home biology tutor Spinal cord, cerebellum. Nervous system Histological structure of the spinal cord of the thoracic region

Spinal cord, cerebellum. Nervous system Histological structure of the spinal cord of the thoracic region

Nervous system carries out the unification of parts of the body into a single whole (integration), ensures the regulation of various processes, coordination of the functions of various organs and tissues and the interaction of the body with the external environment. It perceives diverse information coming from the external environment and from internal organs, processes it and generates signals that provide responses that are adequate to the acting stimuli. The activity of the nervous system is based on reflex arcs- chains of neurons that provide reactions working organs (target organs) in response to receptor stimulation. In reflex arcs, neurons connected to each other by synapses form three links: receptor (afferent), effector and between them associative (insert).

Departments of the nervous system

Anatomical division of departments nervous system:

(1)central nervous system (CNS) -

includes head and dorsal brain;

(2)peripheral nervous system - includes peripheral nerve ganglia (nodes), nerves and nerve endings(described in the section "Nervous tissue").

Physiological division of the departments of the nervous system(depending on the nature of the innervation of organs and tissues):

(1)somatic (animal) nervous system - controls mainly the functions of voluntary movement;

(2)autonomic (vegetative) nervous system - regulates the activity of internal organs, vessels and glands.

The autonomic nervous system is divided into interacting with each other sympathetic and parasympathetic divisions, which differ in the localization of peripheral nodes and centers in the brain, as well as the nature of the effect on internal organs.

The somatic and autonomic nervous system includes links located in the central nervous system and the peripheral nervous system. Functionally leading fabric organs of the nervous system is nervous tissue, including neurons and glia. Clusters of neurons in the CNS are commonly referred to as cores, and in the peripheral nervous system ganglia (nodes). Bundles of nerve fibers in the central nervous system are called paths, in the peripheral nerves.

Nerves(nerve trunks) connect the nerve centers of the brain and spinal cord with receptors and working organs. They are formed in bundles myelin and unmyelinated nerve fibers which are united by connective tissue components (shells): endoneurium, perineurium and epineurium(Fig. 114-118). Most nerves are mixed, that is, they include afferent and efferent nerve fibers.

Endoneurium - thin layers of loose fibrous connective tissue with small blood vessels surrounding individual nerve fibers and linking them into a single bundle.

Perineurium - a sheath covering each bundle of nerve fibers from the outside and giving partitions deep into the bundle. It has a lamellar structure and is formed by concentric layers of flattened fibroblast-like cells connected by tight and gap junctions. Between the layers of cells in the spaces filled with liquid, there are components basement membrane and longitudinally oriented collagen fibers.

epineurium - 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 (see Fig. 114).

Nerve structures revealed by various methods coloring. Various histological staining methods allow more detailed and selective study of individual components

nerve. So, osmization gives contrast staining of the myelin sheaths of nerve fibers (allowing you to assess their thickness and differentiate between myelinated and non-myelinated fibers), but the processes of neurons and connective tissue components of the nerve remain very weakly stained or unstained (see Fig. 114 and 115). When painting hematoxylin-eosin myelin sheaths are not stained, the processes of neurons have a slightly basophilic staining, however, the nuclei of neurolemmocytes in nerve fibers and all connective tissue components of the nerve are well detected (see Fig. 116 and 117). At stained with silver nitrate the processes of neurons are brightly stained; myelin sheaths remain unstained, the connective tissue components of the nerve are poorly detected, their structure is not traced (see Fig. 118).

Nerve ganglia (nodes)- structures formed by clusters of neurons outside the CNS - 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.

Sensory ganglia (knots) of the spinal nerves spindle-shaped and covered capsule of dense fibrous connective tissue. On the periphery of the ganglion are dense clusters of bodies pseudounipolar neurons, and the central part is occupied by their processes and thin layers of endoneurium located between them, bearing vessels (Fig. 121).

Pseudo-unipolar sensory neurons are characterized by a spherical body and a light nucleus with a clearly visible nucleolus (Fig. 122). The cytoplasm of neurons contains numerous mitochondria, cisterns of the granular endoplasmic reticulum, elements of the Golgi complex (see Fig. 101), lysosomes. Each neuron is surrounded by a layer of flattened oligodendroglia cells adjacent to it. or mantle gliocytes) with small rounded nuclei; outside the glial membrane there is a thin connective tissue capsule (see Fig. 122). A process departs from the body of a pseudounipolar neuron, dividing in a T-shaped manner into peripheral (afferent, dendritic) and central (efferent, axonal) branches, which are covered with myelin sheaths. peripheral process(afferent branch) ends with receptors,

central process(efferent branch) as part of the posterior root enters the spinal cord (see Fig. 119).

Autonomic nerve ganglia formed by clusters of multipolar neurons, on which numerous synapses form preganglionic fibers- processes of neurons whose bodies lie in the central nervous system (see Fig. 120).

Classification of autonomous ganglia. By localization: ganglia can be located along the spine (paravertebral ganglia) or ahead of him (prevertebral ganglia) as well as in the wall of organs - the heart, bronchi, digestive tract, bladder, etc. (intramural ganglia- see, for example, fig. 203, 209, 213, 215) or near their surface.

