways.
3. Bark hemispheres big brain represents 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.

Cytoarchitectonics bark big brain. Multipolar neurons of the cortex are very diverse in form. Among them are pyramidal, stellate, fusiform, arachnid and horizontal neurons. pyramidal neurons make up the main and most specific form for the cerebral cortex. Their sizes vary from 10 to 140 microns. They have an elongated triangular body, the apex of which faces the surface of the cortex. 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: 1. Molecular 2. External granular 3. Pyramidal neurons 4. Internal granular 5. Ganglionic 6. Layer of polymorphic cells.

Modular organization of the cortex. Repeating blocks of neurons have been described in the cerebral cortex. They have the form of cylinders or columns, with a diameter of 200-300 microns. passing vertically through the entire thickness of the cortex. The column includes: 1. Afferent pathways 2. System of local connections - a) axo-axon cells b) "candelabra" cells c) basket cells d) cells with a double bouquet of dendrites f) cells with an axon bundle 3. Efferent pathways

Hemato- brain barrier includes: a) endothelium of blood capillaries b) basement membrane c) perivascular limiting glial membrane
4. Cerebellum located above the medulla oblongata and the pons and is a center of balance, maintaining muscle tone, coordination of movements and control of complex and automatically performed motor acts. It is formed by two hemispheres with a large number of grooves and convolutions on the surface and a narrow middle part and is connected to other parts of the brain by three pairs of legs.

bark cerebellum is a nerve center of the screen type and is characterized by a highly ordered arrangement of neurons, nerve fibers and glial cells. It distinguishes three layers: 1. molecular containing a relatively small number of small cells. 2. ganglionic formed by one row of bodies of large pear-shaped cells. 3. granular with a large number of well-lying cells.
5. Organs feelings provide information about the state and changes in the external environment and the activities of the systems of the organism itself. They form the peripheral sections of the analyzers, which also include intermediate sections and central sections.

Organs smell. The olfactory analyzer is represented by two systems - the main and vomeronasal, each of which has three parts: peripheral, intermediate, and central. The main olfactory organ, which is the peripheral part of the sensory system, is represented by a limited area of ​​​​the nasal mucosa, the olfactory region, which covers the upper and partly the middle shells of the nasal cavity in humans, as well as the upper septa.

Structure. The main olfactory organ, the peripheral part of the olfactory analyzer, consists of a layer of multi-row epithelium 90 μm high, in which olfactory neurosensory cells, supporting and basal epitheliocytes are distinguished. The vomeronasal organ consists of receptor and respiratory parts. The receptor part of the structure is similar to the olfactory epithelium of the main olfactory organ. The main difference is that the olfactory clubs of the receptor cells of the vomeronasal organ bear on their surface not cilia capable of active movement, but motionless microvilli.
6. Organs vision The eye consists of an eyeball containing photoreceptor (neurosensory) cells and an auxiliary apparatus, which includes the eyelids, lacrimal apparatus and oculomotor muscles.

Stenko eye apples It is formed by three shells 1 outer fibrous (consists of the sclera and cornea), 2 middle vascular (include own choroid, ciliary body and iris) and 3 inner - reticulate, connected to the brain by the optic nerve.

1 Fibrous sheath- external, consists of a sclera of a dense opaque shell covering the posterior 5/6 surfaces of the eyeball, the cornea is a transparent anterior section covering the anterior 1/6.

2 Choroid includes the choroid itself, the ciliary body and the iris. The choroid proper nourishes the retina, it consists of loose fibrous connective tissue with a high content of pigment cells. It consists of four plates. 1. supravascular- external, lies on the border with the sclera 2 vascular- contains arteries and veins providing blood supply to the choriocapillary plate 3. choriocapillary- flattened dense network of capillaries of uneven caliber 4. basel- includes the basement membrane of the capillaries.

b) cranial ciliary body- a thickened anterior portion of the choroid, which looks like a muscular-fibrous ring located between the dentate line and the root of the iris.

3. Mesh shell-
7. Sclera- formed by a dense fibrous connective tissue consisting of flattened bundles of collagen fibers.

Cornea-convex outwards transparent plate, thickening from the center to the periphery. includes five layers: anterior and posterior epithelium, stroma, anterior and posterior border

iris-the most anterior part of the choroid separating the anterior and posterior chambers of the eye. The basis is formed by loose connective tissue with a large number of vessels and cells

lens- a transparent biconvex body, which is held by the fibers of the ciliary girdle.

ciliary body- a thickened anterior portion of the choroid, in the form of a muscular-fibrous ring located between the dentate line and the root of the iris.

vitreous body- transparent jelly-like mass, which some authors consider as a special connective tissue.
8. Mesh shell- inner light-sensitive membrane of the eye. It is subdivided into the visual part lining the inside of the back, most of the eyeball to the dentate line. and the anterior blind part covering the ciliary body and the posterior surface of the iris.

Neurons retina form a three-membered chain of radially located cells connected to each other by synapses: 1) neurosensory 2) bipolar 3) ganglionic.

rod neurosensory cells- with narrow, elongated peripheral processes. The outer segment of the process is cylindrical and contains a stack of 1000-1500 membrane discs. The membranes of the disks contain the visual pigment rhodopsin, which includes protein and vitamin A aldehyde.

cone neurosensory cells similar in structure to rods. The outer segments of their peripheral process are conical in shape and contain membranous discs formed by folds of the plasmolemma. The structure of the inner segment of the cones is similar to that of the rods, the nucleus is larger and lighter than that of the rod cells, the central process ends in the outer reticular layer with a triangular extension.
9. Organ equilibrium will include specialized receptor zones in the sac, uterus and ampullae of the semicircular canals.

Pouch And matochka contain spots (macula) - areas in which the single-layer squamous epithelium of the membranous labyrinth is replaced prismatically. The macula includes 7.5-9 thousand sensory epithelial cells connected by complexes of compounds with supporting cells and covered with an otolithic membrane. The macula of the uterus is horizontal and the macula of the sac is vertical.

sensory- epithelial cells contain numerous mitochondria, developed aER and a large Golgi complex, one eccentrically lying cilium and 40-80 rigid stereocilia of various lengths are located on the apical pole.

Ampoules of the semicircular canals form protrusions-ampullary scallops, located in a plane perpendicular to the axis of the canal. The scallops are lined with prismatic epithelium containing cells of the same types as the macula.

ampoule scallops perceive angular accelerations: when the body rotates, an endolymph current occurs, which deflects the dome, which stimulates the hair cells due to the bending of the stereocilia.

Functions of the organ of balance consists in the perception of gravity, linear and globular accelerations, which are converted into nerve signals transmitted to the central nervous system, which coordinates the work of the muscles, which allows you to maintain balance and navigate in space.

Ampullary scallops perceive angular accelerations; when the body rotates, an endolymph current occurs, which deflects the bath, which stimulates the hair cells due to the bending of the stereocilia.
10. Organ hearing located along the entire length of the cochlear canal.

cochlear canal The membranous labyrinth is filled with endolymph and is surrounded by two canals containing perilymph, the scala tympani and the vestibular scala. Together with both ladders, it is enclosed in a bone cochlea, which forms 2.5 turns around the central bone rod (cochlear axis). The channel has a triangular formula on the section, and its outer wall, formed by the vascular strip, fuses with the wall of the bone cochlea. It is separated from the vestibular ladder lying above it. vestibular membrane, and from the scala tympani below it, the basilar plate.

spiral organ formed by receptor sensory epithelial cells and a variety of supporting cells: a) Sensory epithelial cells are associated with afferent and efferent nerve endings and are divided into two types: 1) internal hair cells are large, pear-shaped, located in one row and completely on all sides surrounded by inner flank cells. 2) outer hair cells are prismatic in shape, lie in cup-shaped depressions of the outer flank cells. They are located in 3-5 rows and come into contact with supporting cells only in the area of ​​the basal and apical surfaces.
11. Organ taste the peripheral part of the taste analyzer is represented by receptor epithelial cells in the taste buds. They perceive taste (food and non-food) irritations, generate and transmit receptor potential to afferent nerve endings in which nerve impulses appear. Information enters the subcortical and cortical centers.

