In addition to neurons, nervous tissue includes cells neuroglia – neurogliocytes. They were discovered in the 19th century. German cytologist R. Virchow, who defined them as cells connecting neurons (Greek. glia- glue) filling the spaces between them. Subsequently, it was revealed that neurogliocytes are a very large group of cellular elements, differing in their structure, origin and functions. It became clear that neuroglia function in the brain not only as trophic (nutritive) or supporting tissue. Glial cells also take part in specific nervous processes, actively influencing the activity of neurons.
Neuroglial cells have a number of common features structures with neurons. Thus, tigroid (Nissl substance) was found in the cytoplasm of gliocytes; glial cells, like neurons, have processes.
At the same time, gliocytes are significantly smaller in size than neurons (3-4 times), and there are 5-10 times more of them than nerve cells. The processes of glial cells are not differentiated either by structure or function. Glial cells retain the ability to divide throughout the life of the organism. Thanks to this feature, they (when such division becomes pathological) can be the basis for the formation of tumors - gliomas in the nervous system. The increase in brain mass after birth also occurs primarily due to the division and development of neuroglial cells.
There are several types of glial cells. The main ones are astrocytes, oligodendrocytes, ependymocytes and microglia (Fig. 10). Gliocytes also include cells found in the peripheral nervous system - Schwann cells (lemmocytes) and satellite cells in the nerve ganglia.
Ependymal glia. Ependymocytes form a single layer of cells ependyma, which lines the cavities nervous system– spinal canal, ventricles of the brain, cerebral aqueduct). Ependymocytes have a cubic or cylindrical shape. In the early stages of development, they have cilia facing the brain cavities. They help push cerebrospinal fluid (CSF). Later, the cilia disappear, remaining only in some areas, for example in the water supply.
Ependymal cells actively regulate the exchange of substances between the brain and blood, on the one hand, and the cerebrospinal fluid and blood, on the other. For example, ependymocytes, located in the area of the choroid plexus and covering the protrusions of the pia mater (see 4.1), take part in filtration chemical compounds from blood capillaries into cerebrospinal fluid. Some ependymal cells have long cytoplasmic processes that extend deeply into the brain tissue. In such ependymocytes in the third ventricle (diencephalon cavity), the processes end in a lamellar extension on the blood capillaries of the pituitary gland. In this case, ependymocytes participate in the transport of substances from the cerebrospinal fluid into the circulatory network of the pituitary gland.
Astrocytic glia. Astrocytes located in all parts of the nervous system. These are the largest and most numerous of the glial cells. There are two types of astrocytes - fibrous and protoplasmic. Fibrous astrocytes have long, straight, non-branching processes. These cells are located mainly in the white matter between the fibers. Protoplasmic astrocytes have many short, highly branched processes and lie primarily in the gray matter.
The functions of astrocytes are very diverse. They fill the space between the bodies of neurons and their fibers, thus performing supporting and insulating functions. During embryonic development, neurons move along the processes of astrocytes. Astrocytes also form a scar when nerve tissue is destroyed.
Astrocytes actively participate in the metabolism of the nervous system. They regulate water-salt metabolism, being a kind of sponge that absorbs excess water and quickly releases it. With the outflow of water from the nervous system, the volume of astrocytes decreases sharply. The phenomena of cerebral edema are often associated with changes in the structure of these cells. Astrocytes can, in addition, regulate the concentration of ions in the intercellular environment. For example, with the rapid release of K + ions there during the generation of an action potential, part of the potassium is absorbed by astrocytic glia. Astrocytes also participate in the metabolism of neurotransmitters, which they can capture from the synaptic cleft. In general, we can say that this type of neuroglia maintains the constancy of the intercellular environment of the brain.
Another function of astrocytes is that they take part in the work of the blood-brain barrier (BBB) - the barrier between blood (Greek. haimatos, blood) and brain. The BBB is a complex anatomical, physiological and biochemical system that determines which substances penetrate into the central nervous system from the blood and at what speed. The existence of the BBB is due to the fact that neurons are very sensitive to the effects of various chemical compounds on them, and if a neuron dies, it cannot be replaced by a new cell. The BBB arises, first of all, due to the characteristics of the capillary walls, the permeability of which in the nervous system is much lower than in other parts of the body. In addition, between the capillaries and neurons there is a layer of astrocytes, which form special outgrowths - legs that wrap around the blood capillary like a cuff. In this way, astrocytes can retain some of the harmful substances trying to penetrate from the blood into the brain.
Thanks to the BBB penetration chemical substances from the blood into the nervous tissue is very limited. The BBB does not allow a number of compounds to pass to neurons - first of all, these are toxins (poisons produced by microorganisms, plants and animals) and metabolic waste. The BBB also does not allow certain substances from food to pass through if they can have a harmful effect on the nervous system. It also limits the passage of certain medications into the brain. In this regard, pharmacologists, when developing new drugs, pay special attention to the creation of molecules that could cross the BBB. Disturbances in the functioning of the BBB can lead to various diseases. For example, when body temperature rises, contacts between glial stalks and a blood vessel are disrupted, which increases the likelihood of infectious agents entering the brain.
Oligodendroglia. Oligode Ndrocytes are much smaller than astrocytes. Their processes are few. These cells are found in both gray and white matter, being satellites of neurons and nerve fibers.
Just like astrocytes, oligodendrocytes perform a trophic function, and a number of nutrients enter neurons through them. It is assumed that oligodendrocytes are involved in the regeneration of nerve fibers. But oligodendroglia also have a specific function: with the help of these cells, sheaths are formed around nerve fibers (see above). In unmyelinated fibers, chains of oligodendrocytes are located along the entire fiber. Individual cells wrap around small sections of the fiber, isolating it from other fibers. This ensures that the nerve impulse is carried along each fiber in isolation, without affecting the processes occurring in neighboring fibers.
In the peripheral nervous system, analogues of oligodendrocytes are Schwann cells, which also form sheaths (both myelinated and non-myelinated) around the fibers.
Microglia. Microgliocytes the smallest of the glial cells. Their main function is protective. They are phagocytes of the nervous system, for which they are also called glial macrophages. The number of these cells varies greatly depending on the functional state of the nervous system. Under various exo- and endogenous harmful influences (trauma, inflammation, etc.), they sharply increase in size, begin to divide and rush to the lesion. Here, microgliocytes eliminate foreign cells, such as bacteria, and various types of tissue debris by phagocytosis.
Microglial cells play important role in the development of nervous system lesions in AIDS. Together with blood cells, they spread the immunodeficiency virus throughout the central nervous system.
Neuroglia is a collection of nervous tissue cells. Neuroglia performs trophic, delimiting, secretory and protective functions.
The central nervous system contains macroglia and microglia.
Macroglia are of neural origin and are divided into epindemocytes, astrocytes and oligodendrocytes. Epidemocytes line the ventricles of the brain and the central canal of the spinal cord. Astrocytes perform supporting and delimiting functions. Oligodendrocytes are involved in the myelination of axons.
Microglia are phagocytic, branching cells that are located in the gray and white matter of the brain.
In the peripheral nervous system, neuroglia are represented by lemmocytes (Schwann cells) and satellite cells.
Schwann cells form along the axons of the peripheral nervous system. Provide myelination of neurons, perform supporting and trophic functions. Satellite cells provide life support to neurons of the peripheral nervous system.
2nd part Reflex arcs can be of two types:
simple - monosynaptic reflex arcs (reflex arc of the tendon reflex), consisting of 2 neurons (receptor (afferent) and effector), there is 1 synapse between them;
complex – polysynaptic reflex arcs. They consist of 3 neurons (there may be more) - a receptor, one or more intercalary and an effector.
12) question General plan of the structure of the nervous system.
All nervous system divided into central and peripheral. To the central nervous system includes the brain and spinal cord. They spread throughout the body nervous fibers - peripheral nervous system. It connects the brain with the senses and with the executive organs - muscles and glands.
2) Development
Human nervous system develops from the outer germ layer - ectoderm.
3) functions
The main functions of the nervous system are receiving, storing and processing information from the external and internal environment, regulating and coordinating the activities of all organs and organ systems.
13) question Peripheral nervous system:
departments: sensory nerves, motor nerves are divided into: somatic and autonomic; divided into: sympathetic and parasympathetic
14) question Cranial and spinal nerves
To
classification and functions: Numbering Name Functions
I Olfactory Sensitivity to odors
II Visual Transmission of visual stimuli to the brain
III Oculomotor Eye movements, pupillary reaction to light exposure
IV Block Eye movement downward, outward
V Trigeminal Facial, oral, pharyngeal sensitivity; activity of the muscles responsible for the act of chewing
VI Abductor Movement of the eyes outward
VII Facial Movement of muscles (facial muscles, stapedius); activity of the salivary gland, sensitivity of the anterior part of the tongue
VIII Auditory Transmission of sound signals and impulses from the inner ear
IX Glossopharyngeal Movement of the levator pharyngeal muscle; activity of paired salivary glands, sensitivity of the throat, middle ear cavity and auditory tube
X Vagus Motor processes in the muscles of the throat and some parts of the esophagus; providing sensitivity in the lower part of the throat, partially in the ear canal and eardrums, the dura mater of the brain; activity of smooth muscles (gastrointestinal tract, lungs) and cardiac
XI Additional Abduction of the head in various directions, shrugging of the shoulders and adduction of the shoulder blades to the spine
XII Sublingual Movements and movements of the tongue, acts of swallowing and chewing
15) question Autonomic nervous system:
Centers of the autonomic nervous system. The highest autonomic center is the hypothalamus. The hypothalamus is a collection of about 50 pairs of nuclei, which are combined into groups: preoptic anterior, middle, external and posterior. The role of various groups of hypothalamic nuclei is determined by their connection with the sympathetic or parasympathetic divisions of the ANS. Irritation of the anterior nuclei of the hypothalamus causes changes in the body similar to those observed when the parasympathetic nervous system is activated. Stimulation of the posterior nuclei of the hypothalamus is accompanied by effects similar to stimulation of the sympathetic nervous system. The main structural and functional features of the hypothalamus are the following:
Neurons of the hypothalamus have a receptor function - they are able to directly detect changes chemical composition blood and cerebrospinal fluid. This is achieved, firstly, due to the powerful network of capillaries and their exceptionally high permeability; secondly, due to the fact that the hypothalamus contains cells that are selectively sensitive to changes in blood parameters. These “receptor” neurons of the hypothalamus practically do not adapt. They generate impulses until one or another indicator of the body is normalized as a result of the adaptive work of autonomic effectors.