Functionally, autonomic nerve ganglia are divided into sympathetic and parasympathetic. These ganglia differ in their localization (sympathetic lie para- and prevertebral, parasympathetic - intramural or near organs), as well as the localization of neurons that give rise to preganglionic fibers, the nature of neurotransmitters and the direction of reactions mediated by their cells. Most internal organs have dual autonomic innervation. Overall plan the structures of the sympathetic and parasympathetic nerve ganglia are similar.

The structure of the autonomous ganglia. The autonomous ganglion is externally covered with connective tissue. capsule and contains diffuse or clustered bodies multipolar neurons, their processes in the form of non-myelinated or (rarely) myelinated fibers and endoneurium (Fig. 123). The bodies of neurons are basophilic, irregular shape, contain an eccentrically located core; there are multinucleated and polyploid cells. Neurons are surrounded (usually incompletely) by sheaths of glial cells (satellite glial cells, or mantle gliocytes). Outside of the glial membrane is a thin connective tissue membrane (Fig. 124).

intramural ganglia and the pathways associated with them, due to their high autonomy, the complexity of the organization and the peculiarities of the mediator exchange, are distinguished by some authors as an independent metasympathetic division autonomic nervous system. Three types of neurons are described in the intramural ganglia (see Fig. 120):

1) Long-axon efferent neurons (type I Dogel cells) with short dendrites and a long axon extending beyond the node

to the cells of the working organ, on which it forms motor or secretory endings.

2)Equal 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 cells of types I and III. They are part of the local reflex arcs as a receptor link, which are closed without a nerve impulse entering the central nervous system.

3)Association cells (Dogel type III cells)- local intercalary neurons, connecting 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.

Reflex arcs in the somatic (animal) and autonomic (vegetative) parts of the nervous system have a number of features (see Fig. 119 and 120). The main differences are in the associative and effector links, since the receptor link is similar: it is formed by afferent pseudo-unipolar neurons, whose bodies are located in sensory ganglia. The peripheral processes of these cells form sensory nerve endings, while the central processes enter the spinal cord as part of the posterior roots.

Associative link in the somatic arc it is represented by intercalary neurons, the dendrites and bodies of which are located in posterior horns of the spinal cord and axons go to front horns, transmitting impulses to the bodies and dendrites of efferent neurons. In the autonomous arc, the dendrites and bodies of the intercalary neurons are located in lateral horns of the spinal cord and axons (preganglionic fibers) leave the spinal cord as part of the anterior roots, heading to one of the autonomous ganglia, where they end on the dendrites and bodies of efferent neurons.

Effector link in the somatic arch it is formed by multipolar motor neurons, the bodies and dendrites of which lie in the anterior horns of the spinal cord, and the axons leave the spinal cord as part of the anterior roots, go to the sensory ganglion and then, as part of the mixed nerve, to the skeletal muscle, on the fibers of which their branches form neuromuscular synapses. In the autonomous arc, the effector link is formed by multipolar neurons, the bodies of which lie in the autonomous ganglia, and the axons (postganglionic fibers) as part of the nerve trunks and their branches are sent to the cells of the working organs - smooth muscles, glands, heart.

Central nervous system organs Spinal cord

Spinal cord has the appearance of a rounded cord, expanded in the cervical and lumbosacral regions and penetrated by the central canal. It consists of two symmetrical halves, divided in front anterior median fissure, behind - posterior median sulcus and is characterized by a segmental structure; a pair is associated with each segment front (motor, ventral) and a pair back (sensitive, dorsal) roots. In the spinal cord there are Gray matter, located in its central part, and white matter, lying on the periphery (Fig. 125).

Gray matter on the cross section it looks like a butterfly (see Fig. 125) and includes paired anterior (ventral), posterior (dorsal) and lateral (lateral) horns. The horns of the gray matter of both symmetrical parts of the spinal cord are connected to each other in the area anterior and posterior gray commissures. The gray matter contains the bodies, dendrites and (partly) axons of neurons, as well as glial cells. Between the bodies of neurons is neuropil- a network formed by nerve fibers and processes of glial cells. Neurons are located in the gray matter in the form of clusters that are not always sharply demarcated. (kernels).

The posterior horns contain several nuclei formed multipolar interneurons, on which the axons of the pseudounipolar cells of the sensitive ganglia terminate (see Fig. 119), as well as the fibers of the descending pathways from the supraspinal centers lying above. Axons of intercalary neurons a) terminate in the gray matter of the spinal cord on motor neurons lying in the anterior horns (see Fig. 119); b) form intersegmental connections within the gray matter of the spinal cord; c) exit into the white matter of the spinal cord, where they form ascending and descending pathways (tracts).

Lateral horns, well expressed at the level of the thoracic and sacral segments of the spinal cord, contain nuclei formed by the bodies multipolar intercalary neurons, which belong to the sympathetic and parasympathetic divisions of the autonomic nervous system (see Fig. 120). On the dendrites and bodies of these cells, axons terminate: a) pseudo-unipolar neurons that carry impulses from receptors located in internal organs, b) neurons of the centers of regulation of autonomic functions, whose bodies are located in the medulla oblongata. The axons of autonomic neurons, leaving the spinal cord as part of the anterior roots, form a pregan-

glionic fibers leading to the sympathetic and parasympathetic nodes.

