The cerebellum is the central organ of balance and coordination of movements. It is formed by two hemispheres with a large number of grooves and convolutions, and a narrow middle part - a worm.
The bulk of the gray matter in the cerebellum is located on the surface and forms its cortex. A smaller part of the gray matter lies deep in the white matter in the form of the central nuclei of the cerebellum.
There are 3 layers in the cerebellar cortex: 1) the outer molecular layer contains relatively few cells, but many fibers. It distinguishes between basket and stellate neurons, which are inhibitory. Star-shaped - slow down vertically, basket-shaped - send axons over long distances, which end on the bodies of pear-shaped cells. 2) The middle ganglionic layer is formed by one row of large pear-shaped cells, first described by the Czech scientist Jan Purkinje. The cells have a large body, 2-3 short dendrites extend from the top, which branch in a small layer. 1 axon departs from the base, which goes into the white matter to the cerebellar nuclei. 3) The inner granular layer is characterized by a large number of tightly lying cells. Among the neurons, granule cells, Golgi cells (stellate), and fusiform horizontal neurons are distinguished here. Granule cells are small cells that have short dendrites, the latter forming excitatory synapses with mossy fibers in the cerebellar glamelurs. The granule cells excite the mossy fibers, and the axons go into the molecular layer and transmit information to the piriform cells and all the fibers located there. It is the only excitatory neuron in the cerebellar cortex. Golgi cells lie under the bodies of pear-shaped neurons, axons go to the cerebellar glameruli, and can inhibit impulses from mossy fibers to granule cells.
Afferent pathways enter the cerebellar cortex through 2 types of fibers: 1) liana-shaped (climbing) - they rise from the white matter through the granular and ganglionic layers. They reach the molecular layer, form synapses with the dendrites of pear-shaped cells and excite them. 2) Bryophytes - from the white matter they enter the granular layer. Here they form synapses with the dendrites of granular cells, and the axons of granular cells go into the molecular layer, forming synapses with the dendrites of pear-shaped neurons, which form inhibitory nuclei.
The cerebral cortex. Development, neural composition and layered organization. The concept of cyto- and myeloarchitectonics. Blood-brain barrier. Structural and functional unit of the cortex.
The cerebral cortex is the highest and most complexly organized nerve center of the screen type, whose activity ensures the regulation of various body functions and complex forms of behavior. The cortex is made up of a layer of gray matter. Gray matter contains nerve cells, nerve fibers, and neuroglial cells.
Among the multipolar neurons of the cortex, pyramidal, stellate, fusiform, arachnid, horizontal, "candelabra" cells, cells with a double bouquet of dendrites, and some other types of neurons are distinguished.
Pyramidal neurons constitute the main and most specific form for the cortex of the hemispheres. They have an elongated cone-shaped body, the apex of which faces the surface of the cortex. Dendrites extend from the apex and lateral surfaces of the body. Axons originate from the base of the pyramidal cells.
Pyramidal cells of different layers of the cortex differ in size and have different functional significance. Small cells are intercalary neurons. The axons of the large pyramids take part in the formation of motor pyramidal pathways.
The neurons of the cortex are located in unsharply demarcated layers, which are designated by Roman numerals and numbered from outside to inside. Each layer is characterized by the predominance of any one type of cell. There are six main layers in the cerebral cortex:
I - The molecular layer of the cortex contains a small number of small associative horizontal Cajal cells. Their axons run parallel to the surface of the brain as part of the tangential plexus of nerve fibers of the molecular layer. However, the bulk of the fibers of this plexus is represented by branching of the dendrites of the underlying layers.
II - The outer granular layer is formed by numerous small pyramidal and stellate neurons. The dendrites of these cells rise into the molecular layer, and the axons either go into the white matter, or, forming arcs, also enter the tangential plexus of fibers of the molecular layer.
