The spinal cord is located in the spinal canal and has the appearance of a rounded cord in cross section, expanded in the cervical and lumbar regions. 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. Each segment is associated with a pair of anterior (ventral) and a pair of posterior (dorsal) roots. The spinal cord is composed of centrally located gray matter and surrounding white matter. The gray matter on the cut has the shape of a butterfly. The protrusions of gray matter that stretch along the spinal cord are called pillars. There are back, side and front pillars. The pillars on the cross section are called horns. The gray matter consists of grouped multipolar neurons and neurogliocytes, unmyelinated and thin myelinated fibers.

Clusters of neurons that share a common morphology and function are called nuclei. . In the posterior horns there are:

· Lissauer marginal zone - the place of branching of the fibers of the dorsal roots when they enter the spinal cord;

· spongy substance , represented by a large-loop glial skeleton with large neurons;

· gelatinous (gelatinous) substances o, formed by neuroglia with small nerve cells;

· own nucleus of the posterior horn , consisting of beam cells, the processes of which, passing through the anterior commissure into the lateral funiculus of the opposite side of the spinal cord, reach the cerebellum as part of the anterior spinal tract;

· clark core , which also consists of beam cells, the axons of which, passing as part of the posterior spinal cerebellar tract, are connected with the cerebellum.

The intermediate zone of gray matter surrounds the spinal canal, which is lined with ependymoglia. In the intermediate zone there are nuclei:

· medial, consisting of beam cells, the neurons of which join the anterior spinal cerebellar tract;

· lateral, located in the lateral horns, consisting of a group of associative cells, which are the first neuron of the efferent sympathetic pathway.

The largest nerve cells lie in the anterior horns, as part of the posterior and anterior medial nuclei, formed by motor (radicular) neurons, the axons of which exit the spinal cord as part of the anterior roots and innervate the muscles of the body. The posterior and anterior lateral nuclei are also formed by motor neurons that innervate the muscles of the upper and lower extremities.

The white matter is represented by longitudinally running pulpy nerve fibers collected in bundles that make up the pathways of the spinal cord. In the white matter, there are: posterior, lateral and anterior funiculus.

The bundles are divided into two groups: some connect only certain parts of the spinal cord and lie in the anterior and lateral cords directly at the gray matter, forming their own pathways of the spinal cord. Another group of bundles connects the spinal cord and brain.

There are ascending and descending paths. The ascending pathways form the posterior funiculus and ascend into the medulla oblongata.

Distinguish gentle Gaulle bundle, formed by axons of sensory cells, the receptors of which lie in the lower half of the body and wedge-shaped bundle of Burdach , whose receptors perceive excitation in the upper half of the body. These bundles end in the nuclei of the medulla oblongata. These are the ways of tactile, pain, temperature sensitivity.

The lateral funiculus consists of the ascending tracts of the spinocerebellar anterior and spinocerebellar posterior. Irritation along these pathways reaches the anterior part of the cerebellum and switches to motor pathways from the cerebellum to the red nucleus.

Downstream paths include:

1. Pathways connecting the spinal cord with the cerebral cortex: pyramidal, corticospinal way and anterior corticospinal path lying in the anterior funiculus. These pathways are of great importance for the implementation of conscious coordinated body movements. All motor impulses of these movements are transmitted through the pyramidal pathways. bulbospinal the path also carries impulses from the cerebral cortex.

2. Communication with the medulla oblongata is carried out vestibulospinal path (deuterospinal), which is of great importance for maintaining and correct orientation of the body in space, since to the cells of the nucleus Deiters processes of neurons with receptor apparatuses in the semicircles of the vestibular apparatus are suitable.

3. Communication with the cerebellum and midbrain is carried out rubrospinal path coming from the cells of the red nuclei of the spinal cord. The impulses along this path control all automatic movements.

4. No less important is the connection of the spinal cord with the quadrigemina of the midbrain, which is carried out tectospinal and reticulospinal way. The quadrigemina receives fibers from the optic nerve and from the occipital region of the cortex, and the impulses traveling along this path to motor neurons provide clarification and direction of movements.