The anterior horns contain multipolar motor neurons (motoneurons), combined into nuclei, each of which usually stretches into several segments. There are large α-motor neurons and smaller γ-motor neurons scattered among them. On the processes and bodies of motor neurons there are numerous synapses that have excitatory and inhibitory effects on them. On motor neurons end: collaterals of the central processes of pseudo-unipolar cells of sensory nodes; intercalary neurons, whose bodies lie in the posterior horns of the spinal cord; axons of local small intercalary neurons (Renshaw cells) associated with collaterals of axons of motor neurons; fibers of the descending pathways of the pyramidal and extrapyramidal systems, carrying impulses from the cerebral cortex and nuclei of the brain stem. The bodies of motor neurons contain large clumps of chromatophilic substance (see Fig. 100) and are surrounded by gliocytes (Fig. 126). Motor neuron axons leave the spinal cord front roots, sent to the sensitive ganglion and then, as part of the mixed nerve, to the skeletal muscle, on the fibers of which they form neuromuscular synapses(see fig. 119).

Central channel (see Fig. 128) passes in the center of the gray matter and is surrounded front and posterior gray spikes(see fig. 125). It is filled with cerebrospinal fluid and is lined with a single layer of cuboidal or columnar ependymal cells, the apical surface of which is covered with microvilli and (partially) cilia, while the lateral surfaces are connected by complexes of intercellular junctions.

White matter of the spinal cord surrounds gray (see Fig. 125) and is divided by the anterior and posterior roots into symmetrical rear, side and anterior cords. It consists of longitudinally running nerve fibers (mainly myelinated), forming descending and ascending pathways (tracts). The latter are separated from each other by thin layers of connective tissue and astrocytes, which are also found inside the tracts (Fig. 127). The pathways include two groups: propriospinal (carry out communication between different parts of the spinal cord) and supraspinal pathways (provide communication between the spinal cord and brain structures - ascending and descending tracts).

Cerebellum

Cerebellum is part of the brain and is the center of balance, supporting

zhaniya muscle tone and coordination of movements. It is formed by two hemispheres with a large number of grooves and convolutions on the surface and a narrow middle part (worm). Gray matter forms cerebellar cortex and kernels; the latter lie in the depths of it white matter.

Cerebellar cortex characterized by a high orderliness of the location of neurons, nerve fibers and glial cells of all types. It is distinguished by the richness of interneuronal connections, which ensure the processing of various sensory information entering it. There are three layers in the cerebellar cortex (from outside to inside): 1) molecular layer; 2) layer of Purkinje cells (layer of pear-shaped neurons); 3) granular layer(Fig. 129 and 130).

molecular layer contains a relatively small number of small cells, it contains bodies basket and stellate neurons. basket neurons located in the inner part of the molecular layer. Their short dendrites form bonds with parallel fibers in the outer part of the molecular layer, and a long axon runs across the gyrus, giving off collaterals at certain intervals, which descend to the bodies of Purkinje cells and, branching, cover them like baskets, forming inhibitory axo-somatic synapses (see Fig. 130). stellate neurons- small cells, the bodies of which lie above the bodies of basket neurons. Their dendrites form connections with parallel fibers, and axon ramifications form inhibitory synapses on the dendrites of Purkinje cells and may be involved in the formation of a basket around their bodies.

Layer of Purkinje cells (layer of pear-shaped neurons) contains bodies of Purkinje cells lying in one row, braided with collaterals of axons of basket cells (“baskets”).

Purkinje cells (pear-shaped neurons)- large cells with a pear-shaped body containing well-developed organelles. 2-3 primary (stem) dendrites extend from it into the molecular layer, intensively branching with the formation of terminal (terminal) dendrites, reaching the surface of the molecular layer (see Fig. 130). The dendrites contain numerous spines- contact zones of excitatory synapses formed by parallel fibers (axons of granular neurons) and inhibitory synapses formed by climbing fibers. The axon of the Purkinje cell departs from the base of its body, becomes covered with a myelin sheath, penetrates the granular layer and penetrates the white matter, being the only efferent pathway of its cortex.

Granular layer contains closely spaced bodies granular neurons, large stellate neurons(Golgi cells), as well as cerebellar glomeruli- special rounded complex synaptic contact zones between mossy fibers, dendrites of granular neurons and axons of large stellate neurons.

Granular neurons- the most numerous neurons of the cerebellar cortex - small cells with short dendrites that look like a "bird's foot", on which rosettes of mossy fibers form numerous synaptic contacts in the glomeruli of the cerebellum. The axons of granular neurons are sent to the molecular layer, where they divide in a T-shape into two branches running parallel to the length of the gyrus. (parallel fibers) and forming excitatory synapses on the dendrites of Purkinje cells, basket and stellate neurons, and large stellate neurons.

Large stellate neurons (Golgi cells) larger than granular neurons. Their axons within the glomeruli of the cerebellum form inhibitory synapses on the dendrites of granular neurons, and long dendrites rise into the molecular layer, where they branch and form connections with parallel fibers.

Afferent fibers of the cerebellar cortex include bryophytes and climbing fibers(see Fig. 130), which penetrate into the cerebellar cortex from the spinal cord, medulla oblongata and bridge.