III - The widest layer of the cerebral cortex is pyramidal. It contains pyramidal neurons, and spindle cells. The apical dendrites of the pyramids go into the molecular layer, the lateral dendrites form synapses with adjacent cells of this layer. The axon of the pyramidal cell always departs from its base. In small cells, it remains within the cortex; in large cells, it forms a myelin fiber that goes to the white matter of the brain. Axons of small polygonal cells are sent to the molecular layer. The pyramidal layer performs mainly associative functions.
IV - The inner granular layer in some areas of the cortex is very strongly developed (for example, in the visual and auditory cortex), while in others it may be almost absent (for example, in the precentral gyrus). This layer is formed by small stellate neurons. It consists of a large number of horizontal fibers.
V - The ganglionic layer of the cortex is formed by large pyramids, and the region of the motor cortex (precentral gyrus) contains giant pyramids, which were first described by the Kyiv anatomist V. A. Bets. The apical dendrites of the pyramids reach the 1st layer. The axons of the pyramids are projected to the motor nuclei of the brain and spinal cord. The longest axons of Betz cells in the pyramidal pathways reach the caudal segments of the spinal cord.
VI - The layer of polymorphic cells is formed by neurons of various shapes (fusiform, stellate). The axons of these cells go into the white matter as part of the efferent pathways, and the dendrites reach the molecular layer.
Cytoarchitectonics - features of the location of neurons in different parts of the cerebral cortex.
Among the nerve fibers of the cerebral cortex, one can single out associative fibers that connect individual parts of the cortex of one hemisphere, commissural fibers that connect the cortex of different hemispheres, and projection fibers, both afferent and efferent, that connect the cortex with the nuclei of the lower parts of the central nervous system.
autonomic nervous system. General structural characteristics and main functions. The structure of sympathetic and parasympathetic reflex arcs. Differences between vegetative reflex arcs and somatic ones.
The nervous system is usually divided into several departments. According to topographic features, it is divided into central and peripheral sections, according to functional features - into somatic and vegetative sections. The central division, or central nervous system, includes the brain and spinal cord. The peripheral division, or peripheral nervous system, includes all nerves, that is, all peripheral pathways, which consist of sensory and motor nerve fibers. The somatic department, or somatic nervous system, includes cranial and spinal nerves that connect the central nervous system with organs that perceive external stimuli - with the skin and the apparatus of movement. The autonomic department, or the autonomic nervous system, provides a connection between the central nervous system and all internal organs, glands, vessels and organs, which include smooth muscle tissue. The autonomic division is divided into the sympathetic and parasympathetic parts, or the sympathetic and parasympathetic nervous system.
The central nervous system includes the brain and spinal cord. There are certain relationships between the mass of the brain and spinal cord: as the organization of the animal increases, the relative mass of the brain increases in comparison with the spinal cord. In birds, the brain is 1.5-2.5 times larger than the spinal cord, in ungulates - 2.5-3 times, in carnivores - 3.5-5 times, in primates - 8-15 times.
Spinal cord- medulla spinalis lies in the spinal canal, occupying approximately 2/3 of its volume. In cattle and horses, its length is 1.8-2.3 m, weight 250-300 g, in pigs - 45-70 g. It looks like a cylindrical cord, somewhat flattened dorsoventrally. There is no clear boundary between the brain and spinal cord. It is believed that it passes at the level of the cranial margin of the atlas. In the spinal cord, cervical, thoracic, lumbar, sacral and caudal parts are distinguished according to their location. In the embryonic period of development, the spinal cord fills the entire spinal canal, but due to the high growth rate of the skeleton, the difference in their length becomes larger. As a result, the brain in cattle ends at the level of the 4th, in the pig - in the region of the 6th lumbar vertebra, and in the horse - in the region of the 1st segment of the sacral bone. The median dorsal sulcus (gutter) runs along the spinal cord on its dorsal side. A connective tissue dorsal septum departs from it deep into. On the sides or median sulcus are smaller dorsal lateral sulci. On the ventral side there is a deep median ventral fissure, and on the sides of it are ventral lateral grooves (troughs). At the end, the spinal cord sharply narrows, forming a brain cone, which passes into the terminal thread. It is formed by connective tissue and ends at the level of the first tail vertebrae.
