To control the work of internal organs, motor functions, timely receipt and transmission of sympathetic and reflex impulses, pathways are used spinal cord... Disturbances in the transmission of impulses lead to serious disruptions in the work of the whole organism.

What is the conductive function of the spinal cord?

1. Associative pathways.
2. Commissural connections.
3. Projection nerve fibers.

The sensory and motor pathways provide a strong connection between the spinal cord and brain, internal organs, the muscular system and the musculoskeletal system. Thanks to the fast transmission of impulses, all body movements are carried out in a coordinated manner, without perceptible efforts on the part of the person.

How are the conducting spinal tracts formed?

The classification of the pathways depends on the functional characteristics of the nerve fibers:

• The ascending pathways of the spinal cord - read and transmit signals: from the skin and mucous membranes of a person, life support organs. Provide the performance of the functions of the musculoskeletal system.
• Descending pathways of the spinal cord - transmit impulses directly to the working organs of the human body - muscle tissues, glands, etc. Connected directly to the cortical part of the gray matter. The transmission of impulses occurs through the spinal neural connection to the internal organs.

The spinal cord has a double direction of the pathways, which provides fast impulse transmission of information from the controlled organs. The conductive function of the spinal cord is carried out due to the efficient transmission of impulses along the nerve tissue.

In medical and anatomical practice, the following terms are commonly used:

Where are the pathways of the brain of the back

The morphofunctional characteristic of the descending pathways of the spinal cord limits the direction of impulses in only one direction. The irritation of the synapses is carried out from the presynaptic to the postsynaptic membrane.

The following possibilities and location of the main ascending and descending pathways correspond to the conduction function of the spinal cord and brain:

• Associative pathways are “bridges” connecting the areas between the cortex and the nuclei of the gray matter. Consist of short and long fibers. The first, are located within one half or lobe of the cerebral hemispheres.
  Long fibers are capable of transmitting signals through 2-3 gray matter segments. In the spinal substance, neurons form intersegmental bundles.
• Commissural fibers - form the corpus callosum, connecting the newly formed parts of the spinal cord and brain. Disperse in a radiant way. Located in the white matter of the brain tissue.
• Projection fibers - the location of the pathways in the spinal cord allows impulses to reach the cerebral cortex as quickly as possible. By their nature and functional features, projection fibers are divided into ascending (afferent pathways) and descending.
  The former are divided into exteroreceptive (vision, hearing), proprioceptive (motor functions), interoreceptive (communication with internal organs). The receptors are located between the spinal column and the hypothalamus.

The anatomy of the pathways is quite difficult for a person who does not have medical education. But the neural transmission of impulses is what makes the human body a single whole.

Consequences of damage to the conducting paths

Inside the gray matter, there are pathways that control the work of internal organs, as well as motor functions. Associative pathways are responsible for pain and tactile sensations. Motor - for the reflex functions of the body.

As a result of trauma, malformations or diseases of the spinal cord, conduction can decrease or completely stop. This happens due to the death of nerve fibers. For a complete violation of the conduction of impulses of the spinal cord, paralysis, lack of sensitivity of the limbs is characteristic. Disruptions in the work of internal organs begin, for which the damaged neural connection is responsible. So, with damage to the lower part of the spinal cord, urinary incontinence and spontaneous defecation are observed.

The reflex and conductive activity of the spinal cord is disturbed immediately after the onset of degenerative pathological changes. There is a death of nerve fibers that are difficult to restore. The disease progresses rapidly and a gross violation of conduction occurs. For this reason, it is necessary to start drug treatment as early as possible.

How to restore patency in the spinal cord

Drug treatment

For additional stimulation of nerve cells, electrical impulse therapy is performed to help maintain muscle tone.

Surgery

• Elimination of catalysts that have caused the paralysis of the work of neural connections.
• Spinal cord stimulation to restore lost functions.

Traditional medicine for conduction disorders

The most popular are:

Completely restore neural connections after an injury it is quite difficult. Much depends on a quick appeal to a medical center and qualified assistance from a neurosurgeon. The more time elapses from the onset of degenerative changes, the less chances of restoration of the functional capabilities of the spinal cord.

The nervous system is usually subdivided into several departments. According to topographic characteristics, it is divided into central and peripheral sections, according to functional characteristics - into somatic and vegetative sections. The central division, or central nervous system, includes the brain and spinal cord. The peripheral section, or peripheral nervous system, includes all nerves, that is, all peripheral pathways, which consist of sensory and motor nerve fibers. The somatic division, or the somatic nervous system, includes the cranial and spinal nerves that connect the central nervous system with organs that perceive external stimuli - with the skin and the apparatus of movement. The vegetative division, or the autonomic nervous system, provides a connection between the central nervous system and all internal organs, glands, blood vessels and organs, which include smooth muscle tissue. The vegetative division is divided into the sympathetic and parasympathetic parts, or the sympathetic and parasympathetic nervous system.