The hypothalamus has extensive bilateral connections with the limbic system, with the cortex big brain, with the central gray matter of the midbrain, somatic nuclei of the brain stem. These connections are made not only by nerve cells, but also by neurosecretory cells, the axons of which go to the limbic system, thalamus, and medulla oblongata.
The hypothalamus produces its own hormones involved in the regulation of autonomic functions. The effector hormones oxytocin and vasopressin are produced in the neurons of the nuclei of the anterior group of the hypothalamus (supraoptic and paraventricular nuclei) in an inactive state, then enter the neurohypophysis, where they are activated and then secreted into the blood. Hypothalamic releasing hormones (liberins) stimulate the function of the pituitary gland, and statins (inhibiting hormones) inhibit it. These hormones are produced by neurons of the arcuate and ventromedial nuclei of the hypothalamus and regulate the production of tropic hormones of the pituitary gland. Libirins and statins of the hypothalamus are released from the nerve processes in the area of the median eminence and through the hypothalamic-pituitary portal system they enter the adenohypophysis with the blood. Inverse regulation negative connection, in which the hypothalamus, pituitary gland and peripheral endocrine glands participate, is carried out in the absence of influences from the overlying parts of the central nervous system.
The hypothalamus contains centers for the regulation of water and salt metabolism (supraoptic and paraventricular nuclei); protein, carbohydrate and fat metabolism; regulatory centers of cardio-vascular system, endocrine glands; center of hunger (lateral hypothalamic nucleus) and satiety (ventrolateral nucleus); thirst center; drinking cessation center; center for regulating urination; center of sleep and wakefulness (suprachiasmatic nucleus); sexual behavior center; centers that provide human emotional experiences, and other centers involved in the processes of adaptation of the body.
Peripheral department:
autonomic (autonomic) nerves, branches and nerve fibers emerging from the brain and spinal cord;
vegetative (autonomous, visceral) plexuses;
nodes (ganglia) of the autonomic (autonomous, visceral) plexuses;
sympathetic trunk (right and left) with its nodes (ganglia), internodal and connecting branches and sympathetic nerves;
terminal nodes (ganglia) of the parasympathetic part of the autonomic nervous system.
The autonomic nervous system performs a number of functions:
Manages activities internal organs, blood and lymphatic vessels, innervating smooth muscle cells and glandular epithelium.
Regulates metabolism, adapting its level to a decrease or increase in organ function. Thus, it carries out an adaptive-trophic function, which is based on the transport of axoplasm - the process continuous movement various substances from the neuron body along processes in the tissue. Some of them are included in metabolism, others activate metabolism, improving tissue trophism.
Coordinates the work of all internal organs, maintaining the constancy of the internal environment of the body.
Finite brain.
1) localization of gray and white matter
White matter of the brain consists of a large number of nerve fibers that fill the space between the cerebral cortex and the basal ganglia. They spread in different directions and form the pathways of the cerebral hemispheres.
17. Spinal cord .● The spinal cord has the form of a thick cord, the diameter of which is about 1 cm. The length of the spinal cord in an adult is 43 cm. Weight is from 34 to 38 grams, which is 2% of the mass of the brain. It is somewhat flattened in the anteroposterior direction. The spinal cord has a segmental structure. At the level of the foramen magnum, it passes into the brain, and at the level of 1-2 lumbar vertebrae it ends with the conus medullaris, from which the filum terminale, surrounded by the roots of the lumbar and sacral spinal nerves, departs. In the places where the nerves exit to the upper and lower extremities there are thickenings - cervical and lumbar (lumbosacral). In uterine development, these thickenings are not pronounced. Cervical thickening - at the level of V-VI cervical segments and lumbosacral thickening - in the region of III-IV lumbar segments. There are no morphological boundaries between the segments of the spinal cord, so the division into segments is functional.
The anterior median fissure and posterior median sulcus divide the spinal cord into two symmetrical halves. Each half, in turn, has two weakly defined longitudinal grooves, from which emerge the anterior and posterior roots of the spinal nerves. The anterior root consists of processes of motor (motor, efferent, centrifugal) nerve cells located in the anterior horn of the spinal cord. The dorsal root, sensitive (afferent, centripetal), is represented by a set of central processes of pseudounipolar cells penetrating into the spinal cord, the bodies of which form the spinal ganglion.
31 pairs of spinal nerves depart from the spinal cord: 8 pairs of cervical, 12 pairs of thoracic, 5 pairs of lumbar, 5 pairs of sacral and a pair of coccygeal. The section of the spinal cord corresponding to two pairs of roots (two anterior and two posterior) is called a segment.
The anterior roots perform various functions. The dorsal roots contain only afferent fibers and conduct sensory impulses to the spinal cord, while the anterior roots contain efferent fibers that transmit motor impulses from the spinal cord to the muscles.
● Structure and functions. The spinal cord is located in the spinal canal and is covered by membranes. The spinal cord begins at the level of the foramen magnum of the skull and ends at the level of the second lumbar vertebra. Below are the spinal cord membranes that surround the roots of the lower spinal nerves. If you look at a cross section of the spinal cord, you can see that its central part is occupied by a butterfly-shaped gray matter consisting of nerve cells. In the center of the gray matter, a narrow central canal filled with cerebrospinal fluid is visible. Outside the gray matter is the white matter. It contains nerve fibers that connect spinal cord neurons to each other and to neurons in the brain. Spinal nerves depart from the spinal cord in symmetrical pairs; there are 31 pairs of them. Each nerve begins from the spinal cord in the form of two cords, or roots, which, when connected, form a nerve. Spinal nerves and their branches travel to muscles, bones, joints, skin and internal organs. The spinal cord in our body performs two functions: reflex and conductive. The reflex function of the spinal cord is the response of the nervous system to irritation. The spinal cord contains the centers of many unconditioned reflexes, for example, reflexes that provide movement of the diaphragm and respiratory muscles. The spinal cord (under the control of the brain) regulates the functioning of internal organs: heart, kidneys, digestive organs. The spinal cord closes reflex arcs that regulate the functions of the flexor and extensor skeletal muscles of the trunk and limbs. Reflexes are innate (which can be determined from birth) and acquired (formed during life during learning), they are closed on various levels. For example, the knee reflex closes at the level of the 3rd-4th lumbar segments. By checking it, the doctor makes sure that all elements of the reflex arc are intact, including segments of the spinal cord. The conductor function of the spinal cord is to transmit impulses from the periphery (from the skin, mucous membranes, internal organs) to the center (brain) and vice versa. The conductors of the spinal cord, which make up its white matter, transmit information in the ascending and descending directions. An impulse about an external influence is sent to the brain, and a certain sensation is formed in a person (for example, you are stroking a cat, and you have a feeling of something soft and smooth in your hand). Centrifugal fibers emerge from the spinal cord, along which impulses go to the organs and tissues. Damage to the spinal cord disrupts its functions: areas of the body located below the site of injury lose sensitivity and the ability to move voluntarily. The brain has a great influence on the activity of the spinal cord. Everything is under the control of the brain complex movements: walking, running, work. The spinal cord is a very important anatomical structure. Its normal functioning ensures all human life. Knowledge of the structure and functioning of the spinal cord is necessary for diagnosing diseases of the nervous system.
●The anterior roots of the spinal cord are nerve endings that are contained in the gray matter. The dorsal roots are sensitive cells, or rather, their processes. The spinal ganglion is located at the junctions of the anterior and posterior roots. This node is created by sensitive cells.
The roots of the human spinal cord extend from the spinal column on either side. With left and right side thirty-one roots come off.
A segment is a specific part of an organ located between each pair of such roots. If you remember the mathematics, it turns out that each person has thirty-one such segments:
five segments are in the lumbar region;
five sacral segments;
eight cervical;
twelve breasts;
one coccygeal.
On a cross section of the spinal cord, the gray matter is shaped like a butterfly or the letter “H”, with a wider anterior horn and a narrow posterior horn. The anterior horns contain large nerve cells - motor neurons.
The gray matter of the dorsal horns of the spinal cord is heterogeneous. The bulk of the nerve cells of the posterior horn form their own nucleus, and at the base of the posterior horn there is a noticeable well-defined layer of white matter, the thoracic nucleus, consisting of large nerve cells.
The cells of all nuclei of the dorsal horns of the gray matter are, as a rule, intercalary, intermediate neurons, the processes of which go in the white matter of the spinal cord to the brain.
The composition of cells located in the posterior and anterior horns of the spinal cord is heterogeneous. Sensitive cells are located in the dorsal horns, the processes of which pass through the midline of the spinal cord into the lateral column of the opposite side and form the path of superficial sensitivity. At the base of the dorsal horn there is a separate group of cells belonging to the cerebellar proprioception system. The processes of these cells are directed to the lateral columns of the spinal cord (the anterior one crosses at the level of its own segment, the posterior one goes to the lateral cord of its own side) and, as part of the spinocerebellar tracts, reach the nucleus of the tent of the cerebellar vermis.
In addition, in the anterior and posterior horns of the spinal cord there is a large number of interneurons, ensuring the closure of reflex arcs, communication between the higher and lower located segments of the spinal cord, communication between the halves of the spinal cord, ensuring desynchronization of the work of the large motor neurons of the anterior horns of the spinal cord and reciprocal inhibition (Renshaw cells). Between the gray matter cells are glial cells.