Development. The source of development of taste bud cells is the embryonic stratified epithelium of the papillae. It undergoes differentiation under the inducing influence of the endings of the nerve fibers of the lingual, glossopharyngeal and vagus nerves.

Structure. Each taste bud has an ellipsoid shape and occupies the entire thickness of the multilayered epithelial layer of the papilla. It consists of dense 40-60 cells adjacent to each other, among which there are 5 types of sensory epithelial cells ("light" narrow and "light" cylindrical), "dark" supporting , basal young-differentiated and peripheral (perihemmal).
12. arteries subdivided on three type 1. elastic 2. muscular and 3. mixed.

arteries elastic type characterized by a large lumen and a relatively thin wall (10% of diameter) with a strong development of elastic elements. These include the largest vessels, the aorta and the pulmonary artery, in which blood moves at high speed and under high pressure.

Muscular type arteries distribute blood to organs and tissues and make up the majority of the arteries of the body; their wall contains a significant number of smooth muscle cells, which, by contracting, regulate blood flow. In these arteries, the wall is relatively thick compared to the lumen and has the following features

1) Intima thin, consists of endothelium, subendothelial word (well expressed only in large arteries), fenestrated internal elastic membrane.

2) middle sheath- the thickest; contains circularly arranged smooth muscle cells lying in layers (10-60 layers in large arteries and 3-4 in small ones)

3) Adventitia formed outer elastic membrane (absent in small arteries) and loose fibrous tissue containing elastic fibers.

Arteries muscular- elastic type located between the arteries of the elastic and muscular types and have signs of both. Both elastic and muscle elements are well represented in their wall
13. TO microcirculatory channel vessels with a diameter of less than 100 microns, which are visible only under a microscope. They play a major role in providing trophic, respiratory, excretory, regulatory functions of the vascular system, the development of inflammatory and immune reactions.

Links microcirculatory channels

1) arterial, 2) capillary and 3) venous.

The arterial link includes arterioles and precapillaries.

A) arterioles- microvessels with a diameter of 50-100 microns; their wall consists of three shells, each with one layer of cells

b) precapillaries(precapillary arterioles, or metarterios) - microvessels with a diameter of 14-16 microns extending from arterioles, in the wall of which elastic elements are completely absent

Capillary link represented by capillary networks, the total length of which in the body exceeds 100 thousand km. The diameter of the capillaries ranges from 3-12 microns. The lining of the capillaries is formed by the endothelium, in the cleavages of its basement membrane, special process cells-pericytes are revealed, which have numerous gap junctions with endotheliocytes.

Venous link includes postcapillaries, collecting and muscle venules: a) postcapillaries - vessels with a diameter of 12-30 microns, formed as a result of the fusion of several capillaries. b) collecting venules with a diameter of 30-50 microns are formed as a result of the fusion of postcapillary venules. When they reach a diameter of 50 µm, smooth muscle cells appear in their wall. c) Muscle venules are characterized by a well-developed middle membrane, in which smooth muscle cells lie in one row.
14. Arterioles these are the smallest arterial vessels of the muscular type with a diameter of no more than 50-100 microns, which, on the one hand, are connected with the arteries, and on the other hand, gradually pass into the capillaries. Three membranes are preserved in arterioles: The inner membrane of these vessels consists of endothelial cells with a basement membrane, a thin subendothelial layer, and a thin internal elastic membrane. The middle shell is formed by 1-2 layers of smooth muscle cells with a spiral direction. The outer shell is represented by loose fibrous connective tissue.

Venules- there are three types of venules: post-capillary, collecting and muscular: a) post-capillaries - vessels with a diameter of 12-30 microns, formed as a result of the fusion of several capillaries. b) collecting venules with a diameter of 30-50 microns are formed as a result of the fusion of postcapillary venules. When they reach a diameter of 50 µm, smooth muscle cells appear in their wall. c) Muscle venules are characterized by a well-developed middle membrane, in which smooth muscle cells lie in one row.
15. Vienna a large circle of blood circulation carry out the outflow of blood from the organs, participate in the exchange and depositing functions. There are superficial and deep veins, the latter accompanying the arteries in double quantity. The outflow of blood begins through postcapillary venules. low blood pressure and low blood flow velocity determine the relatively weak development of elastic elements in the veins and their greater extensibility.

Topic 18. NERVOUS SYSTEM

WITH anatomical point of view The nervous system is divided into central (brain and spinal cord) and peripheral (peripheral nerve nodes, trunks and endings).

The morphological substrate of the reflex activity of the nervous system is reflex arcs, which are a chain of neurons of various functional significance, the bodies of which are located in different parts of the nervous system - both in the peripheral nodes and in the gray matter of the central nervous system.

WITH physiological point of view the nervous system is divided into somatic (or cerebrospinal), which innervates the entire human body, except for internal organs, vessels and glands, and autonomous (or autonomic), which regulates the activity of these organs.

The first neuron of each reflex arc is receptor nerve cell. Most of these cells are concentrated in the spinal nodes located along the posterior roots of the spinal cord. The spinal ganglion is surrounded by a connective tissue capsule. Thin layers of connective tissue penetrate from the capsule into the parenchyma of the node, which forms its skeleton, and blood vessels pass through it in the node.

The dendrites of the nerve cell of the spinal ganglion go as part of the sensitive part of the mixed spinal nerves to the periphery and end there with receptors. Neurites together form the posterior roots of the spinal cord, carrying nerve impulses either to the gray matter of the spinal cord, or along its posterior funiculus to the medulla oblongata.

The dendrites and neurites of the cells in the node and outside it are covered with membranes of lemmocytes. The nerve cells of the spinal ganglions are surrounded by a layer of glial cells, which are here called mantle gliocytes. They can be recognized by the round nuclei surrounding the body of the neuron. Outside, the glial sheath of the body of the neuron is covered with a delicate, fine-fibred connective tissue sheath. The cells of this membrane are characterized by an oval-shaped nucleus.

The structure of the peripheral nerves is described in the general histology section.

Spinal cord

It 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 spinal cord is darker - this is his Gray matter. On its periphery there is a lighter white matter. The gray matter on the cross section of the brain is seen in the form of a butterfly. The protrusions of the gray matter are called horns. Distinguish front, or ventral, rear, or dorsal, And lateral, or lateral, horns.

The gray matter of the spinal cord consists of multipolar neurons, non-myelinated and thin myelinated fibers, and neuroglia.

The white matter of the spinal cord is formed by a set of longitudinally oriented predominantly myelinated fibers of nerve cells.

The bundles of nerve fibers that communicate between different parts of the nervous system are called the pathways of the spinal cord.

In the middle part of the posterior horn of the spinal cord is the own nucleus of the posterior horn. It consists of bundle cells, the axons of which, passing through the anterior white commissure to the opposite side of the spinal cord into the lateral funiculus of the white matter, form the ventral spinocerebellar and spinothalamic pathways and go to the cerebellum and optic tubercle.

Interneurons are diffusely located in the posterior horns. These are small cells whose axons terminate within the gray matter of the spinal cord of the same (associative cells) or opposite (commissural cells) side.

The dorsal nucleus, or Clark's nucleus, consists of large cells with branched dendrites. Their axons cross the gray matter, enter the lateral funiculus of the white matter of the same side, and ascend to the cerebellum as part of the dorsal spinocerebellar tract.