There are thickenings in the cervical and lumbar parts of the spinal cord. In connection with the development of limbs in these areas, the number of neurons and nerve fibers increases. In a pig, the cervical thickening is formed by 5-8th neurosegments. Its maximum width at the level of the middle of the 6th cervical vertebra is 10 mm. Lumbar thickening falls on the 5th-7th lumbar neurosegments. In each segment, a pair of spinal nerves departs from the spinal cord with two roots - on the right and on the left. The dorsal root originates from the dorsal lateral groove, the ventral root from the ventral lateral groove. The spinal nerves leave the spinal canal through the intervertebral foramen. The section of the spinal cord between two adjacent spinal nerves is called the neurosegment. Neurosegments are of different lengths and often do not correspond in size to the length of the bone segment. As a result, the spinal nerves depart at different angles. Many of them travel some distance inside the spinal canal before leaving the intervertebral foramen of their segment. In the caudal direction, this distance increases, and from the nerves running inside the spinal canal, behind the cerebral cone, a brush is formed, as it were, called the “horse tail”.
Brain- encephalon - is placed in the cranial box and consists of several parts. In ungulates, the relative mass of the brain is 0.08-0.3% of body weight, which is 370-600 g in a horse, 220-450 g in cattle, 96-150 g in sheep and pigs. In small animals, the relative the mass of the brain is usually greater than that of large ones.
The brain of ungulates is semi-oval. In ruminants - with a wide frontal plane, with almost no protruding olfactory bulbs and noticeable extensions at the level of the temporal regions. In the pig, it is more narrowed in front, with prominent olfactory bulbs. Its length is on average 15 cm in cattle, 10 cm in sheep, and 11 cm in pigs. The brain is divided by a deep transverse fissure into a large brain lying rostrally and a rhomboid brain located caudally. Parts of the brain phylogenetically older, representing the continuation of the projection pathways of the spinal cord, are called the brain stem. It includes the medulla oblongata, the medullary bridge, the middle bridge, part of the diencephalon. Phylogenetically younger parts of the brain form the integumentary part of the brain. It includes the cerebral hemispheres and the cerebellum.
Rhomboid brain- rhombencephalon - is divided into the oblong and hindbrain and contains the fourth cerebral ventricle.
Medulla- medulla oblongata - the most rear part of the brain. Its mass is 10-11% of the mass of the brain; length in cattle - 4.5, in sheep - 3.7, in pigs - 2 cm. .
On its dorsal side there is a diamond-shaped recess - the fourth cerebral ventricle. On the ventral side there are three furrows: median and 2 lateral. Connecting caudally, they pass into the ventral median fissure of the spinal cord. Between the furrows lie 2 narrow elongated rollers - pyramids, in which bundles of motor nerve fibers pass. At the border of the medulla oblongata and spinal cord, the pyramidal tracts intersect - a cross of the pyramids is formed. In the medulla oblongata, gray matter is located inside, in the bottom of the fourth cerebral ventricle in the form of nuclei that give rise to cranial nerves (from VI to XII pairs), as well as nuclei in which impulses are switched to other parts of the brain. The white matter lies externally, predominantly ventrally, forming pathways. Motor (efferent) pathways from the brain to the spinal cord form pyramids. Sensitive pathways (afferent) from the spinal cord to the brain form / posterior legs of the cerebellum, going from the medulla oblongata to the cerebellum. In the mass of the medulla oblongata in the form of a reticular plexus lies an important coordination apparatus of the brain - the reticular formation. It integrates the structures of the brainstem and promotes their involvement in complex, multi-stage responses.
Medulla- a vital area of the central nervous system (CNS), its destruction leads to instant death. Here are the centers of respiration, heartbeat, chewing, swallowing, sucking, vomiting, chewing gum, salivation and juice secretion, vascular tone, etc.