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

In the spinal cord, gray matter located in the central part and white matter lying along the periphery are distinguished.

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

The gray matter in cross section is butterfly-shaped and includes anterior or ventral, posterior or dorsal, and lateral or lateral horns. The gray matter contains the bodies, dendrites and (partly) axons of neurons, as well as glial cells. The main component of the gray matter are multipolar neurons.

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

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

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

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

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

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

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

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

Represents flattened strand located in the spinal canal, about 45 cm long in men and 42 cm in women. In places where the nerves exit to the upper and lower extremities, the spinal cord has two thickenings: cervical and lumbar.

The spinal cord is made up of two types of fabric: outer white (bundles of nerve fibers) and inner gray matter (nerve cell bodies, dendrites and synapses). In the center of the gray matter, a narrow channel with cerebrospinal fluid runs along the entire brain. The spinal cord has segmental structure(31-33 segments), each of its sections is associated with a specific part of the body, 31 pairs of spinal cords depart from the segments of the spinal cord nerves: 8 pairs of cervical (Ci-Cviii), 12 pairs of thoracic (Thi-Thxii), 5 pairs of lumbar (Li-Lv), 5 pairs of sacral (Si-Sv) and a pair of coccygeal (Coi-Coiii).

Each nerve divides into front and back roots. back roots- afferent pathways front roots efferent pathways. Afferent impulses from the skin, motor apparatus, and internal organs enter the spinal cord along the posterior roots of the spinal nerves. The anterior roots are formed by motor nerve fibers and transmit efferent impulses to the working organs. Sensory nerves predominate over motor nerves, so there is a primary analysis of incoming afferent signals and the formation of reactions that are most important for the body at the moment (the transmission of numerous afferent impulses to a limited number of efferent neurons is called convergence).

Total spinal cord neurons is about 13 million. They are subdivided: 1) according to the department of the nervous system - neurons of the somatic and autonomic NS; 2) by appointment - efferent, afferent, insertion; 3) by influence - excitatory and inhibitory.

Functions of neurons in the spinal cord.

Efferent neurons belong to the somatic nervous system and innervate skeletal muscles - motor neurons. There are alpha and gamma motor neurons. A-motor neurons carry out transmission of signals from the spinal cord to skeletal muscles. The axons of each motor neuron divide many times, so each of them covers many muscle fibers, forming a motor motor unit with it. G-motor neurons innervate the muscle fibers of the muscle spindle. They have a high frequency of impulses, receive information about the state of the muscle spindle through intermediate neurons (intercalary). Generate pulses with a frequency of up to 1000 per second. These are phonoactive neurons with up to 500 synapses on their dendrites.

Afferent neurons somatic NS are localized in the spinal ganglia and ganglia of the cranial nerves. Their processes conduct impulses from muscle, tendon, and skin receptors, enter the corresponding segments of the spinal cord, and connect by synapses with intercalary or alpha motor neurons.

Function intercalary neurons consists in the organization of communication between the structures of the spinal cord.

Neurons of the autonomic nervous system are intercalary . Sympathetic neurons located in the lateral horns of the thoracic spinal cord, they have a rare impulse frequency. Some of them are involved in maintaining vascular tone, others in the regulation of the smooth muscles of the digestive system.

The collection of neurons forms the nerve centers.

The spinal cord contains control centers most internal organs and skeletal muscles. Centers skeletal muscle control are located in all parts of the spinal cord and innervate, according to the segmental principle, the skeletal muscles of the neck (Ci-Civ), diaphragm (Ciii-Cv), upper limbs (Cv-Thii), trunk (Thiii-Li), lower limbs (Lii-Sv). When certain segments of the spinal cord or its pathways are damaged, specific motor and sensory disorders develop.

Functions of the spinal cord:

A) provides a two-way connection between the spinal nerves and the brain - a conductive function;

B) carries out complex motor and vegetative reflexes - a reflex function.

Morphofunctional organization of the spinal cord

The spinal cord is the most ancient part of the central nervous system of vertebrates. It is already present in the lancelet, the most primitive representative of the chordates.