The central nervous system includes the brain and spinal cord. There are certain correlations between the mass of the brain and spinal cord: as the organization of the animal increases, the relative mass of the brain increases in comparison with the spinal cord. In birds, the brain is 1.5-2.5 times larger than the spinal cord, in ungulates - 2.5-3, in carnivores - in 3.5-5, in primates - 8-15 times.

Spinal cord- medulla spinalis lies in the spinal canal, occupying about 2/3 of its volume. In cattle and horses, its length is 1.8-2.3 m, weight is 250-300 g, in pigs - 45-70 g. It looks like a cylindrical strand, somewhat flattened dorsoventrally. There is no clear boundary between the brain and spinal cord. It is believed to be at the level of the cranial margin of the atlas. In the spinal cord, the cervical, thoracic, lumbar, sacral and tail parts are distinguished according to their location. During 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 more and more. 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 sacrum. The median dorsal groove (groove) runs along the dorsal side of the spinal cord. The connective tissue dorsal septum departs from it deeply. On the sides or median groove there are smaller dorsal lateral grooves. On the ventral side there is a deep median ventral fissure, and on the sides of it there are ventral lateral grooves (grooves). At the end, the spinal cord narrows sharply, cutting off the cerebral cone, which passes into the filum terminale. It is formed by connective tissue and ends at the level of the first caudal vertebrae.

There are thickenings in the cervical and lumbar spinal cord. In connection with the development of the limbs in these areas, the number of neurons and nerve fibers increases. In a pig, the cervical thickening is formed by 5-8 neurosegments. Its maximum width at the level of the middle of the 6th cervical vertebra is 10 mm. Lumbar thickening occurs in the 5-7th lumbar neurosegments. In each segment, a pair of spinal nerves depart from the spinal cord with two roots - to the right and to the left. The dorsal root departs from the dorsal lateral groove, the ventral root from the ventral lateral groove. From the spinal canal, the spinal nerves exit through the intervertebral foramen. The area of ​​the spinal cord between two adjacent spinal nerves is called a 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 extend 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 going inside the spinal canal, behind the cerebral cone, a kind of brush, called the "cauda equina", is formed.

Brain- encephalon - is placed in the cranium and consists of several parts. In ungulates, the relative weight of the brain is 0.08-0.3% of body weight, which is 370-600 g for a horse, 220-450 g for cattle, 96-150 g for sheep and pigs. the mass of the brain is usually greater than that of large ones.

The brain of ungulates is semi-oval in shape. In ruminants - with a wide frontal plane, with almost no protruding olfactory bulbs and noticeable extensions at the level of the temporal regions. In a pig, it is more narrowed in front, with noticeably protruding olfactory bulbs. Its length is, on average, 15 cm in cattle, 10 cm in sheep, and 11 cm in pigs. By a deep transverse slit in the brain, the brain is divided into a large brain, which lies rostrally, and a rhomboid brain, located caudal. The parts of the brain that are phylogenetically more ancient, which are a continuation of the projection pathways of the spinal cord, are called the brain stem. It includes the medulla oblongata, medullary bridge, middle bridge, part of the diencephalon. The phylogenetically younger parts of the brain form the integumentary part of the brain. It includes the cerebral hemispheres and the cerebellum.

Rhomboid brain- rhombencephalon - is divided into the medulla oblongata and hindbrain and contains the fourth cerebral ventricle.

Medulla- medulla oblongata - the most posterior part of the brain. Its mass is 10-11% of the mass of the brain; length in cattle - 4.5, in sheep - 3.7, in pig - 2 cm.It has the shape of a flattened cone, with the base directed forward and adjacent to the cerebral bridge, and the apex - to the spinal cord, into which it passes without sharp boundaries ...

On its dorsal side there is a diamond-shaped depression - the fourth cerebral ventricle. Three grooves run along the ventral side: the median and 2 lateral. Connecting caudally, they pass into the ventral median fissure of the spinal cord. Between the furrows there are 2 narrow elongated ridges - pyramids, in which bundles of motor nerve fibers pass. On the border of the medulla oblongata and the spinal cord, the pyramidal tracts intersect - a cross of the pyramids is formed. In the medulla oblongata, the gray matter is located inside, in the bottom of the fourth cerebral ventricle, in the form of nuclei giving rise to cranial nerves (pairs VI to XII), as well as nuclei in which impulses are switched to other parts of the brain. The white matter lies outside, mainly ventrally, forming the pathways. The motor (efferent) pathways from the brain to the spinal cord form pyramids. Sensory pathways (afferent) from the spinal cord to the brain form / the posterior legs of the cerebellum, going from the medulla oblongata to the cerebellum. In the mass of the medulla oblongata in the form of a reticular plexus lies an important coordination apparatus of the brain - the reticular formation. It unifies the structures of the brain stem and facilitates their involvement in complex, multi-stage responses.

Medulla- a vital part of the central nervous system (CNS), its destruction leads to instant death. Here are the centers of breathing, heartbeat, chewing, swallowing, sucking, vomiting, chewing gum, salivation and secretion, vascular tone, etc.

Hind brain- metencephalon - consists of the cerebellum and the cerebral bridge.