Hind brain- metencephalon - consists of the cerebellum and the cerebral bridge.
brain bridge- pons - a massive thickening on the ventral surface of the brain, lying across the anterior part of the medulla oblongata up to 3.5 cm wide in cattle, 2.5 cm in sheep and 1.8 ohms in pigs. The bulk of the brain bridge is made up of pathways (descending and ascending) that connect the brain with the spinal cord and individual parts of the brain with each other. A large number of nerve fibers run across the pons to the cerebellum and form the middle cerebellar peduncles. In the bridge there are groups of nuclei, including the nuclei of the cranial nerves (V pair). From the lateral surface of the bridge departs the largest V pair of cranial nerves - trigeminal.
Cerebellum- cerebellum - located above the bridge, the medulla oblongata and the fourth cerebral ventricle, behind the quadrigemina. In front it borders on the cerebral hemispheres. Its mass is 10-11% of the mass of the brain. In sheep and pigs, its length (4-4.5 cm) is greater than its height (2.2-2.7 ohms), in cattle it approaches spherical - 5.6X6.4 cm. In the cerebellum, the middle part is distinguished - the worm and lateral parts - hemispheres of the cerebellum. The cerebellum has 3 pairs of legs. It is connected to the medulla oblongata by its posterior legs (rope bodies), the middle legs to the cerebral bridge, and the anterior (rostral) legs to the midbrain. The surface of the cerebellum is assembled into numerous folded lobules and convolutions, separated by grooves and fissures. The gray matter in the cerebellum is located above - the cerebellar cortex and in depth in the form of nuclei. The surface of the cerebellar cortex in cattle is 130 cm 2 (about 30% in relation to the cerebral cortex) with a thickness of 450-700 microns. The white matter is located under the bark and looks like a tree branch, for which it is called the tree of life.
The cerebellum is the center for coordinating voluntary movements, maintaining muscle tone, posture, and balance.
Rhomboid brain contains the fourth cerebral ventricle. Its bottom is the deepening of the medulla oblongata - the rhomboid fossa. Its walls are formed by the legs of the cerebellum, and the roof by the anterior (rostral) and posterior cerebral sails, which are the choroid plexus. The ventricle communicates rostrally with the cerebral aqueduct, caudally with the central canal of the spinal cord, and through openings in the sail with the subarachnoid space.
big brain- cerebrum - includes the terminal, diencephalon and midbrain. The telencephalon and diencephalon are combined into the forebrain.
The midbrain - mesencephalon - consists of the quadrigemina, the legs of the large brain and the cerebral aqueduct enclosed between them. Covered by large hemispheres. Its mass is 5-6% of the mass of the brain.
The quadrigemina forms the roof of the midbrain. It consists of a pair of rostral (anterior) colliculi and a pair of caudal (posterior) colliculi. The quadrigemina is the center of unconditioned reflex motor acts in response to visual and auditory stimuli. The anterior colliculi are considered subcortical centers of the visual analyzer, the posterior colliculi are considered subcortical centers of the auditory analyzer. In ruminants, the anterior mounds are larger than the posterior mounds; in the pig, the opposite is true.
The cerebral peduncles form the bottom of the midbrain. They look like two thick rollers lying between the visual tracts and the cerebral bridge. Separated by an interpeduncular groove.
Between the quadrigemina and the legs of the large brain in the form of a narrow tube passes the cerebral (Sylvian) aqueduct. Rostrally, it connects with the third, caudally - with the fourth cerebral ventricles. The cerebral aqueduct is surrounded by a substance of the reticular formation.
In the midbrain, the white matter is located externally and represents the conducting afferent and efferent pathways. The gray matter is located in depth in the form of nuclei. The third pair of cranial nerves departs from the brain legs.
diencephalon- diencephalon - consists of visual tubercles - thalamus, epithalamus - epithalamus, hypothalamus - hypothalamus. The diencephalon is located between the terminal.
In the midbrain, covered by the telencephalon. Its mass is 8-9% of the mass of the brain. The visual tubercles are the most massive, centrally located part of the diencephalon. Merging between the saba, they compress the third cerebral ventricle so that it takes the form of a ring that goes around the intermediate mass of the visual tubercles. From above, the ventricle is covered with a vascular cover; communicates with the interventricular foramen with the lateral ventricles, passes aborally into the cerebral aqueduct. The white matter in the thalamus lies on top, gray - inside in the form of numerous nuclei. They serve as switching links from the underlying sections to the cortex and are connected with almost all analyzers. On the basal surface of the diencephalon is the intersection of the optic nerves - chiasm.