Mossy fibers of the cerebellum end with extensions (sockets)- glomeruli of the cerebellum, forming synaptic contacts with the dendrites of granular neurons, on which the axons of large stellate neurons also terminate. The glomeruli of the cerebellum are not completely surrounded on the outside by flat processes of astrocytes.

Climbing fibers of the cerebellum penetrate into the cortex from the white matter, passing through the granular layer to the layer of Purkinje cells and creeping along the bodies and dendrites of these cells, on which they end in excitatory synapses. Collateral branches of climbing fibers form synapses on other neurons of all types.

Efferent fibers of the cerebellar cortex represented by the axons of Purkinje cells, which in the form of myelin fibers are sent to the white matter and reach the deep nuclei of the cerebellum and the vestibular nucleus, on the neurons of which they form inhibitory synapses (Purkinje cells are inhibitory neurons).

cerebral cortex is the highest and most complex organized

ny nerve center, whose activity ensures the regulation of various functions of the body and complex forms of behavior. The cortex is formed by a layer of gray matter covering the white matter, on the surface of the gyri and in the depths of the furrows. Gray matter contains neurons, nerve fibers, and neuroglial cells of all kinds. Based on differences in cell density and structure (cytoarchitectonics), fiber path (myeloarchitectonics) and functional features of various parts of the cortex in it, 52 unsharply demarcated fields distinguish.

Cortical neurons- multipolar, of various sizes and shapes, include more than 60 species, among which two main types are distinguished - pyramidal and non-pyramidal.

pyramidal cells - type of neurons specific for the cerebral cortex; according to various estimates, they make up 50-90% of all cortical neurons. From the apical pole of their cone-shaped (triangular in sections) body, a long (apical) dendrite covered with spines (Fig. 133) extends to the surface of the cortex (Fig. 133), heading into the molecular plate of the cortex, where it branches. Several shorter lateral (lateral) dendrites diverge from the basal and lateral parts of the body deep into the cortex and to the sides of the body of the neuron, which, branching, spread within the same layer where the cell body is located. A long and thin axon departs from the middle of the basal surface of the body, going into the white matter and giving rise to collaterals. Distinguish giant, large, intermediate and small pyramidal cells. The main function of pyramidal cells is to provide connections within the cortex (intermediate and small cells) and the formation of efferent pathways (giant and large cells).

non-pyramidal cells are located in almost all layers of the cortex, perceiving incoming afferent signals, and their axons spread within the cortex itself, transmitting impulses to pyramidal neurons. These cells are very diverse and are predominantly varieties of stellate cells. The main function of non-pyramidal cells is the integration of neural circuits within the cortex.

Cytoarchitectonics of the cerebral cortex. The neurons of the cortex are arranged in unsharply demarcated layers (plates), which are designated by Roman numerals and numbered from outside to inside. On sections stained with hematoxylin-eosin, connections between neurons are not traced, since only

bodies of neurons and the initial sections of their processes

(Fig. 131).

I - molecular plate located under the pia mater; contains a relatively small number of small horizontal neurons with long branching dendrites extending in the horizontal plane from the fusiform body. Their axons are involved in the formation of a tangential plexus of fibers of this layer. In the molecular layer, there are numerous dendrites and axons of cells of deeper layers that form interneuronal connections.

II - outer granular plate It is formed by numerous small pyramidal and stellate cells, the dendrites of which branch and rise into the molecular plate, and the axons either go into the white matter or form arcs and also go to the molecular plate.

III - external pyramidal plate characterized by the predominance pyramidal neurons, the sizes of which increase deep into the layer from small to large. The apical dendrites of the pyramidal cells are directed to the molecular plate, and the lateral ones form synapses with the cells of this plate. The axons of these cells terminate within the gray matter or are directed to the white. In addition to pyramidal cells, the lamina contains a variety of non-pyramidal neurons. The plate performs predominantly associative functions, connecting cells both within a given hemisphere and with the opposite hemisphere.

IV - inner granular plate contains small pyramidal and stellate cells. In this plate, the main part of the thalamic afferent fibers ends. The axons of the cells of this lamina form connections with the cells of the superior and underlying laminae of the cortex.

V - internal pyramidal plate formed large pyramidal neurons, and in the region of the motor cortex (precentral gyrus) - giant pyramidal neurons(Betz cells). Apical dendrites of pyramidal neurons reach the molecular plate, lateral dendrites extend within the same plate. The axons of giant and large pyramidal neurons project to the nuclei of the brain and spinal cord, the longest of them as part of the pyramidal pathways reach the caudal segments of the spinal cord.

VI - multiform plate formed by neurons of various shapes, and its

the outer areas contain larger cells, while the inner areas contain smaller and sparsely located ones. The axons of these neurons go into the white matter as part of the efferent pathways, and the dendrites penetrate to the molecular plasticity.

Myeloarchitectonics of the cerebral cortex. The nerve fibers of the cerebral cortex include three groups: 1) afferent; 2) associative and commissural; 3) efferent.

Afferent fibers come to the cortex from the lower parts of the brain in the form of bundles in the composition vertical stripes- radial beams (see Fig. 132).