Brain bridge- pons - massive thickening on the ventral surface of the brain, lying across the anterior part of the medulla oblongata, up to 3.5 cm wide in cattle, 2.5 cm in sheep and 1.8 ohms in pigs. The bulk of the cerebral bridge is made up of pathways (descending and ascending) that connect the brain with the spinal cord and separate parts of the brain with each other. A large number of nerve fibers run across the bridge to the cerebellum and form the middle pedicles of the cerebellum. In the bridge there are groups of nuclei, including the nuclei of the cranial nerves (V pair). The largest V pair of cranial nerves - the trigeminal nerves - departs from the lateral surface of the bridge.

Cerebellum- cerebellum - located above the bridge, the medulla oblongata and the fourth cerebral ventricle, behind the quadruple. In front, it borders on the cerebral hemispheres. Its mass is 10-11% of the mass of the brain. In sheep and pigs, its length (4-4.5 cm) is greater than height (2.2-2.7 ohms), in cattle it approaches spherical - 5.6X6.4 cm.In the cerebellum, the middle part is distinguished - a worm and lateral parts - cerebellar hemispheres. The cerebellum has 3 pairs of legs. The hind legs (rope bodies) are connected to the medulla oblongata, the middle ones to the cerebral pons, and the anterior (rostral) ones to the midbrain. The surface of the cerebellum is collected in numerous folded lobules and convolutions, separated by grooves and fissures. The gray matter in the cerebellum is located on top - the cerebellar cortex and in the depths in the form of nuclei. The surface of the cerebellar cortex in cattle is 130 cm 2 (about 30% in relation to the cerebellar cortex) with a thickness of 450-700 microns. The white matter is located under the bark and looks like a tree branch, for which it is called the tree of life.

The cerebellum is the center for coordinating voluntary movements, maintaining muscle tone, posture, and balance.

Rhomboid brain contains the fourth cerebral ventricle. Its bottom is the deepening of the medulla oblongata - the rhomboid fossa. Its walls are formed by the legs of the cerebellum, and the roof by the anterior (rostral) and posterior cerebral sails, which are the choroid plexus. The ventricle communicates rostrally with the cerebral aqueduct, caudally - with the central canal of the spinal cord, and through the openings in the sail - with the subarachnoid space.

Big brain- cerebrum - includes the terminal, diencephalon and midbrain. The telencephalon and diencephalon are combined into the forebrain.

The midbrain - mesencephalon - consists of a quadruple, the legs of the large brain and the cerebral aqueduct between them. Covered with large hemispheres. Its mass is 5-6% of the brain mass.

The quadruple forms the roof of the midbrain. It consists of a pair of rostral (anterior) mounds and a pair of caudal (posterior) mounds. The quadruple is the center of unconditioned reflex motor acts in response to visual and auditory stimuli. The anterior hillocks are considered the subcortical centers of the visual analyzer, the posterior hillocks are the subcortical centers of the auditory analyzer. In ruminants, the front mounds are larger than the rear ones, in the pig, on the contrary.

The legs of the large brain form the bottom of the middle brain. They look like two thick ridges lying between the optic tracts and the cerebral bridge. Separated by an inter-pectoral groove.

Between the quadruple and the legs of the large brain in the form of a narrow tube, the cerebral (sylvian) aqueduct runs. Rostrally, it connects with the third, caudally - with the fourth cerebral ventricles. The cerebral aqueduct is surrounded by the substance of the reticular formation.

In the midbrain, the white matter is located outside and is a conductive afferent and efferent pathways... The gray matter is located in the depths in the form of nuclei. The third pair of cranial nerves departs from the cerebral legs.

Diencephalon- diencephalon - consists of visual hillocks - thalamus, epithalamus - epithalamus, hypothalamus - hypothalamus. The diencephalon is located between the final brain.

In the midbrain, covered by the telencephalon. Its mass is 8-9% of the brain mass. The visual hillocks are the most massive, centrally located part of the diencephalon. Growing together between the subwoofer, they squeeze the third cerebral ventricle so that it takes the form of a ring going around the intermediate mass of the optic hillocks. From above, the ventricle is covered with a vascular cover; communicated by the interventricular opening with the lateral ventricles, aborally passes into the cerebral aqueduct. White matter in the thalamus lies on top, gray matter inside in the form of numerous nuclei. They serve as switching links from the underlying departments to the cortex and are associated with almost all analyzers. On the basal surface of the diencephalon is the intersection of the optic nerves - chiasm.

The epithalamus consists of several structures, including the pineal gland and the vascular cover of the third cerebral ventricle (pineal gland is the endocrine gland). Located in the depression between the visual hillocks and the quadruple.

The hypothalamus is located on the basal surface of the diencephalon between the chiasm and the cerebral peduncles. Consists of several parts. Immediately behind the chiasm in the form of an oval tubercle is a gray tubercle. Its apex facing downward is elongated due to the protrusion of the wall of the third ventricle and forms a funnel on which the pituitary gland, the endocrine gland, is suspended. Behind the gray tubercle is a small rounded formation, a mastoid body. The white matter in the hypothalamus is located outside, forms the conducting afferent and efferent pathways. Gray matter - in the form of numerous nuclei, since the hypothalamus is the highest subcortical vegetative center. It contains the centers of respiration, blood and lymph circulation, temperature, sexual functions, etc.