The spinal cord is the caudal part of the CNS. It is placed in the spinal canal and has an unequal length in different representatives of vertebrates.

In humans, the roots of the caudal sections of the spinal cord gather in the caudal section of the spinal canal, forming the so-called cauda equina.

Spinal cord characterized by a segmental structure. The spinal cord is divided into cervical, thoracic, lumbar, sacral and coccygeal regions. Each department consists of several segments. The cervical region includes 8 segments (C 1 - C 8), the thoracic - 12 (Th 1 - Th 12), the lumbar - 5 (L 1 - L 5), the sacral - 5 (S 1 - S 5) and the coccygeal - 1- 3 (Co 1 - Co 3). Two pairs of roots depart from each segment, which correspond to one of the vertebrae and leave the spinal canal through the opening between them.

There are dorsal (rear) and ventral (anterior) roots. The dorsal roots are formed by the central axons of primary afferent neurons, whose bodies lie in the spinal ganglia.

The ventral roots are formed by axons of α- and γ-motoneurons and unmyelinated fibers of neurons of the autonomic nervous system. This distribution of afferent and efferent fibers was established independently at the beginning of the 19th century by C. Bell (1811) and F. Magendie (1822). The different distribution of functions in the anterior and posterior roots of the spinal cord is called the Bell-Magendie law. Segments of the spinal cord and vertebrae correspond to the same metamere. Nerve fibers of a pair of posterior roots go not only to their own metamere, but also above and below - to neighboring metameres. The skin area in which these sensory fibers are distributed is called the dermatome.

The number of fibers in the dorsal root is much greater than in the ventral one.

Neuronal structures of the spinal cord. The central part of the transverse section of the spinal cord is occupied by gray matter. Surrounding the gray matter is white matter. In the gray matter, anterior, posterior, and lateral horns are distinguished, and in the white matter, columns (ventral, dorsal, lateral, etc.).

The neuronal composition of the spinal cord is quite diverse. There are several types of neurons. The bodies of the neurons of the spinal ganglia are located outside the spinal cord. The axons of these neurons enter the spinal cord. The neurons of the spinal ganglia are unipolar or pseudo-unipolar neurons. In the spinal ganglia lie the bodies of somatic afferents that innervate mainly skeletal muscles. The bodies of other sensitive neurons are located in the tissue and in the intramural ganglia of the autonomic nervous system and provide sensitivity only to the internal organs. They are of two types: large - with a diameter of 60-120 microns and small - with a diameter of 14-30 microns. Large ones give myelinated fibers, and small ones - myelinated and unmyelinated. Nerve fibers of sensitive cells are classified into A-, B- and C-fibers according to the speed of conduction and diameter. Thick myelinated A fibers with a diameter of 3 to 22 microns and a conduction speed of 12 to 120 m / s are divided into subgroups: alpha fibers - from muscle receptors, beta fibers - from tactile and baroreceptors, delta fibers - from thermoreceptors, mechanoreceptors and pain receptors. To group B fibers include myelinated fibers of medium thickness with a speed of excitation of 3-14 m/s. They mainly convey the sensation of pain. To type C afferents include the majority of non-myelinated fibers with a thickness of not more than 2 microns and a conduction speed of up to 2 m / s. These are fibers that come from pain, chemo- and some mechanoreceptors.

In the gray matter of the spinal cord, the following elements are distinguished:

1) efferent neurons (motoneurons);

2) intercalary neurons;

3) neurons of the ascending tracts;

4) intraspinal fibers of sensitive afferent neurons.

motor neurons concentrated in the anterior horns, where they form specific nuclei, all of whose cells send their axons to a specific muscle. Each motor nucleus usually stretches over several segments, therefore their axons, which innervate the same muscle, leave the spinal cord as part of several ventral roots.