Association and commissural fibers - intracortical fibers that connect different areas of the cortex within one or in different hemispheres, respectively. These fibers form bundles (stripes) which run parallel to the surface of the cortex in plate I (tangential plate), in plate II (dysfibrous plate, or Bechterew's strip), in plate IV (strip of outer granular plate, or outer strip of Bayarzhe) and in plate V (strip of inner granular lamina, or inner strip of Bayarzhe) - see fig. 132. The last two systems are plexuses formed by the terminal sections of afferent fibers.

Efferent fibers connect the cortex with subcortical formations. These fibers run in a downward direction as part of the radial rays.

Types of structure of the cerebral cortex.

In certain areas of the cortex associated with the performance of various functions, the development of certain layers of it predominates, on the basis of which they distinguish agranular and granular types of bark.

Agranular type of bark characteristic of its motor centers and is distinguished by the greatest development of plates III, V and VI of the cortex with a weak development of plates II and IV (granular). Such areas of the cortex serve as sources of descending pathways.

Granular type of bark characteristic of the areas of location of sensitive cortical centers. It is distinguished by a weak development of layers containing pyramidal cells, with a significant severity of granular (II and IV) plates.

White matter of the brain represented by bundles of nerve fibers that rise to the gray matter of the cortex from the brainstem and descend to the brainstem from the cortical centers of the gray matter.

ORGANS OF THE NERVOUS SYSTEM

Organs of the peripheral nervous system

Rice. 114. Nerve (nerve trunk). cross section

Coloring: osmirovanie

1 - nerve fibers; 2 - endoneurium; 3 - perineurium; 4 - epineurium: 4.1 - adipose tissue, 4.2 - blood vessel

Rice. 115. Section of a nerve (nerve trunk)

Coloring: osmirovanie

1 - myelin fiber: 1.1 - neuron process, 1.2 - myelin sheath;

2- unmyelinated fiber; 3 - endoneurium; 4 - perineurium

Rice. 116. Nerve trunk (nerve). cross section

Stain: hematoxylin-eosin

1 - nerve fibers; 2 - endoneurium: 2.1 - blood vessel; 3 - perineurium; 4 - epineurium: 4.1 - fat cells, 4.2 - blood vessels

Rice. 117. Section of the nerve trunk (nerve)

Stain: hematoxylin-eosin

1 - myelin fiber: 1.1 - neuron process, 1.2 - myelin sheath, 1.3 - neurolemmocyte nucleus; 2 - unmyelinated fiber; 3 - endoneurium: 3.1 - blood vessel; 4 - perineurium; 5 - epineurium

Rice. 118. Section of the nerve trunk (nerve)

1 - myelin fiber: 1.1 - neuron process, 1.2 - myelin sheath; 2 - unmyelinated fiber; 3 - endoneurium: 3.1 - blood vessel; 4 - perineurium

Rice. 119. Somatic reflex arc

1.Receptor link formed afferent (sensory) pseudo-unipolar neurons, whose bodies (1.1) are located in the sensory nodes of the spinal nerve (1.2). The peripheral processes (1.3) of these cells form sensory nerve endings (1.4) in the skin or skeletal muscle. The central processes (1.5) enter the spinal cord as part of back roots(1.6) and are sent to posterior horns of gray matter forming synapses on the bodies and dendrites of intercalary neurons (three-neuron reflex arcs, A), or pass into the anterior horns to motor neurons (two-neuron reflex arcs, B).

2.Associative link presented (2.1), whose dendrites and bodies lie in the posterior horns. Their axons (2.2) are sent to front horns, passing nerve impulses on the bodies and dendrites of effector neurons.

3.Efferent link formed multipolar motor neurons(3.1). The bodies and dendrites of these neurons lie in the anterior horns, forming the motor nuclei. Axons (3.2) of motor neurons leave the spinal cord as part of anterior roots(3.3) and further as part of the mixed nerve (4) are sent to the skeletal muscle, where the branches of the axon form neuromuscular synapses (3.4)

Rice. 120. Autonomous (vegetative) reflex arc

1.Receptor link formed afferent (sensory) pseudo-unipolar neuron mi, whose bodies (1.1) lie in the sensory nodes of the spinal nerve (1.2). The peripheral processes (1.3) of these cells form sensory nerve endings (1.4) in the tissues of the internal organs. The central processes (1.5) enter the spinal cord as part of back of them stubs(1.6) and are sent to lateral horns of gray matter forming synapses on the bodies and dendrites of interneurons.

2.Associative link presented multipolar interneurons(2.1), whose dendrites and bodies are located in the lateral horns of the spinal cord. The axons of these neurons are preganglionic fibers (2.2). They leave the spinal cord as part of anterior roots(2.3), heading to one of the autonomic ganglia, where they end on the bodies and dendrites of their neurons.