The terminal brain - telencephalon - is formed by two hemispheres, separated by a deep longitudinal slit and connected by the corpus callosum. Its mass in (cattle 250-300 g, in sheep and pigs 60-80 g, which is 62-66% of the mass of the brain. In each hemisphere there is a dorolaterally located cloak, ventromedially - the olfactory brain, in depth - the striatum and the lateral ventricle The back ventricles are separated by a transparent septum, and the interventricular opening communicates with the third cerebral ventricle.

The olfactory brain consists of several parts, visible on the ventral surface of the telencephalon. Rostrally, slightly protruding beyond the cloak, there are 2 olfactory bulbs. They occupy the fossa of the ethmoid bone. Through a hole in the perforated plate of the bone, olfactory filaments enter them, which together form the olfactory nerve. The bulbs are the primary olfactory centers. From them the olfactory tracts depart - afferent pathways. The lateral olfactory tract reaches the pear-shaped lobes located laterally from the cerebral peduncles. The medial olfactory tracts reach the medial surface of the cloak. The olfactory triangles lie between the tracts. The piriform lobes and olfactory triangles are secondary olfactory centers. In the depths of the olfactory brain, at the bottom of the lateral ventricles, the rest of the olfactory brain is located. They connect the olfactory brain to other parts of the brain. The striatum is located in the depths of the hemispheres and is a basal complex of nuclei, which are subcortical motor centers.

The cloak reaches its greatest development in higher mammals. It contains the highest centers of all animal life. The surface of the cloak is covered with convolutions and grooves. In cattle, its surface is 600 cm 2. The gray matter in the cloak is located on top - this is the cortex of the cerebral hemispheres. The white matter is inside - these are the pathways. The functions of different parts of the cortex are unequal, the structure is mosaic, which made it possible to distinguish several lobes (frontal, parietal, temporal, occipital) and several tens of fields in the hemispheres. The fields differ from each other in their cytoarchitectonics - the location, number and shape of cells and myeloarchitectonics - in the location, number and shape of fibers.

The meninges are meninges. The spinal cord and brain are covered with hard, arachnoid and soft membranes.

The hard shell is the most superficial, thickest, formed by dense connective tissue, poor in blood vessels. It grows together with the bones of the skull and vertebrae with ligaments, folds and other formations. It descends into the longitudinal slit between the cerebral hemispheres in the form of a crescent ligament (cerebral sickle) and separates the cerebrum from the rhomboid membranous tentorium of the cerebellum. Between it and the bones, there is not everywhere a developed epidural space, filled with loose connective and adipose tissue. Veins pass here. From the inside, the dura mater is lined with tissue. Between it and the arachnoid membrane there is a subdural space filled with cerebrospinal fluid. The arachnoid membrane is formed by loose connective tissue, delicate, avascular, does not enter the furrows. On both sides it is covered with endothelium and is separated by subdural and jaubarachnoid (subarachnoid) spaces from other membranes. It joins the membranes with the help of ligaments, as well as vessels and nerves passing through it.

The soft shell is thin, but dense, with a large number of vessels, for which it is also called vascular. It enters all the grooves and crevices of the brain and spinal cord, as well as the cerebral ventricles, where it forms the vascular covers.

The intershell spaces, cerebral ventricles and the central spinal canal are filled with cerebrospinal fluid, which is the internal environment of the brain and protects it from harmful effects, regulates intracranial pressure, and performs a protective function. A liquid is formed. Mainly in the vascular caps of the ventricles, flows into the venous bed. Normally, its amount is constant.

Vessels of the brain and spinal cord. The spinal cord is supplied with blood through the branches extending from the vertebral, intercostal, lumbar and sacral arteries. In the spinal canal, they form the spinal arteries that run in the grooves and central fissure of the spinal cord. The blood reaches the brain through the vertebral and internal carotid (in cattle - through the internal jaw) arteries.

The nervous system 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 first includes the brain and spinal cord, the second unites peripheral nerve nodes, trunks and endings.

From a physiological point of view, the nervous system is divided into somatic, which innervates the whole body, except for the internal organs, blood vessels and glands, and autonomous, or vegetative, which regulates the activity of these organs.

The nervous system develops from the neural tube and ganglion plate. From the cranial part of the neural tube, the brain and sensory organs are differentiated. From the trunk of the neural tube and ganglion plate, the spinal cord, spinal and vegetative nodes and chromaffin tissue of the body are formed.

The mass of cells in the lateral parts of the neural tube increases especially rapidly, while its dorsal and ventral parts do not increase in volume and retain their ependymal character. The thickened lateral walls of the neural tube are divided by the longitudinal groove into the dorsal - winged and ventral - main plate. At this stage of development, three zones can be distinguished in the lateral walls of the neural tube: the ependyma lining the canal, the mantle layer and the marginal veil. In the future, the gray matter of the spinal cord develops from the mantle layer, and its white matter develops from the marginal veil.