18. Brain .
● The brain consists of five sections: the medulla oblongata, cerebellum, midbrain, diencephalon and forebrain.
The medulla oblongata is a continuation of the spinal cord. It contains the nuclei of the VIII-XII pairs of cranial nerves. Vital centers for the regulation of respiration, cardiovascular activity, digestion, and metabolism are located here. The nuclei of the medulla oblongata take part in the implementation of unconditioned food reflexes (separation of digestive juices, sucking, swallowing), protective reflexes (vomiting, sneezing, coughing, blinking). The conductor function of the medulla oblongata is to transmit impulses from the spinal cord to the brain and in the opposite direction.
The cerebellum and pons form the hindbrain. The nerve pathways connecting the forebrain and midbrain with the medulla oblongata and spinal cord pass through the bridge. The pons contains the nuclei of the V-VIII pairs of cranial nerves. The gray matter of the cerebellum is located outside and forms the cortex with a layer of 1-2.5 mm. The cerebellum is formed by two hemispheres connected by the vermis. The cerebellar nuclei provide coordination of complex motor acts of the body. The large hemispheres of the brain, through the cerebellum, regulate the tone of skeletal muscles and coordinate body movements. The cerebellum takes part in the regulation of some autonomic functions (blood composition, vascular reflexes).
Midbrain located between the pons and the diencephalon. Consists of the quadrigeminal peduncle and cerebral peduncles. Through the midbrain there are ascending pathways to the cerebral cortex and cerebellum and descending pathways to the medulla oblongata and spinal cord (conducting function). The midbrain contains the nuclei of the III and IV pairs of cranial nerves. With their participation, primary orientation reflexes to light and sound are carried out: eye movement, turning the head towards the source of irritation. The midbrain is also involved in maintaining skeletal muscle tone.
The diencephalon is located above the midbrain. Its main divisions are the thalamus (visual thalamus) and the hypothalamus (subthalamic region). Centripetal impulses from all receptors of the body (with the exception of the olfactory) pass through the thalamus to the cerebral cortex. Information receives the appropriate emotional coloring in the thalamus and is transmitted to the cerebral hemispheres. The hypothalamus is the main subcortical center for the regulation of the body's autonomic functions, all types of metabolism, body temperature, constancy of the internal environment (homeostasis), and the activity of the endocrine system. The hypothalamus contains centers for feelings of satiety, hunger, thirst, and pleasure. The nuclei of the hypothalamus are involved in the regulation of the alternation of sleep and wakefulness.
The forebrain is the largest and most developed part of the brain. It is represented by two hemispheres - left and right, separated by a longitudinal fissure. The hemispheres are connected by a thick horizontal plate - the corpus callosum, which is formed by nerve fibers running transversely from one hemisphere to the other. Three sulci - central, parieto-occipital and lateral - divide each hemisphere into four lobes: frontal, parietal, temporal and occipital. The outside of the hemisphere is covered by a layer of gray matter - the cortex; inside there are white matter and subcortical nuclei. The subcortical nuclei are a phylogenetically ancient part of the brain that controls unconscious automatic actions (instinctive behavior).
The cerebral cortex has a thickness of 1.3-4.5 mm. Due to the presence of folds, convolutions and grooves, the total area of the cortex adult human is 2000-2500 cm2. The cortex consists of 12-18 billion nerve cells arranged in six layers.
Although the cerebral cortex functions as a single whole, the functions of its individual sections are not the same. The sensory (sensitive) zones of the cortex receive impulses from all receptors of the body. Thus, the visual zone of the cortex is located in the occipital lobe, the auditory zone - in the temporal lobe, etc. In the associative zones of the cortex, storage, evaluation, comparison of incoming information with previously received information, etc. are carried out. Thus, the processes of memorization and learning occur in this zone , thinking. Motor areas are responsible for conscious movements. From them, nerve impulses travel to the striated muscles.
The white matter of the forebrain is formed by nerve fibers that connect different parts of the brain.
Thus, the cerebral hemispheres are the highest department of the central nervous system, providing the highest level of adaptation of the body to changing conditions external environment. The cerebral cortex is the material basis of mental activity.
● The lateral ventricles are cavities in the brain that contain cerebrospinal fluid. These ventricles are the largest in the ventricular system. The left ventricle is called the first, and the right - the second. It is worth noting that the lateral ventricles communicate with the third ventricle through the interventricular or Monroe foramina. Their location is below the corpus callosum, on both sides of the midline, symmetrically. Each lateral ventricle has an anterior horn, a posterior horn, a body, and an inferior horn.
The third ventricle is located between the visual tuberosities. It has a ring-shaped form because the intermediate visual tuberosities grow into it. The walls of the ventricle are filled with central gray medulla. It contains subcortical autonomic centers. The third ventricle communicates with the midbrain aqueduct. Posterior to the nasal commissure, it communicates through the interventricular foramen with the lateral ventricles of the brain.
The fourth ventricle is located between the medulla oblongata and the cerebellum. The vault of this ventricle is the cerebral velum and the worm, and the bottom is the pons and medulla oblongata.
This ventricle is a remnant of the cavity of the brain bladder, the ventricles of the brain, located posteriorly. That is why this is a common cavity for the parts of the hindbrain that make up the rhombencephalon - the cerebellum, medulla oblongata, isthmus and pons.
The fourth ventricle is shaped like a tent, in which you can see the bottom and roof. It is worth noting that the bottom or base of this ventricle has a diamond shape; it is, as it were, pressed into the posterior surface of the pons and medulla oblongata. That is why it is commonly called the diamond-shaped fossa. The spinal cord canal is open in the posteroinferior corner of this fossa. In this case, in the anterosuperior corner there is a connection between the fourth ventricle and the aqueduct.
The lateral angles blindly end in the form of two recesses that bend ventrally near the inferior cerebellar peduncles.
The lateral ventricles of the brain have relatively large sizes and have a C-shape. In the cerebral ventricles, cerebrospinal fluid or cerebrospinal fluid is synthesized, which then ends up in the subarachnoid space. If the outflow of cerebrospinal fluid from the ventricles is disrupted, the person is diagnosed with hydrocephalus.
●WHAT ARE THE HUMAN MINDINGS
The human brain consists of soft tissues that are susceptible to mechanical damage. The meninges directly cover the brain, keeping it safe during walking, running, or accidental impacts.
Liquor constantly circulates between the layers. Cerebrospinal fluid flows around the human brain, due to which it is constantly in a suspended state, which provides additional shock absorption.
In addition to protection from mechanical stress, each of the three shells performs several secondary functions.
FUNCTIONS OF THE BRAIN MEMBRANES
The human spinal cord is protected by three membranes that originate in the mesoderm (middle germ layer). Each layer has its own functions and anatomical structure.
It is customary to distinguish:
anatomical location of the meninges The dura mater is the densest among all protective layers. The outer surface is adjacent to the inner part of the skull. The dura mater of the brain is involved in the formation of processes that separate several important areas from each other. Among them: the falx medullaris, the tentorium and falx of the cerebellum, the diaphragm sellae.
The arachnoid membrane - in addition to its protective function, is involved in the circulation of cerebrospinal fluid. Forms the interarachnoid space through which cerebrospinal fluid circulates.
Soft or vascular membrane - using glial tissue fuses with the surface of the spinal cord. Inside the layer are arteries and numerous vessels that envelop the brain. The layer is involved in the functioning of the blood supply system.
●Types of brain pathways
There are associative, commissural and projection pathways of the brain. The first pathways of the brain connect different parts of the gray matter located in the same hemisphere. Among them there are short and long ones. Short association pathways are located within the medulla - intralobar fibers. They are also divided into intracortical (arc-shaped), when the bundle of fibers does not leave the cortex and goes around the gyrus in the shape of an arc; and extracortical, when the nerve pathway extends beyond the gray matter. Long associative pathways connect groups of nerve cells located in the same hemisphere, but in its different lobes. The most significant of them include the superior longitudinal fasciculus (connects the cortex of the frontal, parietal and occipital lobes), the inferior longitudinal fasciculus (connects the temporal and occipital lobes) and the uncinate fasciculus (connects the frontal lobe with the anterior part of the temporal lobe). Commissural or commissural nerve tracts connect areas of gray matter of different hemispheres. With their help, the activity of similar nerve centers of the cerebral hemispheres is coordinated. The transitions of commissural fibers from one hemisphere to the other form adhesions. There are three of them: the corpus callosum, the anterior commissure and the fornix commissure. The corpus callosum is formed by fibers connecting new parts of the brain; in the white matter of the hemispheres, these fibers diverge in a fan-shaped manner. The genu and beak of the corpus callosum carry fibers from the frontal lobes of the brain; in the white matter, bundles of these fibers form the frontal forceps on the sides of the longitudinal fissure of the brain. The areas of the cortex of the central gyri, temporal, parietal lobes are connected through the trunk of the corpus callosum. The splenium of the corpus callosum carries fibers from the posterior regions of the parietal as well as the occipital lobes. In the white matter on the sides of the longitudinal fissure of the brain, bundles of these fibers form the nuchal forceps. The fornix commissure connects the gray matter of the temporal lobes and hippocampus of different hemispheres. The anterior commissure consists of fibers coming from the medial areas of the cortex of the temporal lobes and the cortex of the olfactory triangles. Projection pathways of the brain
In addition to associative and commissural pathways, there are also projection pathways that connect the gray matter of the cerebral hemispheres with the underlying structures of the central nervous system, including the spinal cord, as well as simply various clusters of neurons, different parts of the central nervous system with each other. Thanks to projection fibers, the interconnection and joint activity of the central nervous system structures is realized. Among the projection pathways, ascending (afferent) and descending (efferent) are distinguished. The former carry information to the brain received from receptors of both the external and internal environment. In this regard, according to the nature of the information, the ascending pathways are exteroceptive (impulses from pain, temperature, tactile receptors of the skin and impulses from the sensory organs - visual, gustatory, auditory, olfactory), proprioceptive (carry impulses from muscle-tendon receptors -articular apparatus about body position, muscle work, etc.) and interoceptive (conduct information about internal environment body, received from receptors of internal organs and blood vessels).