The medial intermediate nucleus is located in the intermediate zone, the neurites of its cells join the ventral spinocerebellar tract of the same side, the lateral intermediate nucleus is located in the lateral horns and is a group of associative cells of the sympathetic reflex arc. The axons of these cells leave the spinal cord together with the somatic motor fibers as part of the anterior roots and separate from them in the form of white connecting branches of the sympathetic trunk.

The largest neurons of the spinal cord are located in the anterior horns, they also form nuclei from the bodies of nerve cells, the roots of which form the bulk of the fibers of the anterior roots.

As part of the mixed spinal nerves, they enter the periphery and end with motor endings in the skeletal muscles.

The white matter of the spinal cord is composed of myelin fibers running longitudinally. The bundles of nerve fibers that communicate between different parts of the nervous system are called the pathways of the spinal cord.

Brain

In the brain, gray and white matter are also distinguished, but the distribution of these two components is more complicated here than in the spinal cord. The main part of the gray matter of the brain is located on the surface of the cerebrum and cerebellum, forming their cortex. The other (smaller) part forms numerous nuclei of the brain stem.

brain stem. All nuclei of the gray matter of the brainstem are composed of multipolar nerve cells. They have endings of neurite cells of the spinal ganglia. Also in the brain stem there are a large number of nuclei designed to switch nerve impulses from the spinal cord and brain stem to the cortex and from the cortex to the spinal cord's own apparatus.

in the medulla oblongata there are a large number of nuclei of the own apparatus of cranial nerves, which are mainly located in the bottom of the IV ventricle. In addition to these nuclei, there are nuclei in the medulla oblongata that switch impulses entering it to other parts of the brain. These kernels include the lower olives.

In the central region of the medulla oblongata is located the reticular substance, in which there are numerous nerve fibers that go in different directions and together form a network. This network contains small groups of multipolar neurons with long few dendrites. Their axons spread in ascending (to the cerebral cortex and cerebellum) and descending directions.

The reticular substance is a complex reflex center associated with the spinal cord, cerebellum, cerebral cortex and hypothalamic region.

The main bundles of myelinated nerve fibers of the white matter of the medulla oblongata are represented by cortico-spinal bundles - pyramids of the medulla oblongata, lying in its ventral part.

Bridge of the brain consists of a large number of transversely running nerve fibers and nuclei lying between them. In the basal part of the bridge, the transverse fibers are separated by pyramidal pathways into two groups - posterior and anterior.

midbrain consists of the gray matter of the quadrigemina and the legs of the brain, which are formed by a mass of myelinated nerve fibers coming from the cerebral cortex. The tegmentum contains a central gray matter composed of large multipolar and smaller spindle-shaped cells and fibers.

diencephalon mainly represents the visual tubercle. Ventral to it is a hypothalamic (hypothalamic) region rich in small nuclei. The visual tubercle contains many nuclei delimited from each other by layers of white matter, they are interconnected by associative fibers. In the ventral nuclei of the thalamic region, ascending sensory pathways end, from which nerve impulses are transmitted to the cortex. Nerve impulses to the visual hillock from the brain go along the extrapyramidal motor pathway.

In the caudal group of nuclei (in the pillow of the thalamus), the fibers of the optic pathway end.

hypothalamic region is a vegetative center of the brain that regulates the main metabolic processes: body temperature, blood pressure, water, fat metabolism, etc.

Cerebellum

The main function of the cerebellum is to ensure balance and coordination of movements. It has a connection with the brain stem through afferent and efferent pathways, which together form three pairs of cerebellar peduncles. On the surface of the cerebellum there are many convolutions and grooves.

Gray matter forms the cerebellar cortex, a smaller part of it lies deep in the white matter in the form of central nuclei. In the center of each gyrus there is a thin layer of white matter, covered with a layer of gray matter - the bark.

There are three layers in the cerebellar cortex: outer (molecular), middle (ganglionic) and inner (granular).

Efferent neurons of the cerebellar cortex pear-shaped cells(or Purkinje cells) make up the ganglion layer. Only their neurites, leaving the cerebellar cortex, form the initial link of its efferent inhibitory pathways.

All other nerve cells of the cerebellar cortex are intercalated associative neurons that transmit nerve impulses to pear-shaped cells. In the ganglionic layer, the cells are arranged strictly in one row, their cords, branching abundantly, penetrate the entire thickness of the molecular layer. All branches of the dendrites are located only in one plane, perpendicular to the direction of the convolutions, therefore, with a transverse and longitudinal section of the convolutions, the dendrites of the pear-shaped cells look different.

The molecular layer consists of two main types of nerve cells: basket and stellate.

basket cells located in the lower third of the molecular layer. They have thin long dendrites, which 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 piriform cells.

stellate cells are above the basket. There are two forms of stellate cells: small stellate cells, which are equipped with thin short dendrites and weakly branched neurites (they form synapses on the dendrites of pear-shaped cells), and large stellate cells, which have long and highly branched dendrites and neurites (their branches connect with the dendrites of pear-shaped cells). cells, but some of them reach the bodies of pear-shaped cells and are part of the so-called baskets). Together, the described cells of the molecular layer represent a single system.

The granular layer is represented by special cellular forms in the form grains. These cells are small in size, have 3 - 4 short dendrites, ending in the same layer with terminal branches in the form of a bird's foot. Entering into a synaptic connection with the endings of excitatory afferent (mossy) fibers entering the cerebellum, the dendrites of the granule cells form characteristic structures called cerebellar glomeruli.

The processes of granule cells, reaching the molecular layer, form in it T-shaped divisions into two branches, oriented parallel to the surface of the cortex along the gyri of the cerebellum. These fibers, running in parallel, cross the branching of the dendrites of many pear-shaped cells and form synapses with them and the dendrites of basket cells and stellate cells. Thus, the neurites of the granule cells transmit the excitation they receive from mossy fibers over a considerable distance to many pear-shaped cells.

The next type of cells are spindle-shaped horizontal cells. They are located mainly between the granular and ganglionic layers, from their elongated bodies long, horizontally extending dendrites extend in both directions, ending in the ganglionic and granular layers. 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 pathways and have a stimulating effect on the pear-shaped cells. 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 through the spinocerebellar and vestibulocerebellar pathways. They cross the granular layer, adjoin pear-shaped cells and spread along their dendrites, ending on their surface with synapses. These fibers transmit excitation to pear-shaped cells. When various pathological processes occur in pear-shaped cells, it leads to a disorder in the coordination of movement.

cerebral cortex

It is represented by a layer of gray matter about 3 mm thick. It is very well represented (developed) in the anterior central gyrus, where the thickness of the cortex reaches 5 mm. A large number of furrows and convolutions increases the area of ​​the gray matter of the brain.

There are about 10-14 billion nerve cells in the cortex.

Different parts of the cortex differ from each other in the location and structure of the cells.

Cytoarchitectonics of the cerebral cortex. The neurons of the cortex are very diverse in form, they are multipolar cells. They are divided into pyramidal, stellate, fusiform, arachnid and horizontal neurons.

Pyramidal neurons make up the bulk of the cerebral cortex. Their bodies have the shape of a triangle, the apex of which faces the surface of the cortex. From the top and side surfaces of the body depart dendrites, ending in different layers of gray matter. Neurites originate from the base of the pyramidal cells, in some cells they are short, forming branches within a given area of ​​the cortex, in others they are long, entering the white matter.

Pyramidal cells of different layers of the cortex are different. Small cells are intercalary neurons, the neurites of which connect separate parts of the cortex of one hemisphere (associative neurons) or two hemispheres (commissural neurons).