Simultaneously with the development of the spinal cord, spinal and peripheral autonomic nodes are laid. The initial material for them is the cellular elements of the ganglion lamina, differentiating into neuroblasts and glioblasts, from which neurons and maytic gliocytes of the spinal ganglia are formed. Part of the cells of the ganglion lamina migrate to the periphery to the sites of localization of the autonomic nerve ganglia and chromaffin tissue.

1. 
   ^ Spinal cord: morphological and functional characteristics; structure of gray and white matter.

The gray matter in the cross section of the brain is represented in the form of the letter "H" or a butterfly. The protrusions of the gray matter are called horns. Distinguish between anterior, or ventral, posterior, or dorsal, and lateral, or lateral, horns.

The gray matter of the spinal cord consists of neuronal bodies, myelin-free and thin myelin fibers, and neuroglia. The main constituent of the gray matter, which distinguishes it from white, are multipolar neurons.

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

Among the neurons of the spinal cord can be distinguished: neurites, radicular cells, internal, bundle.

In the hind horns, there are: a spongy layer, a gelatinous substance, its own nucleus of the hind horn and a pectoral nucleus. The hind horns are rich in diffusely located intercalated cells. In the middle of the hind horn is the own nucleus of the hind horn.

The thoracic nucleus (Clarke's nucleus) consists of large interneurons with highly branched dendrites.

Of the structures of the posterior horn, of particular interest are the gelatinous substance, which stretches continuously along the spinal cord in plates I-IV. Neurons produce enkephalin, an opioid-type peptide that inhibits pain. The gelatinous substance has an inhibitory effect on the functions of the spinal cord.

In the anterior horns, the largest neurons of the spinal cord are located, which have a body diameter of 100-150 microns and form nuclei of significant volume. This is the same as the neurons of the nuclei of the lateral horns, radicular cells. These nuclei represent the somatic motor centers. In the anterior horns, the medial and lateral groups of motor cells are most pronounced. The first innervates the muscles of the trunk and is well developed throughout the spinal cord. The second is located in the region of the cervical and lumbar thickenings and innervates the muscles of the limbs.

1. 
   ^ Brain: morphofunctional characteristics.

The brain is enclosed in a secure cranial membrane. In addition, it is covered with connective tissue sheaths - hard, arachnoid and soft.

In the brain, gray and white matter are distinguished, but the distribution of these two constituent parts 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. The smaller part forms numerous nuclei of the brainstem.

The brain stem includes the medulla oblongata, pons, cerebellum and structures of the midbrain and diencephalon. All nuclei of the gray matter of the brain stem are composed of multipolar neurons. Distinguish between the nuclei of the cranial nerves and the switching nuclei.

The medulla oblongata is characterized by the presence of the nuclei of the hypoglossal, accessory, vagus, glossopharyngeal, vestibular cochlear nerves. In the central region of the medulla oblongata, an important coordination apparatus of the brain is located - the reticular formation.

The bridge is divided into dorsal (tegmental) and ventral parts. The dorsal part contains the fibers of the pathways of the medulla oblongata, the nuclei of the V-VIII cranial nerves, the reticular formation of the pons.

The midbrain consists of the roof of the midbrain (quadruple), the lining of the midbrain, the substantia nigra and the legs of the brain. The black matter got its name due to the fact that melanin is contained in its small fusiform neurons.

In the diencephalon, the visual hillock predominates in volume. Ventrally from it is the hypothalamic (submouth) region rich in small nuclei. Nerve impulses to the visual tubercle from the brain go along the extrapyramidal motor path.

1. 
   ^ Cerebellum: structure and morphofunctional characteristics.

The bulk of the gray matter in the cerebellum is located on the surface and forms its cortex. A smaller part of the gray matter lies deep in the white matter in the form of central nuclei. In the cerebellar cortex, three layers are distinguished: the outer layer is the molecular layer, the middle layer is the ganglion layer, and the inner layer is granular.

The ganglion layer contains piriform neurons. They have neurites, which, leaving the cerebellar cortex, form the initial link of its efferent inhibitory pathways.

The molecular layer contains two main types of neurons: basket and stellate. Basket neurons are found in the lower third of the molecular layer. These are small irregularly shaped cells about 10-20 microns in size. Their thin long dendrites branch mainly in a plane located transverse to the gyrus. Long neurites of cells always run across the gyrus and parallel to the surface above the pear-shaped neurons. The activity of the neurites of the basket neurons causes inhibition of the piriform neurons.

Stellate neurons lie above the baskets and are of two types. Small stellate neurons are equipped with thin short dendrites and weakly branched neurites that form synapses on the dendrites of the pear-shaped cells. Large stellate neurons, unlike small ones, have long and highly branched dendrites and neurites.