Interneurons are localized in the intermediate zone of gray matter. Their axons extend both within the segment and into the nearest neighboring segments. Interneurons- a heterogeneous group, the dendrites and axons of which do not leave the limits of the spinal cord. Interneurons form synaptic contacts only with other neurons, and they are the majority. Interneurons account for about 97% of all neurons. In size, they are smaller than α-motor neurons, capable of high-frequency impulses (above 1000 per second). For propriospinal intercalary neurons a characteristic property is to send long axons through several segments and terminate on motor neurons. At the same time, fibers of various descending tracts converge on these cells. Therefore, they are relay stations on the way from overlying neurons to motor neurons. A special group of intercalary neurons is formed by inhibitory neurons. These include, for example, Renshaw cells.

Ascending tract neurons are also entirely within the CNS. The bodies of these neurons are located in the gray matter of the spinal cord.

Central endings of primary afferents have their own characteristics. After entering the spinal cord, the afferent fiber usually gives rise to ascending and descending branches, which can travel considerable distances along the spinal cord. The terminal branches of one nerve afferent fiber have numerous synapses on one motor neuron. In addition, it was found that one fiber coming from the stretch receptor forms synapses with almost all motor neurons of this muscle.

Roland's gelatinous substance is located in the dorsal part of the dorsal horn.

The most accurate idea of ​​the topography of the nerve cells of the gray matter of the spinal cord is given by dividing it into successive layers or plates, in each of which, as a rule, neurons of the same type are grouped.

According to these data, the entire gray matter of the spinal cord was divided into 10 plates (Rexed) (Fig. 2.2).

I - marginal neurons - give rise to the spinothalamic tract;

II-III - gelatinous substance;

I-IV - in general, the primary sensory area of ​​the spinal cord (afferentation from exteroreceptors, afferentation from skin and pain sensitivity receptors);

Rice. 2.2. Division of the gray matter of the spinal cord into plates (according to Rexed)

V-VI - intercalary neurons are localized, which receive inputs from the posterior roots and descending tracts (corticospinal, rubrospinal);

VII-VIII - propriospinal intercalary neurons are located (from proprioreceptors, fibers of the vestibulo-spinal and reticulo-spinal
tracts), axons of propriospinal neurons;

IX - contains the bodies of α- and γ-motor neurons, presynaptic fibers of the primary afferents from muscle stretch receptors, the end of the fibers of the descending tracts;

X - surrounds the spinal canal and contains, along with neurons, a significant amount of glial cells and commissural fibers.

Properties of the nerve elements of the spinal cord. The human spinal cord contains approximately 13 million neurons.

α-motor neurons are large cells with long dendrites, having up to 20,000 synapses, most of which are formed by the endings of intraspinal intercalary neurons. The speed of conduction along their axon is 70-120 m/s. Rhythmic discharges with a frequency of not more than 10-20 pulses / s are characteristic, which is associated with pronounced trace hyperpolarization. These are the output neurons. They transmit signals to skeletal muscle fibers produced in the spinal cord.

γ-motor neurons are smaller cells. Their diameter is not more than 30-40 microns, they do not have direct contact with the primary afferents.
γ-motoneurons innervate intrafusal (intrafusiform) muscle fibers.

They are monosynaptically activated by the fibers of the descending tracts, which plays an important role in α-, γ-interaction. The speed of conduction along their axon is lower - 10-40 m/s. The pulse frequency is higher than that of α-motor
neurons, - 300-500 pulses / s.

In the lateral and anterior horns there are preganglionic neurons of the autonomic nervous system - their axons are sent to the ganglion cells of the sympathetic nerve chain and to the intramural ganglia of the internal organs.

The bodies of sympathetic neurons, whose axons form preganglionic fibers, are located in the intermediolateral nucleus of the spinal cord. Their axons belong to the B-fiber group. They are characterized by constant tonic impulsation. Some of these fibers are involved in maintaining vascular tone, while others provide the regulation of visceral effector structures (smooth muscles of the digestive system, glandular cells).

The bodies of parasympathetic neurons form the sacral parasympathetic nuclei. They are located in the gray matter of the sacral spinal cord. Many of them are characterized by background impulse activity, the frequency of which increases, for example, as the pressure in the bladder increases.