3.Efferent link formed multipolar or bipolar neurons, whose bodies (3.1) lie in autonomous ganglia (3.2). The axons of these cells are postganglionic fibers (3.3). As part of the nerve trunks and their branches, they are sent to the cells of the working organs - smooth muscles, glands, heart, forming endings on them (3.4). In the vegetative ganglia, in addition to "long-axon" efferent neurons - Dogel type I (DI) cells, there are "equally outgrowth" afferent neurons - Dogel type II (DII) cells, which are part of the local reflex arcs as a receptor link, and type III associative cells Dogelya (DIII) - small intercalary neurons

Rice. 121. Sensory ganglion of the spinal nerve

Stain: hematoxylin-eosin

1 - back spine; 2 - sensitive ganglion of the spinal nerve: 2.1 - connective tissue capsule, 2.2 - bodies of pseudo-unipolar sensory neurons, 2.3 - nerve fibers; 3 - front spine; 4 - spinal nerve

Rice. 122. Pseudo-unipolar neuron of the sensory ganglion of the spinal nerve and its tissue microenvironment

Stain: hematoxylin-eosin

1 - body of a pseudo-unipolar sensitive neuron: 1.1 - nucleus, 1.2 - cytoplasm; 2 - satellite glial cells; 3 - connective tissue capsule around the body of the neuron

Rice. 123. Autonomous (vegetative) ganglion from the solar plexus

1 - preganglionic nerve fibers; 2 - autonomous ganglion: 2.1 - connective tissue capsule, 2.2 - bodies of multipolar autonomic neurons, 2.3 - nerve fibers, 2.4 - blood vessels; 3 - postganglionic fibers

Rice. 124. Multipolar neuron of the autonomic ganglion and its tissue microenvironment

Stain: iron hematoxylin

1 - body of a multipolar neuron: 1.1 - nucleus, 1.2 - cytoplasm; 2 - the beginning of processes; 3 - gliocytes; 4 - connective tissue sheath

Organs of the central nervous system

Rice. 125. Spinal cord (cross section)

Colour: silver nitrate

1 - gray matter: 1.1 - anterior (ventral) horn, 1.2 - posterior (dorsal) horn, 1.3 - lateral (lateral) horn; 2 - anterior and posterior gray adhesions: 2.1 - central canal; 3 - anterior median fissure; 4 - posterior median sulcus; 5 - white matter (tracts): 5.1 - dorsal cord, 5.2 - lateral cord, 5.3 - ventral cord; 6 - soft shell of the spinal cord

Rice. 126. Spinal cord.

Area of gray matter (anterior horns)

Stain: hematoxylin-eosin

1- bodies of multipolar motor neurons;

2- gliocytes; 3 - neuropil; 4 - blood vessels

Rice. 127. Spinal cord. area of white matter

Stain: hematoxylin-eosin

1 - myelinated nerve fibers; 2 - nuclei of oligodendrocytes; 3 - astrocytes; 4 - blood vessel

Rice. 128. Spinal cord. Central channel

Stain: hematoxylin-eosin

1 - ependymocytes: 1.1 - cilia; 2 - blood vessel

Rice. 129. Cerebellum. Bark

(slice perpendicular to the course of the convolutions)

Stain: hematoxylin-eosin

1 - soft shell of the brain; 2 - gray matter (cortex): 2.1 - molecular layer, 2.2 - layer of Purkinje cells (pear-shaped neurons), 2.3 - granular layer; 3 - white matter

Rice. 130. Cerebellum. Plot of bark

Colour: silver nitrate

1 - molecular layer: 1.1 - dendrites of Purkinje cells, 1.2 - afferent (climbing) fibers, 1.3 - neurons of the molecular layer; 2 - layer of Purkinje cells (piri-shaped neurons): 2.1 - bodies of pear-shaped neurons (Purkinje cells), 2.2 - "baskets" formed by collaterals of axons of basket neurons; 3 - granular layer: 3.1 - bodies of granular neurons, 3.2 - axons of Purkinje cells; 4 - white matter

Rice. 131. Cerebral hemisphere. Bark. Cytoarchitectonics

Stain: hematoxylin-eosin

1 - soft shell of the brain; 2 - gray matter: plates (layers) of the cortex are indicated by Roman numerals: I - molecular plate, II - outer granular plate, III - outer pyramidal plate, IV - inner granular plate, V - inner pyramidal plate, VI - multiform plate; 3 - white matter

Rice. 132. Cerebral hemisphere. Bark.

Myeloarchitectonics

(scheme)

1 - tangential plate; 2 - dysfibrous plate (Bekhterev's strip); 3 - radial rays; 4 - strip of the outer granular plate (outer strip of Bayarzhe); 5 - strip of internal granular plate (internal strip of Bayarzhe)

Rice. 133. Large pyramidal neuron of the cerebral hemisphere

Colour: silver nitrate

1 - large pyramidal neuron: 1.1 - neuron body (pericarion), 1.2 - dendrites, 1.3 - axon;

2- gliocytes; 3 - neuropil

Spinal cord- medulla spinalis - lies in the spinal canal, occupying approximately 2/3 of its volume. In cattle and horses, its length is 1.8–2.3 m, weight 250–300 g, in pigs it is 45–70 g. It looks like a cylindrical cord, somewhat flattened dorsoventrally. There is no clear boundary between the brain and spinal cord. It is believed that it runs along the anterior margin of the atlas. In the spinal cord, cervical, thoracic, lumbar, sacral and caudal parts are distinguished according to their location. In the embryonic period of development, the spinal cord fills the entire spinal canal, but due to the high growth rate of the skeleton, the difference in their length becomes larger. As a result, the brain in cattle ends at the level of the 4th, in the pig - in the region of the 6th lumbar vertebra, and in the horse - in the region of the 1st segment of the sacral bone. Along the entire spinal cord along its dorsal surface passes median dorsal groove. Connective tissue departs from it deep into dorsal septum. On the sides of the median sulcus are smaller dorsal lateral grooves. On the ventral surface there is a deep median ventral fissure, and on the sides of it - ventral lateral grooves. At the end, the spinal cord sharply narrows, forming cerebral cone, which goes into terminal thread. It is formed by connective tissue and ends at the level of the first tail vertebrae.