The epithalamus consists of several structures, including the pineal gland and the vascular tegmentum of the third cerebral ventricle (the pineal gland is an endocrine gland). It is located in the depression between the visual tubercles and the quadrigemina.
The hypothalamus is located on the basal surface of the diencephalon between the chiasm and the cerebral peduncles. Consists of several parts. Directly behind the chiasma in the form of an oval tubercle is a gray tubercle. Its downward-facing apex is elongated due to the protrusion of the wall of the third ventricle and forms a funnel on which the pituitary gland, the endocrine gland, is suspended. Behind the gray tubercle is a small rounded formation - the mastoid body. The white matter in the hypothalamus is located outside, forms the conductive afferent and efferent pathways. Gray matter - in the form of numerous nuclei, since the hypothalamus is the highest subcortical autonomic center. It contains the centers of respiration, blood and lymph circulation, temperature, sexual functions, etc.
The end brain - telencephalon - is formed by two hemispheres, separated by a deep longitudinal fissure and connected by the corpus callosum. Its mass in cattle is 250-300 g, in sheep and pigs 60-80 g, which is 62-66% of the mass of the brain. In each hemisphere, a dor-solaterally located cloak is distinguished, ventromedially - the olfactory brain, in depth - striatum and lateral ventricle.The ventricles are separated by a transparent septum.The interventricular foramen communicates with the third cerebral ventricle.
The olfactory brain consists of several parts visible on the ventral surface of the telencephalon. Rostrally, slightly protruding beyond the cloak, lie 2 olfactory bulbs. They occupy the pits of the ethmoid bone. Olfactory filaments enter them through a hole in the perforated plate of the bone, which together form the olfactory nerve. The bulbs are the primary olfactory centers. Olfactory tracts depart from them - afferent pathways. The lateral olfactory tract reaches the pear-shaped lobes, located laterally from the legs of the brain. The medial olfactory tracts reach the medial surface of the mantle. Olfactory triangles lie between the tracts. The pear-shaped lobes and olfactory triangles are the secondary olfactory centers. In the depths of the olfactory brain, at the bottom of the lateral ventricles, the remaining parts of the olfactory brain are located. They connect the olfactory brain with other parts of the brain. The striatum is located in the depths of the hemispheres and is a basal complex of nuclei, which are subcortical motor centers.
The cloak reaches its greatest development in higher mammals. It contains the highest centers of all animal life. The surface of the cloak is covered with convolutions and furrows. In cattle, its surface is 600 cm 2. The gray matter in the raincoat is located on top - this is the cerebral cortex. White matter is inside - these are pathways. The functions of different parts of the cortex are unequal, the structure is mosaic, which made it possible to distinguish several lobes in the hemispheres (frontal, parietal, temporal, occipital) and several dozen fields. The fields differ from each other in their cytoarchitectonics - the location, number and shape of cells and myeloarchitectonics - the location, number and shape of fibers.
Meninges of the brain. The spinal cord and brain are covered with hard, arachnoid and soft membranes.
The hard shell is the most superficial, thick, formed by dense connective tissue, poor in blood vessels. It fuses with the bones of the skull and vertebrae with ligaments, folds and other formations. It descends into the longitudinal gap between the hemispheres of the cerebrum in the form of a falciform ligament (sickle of the cerebrum) and separates the cerebrum from the rhomboid membranous cerebellum. Between it and the bones there is not everywhere a developed epidural space filled with loose connective and adipose tissues. This is where the veins go. From the inside, the dura mater is lined with endothelium. Between it and the arachnoid there is a subdural space filled with cerebrospinal fluid. The arachnoid membrane is formed by loose connective tissue, tender, avascular, does not enter the furrows. On both sides it is covered with endothelium and is separated by subdural and jaubarachnoid (subarachnoid) spaces from other membranes. Attaches to the shells with the help of ligaments, as well as vessels and nerves passing through it.