It is a system of tissues and organs built from nervous tissue. It highlights:

Central region: brain and spinal cord

Peripheral: autonomic and sensory ganglia, peripheral nerves, nerve endings.

There is also a division into:

Somatic (animal, cerebrospinal) department;

Vegetative (autonomous) department: sympathetic and parasympathetic parts.

The nervous system is formed by the following embryonic sources: neural tube, neural crest (ganglion plate) and embryonic placodes. The tissue elements of the membranes are mesenchymal derivatives. At the stage of neuropore closure, the anterior end of the tube expands significantly, the side walls thicken, forming the beginnings of three cerebral vesicles. The bladder lying cranially forms the forebrain, the middle bladder forms the midbrain, and the posterior (rhomboid) brain develops from the third bladder, which passes into the anlage of the spinal cord. Soon after this, the neural tube bends almost at a right angle, and through the narrowing furrows, the first bladder is divided into the final and intermediate sections, and the third cerebral bladder into the medulla oblongata and posterior sections of the brain. Derivatives of the middle and posterior cerebral vesicles form the brainstem and are ancient formations; they retain the segmental principle of structure, which disappears in the derivatives of the diencephalon and telencephalon. In the latter, integrative functions are concentrated. This is how five parts of the brain are formed: the final and diencephalon, middle, medulla oblongata and hindbrain (in humans, this occurs approximately at the end of the 4th week of embryonic development). The telencephalon forms the two hemispheres of the cerebrum.

In the embryonic histo- and organogenesis of the nervous system, the development of different parts of the brain occurs at different rates (heterochronously). Earlier, the caudal parts of the central nervous system (spinal cord, brain stem) are formed; the time of the final formation of brain structures varies greatly. In a number of parts of the brain, this occurs after birth (cerebellum, hippocampus, olfactory bulb); in each part of the brain there are spatio-temporal gradients in the formation of neuronal populations that form a unique structure of the nerve center.

The spinal cord is a part of the central nervous system, in the structure of which the features of the embryonic stages of development of the brain of vertebrates are most clearly preserved: the tubular nature of the structure and segmentation. In the lateral sections of the neural tube, the mass of cells rapidly increases, while its dorsal and ventral parts do not increase in volume and retain their ependymal character. The thickened lateral walls of the neural tube are divided by a longitudinal groove into the dorsal - alar, and ventral - the main plate. At this stage of development, three zones can be distinguished in the lateral walls of the neural tube: ependyma lining the central canal, intermediate (cloak layer) and marginal (marginal veil). The gray matter of the spinal cord subsequently develops from the mantle layer, and its white matter develops from the marginal veil. The neuroblasts of the anterior columns differentiate into motor neurons (motor neurons) of the nuclei of the anterior horns. Their axons exit the spinal cord and form the anterior roots of the spinal nerves. In the posterior columns and the intermediate zone, various nuclei of intercalary (associative) cells develop. Their axons, entering the white matter of the spinal cord, are part of various conducting bundles. The posterior horns include the central processes of the sensory neurons of the spinal nodes.

Simultaneously with the development of the spinal cord, the spinal and peripheral nodes of the autonomic nervous system are laid. The starting material for them is the stem cell elements of the neural crest, which, through divergent differentiation, develop in the neuroblastic and glioblastic directions. Part of the neural crest cells migrate to the periphery to the localization sites of the nodes of the autonomic nervous system, paraganglia, neuroendocrine cells of the APUD series, and chromaffin tissue.

Peripheral nervous system.

The peripheral nervous system combines peripheral nerve nodes, trunks and endings.

Nerve ganglia (nodes) - structures formed by clusters of neurons outside the central nervous system - are divided into sensitive and autonomous (vegetative). Sensory ganglia contain pseudo-unipolar or bipolar (in the spiral and vestibular ganglia) afferent neurons and are located mainly along the posterior roots of the spinal cord (sensory nodes of the spinal nerves) and some cranial nerves. The sensory ganglia of the spinal nerves are fusiform and covered with a capsule of dense fibrous connective tissue. On the periphery of the ganglion there are dense clusters of bodies of pseudo-unipolar neurons, and the central part is occupied by their processes and thin layers of endoneurium located between them, carrying vessels. Autonomic nerve ganglia are formed by clusters of multipolar neurons, on which numerous synapses form preganglionic fibers - processes of neurons whose bodies lie in the CNS.