There are thickenings in the cervical and lumbar parts of the spinal cord. In connection with the development of the limbs, the number of neurons and nerve fibers in these areas increases. At the pig cervical enlargement formed by 5–8 neurosegments. Its maximum width at the level of the 6th cervical vertebra is 10 mm. Lumbar thickening falls on the 5th-7th lumbar neurosegments. In each segment, a pair of spinal nerves departs from the spinal cord with two roots - on the right and on the left. The dorsal root arises from the dorsal lateral groove, the ventral root from the ventral lateral groove. The spinal nerves leave the spinal canal through the intervertebral foramen. The area of the spinal cord between two adjacent spinal nerves is called neurosegment.

Neurosegments are of different lengths and often do not correspond in size to the length of the bone segment. As a result, the spinal nerves depart at different angles. Many of them travel some distance inside the spinal canal before leaving the intervertebral foramen of their segment. In the caudal direction, this distance increases and from the nerves running inside the spinal canal, behind the cerebral cone, a kind of brush is formed, which is called the "ponytail".

Histological structure. On a transverse section of the spinal cord with the naked eye, its division into white and gray matter is visible.

Gray matter is in the middle and looks like the letter H or a flying butterfly. A small hole is visible in its center - a cross section central spinal canal. The area of gray matter around the central canal is called gray commissure. Directed upwards from her dorsal pillars(on a cross section - horns), down - ventral columns (horns) gray matter. In the thoracic and lumbar parts of the spinal cord, there are thickenings on the sides of the ventral columns - lateral pillars, or horns gray matter. The composition of the gray matter includes multipolar neurons and their processes that are not covered with a myelin sheath, as well as neuroglia.

Fig.142. Spinal cord (according to I.V. Almazov, L.S. Sutulov, 1978)

1 - dorsal median septum; 2 - ventral median fissure; 3 - ventral root; 4 - ventral gray commissure; 5 - dorsal gray commissure; 6 - spongy layer; 7 - gelatinous substance; 8 - dorsal horn; 9 - mesh reticular formation; 10 - lateral horn; 11 - ventral horn; 12 - own nucleus of the posterior horn; 13 - dorsal nucleus; 14 - cores of the intermediate zone; 15 - lateral core; 16 - nuclei of the ventral horn; 17 - shell of the brain.

Neurons in different parts of the brain differ in structure and function. In this regard, various zones, layers and cores are distinguished in it. The bulk of the neurons of the dorsal horns are associative, intercalary neurons that transmit the nerve impulses that come to them either to motor neurons, or to the lower and upper parts of the spinal cord, and then to the brain. The axons of sensory neurons of the spinal ganglia approach the dorsal columns. The latter enter the spinal cord in the region of the dorsal lateral grooves in the form of dorsal roots. The degree of development of the dorsal lateral columns (horns) is directly dependent on the degree of sensitivity.

The ventral horns contain motor neurons. These are the largest multipolar nerve cells in the spinal cord. Their axons form the ventral roots of the spinal nerves, extending from the spinal cord in the region of the ventral lateral sulcus. The development of the ventral horns depends on the development of the locomotor apparatus. The lateral horns contain neurons belonging to the sympathetic nervous system. Their axons leave the spinal cord as part of the ventral roots and form the white connecting branches of the borderline sympathetic trunk.

white matter forms the periphery of the spinal cord. In the area of thickening of the brain, it prevails over the gray matter. Consists of myelinated nerve fibers and neuroglia. The myelin sheath of the fibers gives them a whitish-yellowish color. The dorsal septum, ventral fissure and pillars (horns) of the gray matter divide the white matter into cords: dorsal, ventral and lateral. Dorsal cords do not connect with each other, since the dorsal septum reaches the gray commissure. Lateral cords separated by a mass of gray matter. Ventral cords communicate with each other in the area white spike- an area of white matter lying between the ventral fissure and the gray commissure.

Complexes of nerve fibers passing in the cords form pathways. More deeply lying complexes of fibers form conducting paths connecting different segments of the spinal cord. Together they amount to own apparatus spinal cord. More superficially located complexes of nerve fibers form afferent (sensory, or ascending) and efferent (motor, or descending) projection pathways connecting the spinal cord to the brain. Sensory pathways from the spinal cord to the brain run in the dorsal cords and in the superficial layers of the lateral cords. The motor pathways from the brain to the spinal cord run in the ventral cords and in the middle sections of the lateral cords.

The spinal cord (SM) consists of 2 symmetrical halves, separated in front by a deep fissure and behind by a commissure. The transverse section clearly shows the gray and white matter. The gray matter of the SM on the cut has the shape of a butterfly or the letter "H" and has horns - anterior, posterior and lateral horns. The gray matter of the SM consists of bodies of neurocytes, nerve fibers and neuroglia.