The soft shell is thin, but dense, with a large number of vessels, for which it is also called vascular. It enters all the furrows and fissures of the brain and spinal cord, as well as into the cerebral ventricles, where it forms vascular covers.
The intershell spaces, the cerebral ventricles and the central spinal canal are filled with cerebrospinal fluid, which is the internal environment of the brain and protects it from harmful effects, regulates intracranial pressure, and performs a protective function. A liquid is formed. Mainly in the vascular covers of the ventricles, flows into the venous bed. Normally, its amount is constant.
Vessels of the brain and spinal cord. The spinal cord is supplied with blood by branches extending from the vertebral, intercostal, lumbar and sacral arteries. In the spinal canal they form the spinal arteries running in the sulci and the central fissure of the spinal cord. Blood enters the brain through the vertebral and internal carotid (in cattle - through the internal maxillary) arteries.
The spinal cord is located in the spinal canal and has the appearance of a rounded cord in cross section, expanded in the cervical and lumbar regions. It consists of two symmetrical halves, separated anteriorly by a median fissure and posteriorly by a median sulcus, and is characterized by a segmental structure. Each segment is associated with a pair of anterior (ventral) and a pair of posterior (dorsal) roots. The spinal cord is composed of centrally located gray matter and surrounding white matter. The gray matter on the cut has the shape of a butterfly. The protrusions of gray matter that stretch along the spinal cord are called pillars. There are back, side and front pillars. The pillars on the cross section are called horns. The gray matter consists of grouped multipolar neurons and neurogliocytes, unmyelinated and thin myelinated fibers.
Clusters of neurons that share a common morphology and function are called nuclei. . In the posterior horns there are:
· Lissauer marginal zone - the place of branching of the fibers of the dorsal roots when they enter the spinal cord;
· spongy substance , represented by a large-loop glial skeleton with large neurons;
· gelatinous (gelatinous) substances o, formed by neuroglia with small nerve cells;
· own nucleus of the posterior horn , consisting of beam cells, the processes of which, passing through the anterior commissure into the lateral funiculus of the opposite side of the spinal cord, reach the cerebellum as part of the anterior spinal tract;
· clark core , which also consists of beam cells, the axons of which, passing as part of the posterior spinal cerebellar tract, are connected with the cerebellum.
The intermediate zone of gray matter surrounds the spinal canal, lined with ependymoglia. In the intermediate zone there are nuclei:
· medial, consisting of beam cells, the neurons of which are attached to the anterior spinal cerebellar tract;
· lateral, located in the lateral horns, consisting of a group of associative cells, which are the first neuron of the efferent sympathetic pathway.
The largest nerve cells lie in the anterior horns, as part of the posterior and anterior medial nuclei, formed by motor (radicular) neurons, the axons of which exit the spinal cord as part of the anterior roots and innervate the muscles of the body. The posterior and anterior lateral nuclei are also formed by motor neurons that innervate the muscles of the upper and lower extremities.
The white matter is represented by longitudinally running pulpy nerve fibers collected in bundles that make up the pathways of the spinal cord. In the white matter, there are: posterior, lateral and anterior funiculus.
The bundles are divided into two groups: some connect only certain parts of the spinal cord and lie in the anterior and lateral cords directly at the gray matter, forming their own pathways of the spinal cord. Another group of bundles connects the spinal cord and brain.
There are ascending and descending paths. The ascending pathways form the posterior funiculus and ascend into the medulla oblongata.
Distinguish gentle Gaulle bundle, formed by axons of sensory cells, the receptors of which lie in the lower half of the body and wedge-shaped bundle of Burdach , whose receptors perceive excitation in the upper half of the body. These bundles end in the nuclei of the medulla oblongata. These are the ways of tactile, pain, temperature sensitivity.
The lateral funiculus consists of the ascending tracts of the spinocerebellar anterior and spinocerebellar posterior. Irritation along these pathways reaches the anterior part of the cerebellum and switches to motor pathways from the cerebellum to the red nucleus.