Exteroceptive pathways of the brain
The exteroceptive pathways of the brain that carry information from the skin receptor apparatus include the lateral and anterior spinothalamic tracts. Temperature and pain sensitivity are carried out along the lateral spinothalamic tract. The path consists of two neurons. The body of the first lies in the spinal ganglion, its dendrites end in the skin and mucous membranes. Along the axons, impulses enter the dorsal roots into the spinal cord, where they pass to the body of the second neuron in the dorsal horns. In the spinal cord, the axon of the second neuron passes to the opposite side (segmental transition). Along the lateral cord, the bundle rises into the brain bulb, where it is located behind the olive nucleus. Along the tegmentum of the pons and midbrain, the axon of the second neuron goes to the anterior tubercle of the thalamus and forms a synapse with the body of the neuron of the thalamocortical projection of the lateral spinothalamic pathway (it is possible to consider a three-neuron lateral spinocortical pathway of temperature and pain sensitivity). The axon of this neuron passes through the middle of the posterior femur of the internal capsule and forms synapses with neurons in the cortex of the postcentral gyrus. The pathway from the receptors of touch and pressure is represented by the anterior spinothalamic tract. This pathway is three-neuron. The body of the first neuron is located in the spinal sensory ganglion. The cells send axons to the dorsal root, from where they pass into the dorsal horn and are interrupted, connecting with the body of the second neuron. In turn, its central processes penetrate through the anterior gray commissure into the anterior horn of the opposite side. As part of the anterior cord, the axon of the second neuron follows to the overlying sections. In the medulla oblongata, the fibers merge with the fibers that form the medial lemniscus. The body of the third neuron lies in the dorsal lateral nucleus of the thalamus; here the central process of the second neuron is interrupted. The fibers extending from the nucleus on their way pass through the posterior thigh of the internal capsule into the cortex of the postcentral gyrus, the cortical center of general sensitivity.
Often, when the horns are damaged on one side, the sense of touch and pressure partially disappears. This is explained by the fact that some of the fibers do not pass to the opposite side and go to the cortex along with other ascending pathways.
Proprioceptive pathways of the brain
Proprioceptive pathways include several pathways. The bulbothalamic tract carries impulses from the receptors of the musculoskeletal system to the postcentral gyrus. The bodies of the first neurons in the spinal ganglion give off central processes to the dorsal root, from where they pass into the dorsal funiculus and further to the thin and cuneate fasciculi, which are located in the medulla oblongata and contain nuclei of the same name, in which the axon of the first connects with the body of the second neuron. Its processes in the interolive layer form the intersection of the medial loops. These fibers that have passed to the opposite side are called internal arcuate. Some fibers of the second neuron form the posterior and anterior arcuate fibers. They, passing along the lateral cord and the inferior cerebellar peduncle, conduct impulses of the muscular-articular sense to the cerebellar vermis. Bypassing the pontine tegmentum, the fibers connect to the body of the third neuron, which is localized in the dorsolateral nucleus of the thalamus. Its processes go to the postcentral gyrus.
Spinal cerebellar tract conductive pathways of the brain
The posterior spinocerebellar tract, or Flexig's bundle, is the path of proprioceptive sensitivity from the receptors of the muscular apparatus to the cortex of the cerebellar vermis. From the body of the first neuron, excitation goes along the axon to the dorsal horn, to the thoracic nucleus, in which the body of the second neuron is located. There is no crossing of fibers in this path; the axon of the third neuron follows through the lower peduncle into the cerebellum. This pathway also contains fibers that can carry impulses to the red nucleus, cerebellar hemispheres and cortex.
The anterior spinocerebellar tract, or Govers' bundle, is a little more complex. What distinguishes him from the back one is that he makes two crosses and as a result returns to his side.
Among the projection pathways of the descending direction, pyramidal and extrapyramidal motor pathways are distinguished. Along the pyramidal tracts, impulses travel from the cortex to the anterior horns of the spinal cord or to the nuclei of the cranial nerves. The pyramidal tracts are divided into the corticonuclear, lateral and anterior corticospinal tract.
The corticonuclear tract begins from the Betz cells of the lower part of the precentral gyrus and goes to the underlying sections, passing through the knee of the internal capsule. In the medulla oblongata, the fibers cross and end in synapses with the body of the second neuron in the nuclei of cranial nerves III to VI and IX to XII. The axons of the second neuron emerge as fibers of the cranial nerves and innervate the organs of the head and neck.
The lateral corticospinal tract, like the anterior one, comes from the Betz cells of the upper two-thirds of the precentral gyrus. The fibers pass through the beginning of the posterior limb of the internal capsule, the cerebral peduncles and the pons. The medulla oblongata is the crossroads of the lateral corticospinal tract, which then continues to the anterior horns of the spinal cord, where the axon of the first neuron contacts the second, giving off motor branches to the muscles. The fibers of the anterior corticospinal tract also cross, but in the spinal cord.
Among the extrapyramidal tracts are the red nucleus-spinal cord, vestibulospinal cord and corticopontine-cerebellar tract.
The red nucleus-spinal tract starts from the red nucleus and immediately crosses, then goes along the underlying sections to the motor neurons of the spinal cord along the lateral cords.
The vestibulospinal tract begins from the nuclei of the VIII pair of cranial nerves, which project to the lateral parts of the superior triangle of the rhomboid fossa, and continues to the nuclei of the anterior cords of the spinal cord. This path makes installation reactions possible.
Corticocerebellar tract from cortical cells of all lobes except the insular lobe. The axons of these cells (corticopontine fibers) pass through the internal capsule. The first neuron is interrupted at the base of the bridge at the nuclei of the second neuron, which also give off crossing axons (transverse fibers of the bridge) going to the cerebellar hemispheres.
19. Cervical plexus.
● The cervical plexus (plexus cervicalis) is formed by the anterior branches of the four upper cervical nerves. Upon exiting through the intervertebral foramen (foramen intervertebrale), these nerves lie on the anterior surface of the deep muscles of the neck at the level of the upper four cervical vertebrae behind the sternocleidomastoid muscle.
The cervical plexus forms sensory, motor (muscular) and mixed branches.
Sensitive branches. The sensory branches give rise to the cutaneous nerves of the neck (transverse cervical nerve, medial, intermediate and lateral supraclavicular nerves, greater auricular nerve and lesser occipital nerve), described above.
Motor branches. The motor branches of the cervical plexus innervate
NEUROGLIA(Greek, neuron nerve + glia glue; syn. glia) - one of the constituent parts of the nervous tissue in the brain and spinal cord, which includes cells of various origins, closely associated with nerve cells and their processes and carrying out supporting, trophic, protective and a number of other functions, as well as playing a certain role in the processes of occurrence, transmission and conduction of nerve impulses.
Story
The term “neuroglia” was proposed in 1846 by R. Virchow, who first discovered special stellate and spindle-shaped cells lining the walls of the ventricles of the brain and the central canal of the spinal cord. A great contribution to the study of the structure of N. was made by the works of Deiters (O. F. C. Deiters, 1865), Weigert (K. Weigert, 1895), S. Ramon y Cajal (1913), Ortega (P. del Rio Hortega, 1919, 1921), A. I. Smirnov (1935), M. M. Aleksandrovskaya (1950), A. P. Avtsyn (1967), etc. A detailed study of the fine structure of N., its physiol, and biochemical features began in 60s 20th century in connection with the introduction into practice scientific research methods of electron microscopy, histo- and radiochemistry, extra- and intracellular removal of bioelectric potentials, etc. However, many questions regarding physiol, the importance of N. in the activity of the nervous system, as well as biochemical processes occurring in N., remain unexplored.
Morphology
Neuroglia consists of two genetically various types: macroglia, among the cut cells there are astrocytes, oligodendrocytes and ependymocytes, and microglia, the cut cells are called glial macrophages or microgliocytes. Some researchers consider the satellite cells of the VNS ganglia, and the neurolemmocytes of the peripheral nerves as peripheral Neuroglia. (see Ganglia, Nerve fibers).
Astrocytes develop during embryogenesis from epithelial cells of the neural tube, forming spongioblasts, which turn into neuroblasts and then into astrocytes. Oligodendrocytes are also of ectodermal origin. In their development they pass through the oligodendroblast stage. Ependymocytes also develop from the epithelial cells of the neural tube. Glial macrophages are mesodermal elements, because they are formed from histiocytes of the pia mater, migrating into the brain along the walls of blood vessels.
Developing microglial cells are called mesoglioblasts.
Astrocytes(syn.: astroglia, entoglia, classical glia). Based on localization, a distinction is made between plasma astrocytes located in close proximity to the body of the nerve cell (Fig. 1), designated as satellites of the nerve cell, and fibrous astrocytes. The latter may be located among the processes of nerve cells (Fig. 2 and 3).
Astrocytes are small stellate or spindle-shaped cells, the body diameter of which is 8-15 microns. For light-optical examination of astrocytes, special staining methods are used: gold-sulem staining (according to Ramon y Cajal), silver impregnation (according to Golgi, Bielschowsky - Gros - Lavrentiev methods). Astrocyte processes are also identified using staining methods according to Snesarev, Weigert, etc. Astrocyte nuclei are identified using staining used for survey methods of studying c. n. With. (cresyl violet, toluidine blue, hematoxylin, etc.).
In light optical examination, astrocytes have larger nuclei compared to oligodendrocytes and glial macrophages. The nuclei of astrocytes are oval, lightly colored, and contain small chromatin grains. The nucleolus is usually poorly expressed. In the cytoplasm, gliosomes (mitochondria) and fibrils are detected (see). Thin numerous processes extending in all directions extend from the body of the astrocyte. Astrocytes are characterized by the so-called vascular pedicles* which are in contact with the basement membranes of the capillaries.