Large pyramids and their processes form pyramidal pathways that project impulses to the corresponding centers of the trunk and spinal cord.

In each layer of cells of the cerebral cortex there is a predominance of some types of cells. There are several layers:

1) molecular;

2) external granular;

3) pyramidal;

4) internal granular;

5) ganglionic;

6) a layer of polymorphic cells.

IN molecular layer of the cortex contains a small number of small spindle-shaped cells. Their processes run parallel to the surface of the brain as part of the tangential plexus of nerve fibers of the molecular layer. In this case, the bulk of the fibers of this plexus is represented by branching of the dendrites of the underlying layers.

Outer granular layer is a cluster of small neurons that have a different shape (mostly rounded) and stellate cells. The dendrites of these cells rise into the molecular layer, and the axons go into the white matter or, forming arcs, go into the tangential plexus of the fibers of the molecular layer.

pyramid layer- the largest in thickness, very well developed in the precentral gyrus. The sizes of pyramidal cells are different (within 10 - 40 microns). From the top of the pyramidal cell, the main dendrite departs, which is located in the molecular layer. The dendrites coming from the lateral surfaces of the pyramid and its base are of insignificant length and form synapses with adjacent cells of this layer. In this case, you need to know that the axon of the pyramidal cell always departs from its base. The inner granular layer in some areas of the cortex is very strongly developed (for example, in the visual cortex), but in some areas of the cortex it may be absent (in the precentral gyrus). This layer is formed by small stellate cells, it also includes a large number of horizontal fibers.

The ganglionic layer of the cortex consists of large pyramidal cells, and the region of the precentral gyrus contains giant pyramids, described for the first time by the Kyiv anatomist V. Ya. Bets in 1874 (Bets cells). Giant pyramids are characterized by the presence of large lumps of basophilic substance. The neurites of the cells of this layer form the main part of the cortico-spinal tracts of the spinal cord and terminate in synapses on the cells of its motor nuclei.

Layer of polymorphic cells formed by spindle-shaped neurons. The neurons of the inner zone are smaller and lie at a great distance from each other, while the neurons of the outer zone are larger. The neurites of the cells of the polymorphic layer go into the white matter as part of the efferent pathways of the brain. Dendrites reach the molecular layer of the cortex.

It must be borne in mind that in different parts of the cerebral cortex, its different layers are represented differently. So, in the motor centers of the cortex, for example, in the anterior central gyrus, layers 3, 5 and 6 are highly developed and layers 2 and 4 are underdeveloped. This is the so-called agranular type of cortex. Descending pathways of the central nervous system originate from these areas. In the sensitive cortical centers, where the afferent conductors coming from the organs of smell, hearing and vision end, the layers containing large and medium pyramids are poorly developed, while the granular layers (2nd and 4th) reach their maximum development. This type is called the granular type of the cortex.

Myeloarchitectonics of the cortex. In the cerebral hemispheres, the following types of fibers can be distinguished: associative fibers (connect individual parts of the cortex of one hemisphere), commissural (connect the cortex of different hemispheres) and projection fibers, both afferent and efferent (connect the cortex with the nuclei of the lower parts of the central nervous system).

The autonomic (or autonomic) nervous system, according to various properties, is divided into sympathetic and parasympathetic. In most cases, both of these species simultaneously take part in the innervation of organs and have an opposite effect on them. So, for example, if irritation of the sympathetic nerves delays intestinal motility, then irritation of the parasympathetic nerves excites it. The autonomic nervous system also consists of central sections, represented by the nuclei of the gray matter of the brain and spinal cord, and peripheral sections - nerve nodes and plexuses. The nuclei of the central division of the autonomic nervous system are located in the middle and medulla oblongata, as well as in the lateral horns of the thoracic, lumbar and sacral segments of the spinal cord. The nuclei of the craniobulbar and sacral divisions belong to the parasympathetic, and the nuclei of the thoracolumbar division belong to the sympathetic nervous system. The multipolar nerve cells of these nuclei are associative neurons of the reflex arcs of the autonomic nervous system. Their processes leave the central nervous system through the anterior roots or cranial nerves and end in synapses on the neurons of one of the peripheral ganglia. These are the preganglionic fibers of the autonomic nervous system. The preganglionic fibers of the sympathetic and parasympathetic autonomic nervous systems are cholinergic. The axons of the nerve cells of the peripheral ganglions emerge from the ganglia in the form of postganglionic fibers and form terminal apparatuses in the tissues of the working organs. Thus, morphologically, the autonomic nervous system differs from the somatic one in that the efferent link of its reflex arcs is always binomial. It consists of central neurons with their axons in the form of preganglionic fibers and peripheral neurons located in peripheral nodes. Only the axons of the latter - postganglionic fibers - reach the tissues of the organs and enter into a synaptic connection with them. Preganglionic fibers in most cases are covered with a myelin sheath, which explains the white color of the connecting branches that carry sympathetic preganglionic fibers from the anterior roots to the ganglia of the sympathetic border column. Postganglionic fibers are thinner and in most cases do not have a myelin sheath: these are fibers of gray connecting branches that run from the nodes of the sympathetic border trunk to the peripheral spinal nerves. The peripheral nodes of the autonomic nervous system lie both outside the organs (sympathetic prevertebral and paravertebral ganglia, parasympathetic nodes of the head), and in the wall of organs as part of the intramural nerve plexuses that occur in the digestive tract, heart, uterus, bladder, etc.

CHELYABINSK STATE MEDICAL ACADEMY

DEPARTMENT OF HISTOLOGY, CYTOLOGY AND EMBRYOLOGY

Lecture

Nervous system. Spinal cord. Spinal ganglion.

1. General characteristics of the nervous system and its division.

2.Anatomical structure of the spinal cord.

3. Characteristics of the gray matter of the spinal cord.

4. Characteristics of the white matter of the spinal cord.

5. Kernels of the spinal cord and their significance.

6. Conducting paths: concept, varieties, location, meaning.

7. Characteristics of the spinal ganglion.

8. The concept of the reflex arc of the somatic nervous system.

slide list

1. Spinal cord. Building plan. 472

2. Gray matter at various levels of the spinal cord. 490.

3. Spinal cord. Anterior horns. 475.

4. Spinal brain. Back horns. 468.

5. Spinal cord. Ependymal glia.

6. The motor nucleus of the anterior horn. 795.

7. White matter of the spinal cord. 470.

8. Spinal ganglion 476.

9. Spinal ganglion (scheme). 799.

10. Spinal ganglion. neurocytes. Glia. 467.

11. Spinal ganglion with silver impregnation. 466.

12. Scheme of the reflex arc of the somatic nervous system. 473.

13. Nerny cells of the spinal cord. 458.

14. Conducting pathways of the spinal cord (diagram) 471.

The human nervous system is usually divided from an anatomical point of view into the central and peripheral nervous systems. The central nervous system includes the brain and spinal cord, and the peripheral nervous system includes all peripherally located organs of the nervous system, including nerve endings, peripheral nerves, nerve nodes and nerve plexuses.

From a physiological (functional) point of view, the nervous system is divided into the cerebrospinal (somatic), innervating skeletal muscles, and the autonomic nervous system, innervating internal organs, glands and blood vessels.

The somatic nervous system includes the brain and spinal cord, as well as part of the conductors associated with the function of movement. The autonomic nervous system is represented by some departments located in the brain and spinal cord, as well as autonomic ganglia, nerve conductors and end devices.

Spinal ganglia (spinal ganglia)

The intervertebral ganglia lie in the intervertebral foramen. They are surrounded by a thick connective tissue sheath, from which numerous layers of connective tissue extend into the organ, surrounding the body of each neuron. The connective tissue base of the node is richly vascularized. Neurons lie in nests, tightly adjacent to each other. Nests of cells are located mainly along the periphery of the spinal ganglion. The number of neurons in one node in a dog, for example, reaches 18,000 on average.