Nerve. Building and regeneration. Spinal ganglia. Morphofunctional characteristics.

Nerves (nerve trunks) connect the nerve centers of the brain and spinal cord with receptors and working organs. They are formed by bundles of myelinated and non-myelinated fibers, which are united by connective tissue components (shells): endoneurium, perineurium and epineurium. Most of the nerves are mixed, i.e. include afferent and efferent fibers.

Endoneurium - thin layers of loose fibrous connective tissue with small blood vessels, surrounding individual nerve fibers and linking them into a single bundle. The perineurium is a sheath that covers each bundle of nerve fibers from the outside and extends the partitions deep into the bundle. It has a lamellar structure and images of concentric layers of flattened fibroblast-like cells connected by dense and slotted joints. Between the layers of cells in the spaces filled with liquid, there are components of the basement membrane and longitudinally oriented collagen fibers. Epineurium is the outer sheath of the nerve that binds bundles of nerve fibers together. It consists of dense fibrous connective tissue containing fat cells, blood and lymph vessels.

Spinal cord. Morphofunctional characteristics. Development. Structure of gray and white matter. neural composition.

The spinal cord consists of two symmetrical halves, delimited from each other in front by a deep median fissure, and behind by a connective tissue septum. The inner part of the organ is darker - this is its gray matter. On the periphery of the spinal cord is a lighter white matter. The gray matter of the spinal cord consists of the bodies of neurons, unmyelinated and thin myelinated fibers and neuroglia. The main component of gray matter, which distinguishes it from white, are multipolar neurons. The protrusions of the gray matter are called horns. There are anterior, or ventral, posterior, or dorsal, and lateral, or lateral, horns. During the development of the spinal cord, neurons are formed from the neural tube, grouped in 10 layers, or in plates. Characteristic of a person

the following architectonics of the indicated plates: plates I-V correspond to the posterior horns, plates VI-VII - to the intermediate zone, plates VIII-IX - to the anterior horns, plate X - to the zone of the near-central canal. The gray matter of the brain consists of three types of multipolar neurons. The first type of neurons is phylogenetically older and is characterized by a few long, straight, and weakly branching dendrites (isodendritic type). The second type of neurons has a large number of strongly branching dendrites that intertwine, forming "tangles" (idiodendritic type). The third type of neurons, in terms of the degree of development of dendrites, occupies an intermediate position between the first and second types. The white matter of the spinal cord is a collection of longitudinally oriented predominantly myelinated fibers. The bundles of nerve fibers that communicate between different parts of the nervous system are called the pathways of the spinal cord.

Brain. Sources of development. General morphofunctional characteristics of the cerebral hemispheres. Neuronal organization of the cerebral hemispheres. Cyto- and myeloarchitectonics of the cerebral cortex. Age-related changes in the cortex.

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

Structure. The cerebral cortex is represented by a layer of gray matter. It is most strongly developed in the anterior central gyrus. The abundance of furrows and convolutions significantly increases the area of ​​​​the gray matter of the brain .. Its various parts, which differ from each other in some features of the location and structure of cells (cytoarchitectonics), the location of fibers (myeloarchitectonics) and functional significance, are called fields. They are places of higher analysis and synthesis of nerve impulses. sharply defined

there are no boundaries between them. The cortex is characterized by the arrangement of cells and fibers in layers. The development of the human cerebral cortex (neocortex) in embryogenesis occurs from the ventricular germinal zone of the telencephalon, where poorly specialized proliferating cells are located. Neocortical neurocytes differentiate from these cells. In this case, the cells lose their ability to divide and migrate to the emerging cortical plate. First, the neurocytes of future layers I and VI enter the cortical plate, i.e. the most superficial and deep layers of the cortex. Then neurons of layers V, IV, III and II are built into it in the direction from the inside and outwards. This process is carried out due to the formation of cells in small areas of the ventricular zone at different periods of embryogenesis (heterochronous). In each of these areas, groups of neurons are formed, sequentially lining up along one or more fibers.

radial glia in the form of a column.