Plasma astrocytes have more processes than fibrous astrocytes, and they branch more often; fibrous astrocytes have longer and less branched processes. The processes of astrocytes in contact with each other form a thin delicate layer on the surface of the cerebral cortex under the pia mater - the outer glial limiting membrane. Astrocyte processes also form a thin layer near the walls of the ventricles of the brain.
For electron microscopic examination of astrocytic glia, the preparation is fixed by perfusion of the brain with glutaraldehyde solutions followed by immersion in osmium tetroxide.
Electron microscopically, astrocytes are characterized by a light, electron-transparent cytoplasm containing a relatively small number of organelles. The body of astrocytes has an uneven contour and seems to repeat the outlines of the axons and dendrites adjacent to it. Most astrocytes have a relatively large cytoplasm; Astrocytes are less common, in which the cytoplasm surrounds the nucleus with only a narrow rim. Large round or oval kernels do not have pronounced folding; chromatin (see) of the nuclei forms small clusters near the nuclear membrane, and is also scattered diffusely in the form of small clumps in the karyoplasm. In the cytoplasm of plasmatic astrocytes, the elements of the endoplasmic reticulum are very poorly developed: the granular reticulum is represented by single short tubes, the agranular reticulum - by clusters of a few small vesicles and vacuoles. In the cytoplasm, in addition to mitochondria, a few more or less evenly distributed polysomes are detected; lysosomes (see) and osmiophilic bodies are occasionally found.
The differences between plasmatic and fibrous astrocytes are especially clearly visible during electron microscopic examination. Fibrous astrocytes are characterized by numerous bundles of fibrils (the thickness of each fibril is 8-9 nm), which are located in the cytoplasm of both the body of the fibrous astrocyte and its processes (Fig. 3). Light-optical fibrils appear as a single structure, while electron microscopy reveals that individual fibrils are formed by bundles of microfibrils. It has been proven that the fibrils themselves are special intracellular elements that perform specific functions. As the processes become thinner and move away from the cell body, the number of fibrils gradually decreases. Fibrils are distributed unevenly in the processes of astrocytes; some processes, relatively small in diameter, may contain numerous fibrils.
Single mitochondria are found in the processes of plasmatic astrocytes. Unlike axons, dendrites and processes of oligodendrogliocytes, the processes of astrocytes have an uneven contour - they seem to fill the space between the processes of nerve cells.
According to Wolff (J. Wolff, 19G3), astrocytes make up 45-60% of the volume of gray matter in the brain. In c. n. With. there is no actual intercellular space; between the densely located processes of nerve cells and N. cells filling the space between the nerve cells, only gaps with a width of approx. 20 nm. In the adult brain, according to Schlotz (1959), there are approx. 150-200 billion N. cells, which is more than 10 times the number of nerve cells.
The pericapillary space, according to electron microscopic examination, is filled with astrocyte processes (Fig. 4). Astrocyte processes cover more than 85% of the surface of capillaries; they are often located near synapses; large processes contact the bodies of nerve cells. Specialized contacts such as desmosomes (see) both between neighboring N. cells and between glial and nerve cells have been described. These contacts are apparently the sites of the most active ion exchange.
Oligodendrocytes(syn.: oligoglia, oligodendroglia) are smaller round cells than astrocytes (diameter, approx. 7-10 microns) with a small number (2-3) of thin processes, which stretch a short distance from the cell body. Oligodendrocytes have a round or oval nucleus rich in chromatin. In the narrow rim of the cytoplasm there is a relatively large number of organelles.” The poverty of processes, apparently, served as the basis for the name of these cells (oligo - small). When sections of nervous tissue are stained with cresyl violet, oligodendrocytes are most often identified as satellite cells of large neurons (perineuronal). Oligodendrocytes are located in the gray matter of the brain near clusters of myelin fibers (perifascicular); in the white matter of the brain and spinal cord they often stretch in a chain among bundles of nerve fibers (interfascicular).
Electron microscopic studies carried out by Paley (1958), J. E. Hartmann (1958), Schultz, Pease (1959), A. Peters (1960), A. L. Mikeladze and E.I. Dzamoeva (1970), supplemented the characteristics of oligodendrocytes. Compared to astrocytes, they have a higher electron density of the nucleus and cytoplasm; in the cytoplasm of oligodendrocytes, numerous polysomes and ribosomes (see), small mitochondria, microtubules are visible, the granular and agranular network is quite well developed, and lipid inclusions are found. Unlike astrocytes, there are no fibrils in the cytoplasm of oligodendrocytes. The bodies of oligodendrocytes have a more regular rounded shape and a smoother contour than astrocytes (Fig. 5 - 7).
Depending on the degree of electron density of the cytoplasm and karyoplasm, oligodendrocytes are divided into three types: light, more osmiophilic and intensely osmiophilic. In accordance with this, certain differences are observed in their ultrastructure, especially in the ultrastructure of the nucleus. Light oligodendrocytes with moderately electron-dense cytoplasm have a light nucleus with electron-transparent karyoplasm, a small amount of fine-granular chromatin relatively evenly distributed throughout the karyoplasm, which, however, forms small clusters near the nuclear membrane. The nucleolus of such cells is usually small. Oligodendrocytes with such nuclei are often satellite cells of large neurons.
More osmiophilic oligodendrocytes have a round or oval nucleus, often with an uneven contour, containing large clumps of chromatin, which are located not only near the nuclear membrane, but also at a distance from it.
Intensely osmiophilic oligodendrocytes are characterized by osmiophilic karyoplasm, an indistinct nucleolus, and prominent electron-dense cytoplasm. In oligodendrocytes with osmiophilic cytoplasm, the number of polysomes increases.
In light oligodendrocytes, mitochondria, single tubes of a granular network, and a few polysomes are visible, which resembles the ultrastructure of astrocytes.
Ependymocytes form a dense layer of cellular elements lining the spinal canal and all ventricles of the brain. In their ultrastructure they are similar to other macroglial cells (see Ependyma).
Microgliocytes(syn.: glial macrophages, microglia, mesoglia, Ortega cells) as a special type of cells were described by Ortega in 1919. They are small cells (cell body diameter approx. 5 µm). The best histol method for identifying microgliocytes is impregnation with silver carbonate. The nuclei of these cells, intensely stained with basic dyes (see Basophilia), have an irregular triangular or elongated shape and are rich in chromatin.
Microgliocytes are characterized by a few, tortuous processes localized in hl. arr. near capillaries. According to electron microscopic examination, these cells have a small amount of cytoplasm and several short processes (Fig. 8). A characteristic feature of N. cells of this type is that their nuclei and cytoplasm are intensively impregnated with various dyes used for both light and electron microscopy. Therefore, microgliocytes during electron microscopic examination are especially clearly distinguished from other elements of brain tissue by their high degree of osmiophilia and electron density (Fig. 9).
Physiology
N.'s cells, along with the brain vessels and meninges, form the stroma of brain tissue. Closely associated with the bodies and processes of nerve cells, N.'s cells provide not only a supporting, but also a trophic function: N. is involved in ensuring the metabolism of the nerve cell (see). N. cells phagocytose the decay products of nerve cells. Astrocytes with a vascular stalk provide communication between nerve cells and the bloodstream. Astrocytes also participate in ensuring the function of maintaining homeostasis; they are the first to respond to various changes in the water-salt balance, thereby maintaining the constants of water-electrolyte metabolism.
The main function of oligodendrocytes is the formation of myelin in the nervous system and maintaining its integrity (see Myelination). Oligodendrocytes take part in ensuring the metabolism of nerve cells, as evidenced by experiments indicating interdependent changes in the metabolism of neurons and oligodendrogliocytes. With significant function and load around nerve cells, the number of their satellite cells noticeably increases, reactive changes in neurons are accompanied by pronounced changes in perineuronal glia.
Glial satellite cells (astrocytes and oligodendrocytes) play an important role in providing specific functions of nerve cells. The sensitivity of neuroglial cells to ionic changes in the environment significantly exceeds the sensitivity of neurons. This is due to both the high activity of glial Na + -K + -dependent ATPase and the higher permeability of the N. cell membrane for potassium ions. Potassium ions leaving neurons or axons during the repolarization phase easily penetrate the membranes of N. cells, causing their depolarization. At the same time, metabolism is activated in N cells. It has been established that an increase in the concentration of potassium in the environment activates the synthesis of amino acids and proteins in brain cells. At the same time, metabolic shifts in the nerves occur much earlier and are more pronounced than in neurons. When neurons are excited, the content of RNA and protein in them increases and the activity of respiratory enzymes increases, while the content of RNA and protein in nearby glial cells decreases.
The main function of microgliocytes is phagocytosis (see), although other N. cells participate in this process.
An important indicator of fiziol, the activity of N. cells is their electrical activity. The membrane potential of N. cells is significantly higher than the membrane potential of nerve cells. Thus, in vertebrates, the membrane potential of N. cells is approx. 90 mV, and the level of membrane potential of nerve cells ranges from 60 to 80 mV. Since N.'s cells have low permeability to all ions except potassium ions, the high level of membrane potential of its cells is determined by the concentration of potassium cations in the cytoplasm (up to 110 mmol). Another feature of electrical processes in N. is that, unlike neurons that respond to the action of various stimuli with local or spreading processes in the form of spikes, N. cells respond only with gradual, slow wave-like changes in the level of membrane potential. N.'s depolarization (i.e., a decrease in membrane potential) develops slowly, reaching a maximum in a time from 50-500 ms to 4-5 minutes: the amount of depolarization depends on the initial level of membrane potential. The initial level of membrane potential is also reached slowly, passing through the hyperpolarization stage. Thus, the excitation of nerve cells (more precisely, a certain population of nerve cells) is accompanied by N.’s depolarization in this area of the c. n. With. N.'s repolarization (i.e., the process of restoring the initial level of the membrane potential of N.'s cells) reflects the process of cleansing the intercellular space from potassium ions (they are released when nerve cells are excited), which occurs with the participation of N. At the same time, N.'s cells remove the excess neurotransmitter released synaptic endings.