The neurons in the spinal ganglion are false unipolars. In lower vertebrates, such as fish, these cells are bipolar. In humans, in ontogenesis (at 3-4 months of uterine life), the node neurons are also bipolar with an eccentrically lying nucleus. Then the processes converge and the body part is extended, as a result of which the definitive neurons acquire one process that extends from the body and divides in a T-shape. The dendrite goes to the periphery and ends with a receptor. The axon travels to the spinal cord. In the process of ontogenesis, the relationship between the bodies of the neuron and the process becomes much more complicated. In the ganglia of an adult organism, the processes of neurons coil in a spiral, and then make several twists around the body. The degree of development of these structures in different intervertebral nodes is not the same. The greatest difficulty in twisting processes around neurons is observed in the nodes of the cervical region (in humans, up to 13 curls), since the cervical nodes are associated with the innervation of the upper limbs. The organization of these nodes is more complex than the lumbosacral nodes and especially the chest ones.

In the neuroplasm of the false unipolars of higher vertebrates and humans, the endoplasmic reticulum is highly developed, consisting of parallel tubules. Mitochondria lie throughout the cytoplasm, the arrangement of ridges in them is transverse. The cytoplasm contains many protoneurofibrils, lysosomes, as well as pigment and polysaccharide granules.

The bodies of false unipolars are surrounded by oligodendroglial cells. The plasma membranes of glial cells and neurons are in close contact. The number of gliocytes around one neuron can reach 12. They perform a trophic function and are also involved in the regulation of metabolism.

The central sections of the node consist of bundles of pulpy nerve fibers, which are T-shaped branches of the processes of false unipolars. The posterior root is thus formed by these processes. The proximal part of the root is represented by axons entering the spinal cord, and the distal part of the posterior root connects to the anterior root and forms a mixed spinal nerve.

The development of the intervertebral ganglia is carried out due to the ganglionic plate, which is formed in the process of closing the neural tube. The formation of the ganglionic plate occurs due to the transitional region lying between the medial sections of the neural plate and the skin ectoderm. This area consists of lower cells with soft and sparse yolk inclusions.

When the neural groove closes into a tube and its edges grow together, the material of the neural folds is sandwiched between the neural tube and the skin ectoderm closing over it. The cells of the neural folds are redistributed into one layer, forming a ganglionic plate, which has very wide development potentials.

At first, the plate material is homogeneous and consists of ganglioblasts, which then differentiate into neuroblasts and glioblasts. On neuroblasts, the formation of two processes, an axon and a dendrite, occurs at opposite ends. In most sensitive ganglia, due to uneven cell growth, the places of origin of both processes converge and a part of the cell body is elongated, which leads to the appearance of a pseudo-unipolar cell shape. In lower vertebrates, in all ganglia, and in higher ones, in the ganglia of the 8th pair of cranial nerves, the bipolar form of neurons is preserved in vivo. Asynchronous differentiation of neurons was shown not only in the ganglia belonging to different segments of the body, but also in the same ganglion.

The functional significance of the intervertebral ganglia is very high, since they contain the bulk of sensory neurons that supply receptors to both the skin and internal organs.

Spinal cord

The spinal cord lies in the spinal canal, has the form of a cylindrical cord 42-45 cm long. In an adult, the spinal cord stretches from the upper edge of the 1st cervical to the upper edge of the 2nd lumbar vertebra, and in a three-month-old embryo it reaches the 5th lumbar vertebrae. From the end of the spinal cord stretches the terminal thread, formed by the membranes of the brain, which is attached to the coccygeal vertebrae. The spinal cord is characterized by a segmental structure. The spinal cord is divided into 31 segments: cervical - 8, thoracic - 12, lumbar - 5, sacral - 5, coccygeal - 1. The segment of the spinal cord is a kind of structural and functional unit. At the level of one segment, some reflex arcs can be realized.

The spinal cord consists of two symmetrical halves connected to each other by a narrow bridge. Passes through the center of the spinal cord central channel, which is a remnant of the cavity of the neural tube. The central canal is lined with ependymal glia, the processes of which are connected and reach the surface of the brain, where they form the border glial membrane. The central canal expands upward into the cavity of the 4th ventricle. The lumen of the canal in an adult is obliterated. In front, both halves are separated by the anterior median neck, and behind by the posterior septum. From the surface, the spinal cord is covered with several meninges. The pia mater is tightly adherent to the surface of the spinal cord and contains numerous blood vessels and nerves. The dura mater forms a tight sheath or sheath for the spinal cord and roots. The arachnoid is located between the dura and pia mater. The spinal cord is made up of gray and white matter. The gray matter of the spinal cord has the appearance of a butterfly or N. Gray matter forms protrusions or horns. There are anterior and posterior horns. The anterior horns are broad, thick and short, while the posterior horns are thin, narrow and long. The anterior and posterior horns stretch along the entire length of the spinal cord. At the level of the last cervical, all thoracic and first lumbar segments, lateral horns stretch. The quantitative ratio of gray and white matter at different levels of the spinal cord is not the same. The lower segments contain more gray matter than white matter. In the middle, and especially in the upper thoracic segments, the amount of white matter predominates over gray. In the cervical thickening, the amount of gray matter increases significantly, but the mass of white matter also increases. Finally, in the upper cervical segments, the gray matter decreases in volume. The part of the gray matter in front of the central canal is called the anterior gray commissure, and the gray matter behind the central canal forms the posterior gray commissure (commissure). The horns of the gray matter divide the white matter into separate sections - columns or cords. There are anterior, lateral and posterior cords or columns. The posterior cords are delimited by the posterior septum and the posterior horns. The anterior cords are limited by the anterior median fissure and the anterior horns. The lateral horns are delimited by the anterior and posterior horns.

The stroma of the gray matter of the spinal cord is formed by short-beamed (plasmic) astrocytic glia. On transverse sections of gray matter, the following unsharply demarcated sections can be distinguished: posterior horns, intermediate zone and anterior horns. The gray matter consists of numerous multipolar nerve cells and predominantly non-pulmonic nerve fibers. Among the neurons of the spinal cord, radicular, internal and beam cells are distinguished. radicular cells- these are cells whose axons extend beyond the spinal cord and form the anterior roots. As part of the anterior roots, the axons of the motor cells of the spinal cord reach the skeletal muscle fibers, where they end in neuromuscular synapses. Inner neurons- These are cells whose axons do not extend beyond the gray matter of the spinal cord. Beam neurons - these are cells whose axons go into the white matter and form pathways (bundles). In the posterior horns, several zones are conditionally distinguished: the Lissauer marginal zone, the spongy zone, and the gelatinous substance. The marginal zone of Lissauer is the site of entry of axons of nerve cells of the spinal ganglions from the white matter into the gray matter of the posterior horns. The spongy substance contains numerous small beam cells and glial cells. The gelatinous substance is characterized by the content of a large number of glial cells and a few fascicular cells.