Cytoarchitectonics of the cerebral cortex. Multipolar neurons of the cortex are very diverse in shape. Among them are pyramidal, stellate, fusiform, arachnid and horizontal neurons. The neurons of the cortex are located in unsharply demarcated layers. Each layer is characterized by the predominance of any one type of cell. In the motor zone of the cortex, 6 main layers are distinguished: I - molecular, II - external granular, III - nuramid neurons, IV - internal granular, V - ganglionic, VI - layer of polymorphic cells. The molecular layer of the cortex contains a small number of small spindle-shaped associative cells. Their neurites run parallel to the surface of the brain as part of the tangential plexus of the nerve fibers of the molecular layer. The outer granular layer is formed by small neurons that have a rounded, angular and pyramidal shape, and stellate neurocytes. The dendrites of these cells rise into the molecular layer. Neurites either go into the white matter, or, forming arcs, also enter the tangential plexus of fibers of the molecular layer. The widest layer of the cerebral cortex is the pyramidal. From the top of the pyramidal cell, the main dendrite departs, which is located in the molecular layer. The neurite of the pyramidal cell always departs from its base. The inner granular layer is formed by small stellate neurons. It consists of a large number of horizontal fibers. The ganglionic layer of the cortex is formed by large pyramids, and the region of the precentral gyrus contains giant pyramids.

The layer of polymorphic cells is formed by neurons of various shapes.

Myeloarchitectonics of the cortex. Among the nerve fibers of the cerebral cortex, one can single out associative fibers that connect individual parts of the cortex of one hemisphere, commissural fibers that connect the cortex of different hemispheres, and projection fibers, both afferent and efferent, that connect the cortex with the nuclei of the lower parts of the central

nervous system.

Age changes. At the 1st year of life, typification of the shape of pyramidal and stellate neurons, their increase, the development of dendritic and axon arborizations, and intraensemble connections along the vertical are observed. By the age of 3, “nested” groups of neurons, more clearly formed vertical dendritic bundles and bundles of radiant fibers are revealed in the ensembles. By the age of 5-6, neuronal polymorphism increases; the system of intra-ensemble connections along the horizontal becomes more complicated due to the growth in length and branching of the lateral and basal dendrites of pyramidal neurons and the development of the lateral terminals of their apical dendrites. By the age of 9-10, cell groups increase, the structure of short-axon neurons becomes much more complicated, and the network of axon collaterals of all forms of interneurons expands. By the age of 12-14, specialized forms of pyramidal neurons are clearly marked in ensembles; all types of interneurons reach a high level of differentiation. By the age of 18, the ensemble organization of the cortex, in terms of the main parameters of its architectonics, reaches the level of that in adults.

Cerebellum. Structure and morphofunctional characteristics. Neuronal composition of the cerebellar cortex, gliocytes. Interneuron connections.

Cerebellum. It is the central organ of balance and coordination of movements. It is connected to the brainstem by afferent and efferent conducting bundles, which together form three pairs of cerebellar peduncles. There are many convolutions and grooves on the surface of the cerebellum, which significantly increase its area. Furrows and convolutions are created on the cut

characteristic for the cerebellum picture of the "tree of life". The bulk of the gray matter in the cerebellum is located on the surface and forms its cortex. A smaller part of the gray matter lies deep in the white matter in the form of central nuclei. In the center of each gyrus there is a thin layer

white matter, covered with a layer of gray matter - the bark. Three layers are distinguished in the cerebellar cortex: the outer one is the molecular layer, the middle one is the ganglionic layer, or the layer of pear-shaped neurons, and the inner one is granular. The ganglionic layer contains pear-shaped neurons. They have neurites, which, leaving the cerebellar cortex, form the initial link of its efferent