N plays an important role in the integrative activity of the brain. It takes part in the mechanisms of formation of conditioned reflexes and dominants. According to A.I. Roitbak, the establishment of new forms of temporary connections occurs with the help of N., edges myelinate “potential” synaptic terminals and transform them into “actual” ones.
V. S. Rusinov et al. showed that the formation of temporary connections is based on electrotonic forms of signaling, which cannot be carried out without the participation of N. cells (see Conditioned reflex).
Experiments revealed that the application of antiglial gamma globulin, which selectively damages N. cells, to the cortex leads to pronounced changes in the electrical activity of neurons. In this case, the volume of convergence is significantly reduced, up to a complete loss of the ability to analyze and synthesize heterogeneous excitations.
Biochemistry
Progress in the study of the biochemistry of N. cells is associated with the development of methods for their isolation, among which the following are distinguished: 1) the method of micromanipulation, or microrurgy (see), in which N cells are excised from tissue sections using micromanipulators under the control of a microscope. ; 2) a method for obtaining enriched fractions of N. cells and neurons, in which brain tissue is disaggregated by passing it through sieves with decreasing opening sizes, and the resulting cell suspension is centrifuged in a sucrose density gradient and divided into fractions of N. cells and neurons; 3) method of cell and tissue culture (see). However, each individual method is not absolutely sufficient for isolating N. cells in their pure form, therefore, for more reliable biochemical characterization, at least two of the above methods are used. The data obtained in this case are relative and show Ch. arr. qualitative differences in the content of one or another component in different types of N.
The available biochemical characteristics of N.'s cells were obtained mainly as a result of the study of astrocytes and oligodendrocytes, which make up approx. 90% of the total number of N. cells in the brain. Biochemistry, characteristics of microglia and ependyma are not sufficiently developed.
The dense remainder of the N. cortex and brainstem is approx. 20%. Absolute value The dry weight of one glial cell depends on the type of cell and the method of its isolation. Thus, the dry weight of astrocytes, depending on the method of their isolation, ranges from 500-1000 and 500-2000 mg per 1 cell, while the dry weight of oligodendrocytes is much less - 25-100 pg per 1 cell.
The main part of the dense remainder of N.'s cells consists of high-molecular substances - lipids (see), proteins (see), nucleic acids (see), carbohydrates (see) and low-molecular substances - amino acids, nucleotides (ATP) and electrolytes (sodium ions and potassium). The lipid content in astrocytes is approximately 1.5-2 times higher than in neurons; they amount to approx. 1/3 of the total solid residue.
Qualitatively, the lipid composition of N. cells is characterized by the content of almost all classes of lipids - phospholipids, galactolipids, cholesterol, fatty acids, etc. The lipid composition of oligodendrocytes is similar to the composition of myelin. Gangliosides were found in astrocytes and oligodendrocytes.
The protein content in N. cells isolated using various methods varies on a dry weight basis from 30 to 50%. Among the proteins, acidic proteins specific to N cells were found: glia fibrillary acid protein (GFA-pro-tein), concentrated in astrocytes, and protein S-100, contained in astrocytes and oligodendrocytes. Such proteins appear in N. cells on early stages their differentiation. N. cell proteins differ from neuronal proteins in their high content of sulfhydryl (SH) groups. The DNA content in the nuclei of N. cells is approximately the same as in neurons (approx. 6.4 pg per 1 cell). In oligodendrocytes, the RNA content is 1.8-2.0 pg per 1 cell, and in astrocytes it is much higher - 10-12 pg per 1 cell.
Almost all glycogen found in the brain is concentrated in N.; its content is approximately 1-2% of the total dry weight of N. cells.
Determining the content and distribution of low-molecular compounds in N. cells is extremely difficult. It has been established that in astrocytes the concentration of a number of non-essential amino acids (glutamic acid, glutamine, gamma-aminobutyric acid, aspartic acid, glycine, alanine) is 1/3-V8 of their concentration in the whole brain.
N. is characterized by relatively high metabolic activity. The rate of oxygen consumption by N. cells averages up to 200 µmol/hour per 1 g of fresh tissue weight. The experiment showed that the respiratory activity of astrocytes and oligodendrocytes is especially high in cases where succinate is used as a substrate, while oxygen consumption by ependymocytes is most intense in the presence of other substrates - glucose, pyruvate, mannose and lactate. It is calculated that approx. 1/3 of the respiratory activity of the rat cerebral cortex occurs in N. The glycolytic activity of N. cells and neurons is approximately the same as the glycolytic activity found in sections of the cerebral cortex (approximately 200 µmol per 1 hour per 1 g of fresh tissue weight). Activity of oxidative enzymes in oligodendrocytes c. n. With. increases during myelination. Ependymal cells are characterized by high activity of oxidative enzymes. In the N. of peripheral nerves (neurolemmocytes), oxidative enzymes are also characterized by high activity; their uneven distribution is noted: succinate dehydrogenase is localized mainly in the distal parts of cells at the nodes of Ranvier; NAD and NADP diaphorases are distributed evenly throughout the cytoplasm. The activity of Na,K-dependent ATPase in N. cells is higher than in neurons. Carbonic anhydrase is predominantly localized in the cells of N.
It is assumed that N. cells participate in the metabolism of neurotransmitters. They have a highly efficient transport mechanism for the uptake of amino acids and developed enzyme systems for their catabolism. Capture of glutamic acid, gamma-aminobutyric acid, taurine, glycine and aspartic acid by N. cells is important point in the process of inactivation of mediator substances.
With various pathol processes in the nervous system, N. reacts with a change in metabolic activity. Thus, with tumors arising from various types of glial cells (gliomas), an increase in DNA content, intensification of its synthesis, RNA and protein synthesis, and an increase in the activity of oxidative enzymes and phosphorus metabolism enzymes (ATPase and thiamine pyrophosphatase) are observed. These changes are observed in all N. cells, but are most pronounced in astrocytes. During cerebral edema, the activity of ATPase and thiamine pyrophosphatase increases only in astrocytes. With various forms of gliosis, the content of acidic proteins characteristic of astrocytes increases; in astrocytes and oligodendrocytes, the activity of acid hydrolases increases. During convulsions due to poisoning by various toxic substances in the N. of the spinal cord, the content of RNA, proteins and various functions and groups of proteins decreases. It is believed that during epileptiform convulsions the protective function of N. is disrupted; it normally prevents the excessive accumulation of potassium ions in the intercellular space. In patients with parkinsonism, the RNA content in N. increases and the composition of nucleotides changes sharply. With hyperthyroidism, the intensity of protein synthesis in N. decreases, and with hypothyroidism, it increases. It has been noted that N. cells are resistant to hypoxia to a greater extent than neurons, and functional changes in this condition are minimal; at the same time, the activity of lactate dehydrogenase and pentose cycle enzymes decreases, while the activity of succinate dehydrogenase and cytochrome oxidase remains high.
Pathomorphology
N.'s cells in a number of pathol processes can react ambiguously, since their sensitivity to damaging agents and the time of occurrence of the reaction are different. Methods morphol, research (histochemical, cytochemical, electron microscopy) made it possible to reveal subtle disorders in N. in various pathol processes.
N.'s reaction in various patol conditions is expressed in dystrophic changes, which can be reversible and irreversible, and in reparative changes.
Reversible dystrophic changes in astrocytes. Swelling and edema of the processes of astrocytes, located among the processes of nerve cells, are observed with edema and swelling of the brain of various origins (see Edema and swelling of the brain), often due to hypoxia; the swelling process is accompanied by an excess glycogen content in astrocytes, this is mainly observed in astrocytes located near nerve cells, characterized by dark osmiophilic cytoplasm and karyoplasm. In the vascular stalks of astrocytes in contact with the basement membrane of capillaries, glycogen granules are very rare. The development of dystrophic changes in the nerve cell and N. cell is interconnected: the degree of patol, changes in N. cells is largely determined by the severity of destructive changes and the possibility of reparative processes in nerve cells. The reaction of astrocytes to a lack of oxygen is explained by their metabolic characteristics. Hypoxia causes a decrease in the activity of lactate dehydrogenase and pentose cycle enzymes in astrocytes, while the activity of succinate dehydrogenase and cytochrome oxidase remains at a fairly high level. Electron microscopically, acute swelling of astrocytes and their processes is accompanied by the appearance in their cytoplasm of small fragments of membranes, osmiophilic particles, and sometimes large fragments of these structures, which reflects the initial stages of absorption of destroyed neurons by N. cells (see Neuronophagy).
Reparative changes in astrocytes. Astrocyte hypertrophy is characterized by a uniform increase in the volume of the cell body and astrocytic processes (color. Fig. 2). If the increase in the cell body predominates, then such astrocytes are called Nissl mast cells (Fig. 10, a). The cytoplasm of these astrocytes is homogeneous, the nucleus is light with large clumps of chromatin, and the processes are thin. Mast cells are characteristic of progressive paralysis. Hypertrophied astrocytes are usually observed near foci of necrosis, hemorrhages, tumors, etc.
Hypertrophied astrocytes of gigantic size and ugly shapes are found in tuberous sclerosis (Fig. 10, b). In case of brain tumors, as well as regenerative processes, multinucleated giant astrocytes are formed as a result of incomplete cell division (Fig. 10, c). In the large lobulated nuclei of such cells an increased number of chromosomes is found. Hypertrophy of astrocytes occurs due to an increase in specific intracellular structures (ribosomes, polysomes, endoplasmic reticulum, fibrils, etc.) and is accompanied by an intensification of protein synthesis and an increase in the concentration of RNA in the cytoplasm. Increased accumulation of RNA is observed in the nucleoli, the average concentration of DNA and its content in the nucleus increase, and the activity of enzymes in the redox cycle increases. This hypertrophy of astrocytes is compensatory in nature. Hypertrophy of astrocytes with the formation of a significant amount of lysosomes, phagosomes, and lipid inclusions also develops due to the absorption (phagocytosis) of various decay products of pathologically altered cells.