Most of the nerve cells in the gray matter are located diffusely and serve for the internal connections of the spinal cord. Some of them are grouped and form nuclei of the spinal cord. In the posterior horns of the spinal cord lie 2 nuclei: the proper nucleus of the posterior horn and the thoracic nucleus. Proprietary nucleus of the posterior horn consists of bundled nerve cells and lies in the center of the posterior horn. The axons of these cells pass through the anterior gray commissure to the opposite side and enter the lateral funiculus, where they acquire an ascending direction, forming the anterior spinal cerebellar pathway and the spinothalamic pathway. Thoracic nucleus (Clark's nucleus, dorsal nucleus) lies at the base of the posterior horn and is also formed by fascicular cells. This nucleus is located along the entire length of the spinal cord, but reaches its greatest development in the middle cervical and lumbar regions. The axons of the neurons of this nucleus exit into the lateral funiculus of their side and form the posterior spinal cerebellar pathway. Clark's nucleus neurons receive information from receptors in muscles, tendons, and joints and transmit it to the cerebellum via the posterior spinal cerebellar pathway. In recent years, it has been established that neurons of the posterior horn secrete special proteins of the opioid type - enkephalins (methenkephalin and neurotensin), which inhibit pain effects by controlling sensory information entering it (skin, partly visceral and proprioceptive)

Also located in the intermediate zone 2 nuclei: medial and lateral. The medial nucleus of the intermediate zone is built from bundle cells, the axons of which take part in the formation of the anterior spinal cerebellar pathway. The lateral nucleus of the intermediate zone is located in the lateral horns of the spinal cord and is built from radicular cells, the axons of which extend beyond the spinal cord as part of the anterior roots. This nucleus belongs to the sympathetic autonomic nervous system.

In the anterior horns of the spinal cord there are 5 nuclei, consisting of large neurons: 2 medial, 2 lateral and 1 central nuclei. The axons of these neurons are sent as part of the anterior roots to the periphery and end with motor endings in the skeletal muscles. The central nucleus of the anterior horn is called the anterior horn proper nucleus and consists of small cells. This nucleus serves to provide internal connections in the anteriormost horn. The medial nuclei stretch throughout the entire spinal cord and innervate the short and long muscles of the body. The lateral nuclei innervate the muscles of the limbs and are located in the region of the cervical and lumbar thickenings.

White matter is devoid of nerve cells and consists only of myelinated nerve fibers lying longitudinally. Radially arranged thin layers formed by glia protrude from the gray matter into the white matter. The stroma of the white matter of the spinal cord is represented by long-beamed astrocytic glia.

The nervous apparatus of the spinal cord can be divided into 2 types: the own or internal apparatus of the spinal cord and the apparatus of bilateral connections of the spinal cord with the brain.

Own apparatus provides simple reflexes. These reflexes begin with excitation of a sensitive receptor point on the periphery and consist in the processing of a sensitive impulse into a motor impulse sent to the skeletal muscle. The reflex arcs of the own apparatus of the spinal cord usually consist of 3 neurons: sensory, intercalary and motor. The axons of the sensory cells of the spinal ganglion enter through the marginal zone of the posterior horns, where they are divided into 2 branches: a long ascending and a short descending. After passing a certain distance (several segments), each branch gives rise to numerous lateral collaterals, which go to the gray matter of the spinal cord and end on the body of the fascicular cells. The processes of the fascicular cells of their own apparatus are short and can be traced for 4-5 segments. They are always located in the area of ​​white matter directly adjacent to the gray matter. Thus, throughout the entire spinal cord, gray matter is surrounded by a zone of white matter containing short internal pathways of the spinal cord. The processes of the beam cells again return to the gray matter and end at the nuclei of the anterior horn. The third neuron of its own apparatus is represented by the motor cell of the anterior horns of the spinal cord.

Long pathways (apparatus of bilateral connections of the spinal cord with the brain) are bundles of myelinated nerve fibers that carry various types of sensitivity to the brain and effector pathways from the brain to the spinal cord, which end at the motor nuclei of the anterior horns of the spinal cord. All pathways are divided into ascending and descending.

The ascending pathways lie in the posterior and lateral cords. There are 2 ascending pathways in the posterior funiculus: Gaulle's bundle (gentle) and Burdach's bundle (wedge-shaped). These bundles are formed by axons of sensory cells of the spinal ganglion, which enter the spinal cord and go to the posterior columns, where they rise up and end at the ganglion cells of the medulla oblongata, which form the nuclei of Gaulle and Burdach. The neurons of these nuclei are the second neurons, the processes of which reach the thalamus, where the third neuron is located, the processes of which are directed to the cerebral cortex. These tracts conduct tactile sensitivity and musculoskeletal feeling.

There are several ascending pathways in the lateral cords. Anterior dorsal cerebellar pathway (Govers pathway) formed by the axons of the nerve cells of the nucleus proper of the posterior horn, which are partially directed to the lateral funiculus of their side, and mainly pass through the anterior commissure to the lateral funiculus of the opposite side. In the lateral funiculus, this pathway lies on the anterolateral surface. It ends in the vermis of the cerebellum. The impulses following this path do not reach the brain, but pass to the cerebellum, from where they send impulses that automatically regulate movements independent of our consciousness.

Posterior dorsal cerebellar pathway (Flexig pathway) It is formed by the axons of the neurons of Clark's nucleus, which are directed to the lateral funiculus of their side and terminate in the cerebellar vermis. This pathway also carries irritations from the periphery to the cerebellum, which automatically regulate the coordination of movements both when standing and when walking.

The spinothalamic pathway is formed by the axons of the neurons of the nucleus proper of the posterior horn of the opposite side and reaches the thalamus opticus. This path conducts pain and temperature sensitivity. From the thalamus, impulses reach the cerebral cortex.

Descending pathways run in the lateral and anterior cords. pyramidal tract lies in two bundles in the anterior and lateral cords and is formed by axons of giant pyramidal cells (Betz cells) of the cerebral cortex. At different levels of the spinal cord, the fibers of the pyramidal tract enter the gray matter of the spinal cord and form synapses with the neurons of the motor cells of the anterior horns. This way of arbitrary movements.

In addition, there are numerous smaller descending pathways formed by the axons of the neurons of the brainstem nuclei. These include pathways starting in the red nucleus, thalamus, vestibular nucleus, and the bulbar part. Collectively, all these pathways are called extrapyramidal pathways. The fibers of these pathways also enter the gray matter at different levels of the spinal cord and form synapses with the neurons of the anterior horns.

Thus reflex arc of the somatic nervous system It is represented by three neurons: sensory, intercalary and motor. A sensitive neuron is represented by a sensitive cell of the spinal ganglion, which perceives irritation on the periphery with its receptor. Along the axon of the sensitive cell, the impulse is sent to the gray matter, where it forms a synapse with the dendrite or body of the intercalary nerve cell, along the axon of which the impulse is transmitted to the anterior horns of the spinal cord. In the anterior horns, the impulse is transmitted to the dendrite or body of the motor cell, and then along its axon it is directed to the skeletal muscle and causes its contraction.

Regeneration of the nerve fibers of the central nervous system occurs to an extremely small extent. One of the causal factors for this is a rough connective tissue scar, which soon forms in the area of ​​injury and reaches a large size. Nerve fibers, approaching the scar, either partially grow into it and then soon degenerate, or turn back and grow into the pia mater, where they grow chaotically or also degenerate.

In recent years, it has been established that immune responses also develop in the injured area, since when the nervous tissue is damaged, antibodies are produced to modified structures. The resulting immune complexes activate tissue and cellular proteolytic and lipolytic enzymes that act both on destroyed structures and on regenerating nervous tissue. In this regard, immunosuppressants have been widely used in stimulating the regeneration of the spinal cord. Finally, the difficulty of regeneration in the central nervous system is due to disorders of the hemocirculatory bed.

Currently, methods of plastic replacement of damaged areas of the brain and spinal cord with embryonic tissue are being widely developed. In particular, a method is being developed to fill the cavity formations of the injured spinal cord of the embryonic brain tissue with tissue culture. Thus, the Japanese scientist Y Shimizu (1983) obtained a positive effect of restoring the locomotor functions of the hind limbs in dogs after transplantation of a brain tissue culture into the damaged area of ​​the spinal cord. Good results were obtained by approaching the stumps of the spinal cord after removal of a segment of the spinal cord and shortening of the spine. This method is already being used in the clinic.