The abundance of neurocytes determines the gray color of the gray matter of the SM. Morphologically, SM neurocytes are predominantly multipolar. Neurocytes in the gray matter are surrounded by nerve fibers tangled like felt - neuropil. The axons in the neuropil are weakly myelinated, while the dendrites are not at all myelinated. Similar in size, fine structure, and functions, SC neurocytes are arranged in groups and form nuclei.

Among SM neurocytes, the following types are distinguished:

1. Radicular neurocytes - located in the nuclei of the anterior horns, they are motor in function; axons of radicular neurocytes as part of the anterior roots leave the spinal cord and conduct motor impulses to the skeletal muscles.

2. Internal cells - the processes of these cells do not leave the limits of the gray matter of the SC, they end within the given segment or the neighboring segment, i.e. are associative in function.

3. Beam cells - the processes of these cells form the nerve bundles of the white matter and are sent to neighboring segments or overlying sections of the NS, i.e. are also associative in function.

The posterior horns of the SM are shorter, narrower and contain the following types of neurocytes:

a) beam neurocytes - located diffusely, receive sensitive impulses from the neurocytes of the spinal ganglia and transmit along the ascending paths of the white matter to the overlying sections of the NS (to the cerebellum, to the cerebral cortex);

b) internal neurocytes - transmit sensitive impulses from the spinal ganglia to the motor neurocytes of the anterior horns and to neighboring segments.

There are 3 zones in the posterior horns of the CM:

1. Spongy substance - consists of small bundled neurocytes and gliocytes.

2. Gelatinous substance - contains a large number of gliocytes, has practically no neurocytes.

3. Proprietary SM nucleus - consists of bundled neurocytes that transmit impulses to the cerebellum and thalamus.

4. Clark's nucleus (Thoracic nucleus) - consists of bundled neurocytes, the axons of which, as part of the lateral cords, are sent to the cerebellum.

In the lateral horns (intermediate zone) there are 2 medial intermediate nuclei and a lateral nucleus. The axons of the bundle associative neurocytes of the medial intermediate nuclei transmit impulses to the cerebellum. The lateral nucleus of the lateral horns in the thoracic and lumbar SM is the central nucleus of the sympathetic division of the autonomic NS. The axons of the neurocytes of these nuclei go as part of the anterior roots of the spinal cord as preganglionic fibers and terminate on the neurocytes of the sympathetic trunk (prevertebral and paravertebral sympathetic ganglia). The lateral nucleus in the sacral SM is the central nucleus of the parasympathetic division of the autonomic NS.

The anterior horns of the SM contain a large number of motor neurons (motor neurons) that form 2 groups of nuclei:

1. Medial group of nuclei - innervates the muscles of the body.

2. The lateral group of nuclei is well expressed in the region of the cervical and lumbar thickening - it innervates the muscles of the extremities.

According to their function, among the motoneurons of the anterior horns of the SM are distinguished:

1. - motor neurons are large - have a diameter of up to 140 microns, transmit impulses to extrafusal muscle fibers and provide rapid muscle contraction.

2. -small motor neurons - maintain the tone of skeletal muscles.

3. -motoneurons - transmit impulses to intrafusal muscle fibers (as part of the neuromuscular spindle).

Motoneurons are an integrative unit of the SM; they are influenced by both excitatory and inhibitory impulses. Up to 50% of the body surface and motor neuron dendrites are covered with synapses. The average number of synapses per 1 human SC motor neuron is 25-35 thousand. At the same time, 1 motor neuron can transmit impulses from thousands of synapses coming from neurons of the spinal and supraspinal levels.

Reverse inhibition of motor neurons is also possible due to the fact that the axon branch of the motor neuron transmits an impulse to inhibitory Renshaw cells, and the axons of Renshaw cells terminate on the body of the motor neuron with inhibitory synapses.

Axons of motor neurons leave the spinal cord as part of the anterior roots, reach the skeletal muscles, and end on each muscle fiber with a motor plaque.

The white matter of the spinal cord consists of longitudinally oriented predominantly myelinated nerve fibers that form the posterior (ascending), anterior (descending) and lateral (both ascending and descending) cords, as well as glial elements.

The spinal cord (SM) consists of 2 symmetrical halves, separated in front by a deep fissure and behind by a commissure. On the cross section, gray and white matter is clearly visible. The gray matter of the SM on the cut has the shape of a butterfly or the letter "H" and has horns - anterior, posterior and lateral horns. The gray matter of the SM consists of bodies of neurocytes, nerve fibers and neuroglia.

The abundance of neurocytes determines the gray color of the gray matter of the SM. Morphologically, SM neurocytes are predominantly multipolar. Neurocytes in the gray matter are surrounded by nerve fibers tangled like felt - neuropil. The axons in the neuropil are weakly myelinated, while the dendrites are not at all myelinated. Similar in size, fine structure, and functions, SM neurocytes are arranged in groups and form nuclei.

Among SM neurocytes, the following types are distinguished:

2. Internal cells - the processes of these cells do not leave the limits of the gray matter of the SM, end within the given segment or the neighboring segment, i.e. are associative in function.

3. Beam cells - the processes of these cells form nerve bundles of white matter and are sent to neighboring segments or overlying sections of the NS, i.e. are also associative in function.