Basket and stellate neurons of the molecular layer are a single system of intercalary neurons that transmit inhibitory nerve impulses to the dendrites and bodies of piriform cells in a plane transverse to the gyrus. The granular layer is very rich in neurons. The first type of cells in this layer can be considered granular neurons, or grain cells. They have a small volume. The cell has 3-4 short dendrites. The dendrites of the grain cells form characteristic structures called the glomeruli 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.

The third type of cells is made up of spindle-shaped horizontal cells. They are found mainly between the granular and ganglionic layers. Afferent fibers entering the cerebellar cortex are represented by two types - mossy and so-called climbing fibers. Mossy fibers are part of the olivomocerebellar and cerebellopontine pathways. They end in the glomeruli of the granular layer of the cerebellum, where they come into contact with the dendrites of the grain cells.

The climbing fibers enter the cerebellar cortex, apparently through the spinal and cerebellar and vestibulocerebellar pathways. Climbing fibers transmit excitation directly to pear-shaped neurons.

The cerebellar cortex contains various glial elements. The granular layer contains fibrous and protoplasmic astrocytes. There are oligodendrocytes in all layers of the cerebellum. The granular layer and the white matter of the cerebellum are especially rich in these cells. Glial cells with dark nuclei lie in the ganglionic layer between the pear-shaped neurons. Microglia are found in large quantities in the molecular and ganglionic layers.

1. 
   ^ The subject and tasks of human embryology.

In embryogenesis, 3 sections are distinguished: pre-embryonic, embryonic and early post-embryonic.

The actual tasks of embryology is to study the influence of various endogenous and exogenous factors of the microenvironment on the development and structure of germ cells, tissues, organs and systems.

1. 
   ^ Medical embryology.

Medical embryology studies the patterns of development of the human embryo. Particular attention in the course of histology with embryology is drawn to the sources and mechanisms of tissue development, the metabolic and functional characteristics of the mother-placenta-fetus system, which make it possible to establish the causes of deviations from the norm, which is of great importance for medical practice.

Knowledge of human embryology is essential for all doctors, especially those working in the field of obstetrics. This helps in making a diagnosis of violations in the mother-fetus system, identifying the causes of deformities and diseases of children after birth.

Currently, knowledge of human embryology is used to disclose and eliminate the causes of infertility, the birth of test-tube babies, transplantation of fetal organs, the development and use of contraceptives. In particular, the problems of egg culture, in vitro fertilization and embryo implantation into the uterus have become topical.

The process of human embryonic development is the result of long evolution and, to a certain extent, reflects the features of the development of other representatives of the animal world. Therefore, some early stages of human development are very similar to analogous stages of embryogenesis in lower-organized chordates.

Human embryogenesis is a part of his ontogenesis, which includes the following main stages: I - fertilization, and the formation of a zygote; II - crushing and formation of blastula (blastocyst); III - gastrulation - the formation of germ layers and a complex of axial organs; IV - histogenesis and organogenesis of embryonic and extraembryonic organs; V - systems genesis.

Embryogenesis is closely related to progenesis (development and maturation of germ cells) and the early postembryonic period. Thus, tissue formation begins in the embryonic period and continues after the birth of the child.

1. 
   ^ Sex cells: the structure and functions of male and female sex cells, the main stages of their development.

The sperm cell is covered with cytolemma, which in the anterior section contains a receptor - glycosyltransferase, which provides recognition of the receptors of the egg.

The sperm head includes a small dense nucleus with a haploid set of chromosomes, containing nucleoprotamines and nucleohistones. The anterior half of the nucleus is covered with a flat sac that makes up the sperm cap. It contains an acrosome (from the Greek asgop - apex, soma - body). The acrosome contains a set of enzymes, among which hyaluronidase and proteases play an important role. The nucleus of the human sperm contains 23 chromosomes, one of which is sex (X or Y), the rest are autosomes. The tail section of the spermatozoon consists of the intermediate, main and terminal parts.

The intermediate part contains 2 central and 9 pairs of peripheral microtubules surrounded by a spiral mitochondria. Paired protrusions, or "handles", consisting of another protein, dynein, extend from the microtubules. Dynein breaks down ATP.

The main part (pars principalis) of the tail in structure resembles a cilium with a characteristic set of microtubules in the axoneme (9 * 2) +2, surrounded by circularly oriented fibrils, giving elasticity, and a plasmolemma.

The terminal, or end, part of the sperm contains single contractile filaments. Tail movements are whiplike, due to the successive contraction of microtubules from the first to the ninth pair.

In the study of sperm in clinical practice, various forms of sperm are counted in stained smears, counting their percentage (spermiogram).

According to the World Health Organization (WHO), the following indicators are normal characteristics of human sperm: concentration 20-200 million / ml, content of more than 60% of normal forms. Along with normal forms, human sperm always contains abnormal ones - biflagellates, with defective head sizes (macro and microforms), with an amorphous head, with fused heads, immature forms (with remnants of cytoplasm in the neck and tail), with flagellar defects.

Eggs, or oocytes (from Latin ovum - egg), ripen in immeasurably less quantity than sperm. In a woman, during the sexual cycle (B4-28 days), as a rule, one egg matures. Thus, during the childbearing period, about 400 mature eggs are formed.