Astrocyte hyperplasia can be focal or diffuse. Focal hyperplasia occurs near areas of brain destruction, around specific granulomas (gumma, tubercles), cysticerci, multiple sclerosis plaques, and also during the formation of a brain scar. Hyperplasia with gliosis (see) has a peculiar character, which develops with hron, cerebral edema. Hyperplasia of astrocytes is accompanied by increased fibril formation.
Diffuse hyperplasia of astrocytes is observed in cases of widespread brain lesions (with progressive paralysis, neurosyphilis, atrophic processes of the brain).
Division of mature astrocytes usually occurs amitotically. Mitotic activity of astrocytes is observed during malignancy of glial tumors, for example, astrocytomas (see). Astrocytes that are part of astrocytomas may be almost unchanged morphologically or may not differ from hyperplastic astrocytes. Astrocytes of the same nature are also observed in other tumors - polymorphic genetic gliomas, ganglioneuromas, astroblastomas (see Brain, tumors), where they can be found among the cellular elements of the embryonic type.
Irreversible dystrophic changes in astrocytes include clasmatodendrosis, amoeboid (Alzheimer's) glia, homogenizing metamorphosis, involutive (senile) changes (color fig. 1-3).
Clasmatodendrosis - disintegration of astrocyte processes into fragments - can be observed with edema and swelling of the brain, with intoxication, rapidly occurring inf. diseases. This condition can develop very quickly, for example, due to brain injury.
Amoeboid glia, described by Alzheimer (A. Alzheimer, 1910), are characterized by profound destructive changes in astrocytes, which is expressed in the shortening of their processes (Fig. 11, a), lysis of fibrils, hyperchromatosis and shrinkage of nuclei. In appearance, such cells resemble amoebas (hence the name “amoeboid” glia). As the process progresses, coagulation of the cytoplasm and granular disintegration occurs (Fig. 11, b) with karyopyknosis or karyorrhexis and loss of cell boundaries. Data obtained from electron microscopic examination allow us to associate the genesis of amoeboid glia with excessive swelling of the cytoplasm of astrocytes and their processes. Amoeboid glia can be observed in certain acute inf. diseases, brain injury, acute psychosis, insulin coma. Sometimes progressive degeneration of astrocytes occurs with a sharp decrease in cytoplasm. As a result, almost bare large figured or vesicular nuclei remain due to their incomplete division or swelling. These changes occur in hepatocerebral dystrophy and a number of encephalopathies resulting from liver failure. The cause of damage to astrocytes in hepatic encephalopathies is considered to be excess content of endogenous ammonia compounds in the body.
Homogenizing metamorphosis is observed in hypertrophied astrocytes localized in areas of the brain that have been subjected to compression. The cytoplasm is homogenized and the nucleus atrophies. Homogeneous formations are formed from such dead astrocytes elongated shape- so-called Rosenthal fibers.
Involutive changes in astrocytes are observed with progressive presenile brain dystrophy. In these cases, proliferation of astrocytes first occurs, which is then replaced by destructive changes with the appearance of vacuoles in the processes of astrocytes; the process often ends with the development of spongiosis of brain tissue.
In the process of fiziol, aging, N. undergoes complex changes of a dystrophic nature: hypertrophy of astrocytes with proliferation of processes, increased fibril formation, as well as clasmatodendrosis and granular decay are detected. The phagocytic properties of astrocytes in relation to dystrophically altered neurons are enhanced; Neurons undergo phagocytosis, in which the integrity of the plasmalemma is disrupted. In this regard, accumulation of lysosomes and lipofuscin is observed in many astrocytes. However, astrocytes retain high reactive capacity until very old age; Thus, the content of nucleic acids in the nuclei of astrocytes does not change significantly.
Rice. 12. Microscopic specimen of the brain with hyperplasia and hypertrophy of the processes (1) and the body of oligodendrocytes (2); impregnation using the Miyagawa-Alexandrovskaya method; X 400.
Hyperplasia and hypertrophy of oligodendrocytes (Fig. 12) are a pronounced reaction to certain infectious diseases, intoxication of an endogenous and exogenous nature, traumatic and other local damage to the brain. During the destruction of neurons, proliferating satellites - oligodendrocytes - resorb decay products. During a malarial coma, Durk's granulomas are formed from oligodendroglia and microglia around areas of annular hemorrhages. Oligodendrocytes actively participate in phagocytosis, especially during demyelinating processes. At the same time, complete disintegration of the myelin sheath occurs in them, and the number of ribosomes and cisterns of the endoplasmic reticulum increases. Hommes and Leblond (O. R. Hommes, G. P. Leblond, 1967), as well as N. D. Gracheva (1968), observed mitoses in oligodendroglia in the intact brain. E. V. Didimova et al. (1974) found a high percentage of mitoses only when the brain was injured. The formation of multinuclear complexes of oligodendrocytes that have not completely divided is often observed during their hyperplasia.
Irreversible dystrophic changes in oligodendrocytes are expressed in their destruction and atrophy. Destruction is accompanied by the disintegration of cytoplasmic organelles (lysis of ribosomes and polysomes) and the accumulation of lipid inclusions. The cells take on the form of bubbles and disintegrate. Such changes are noted in areas of hron, cerebral edema, as well as with brain tumors.
With atrophy of oligodendrocytes, cell bodies and their processes decrease, and the nuclei shrink. Atrophy is observed in old age, with progressive chorea, amyotrophic lateral sclerosis. In old age, the ultrastructure of oligodendrocytes is characterized by a sharp increase in osmiophilia of the nucleus and cytoplasm. Most oligodendrocytes are dystrophically changed: the contents of the cytoplasm and nucleus are homogenized, organelles disappear; the cells shrink or, conversely, swell.
Ependymocytes in patol, conditions undergo various changes: vacuolization, obesity, necrobiosis and necrosis.
Reversible dystrophic and reparative changes in microgliocytes are expressed in their hypertrophy, hyperplasia, and the so-called. phagocytic reaction. Hypertrophy (Fig. 13, a) is characterized by thickening of cell bodies and processes. The number of inclusions and polysomes increases in the cytoplasm. Microglial hyperplasia can be diffuse or focal. Diffuse hyperplasia (Fig. 14) can be observed in acute and chronic cases. inf. diseases, intoxication, vascular lesions of the brain. Severe hyperplasia is characterized by the appearance of rod-shaped microgliocytes. Focal hyperplasia is observed near local brain damage (tsvetn. Fig. 5), with the formation of inf. granulomas, in the so-called senile plaques in senile dementia, in the molecular layer of the cerebellum in the form of mesoglial syncytium in typhoid and typhus. Microgliocytes rapidly proliferate near retrogradely damaged neurons (when an axon is cut), resulting in the disconnection of interneuronal connections. Penetrating into the cytoplasm of neurons, microgliocytes and their processes phagocytose its decaying particles.
The phagocytic reaction of microglia with the transformation of microgliocytes into granular balls is most clearly manifested during the repair period in foci of destruction of brain tissue. Zh.V. Solovyova, D.D. Orlovskaya (1979) found signs of the phagocytic function of microglia in embryos.
Irreversible dystrophic changes in microgliocytes include dystrophy and atrophy. Dystrophy is characterized by wrinkling or swelling of cell bodies, pyknosis of nuclei, coarsening and fragmentation of processes, and in more severe cases - complete disintegration of cells (color. Fig. 6). It is observed in severe inf. diseases and intoxication with severe hypoxia. With atrophy of microgliocytes (Fig. 13, b), observed in schizophrenia, presenile psychoses, severe chronic conditions, intoxication, and also in extreme old age, the volume of the cell body decreases, a pronounced thinning of the processes and a decrease in their number are noted.
Postmortem changes in neuroglia
Prolonged hypoxia, developing in the preagonal period, leads to a decrease in oxidative and glycolytic processes. The glycolytic pathway of carbohydrate metabolism in the agonal period does not provide the processes of resynthesis of high-energy phosphorus compounds, which leads to a significant decrease in ATP and ADP. The activity of respiratory enzymes (NAD and NADP diaphorase, succinate dehydrogenase, lactate dehydrogenase) sharply decreases. N.'s changes after the death of the organism consist of loss of tinctorial properties, swelling, fragmentation and lysis of cells. Electron microscopically, the earliest sign of autolysis is swelling of astrocyte processes. Subsequently, chromatin is dispersed, the organelles of the cytoplasm of all N. cells are rarefied, especially oligodendrogliocytes, and microglia lose osmiophility. A day after death, lysis of a significant number of cells is observed; after two days, the majority of N cells are lysed. Microglia are the most resistant to autolysis.