It has now been established that cerebrospinal fluid (in case of injury it is pathologically altered) has a negative effect on regeneration processes. The cerebrospinal fluid is able to dissolve damaged or destroyed tissue of the spinal cord (and brain), which is considered as a compensatory-adaptive reaction aimed at removing damaged remnants of the nervous tissue.

In children, glial cells of the spinal cord divide intensively, due to which their number increases, reaching a maximum by the age of 15. All nerve cells are mature, but smaller and do not contain pigment inclusions. Myelination of nerve fibers proceeds intensively in the prenatal period, but finally ends by 2 years. Moreover, afferent fibers are myelinated faster. Among the efferent nerve fibers, the pyramidal tract fibers are the last to myelinate.

Nerve nodes (ganglia) - clusters of neurons outside the central nervous system - are divided into sensitive (sensory) and autonomous (vegetative).

Sensitive (sensory) nerve nodes contain pseudo-unipolar or bipolar (in the spiral and vestibular ganglia) afferent neurons and are located along the posterior roots of the spinal cord (spinal, or spinal nodes) and cranial nerves (V, VII, VIII, IX, X).

Spinal nodes

The spinal (spinal) node (ganglion) has a fusiform shape and is covered with a capsule of dense fibrous connective tissue. On its periphery 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 blood vessels.

Pseudo-unipolar neurons are characterized by a spherical body and a light nucleus with a well-marked nucleolus. Allocate large and small cells, which probably differ in the types of impulses conducted. The cytoplasm of neurons contains numerous mitochondria, GREP cisterns, elements of the Golgi complex, and lysosomes. Each neuron is surrounded by a layer of adjacent flattened oligodendroglia cells (mantle gliocytes, or satellite cells) with small rounded nuclei; outside of the glial membrane there is a thin connective tissue. A process departs from the body of a pseudounipolar neuron, dividing in a T-shape into afferent (dendritic) and efferent (axonal) branches, which are covered with myelin sheaths. The afferent branch ends at the periphery with receptors, the efferent branch enters the spinal cord as part of the posterior root. Since the switching of the nerve impulse from one neuron to another does not occur within the spinal nodes, they are not nerve centers. The neurons of the spinal ganglions contain such neurotransmitters as acetylcholine, glutaminoval acid, substance P, somatostatin, cholecystokinin, VIN, gasgprin.

AUTONOMOUS (VEGETATIVE) NODES

Autonomous (vegetative) nerve nodes (ganglia) can be located along the spine (paravertebral ganglia), or in front of it (prevertebral ganglia), as well as in the wall of the organs of the heart, bronchi, digestive tract, bladder, etc. (tramural ganglia) or near them surfaces. Sometimes they look like small (from a few cells to several tens of cells) clusters of neurons located along some nerves or lying intramurally (microganglia). Preganglionic fibers (myelin) are suitable for the vegetative nodes, containing processes of cells whose bodies lie in the central nervous system. These fibers strongly branch and form numerous synaptic endings on the cells of the vegetative nodes. This results in the convergence of a large number of preganglionic fiber terminals to each ganglion neuron. In connection with the presence of synaptic transmission, vegetative nodes are classified as nerve centers of the nuclear type.

Autonomic nerve ganglions are divided into sympathetic and parasympathetic according to their functional characteristics and localization.

Sympathetic ganglions (para- and prevertebral) receive preganglionic fibers from cells located in the autonomic nuclei of the thoracic and lumbar segments of the spinal cord. The neurotransmitter of preganglionic fibers is acetylcholine, and post-ganglionic fibers is norepinephrine (with the exception of sweat glands and some blood vessels that have cholinergic sympathetic innervation). In addition to these neurotransmitters, enkephalins, VIP, substance P, somatostatin, cholecystokinin are detected in the nodes.

Parasympathetic nerve nodes (intramural, lying near the organs or nodes of the head) receive preganglionic fibers from cells located in the autonomic nuclei of the medulla oblongata and midbrain, as well as the sacral spinal cord. These fibers leave the CNS as part of the III, VII, IX and X pairs of cranial nerves and the anterior roots of the sacral segments of the spinal cord. The neurotransmitter of pre- and postganglionic fibers is acetylcholine. In addition to it, the role of mediators in these ganglia is played by serotonin, ATP (purinergic neurons), and possibly some peptides.

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

The general plan of the structure of the sympathetic and parasympathetic ganglions is similar. The vegetative node is covered with a connective tissue capsule and contains diffusely or groups located bodies of multipolar neurons, their processes in the form of unmyelinated or (less often) myelinated fibers and endoneurium. The bodies of neurons are irregularly shaped, contain an eccentrically located nucleus, surrounded (usually incompletely) by sheaths of glial satellite cells (mantle gliocytes). Often there are multinucleated and polyploid neurons.

In sympathetic nodes, along with large cells, small neurons are described, the cytoplasm of which has intense fluorescence in ultraviolet rays and contains granules of small intensely fluorescent (MIF-) or small granule-containing (MGS-) cells. They are characterized by dark nuclei and a small number of short processes; cytoplasmic granules contain dopamine, as well as serotonin or norepinephrine, in some cells in combination with enkephalin. The terminals of preganglionic fibers terminate on MIF cells, the stimulation of which leads to an increased release of dopamine and other mediators into the perivascular spaces and, possibly, in the area of ​​synapses on the dendrites of large cells. MYTH cells have an inhibitory effect on the activity of effector cells.

Due to their high autonomy, the complexity of organization and the peculiarities of mediator exchange, some authors distinguish intramural nodes and associated pathways as an independent metasympathetic division of the autonomic nervous system. In particular, the total number of neurons in the intramural nodes of the intestine is higher than in the spinal cord, and in terms of the complexity of their interaction in the regulation of peristalsis and secretion, they are compared with a minicomputer. Physiologically, among the neurons of these ganglia, there are pacemaker cells that have spontaneous activity and, through synaptic transmission, act on "slave" neurons that already have an effect on the innervated cells.

The absence of part of the intramural ganglia of the large intestine due to a defect in their intrauterine development in a congenital disease (Hirschsprung's disease) leads to dysfunction of the organ with a sharp expansion of the area above the affected spasmodic segment.

Three types of neurons are described in the intramural nodes:

1) long-axon efferent neurons (Dogel cells

I type) are numerically predominant. These are large or medium-sized efferent neurons with short dendrites and a long axon heading outside the node to the working organ, on the cells of which it forms motor or secretory endings.

2) equidistant afferent neurons (Dogel cells

Type II) contain long dendrites and an axon that extends beyond this ganglion into neighboring ones and forms synapses on cells of types I and III. These cells, apparently, are part of the local reflex arcs as a receptor link, which close without a nerve impulse entering the CNS. The presence of such arcs is confirmed by the preservation of functionally active afferent, associative, and efferent neurons in transplanted organs (for example, the heart);

3) associative cells (type III Dogel cells) - local intercalary neurons, connecting with their processes several cells of types I and II, morphologically similar to type II Dogel cells. The dendrites of these cells do not go beyond the node, and the axons go to other nodes, forming synapses on type I cells.

SPINAL CORD

The spinal cord is located in the spinal canal and has the form of a rounded cord, expanded in the cervical and lumbar regions and penetrated by the central canal. It consists of two symmetrical halves, separated anteriorly by a median fissure, posteriorly by a median sulcus, and 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, gray matter is located in its central part, and white matter lies along the periphery.