The release of an oocyte from the ovary is called ovulation. The oocyte released from the ovary is surrounded by a crown of follicular cells, the number of which reaches 3-4 thousand. It is picked up by the fimbria of the fallopian tube (oviduct) and moves along it. Here the maturation of the reproductive cell ends. The egg cell has a spherical shape, the volume of cytoplasm is larger than that of sperm, and does not have the ability to move independently.

The classification of oocytes is based on the signs of the presence, quantity and distribution of the yolk (lecithos), which is a protein-lipid inclusion in the cytoplasm used to feed the embryo.

There are yolk-free (alecitic), low-yolk (oligolecital), medium-yolk (mesolecital), poly-yolk (polylecital) oocytes.

In humans, the presence of a small amount of yolk in the egg is due to the development of the embryo in the mother's body.

Structure. The human egg cell has a diameter of about 130 microns. A shiny, or transparent, zone (zona pellucida - Zp) and then a layer of follicular cells are adjacent to the cytolemma. The nucleus of the female reproductive cell has a haploid set of chromosomes with the X-sex chromosome, a well-defined nucleolus, and there are many pore complexes in the karyolemma. During the period of oocyte growth, intensive processes of mRNA and rRNA synthesis take place in the nucleus.

In the cytoplasm, the protein synthesis apparatus (endoplasmic reticulum, ribosomes) and the Golgi apparatus are developed. The number of mitochondria is moderate, they are located near the yolk nucleus, where intensive yolk synthesis takes place, the cell center is absent. The Golgi apparatus in the early stages of development is located near the nucleus, and in the process of maturation of the egg it shifts to the periphery of the cytoplasm. Here are the derivatives of this complex - cortical granules, the number of which reaches about 4000, and the size of 1 micron. They contain glycosaminoglycans and various enzymes (including proteolytic ones), are involved in the cortical reaction, protecting the egg from polyspermy.

The transparent, or shiny, zone (zona pellucida - Zp) consists of glycoproteins and glycosaminoglycans. The glittering zone contains tens of millions of Zp3 glycoprotein molecules, each with over 400 amino acid residues linked to many oligosaccharide branches. Follicular cells take part in the formation of this zone: the processes of follicular cells penetrate through the transparent zone, heading for the cytolemma of the egg. The cytolemma of the egg has microvilli located between the processes of follicular cells. Follicular cells perform trophic and protective functions.

The spinal cord is the most ancient and primitive formation of the central nervous system of vertebrates, retaining its morphological and functional segmentation in the most highly organized animals. A characteristic feature of the organization of the spinal cord is the periodicity of its structure in the form of segments with inputs in the form of dorsal roots, cell mass of neurons (gray matter) and outputs in the form of anterior roots.

The human spinal cord has 31-33 segments: 8 cervical, 12 thoracic, 5 lumbar. 5 sacral, 1-3 coccygeal.

There are no morphological boundaries between the segments of the spinal cord, therefore, the division into segments is functional and is determined by the zone of distribution of the fibers of the dorsal root in it and the zone of cells that form the exit of the anterior roots. Each segment through its roots innervates three body metameres and receives information from three body metameres. As a result of overlapping, each metamer of the body is innervated by three segments and transmits signals to three segments of the spinal cord.

The human spinal cord has two thickenings: cervical and lumbar - they contain more neurons than in other parts of it. Fibers entering the posterior roots of the spinal cord perform functions that are determined by where and on which neurons these fibers end. The posterior roots are afferent, sensitive, centripetal. Front - efferent, motor, centrifugal.

The afferent inputs to the spinal cord are organized by the axons of the spinal ganglia lying outside the spinal cord, by the axons of the extra - and intramural ganglia of the sympathetic and parasympathetic divisions of the autonomic nervous system.

The first group of afferent inputs of the spinal cord is formed by sensory fibers coming from muscle receptors, tendon receptors, periosteum, and joint membranes. This group of receptors forms the beginning of proprioceptive sensitivity.

The second group of afferent inputs of the spinal cord starts from the skin receptors: pain, temperature, tactile, pressure - and represents the skin receptor system.

The third group of afferent inputs of the spinal cord is represented by receptive inputs from the visceral organs; it is the viscero-receptive system.

Efferent (motor) neurons are located in the anterior horns of the spinal cord, their fibers innervate all skeletal muscles.

The spinal cord has two functions: conductive and reflex.

The spinal cord performs a conductive function due to the ascending and descending pathways passing through the white matter of the spinal cord. These pathways connect individual segments of the spinal cord to each other. Through long ascending and descending paths, the spinal cord connects the periphery with a two-way connection to the brain. Afferent impulses along the pathways of the spinal cord are conducted to the brain, carrying information about changes in the external and internal environment of the body. In descending pathways, impulses from the brain are transmitted to the effector neurons of the spinal cord and cause or regulate their activity.