Bibliography: Avtsyn A. P. and Rabinovich A. Ya. On the development of brain histiocytes (“mesoglia”) in the human embryo, Proceedings of Psychiat. clinic_1 Moscow. honey. Institute, vol. 3, v. 4, p. 41, 1937; Aleksandrovskaya M. M. Neuroglia in various psychoses, M., 1950; Beletsky V.K. Histogenesis of mesoglia, Sov. psychoneurol., No. 1-2, p. 60, 1932; Blinkov S. M. and Ivanitsky G. R. On the number of glial cells in the human brain, Biophysics, v. 10, century. 5, p. 817, 1965; Glebov R. N. and Bezruchko S. M. Metabolic processes in the neuron-glia system in various physiological and pathological conditions of the nervous system, Zhurn, neuropath, and psychiat., t. 73, century. 7, p. 1088, 1973, bibliogr.; Didimova E.V., Svanidze I.K. and Macharashvili D.N. Features of mitotic division of macroglial cells after trauma to the cerebral cortex, Arch. anat., gistol, and embryol., t. 67, no. 11, p. 63, 1974; Leninger A. Biochemistry, trans. from English, M., 1976; Mikeladze A. L. Structural organization vegetative nuclei of the central nervous system, vol. 1, Tbilisi, 1968; Multi-volume guide to neurology, ed. N. I. Grashchenkova, vol. 1, book. 1, p. 222, M., 1959; Multi-volume guide to pathological anatomy, ed. A. I. Strukova, vol. 2, p. 55, M., 1962; General physiology of the nervous system, ed. P. G. Kostyuk and A. I. Roitbak, p. 607, L., 1979; Peters A., Paley S. and Webster G. Ultrastructure of the nervous system, trans. from English, M., 1972; Roytbak A.I. Neuroglia and the formation of new nerve connections in the cerebral cortex, in the book: Mechanisms of formation and inhibition of conditioned reflexes, ed. V.S. Rusinova, s. 82, M., 1973; Strukov A.I. and Serov V.V. Pathological anatomy, M., 1979; Functions of neuroglia, ed., A. I. Roitbak, Tbilisi, 1979; Shelikhov V.N. et al. On the possible role of neuroglia in the activity of the nervous system, Usp. fiziol, sciences, vol. 6, no. 3, p. 90, 1975, bibliogr.; Biology of neuroglia, ed. by W. F. Windle, Springfield, 1958; Glees P. Neuere Ergebnisse auf dem Gebiet der Neurohistologie, Nissl-Substans, corticale Sinapsen, Neuroglia und intercel-lulaler Raum, Dtsch. Z. Nervenheilk., Bd 184, S. 607, 1963; Hertz L. a. Schousboe A. Ion and energy metabolism of the brain at the cellular level, Int. Rev. Neurobiol., v. 18, p. 141, 1975, bibliogr.; Horstmann E. Was wis-senwir iiber den intercellularen Raum im Zentralnervensystem? Wld Neurol., Bd 3, S. 112, 1962; Kuffler S. W. a. N i-c h o 1 1 s J. G. The physiology of neuroglial cells, Ergebn. Physiol., Bd 57, S. 1, 1966, Bibliogr.; Metabolic compartmentation in the brain, ed. by R. Balazs a. J. E. Cremer, N. Y., 1972; N i s s 1 F. u. Alzheimer A. Histologisehe und histopathologische Arbeiten iiber die Gross-hirnrinde mit besonderer Beriicksichtigung der pathologischen Anatomie der Geistes-krankheiten, Jena, 1910; Pe.n field W. Neuroglia and microglia, in: Special cytology, ed. by E. V. Cowdry, p. 1031, N.Y., 1928; Somjen G. G. Electrophysiology of neuroglia, Ann. Rev. Physiol., v. 37, p. 163, 1975, bibliogr.; Spiel- m e y e r W. Histopathologie des Nerven-systems, B., 1922; Watson W. E. Physiology of neuroglia, Physiol. Rev., v. 54, p. 245, 1974, bibliogr.; W e i- g e r t C. Beitrage zur Kenntnis der norma-len menschlichen Neuroglia, Frankfurt am Main, 1895; Wolff J. Die Astroglia im Gewebsverband des Gehirns, Acta neuropath. (Berl.), Bd 4, S. 33, 1968.
N. N. Bogolepov; P. B. Kazakova, V. P. Tumanov (pathomorphology), Yu. N. Samko, A. I. Roitbak (physics), M. G. Uzbekov (biochemistry).
Neuroglia represents the environment surrounding neurocytes and performing supporting, delimiting, trophic and protective functions in the nervous tissue. The selectivity of metabolism between nervous tissue and blood is ensured, in addition to the morphological characteristics of the capillaries themselves (solid endothelial lining, dense basement membrane), also by the fact that the processes of gliocytes, primarily astrocytes, form a layer on the surface of the capillaries that delimits neurons from direct contact with the vascular wall . Thus, the blood-brain barrier is formed.
Neuroglia consists of cells that are divided into two genetically distinct types:
1) Gliocytes (macroglia);
2) Glial macrophages (microglia).
Gliocytes
Gliocytes, in turn, are divided into:
1) ependymocytes; 2) astrocytes; 3) oligodendrocytes.
Ependymocytes form a dense epithelial-like layer of cells lining the spinal canal and all ventricles of the brain.
Ependymocytes are the first to differentiate from the glioblasts of the neural tube, performing demarcation and support functions at this stage of development. On the inner surface of the neural tube, elongated bodies form a layer of epithelial-like cells. On cells facing the cavity of the neural tube, cilia are formed, the number of which on one cell can reach up to 40. Cilia obviously contribute to the movement of cerebrospinal fluid. Long processes extend from the basal part of the ependymocyte, which branch out to cross the entire neural tube and form the apparatus that supports it. These processes on the outer surface take part in the formation superficial glial limiting membrane, which separates the substance of the tube from other tissues.
After birth, ependymocytes gradually lose their cilia; they are retained only in some parts of the central nervous system (midbrain aqueduct).
In the area of the posterior commissure of the brain, ependymocytes perform a secretory function and form a “subcommissural organ” that secretes a secretion, which is believed to take part in the regulation of water metabolism.
The ependymocytes that cover the choroid plexuses of the ventricles of the brain are cubic in shape; in newborns, cilia are located on their surface, which are later reduced. The cytoplasm of the basal pole forms numerous deep folds and contains large mitochondria, inclusions of fat and pigments.
Astrocytes - these are small star-shaped cells, with numerous processes diverging in all directions.
There are two types of astrocytes:
1) protoplasmic;
2) fibrous (fibrous).
Protoplasmic astrocytes
¨Localization - gray matter of the brain.
¨Dimensions - 15-25 microns, have short and thick, highly branched processes.
¨The core is large, oval, light.
¨Cytoplasm - contains a small amount of endoplasmic reticulum cisterns, free ribosomes and microtubules, and is rich in mitochondria.
¨Function - delimitation and trophic.
Fibrous astrocytes.
¨Localization - white matter of the brain.
¨Dimensions - up to 20 microns, have 20-40 smoothly contoured, long, weakly branching processes that form glial fibers that form a dense network - the supporting apparatus of the brain. The processes of astrocytes on blood vessels and on the surface of the brain, with their terminal extensions, form perivascular glial limiting membranes.
¨The cytoplasm is light in electron microscopic examination, contains few ribosomes and elements of the granular endoplasmic reticulum, is filled with numerous fibrils with a diameter of 8-9 nm, which extend into processes in the form of bundles.
¨The nucleus is large, light-colored, the nuclear envelope sometimes forms deep folds, and the karyoplasm is characterized by uniform electron density.
¨Function is support and isolation of neurons from external influences.
Oligodendrocytes - the most numerous and polymorphic group of gliocytes responsible for the production of myelin in the central nervous system.
¨Localization - they surround the bodies of neurons in the central and peripheral nervous system, are part of the sheaths of nerve fibers and nerve endings.
¨The cell sizes are very small.
¨Shape - different parts of the nervous system are characterized by different shapes of oligodendrocytes (oval, angular). Several short and weakly branched processes extend from the cell body.
¨Cytoplasm - its density is close to that of nerve cells, does not contain neurofilaments.
¨Function - perform a trophic function, participating in the metabolism of nerve cells. They play a significant role in the formation of membranes around cell processes; they are called neurolemmocytes (Schwann cells), and participate in water-salt metabolism, the processes of degeneration and regeneration.
In addition to neurons, nervous tissue includes neuroglial cells - peirogliocytes. They were discovered in the 19th century. German cytologist R. Virchow, who defined them as cells connecting neurons (Greek yXoia - glue), filling the spaces between them and providing them with nutrition. Further studies revealed that neurogliocytes are a very large group of cellular elements that differ in their structure, origin and functions; that gliocytes are present not only in the structures of the central nervous system, but also in the peripheral nervous system. It became clear that neuroglia function in the brain not only as trophic (nutritive) or supporting tissue. Glial cells also take part in specific nervous processes, actively influencing the activity of neurons.
Neuroglial cells have a number of structural features in common with neurons (Fig. 2.11, 2.12). Thus, in the cytoplasm of gliocytes, in addition to other organelles, tigroid (Nissl substance) was found; Glial cells, like neurons, have processes. The gliocyte membrane contains a variety of protein channels, receptor proteins, transporter proteins and pump proteins.
Rice. 2.11.
At the same time, gliocytes are significantly smaller in size than neurons (3-4 times), and there are 8-10 times more of them than nerve cells. The processes of glial cells are not differentiated either by structure or function. Most glial cells retain the ability to divide throughout the life of the organism. Because of this feature, they (when such division becomes pathological) can be the basis for the formation of tumors in the NS - gliomas.
An increase in brain mass after birth also occurs, in particular, due to the division and development of neuroglial cells. Unlike neurons, gliocytes are not able to generate electrical signals (action potentials) and conduct them along their processes. Gliocytes form numerous gap junctions with each other, but there are no such contacts with neurons, although the processes of glial cells can come very close to the bodies and dendrites of nerve cells.
To date, it has been reliably shown that neuroglia within the nervous tissue perform not only support and trophic functions, but also take part in the formation of the nervous system, its development, and regeneration. Glial cells also take part in specific nervous processes, actively influencing the activity of neurons.
Gliocytes of the CPS are represented by macroglial cells, which include astrocytes, oligodendrocytes, ependymocytes and radial glial cells, as well as microglial cells. Gliocytes of the peripheral NS are represented by Schwann cells and ganglion glia cells (satellite cells) (Fig. 2.12).
Rice. 2.12.
A- oligodendrodite, forming the myelin sheath; b- oligodendrocyte, which forms cable-type fibers; V - protoplasmic astrocyte; G - fibrous astrocyte; d - radial gliocyte; e - ependyma; and - amoeboid
microglia; h - branched neuroglia