The gray matter in the cross section looks like a butterfly and includes paired anterior (ventral), posterior (dorsal) and lateral (lateral) horns (in fact, they are continuous columns running along the spinal cord). The horns of the gray matter of both symmetrical parts of the spinal cord are connected to each other with a friend in the area of ​​​​the central gray commissure (commissures). The gray matter contains the bodies, dendrites and (partly) axons of neurons, as well as glial cells. Between the bodies of neurons there is a neuropil - a network formed by nerve fibers and processes of glial cells.

Cytoarchitectonics of the spinal cord. Neurons are located in the gray matter in the form of clusters (nuclei) that are not always sharply demarcated, in which nerve impulses switch from cell to cell (which is why they are referred to as nuclear-type nerve centers). Based on the location of neurons, their cytological features, the nature of connections and functions, B. Rexedom isolated ten plates in the gray matter of the spinal cord, running in the rostro-caudal direction. Depending on the topography of axons, neurons of the spinal cord are divided into: 1) radicular neurons, the axons of which form the anterior roots; 2) internal neurons, the processes of which end within the gray matter of the spinal cord; 3) beam neurons, the processes of which form bundles of fibers in the white matter of the spinal cord as part of the pathways.

The posterior horns contain several nuclei formed by multipolar intercalary neurons of small and medium sizes, on which axons of pseudounipolar cells of the spinal ganglia terminate, carrying a variety of information from receptors, as well as fibers of descending pathways from the supraspinal centers lying above. In the posterior horns, high concentrations of such neurotransmitters like serotonin, enkephalin, substance P.

Axons of intercalary neurons a) terminate in the gray matter of the spinal cord on motor neurons lying in the anterior horns; b) form intersegmental connections within the gray matter of the spinal cord; c) exit into the white matter of the spinal cord, where they form ascending and descending pathways (tracts). Part of the axons in this case passes to the opposite side of the spinal cord.

The lateral horns, well expressed at the level of the thoracic and sacral segments of the spinal cord, contain nuclei formed by the bodies of intercalary neurons that belong to the sympathetic and parasympathetic divisions of the autonomic nervous system. Axons terminate on the dendrites and bodies of these cells: a) pseudo-unipolar neurons that carry impulses from receptors located in the internal organs, b) neurons of the centers of regulation of autonomic functions, the bodies of which are located in the medulla oblongata. The axons of autonomic neurons, leaving the spinal cord as part of the anterior roots, form preganglionic fibers heading to the sympathetic and parasympathetic nodes. In the neurons of the lateral horns, the main mediator is acetylcholine; a number of neuropeptides are also detected - enkephalin, neurotensin, VIP, substance P, somatostat, calcitonin gene-related peptide (PCG).

The anterior horns contain about 2-3 million multipolar motor cells (motoneurons). Motor neurons are combined into nuclei, each of which usually extends into several segments. There are large (body diameter 35-70 microns) alpha motor neurons and smaller (15-35 microns) gamma motor neurons scattered among them.

On the processes and bodies of motor neurons there are numerous synapses (up to several tens of thousands on each), which have excitatory and inhibitory effects on them. On motor neurons

end:

a) collaterals of axons of pseudounipolar cells of the spinal nodes, forming two-neuron (monosynaptic) reflex arcs with them

b) axons of intercalary neurons, the bodies of which lie in the posterior

horns of the spinal cord;

c) axons of Renshaw cells forming inhibitory axo-somatic Ted synapses of these small intercalary GABAergic neurons are located in the middle of the anterior horn and are innervated by collaterals of motor neuron axons;

d) fibers of the descending pathways of the pyramidal and extrapyramidal systems, carrying impulses from the cerebral cortex and nuclei of the brain stem.

Gamma motor neurons, unlike alpha motor neurons, do not have a direct connection with the sensory neurons of the spinal nodes.

Axons of alpha motor neurons give off collaterals, ending on the bodies of intercalary Renshaw cells (see above), and leave the spinal cord as part of the anterior roots, heading in mixed nerves to somatic muscles, on which they end in neuromuscular synapses (motor plaques). Thinner axons of gamma motor neurons have the same course and form endings on the intrafusal fibers of the neuromuscular spindles. The neurotransmitter of the anterior horn cells is acetylcholine.

The central (spinal) canal runs in the center of the gray matter in the central gray commissure (commissure). It is filled with cerebrospinal fluid (CSF) and lined with a single layer of cuboidal or prismatic ependyma cells, the apical surface of which is covered with microvilli and (partially) cilia, while the lateral surfaces are connected by complexes of intercellular junctions.

The white matter of the spinal cord surrounds the gray matter and is divided by the anterior and posterior roots into symmetrical dorsal, lateral and ventral cords. - It consists of longitudinally running nerve fibers (mainly myelinated), forming descending and ascending pathways (tracts). The latter are separated from each other by thin layers of connective tissue and astrocytes (also found inside the tracts). Each tract is characterized by the predominance of fibers formed by the same type of neurons, so the tracts differ significantly in the neurotransmitters contained in their fibers and (like neurons) are divided into monoaminergic, cholinergic, GABAergic, glutamatergic, glycinergic, and peptidergic. Pathways include two groups: propriospinal and supraspinal paths.

Propriospinal pathways own pathways of the spinal cord - formed by axons of intercalary neurons that communicate between its various departments. These paths pass mainly on the border of white and gray matter as part of the lateral and ventral cords.

The supraspinal pathways connect the spinal cord with the structures of the brain and include the ascending spinal-cerebral and descending cerebro-spinal tracts.

The cerebrospinal tracts transmit a variety of sensory information to the brain. Some of these 20 tracts are formed by axons of cells of the spinal ganglions, while the majority are represented by axons of various interneurons, the bodies of which are located on the same or opposite side of the spinal cord.

The cerebro-spinal tracts connect the brain to the spinal cord and include the pyramidal and extrapyramidal systems.

The pyramidal system is formed by long axons of the pyramidal cells of the cerebral cortex and has about a million myelin fibers in humans, which at the level of the medulla oblongata mostly pass to the opposite side and form the lateral and ventral corticospinal tracts. The fibers of these tracts are projected not only to motor neurons, but also to the interneurons of the gray matter. The pyramidal system controls the precise voluntary movements of the skeletal muscles, especially the limbs.

The extrapyramidal system is formed by neurons whose bodies lie in the nuclei of the midbrain and medulla oblongata and the pons, and the axons terminate on motor neurons and intercalary neurons. It controls mainly the tone of the skeletal muscles, as well as the activity of the muscles that maintain the posture and balance of the body.

Detailed information about the topography and projections of the pathways of the spinal cord is given in the course of anatomy.

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

(with the participation of a number of other tissues) forms the nervous system, which ensures 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 central one includes the brain and spinal cord, the peripheral one combines nerve nodes, nerves and nerve endings.

The nervous system develops from neural tube And ganglion plate. The brain and sense organs differentiate from the cranial part of the neural tube. From the trunk part of the neural tube - the spinal cord, from the ganglionic plate spinal and autonomic nodes and chromaffin tissue of the body are formed.

Nerves (ganglia)

Nerve nodes, or ganglia, are clusters of neurons outside the central nervous system. Allocate sensitive And vegetative nerve nodes.

Sensory ganglions lie along the posterior roots of the spinal cord and along the course of the cranial nerves. Afferent neurons in the spiral and vestibular ganglion are bipolar, in other sensitive ganglia - pseudo-unipolar.

spinal ganglion (spinal ganglion)

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. The dendrites of 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.

Most of the internal organs have 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 associated pathways due to their high autonomy, complexity of organization and characteristics of 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. association cells type III.

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.

Equal outgrowth 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 - 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, rich in fibroblasts, macrophages and fat cells. Contains blood and lymphatic vessels, sensitive nerve endings.