brake paths. From the pear-shaped body, 2-3 dendrites extend into the molecular layer, which penetrate the entire thickness of the molecular layer. From the base of the bodies of these cells, neurites depart, passing through the granular layer of the cerebellar cortex into the white matter and ending on the cells of the cerebellar nuclei. The molecular layer contains two main types of neurons: basket and stellate. Basket neurons are located in the lower third of the molecular layer. Their thin long dendrites branch mainly in a plane located transversely to the gyrus. The long neurites of the cells always run across the gyrus and parallel to the surface above the pear-shaped neurons. The stellate neurons lie above the basket cells and are of two types. Small stellate neurons are equipped with thin short dendrites and weakly branched neurites that form synapses. Large stellate neurons have long and highly branched dendrites and neurites. grainy layer. The first type of cells in this layer can be considered granular neurons, or granule cells. The cell has 3-4 short dendrites,

ending in the same layer with terminal branches in the form of a bird's paw. The neurites of the granule cells pass into the molecular layer and in it are divided into two branches, oriented parallel to the surface of the cortex along the gyri of the cerebellum. The second type of cells in the granular layer of the cerebellum are inhibitory large stellate neurons. There are two types of such cells: with short and long neurites. Neurons with short neurites lie near the ganglionic layer. Their branched dendrites spread in the molecular layer and form synapses with parallel fibers - axons of granule cells. Neurites are sent to the granular layer to the glomeruli of the cerebellum and end in synapses at the terminal branches of the dendrites of the granule cells.

A few stellate neurons with long neurites have dendrites and neurites abundantly branching in the granular layer, extending into the white matter. The third type of cells are spindle-shaped horizontal cells. They have a small elongated body, from which long horizontal dendrites extend in both directions, ending in the ganglionic and granular layers. The neurites of these cells give collaterals to the granular layer and go to

white matter. Gliocytes. The cerebellar cortex contains various glial elements. The granular layer contains fibrous and protoplasmic astrocytes. The peduncles of fibrous astrocyte processes form perivascular membranes. All layers in the cerebellum contain oligodendrocytes. The granular layer and white matter of the cerebellum are especially rich in these cells. Glial cells with dark nuclei lie in the ganglion layer between pear-shaped neurons. The processes of these cells are sent to the surface of the cortex and form glial fibers of the molecular layer of the cerebellum. Interneuronal connections. Afferent fibers entering the cerebellar cortex are represented by two types - mossy and so-called climbing fibers. Mossy fibers go as part of the olive-cerebellar and cerebellopontine tracts and indirectly through the granule cells have an exciting effect on the pear-shaped cells.

Climbing fibers enter the cerebellar cortex, apparently, along the dorsal-cerebellar and vestibulocerebellar pathways. They cross the granular layer, adjoin pear-shaped neurons and spread along their dendrites, ending on their surface with synapses. Climbing fibers transmit excitation directly to piriform neurons.

Autonomic (vegetative) nervous system. General morphofunctional characteristics. Departments. Structure of extramural and intramural ganglia.

The ANS is divided into sympathetic and parasympathetic. Both systems simultaneously take part in the innervation of organs and have the opposite effect on them. It consists of the central sections, represented by the nuclei of the gray matter of the brain and spinal cord, and the peripheral ones: nerve trunks, nodes (ganglia) and plexuses.

Due to their high autonomy, the complexity of organization, and the characteristics of mediator metabolism, the intramural ganglia and the pathways associated with them are distinguished into an independent metasympathetic department of the autonomous NS. There are three types of neurons:

Long-axon efferent neurons (Dogel type I cells) with short dendrites and a long axon extending beyond the node to the cells of the working organ, on which it forms motor or secretory endings.

Equally outgrowth afferent neurons (type II Dogel cells) contain long dendrites and an axon that extends beyond this ganglion into neighboring ones and forms synapses on type I and III cells. They are part of the local reflex arcs as a receptor link, which are closed without a nerve impulse entering the central nervous system.

Associative cells (type III Dogel cells) are local intercalary neurons that connect several cells of types I and II with their processes. The dendrites of these cells do not go beyond the node, and the axons go to other nodes, forming synapses on type I cells.