As a reflex center, the spinal cord is able to carry out complex motor and autonomic reflexes. By afferent - sensitive - pathways it is associated with receptors, and efferent - with skeletal muscles and all internal organs.

The gray matter of the spinal cord, the posterior and anterior roots of the spinal nerves, and its own bundles of white matter form the segmental apparatus of the spinal cord. It provides reflex (segmental) function of the spinal cord.

The nerve centers of the spinal cord are segmental or work centers. Their neurons are directly connected to receptors and working organs. The functional diversity of spinal cord neurons, the presence of afferent neurons, interneurons, motor neurons and neurons of the autonomic nervous system in it, as well as numerous forward and reverse, segmental, intersegmental connections and connections with brain structures - all this creates conditions for reflex activity of the spinal cord with the participation of , both their own structures and the brain.

Such an organization allows one to realize all motor reflexes of the body, diaphragm, genitourinary system and rectum, thermoregulation, vascular reflexes, etc.

The nervous system functions according to reflex principles. The reflex is the body's response to external or internal influences and spreads along the reflex arc, i.e. the spinal cord's own reflex activity is carried out by segmental reflex arcs. Reflex arcs are chains of nerve cells.

In the reflex arc, five links are distinguished:

receptor;

sensitive fiber conducting excitation to the centers;

the nerve center, where the switching of excitation from sensory cells to motor cells occurs;

motor fiber carrying nerve impulses to the periphery;

the active organ is a muscle or gland.

The simplest reflex arc includes sensitive and efferent neurons, along which the nerve impulse moves from the place of origin (receptor) to the working organ (effector). The body of the first sensitive (pseudo-unipolar) neuron is located in the spinal node. The dendrite begins with a receptor that perceives external or internal stimulation (mechanical, chemical, etc.) and converts it into a nerve impulse that reaches the body of the nerve cell. From the body of the neuron along the axon, a nerve impulse is sent through the sensory roots of the spinal nerves to the spinal cord, where synapses are formed with the bodies of effector neurons. In each interneuronal synapse, an impulse is transmitted with the help of biologically active substances (mediators). The axon of the effector neuron leaves the spinal cord as part of the anterior roots of the spinal nerves (motor or secretory nerve fibers) and goes to the working organ, causing muscle contraction, strengthening (inhibition) of gland secretion.

Functionally, the reflex centers and spinal reflexes are the nuclei of the spinal cord. In the cervical spinal cord is the center of the phrenic nerve, the center of the pupil constriction. In the cervical and thoracic regions, there are motor centers of the muscles of the upper limbs, chest, abdomen and back. In the lumbar region there are muscle centers of the lower extremities. The sacral region contains the centers of urination, defecation and sexual activity. In the lateral horns of the thoracic and lumbar regions are the centers of perspiration and vasomotor centers.

The spinal cord has a segmental structure. A segment is a segment that gives rise to two pairs of roots. If the frog's back roots are cut on one side, and the front ones on the other, then the legs on the side where the back roots are cut lose sensitivity, and on the opposite side, where the anterior roots are cut, they will be paralyzed. Consequently, the posterior roots of the spinal cord are sensitive, and the anterior ones are motor.

The reflex reactions of the spinal cord depend on the place, the strength of the stimulation, the area of ​​the irritated reflex zone, the speed of conduction along the afferent and efferent fibers, and, finally, on the influence of the brain. The strength and duration of spinal cord reflexes increases with repeated stimulation. Each spinal reflex has its own receptive field and its own localization (location), its own level. For example, the center of the cutaneous reflex is located in the II-IV lumbar segment; Achilles - in the V lumbar and I-II sacral segments; plantar - in the I-II sacral, the center of the abdominal muscles - in the VIII-XII thoracic segments. The most important vital center of the spinal cord is the motor center of the diaphragm, located in the III-IV cervical segments. Damage to it leads to death due to respiratory arrest.

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

In the spinal cord, a gray matter, located in the central part, and a 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 has the appearance of a butterfly and includes anterior or ventral, posterior, or dorsal, and lateral, or lateral, horns. The gray matter contains bodies, dendrites and (partially) the axons of neurons, as well as glial cells. The main constituent parts of the gray matter are multipolar neurons.

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

The axons of the root 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 bundle cells pass in 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. Individual areas of the gray matter of the spinal cord differ significantly from each other in the composition of neurons, nerve fibers and neuroglia.

In the posterior horns, a spongy layer, a gelatinous substance, the own nucleus of the posterior horn, and the thoracic nucleus of Clarke are distinguished. Between the posterior and lateral horns, the gray matter juts out into white strands, as a result of which its netlike loosening is formed, which is called the reticular formation, or reticular formation, of the spinal cord.

The hind horns are rich in diffusely located intercalated cells. These are small multipolar associative and commissural cells, the axons of which end 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 carry out a connection between the sensitive cells of the spinal ganglia and the motor cells of the anterior horns, closing the local reflex arcs.

The neurons of the Clarke nucleus receive information from receptors in muscles, tendons and joints (proprioceptive sensitivity) through the thickest root fibers and transmit it to the cerebellum.

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

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