Downstream paths include:
1. Pathways connecting the spinal cord with the cerebral cortex: pyramidal, corticospinal way and anterior corticospinal path lying in the anterior funiculus. These pathways are of great importance for the implementation of conscious coordinated body movements. All motor impulses of these movements are transmitted through the pyramidal pathways. bulbospinal the path also carries impulses from the cerebral cortex.
2. Communication with the medulla oblongata is carried out vestibulospinal path (deuterospinal), which is of great importance for maintaining and correct orientation of the body in space, since to the cells of the nucleus Deiters processes of neurons with receptor apparatuses in the semicircles of the vestibular apparatus are suitable.
3. Communication with the cerebellum and midbrain is carried out rubrospinal path coming from the cells of the red nuclei of the spinal cord. The impulses along this path control all automatic movements.
4. No less important is the connection of the spinal cord with the quadrigemina of the midbrain, which is carried out tectospinal and reticulospinal way. The quadrigemina receives fibers from the optic nerve and from the occipital region of the cortex, and the impulses traveling along this path to motor neurons provide clarification and direction of movements.
^ Nervous system: general morphofunctional characteristics; sources of development, classification.
The nervous system provides the regulation of all vital processes in the body and its interaction with the external environment. Anatomically, the nervous system is divided into central and peripheral. The first includes the brain and spinal cord, the second combines peripheral nerve nodes, trunks and endings.
From a physiological point of view, the nervous system is divided into somatic, innervating the entire body, except for internal organs, vessels and glands, and autonomous, or autonomic, regulating the activity of these organs.
The nervous system develops from the neural tube and the ganglionic plate. The brain and sense organs differentiate from the cranial part of the neural tube. The spinal cord, spinal and autonomic nodes, and chromaffin tissue of the body are formed from the trunk region of the neural tube and the ganglionic plate.
The mass of cells in the lateral sections of the neural tube increases especially rapidly, while its dorsal and ventral parts do not increase in volume and retain their ependymal character. The thickened lateral walls of the neural tube are divided by a longitudinal groove into the dorsal - alar and ventral - main plate. At this stage of development, three zones can be distinguished in the lateral walls of the neural tube: the ependyma lining the canal, the mantle layer, and the marginal veil. The gray matter of the spinal cord subsequently develops from the mantle layer, and its white matter develops from the marginal veil.
Simultaneously with the development of the spinal cord, spinal and peripheral vegetative nodes are laid. The starting material for them is the cellular elements of the ganglion plate, which differentiate into neuroblasts and glioblasts, from which neurons and mayial gliocytes of the spinal ganglia are formed. Part of the cells of the ganglionic plate migrates to the periphery to the localization of the autonomic nerve ganglia and chromaffin tissue.
^ Spinal cord: morphofunctional characteristics; structure of gray and white matter.
The gray matter on the cross section of the brain is presented in the form of the letter "H" or a butterfly. The protrusions of the gray matter are called horns. There are anterior, or ventral, posterior, or dorsal, and lateral, or lateral, horns.
The gray matter of the spinal cord consists of neuron bodies, non-myelinated and thin myelinated fibers, and neuroglia. The main component of gray matter, which distinguishes it from white, are multipolar neurons.
The white matter of the spinal cord is a collection of longitudinally oriented predominantly myelinated fibers. The bundles of nerve fibers that communicate between different parts of the nervous system are called the pathways of the spinal cord.
Among the neurons of the spinal cord, one can distinguish: neurites, radicular cells, internal, bundle.
In the posterior horns, there are: a spongy layer, a gelatinous substance, a proper nucleus of the posterior horn and a thoracic nucleus. The posterior horns are rich in diffusely located intercalary cells. In the middle of the posterior horn is its own nucleus of the posterior horn.
The thoracic nucleus (Clark's nucleus) consists of large intercalary neurons with highly branched dendrites.
Of the structures of the posterior horn, of particular interest are the gelatinous substance, which stretches continuously along the spinal cord in plates I-IV. Neurons produce enkephalin, an opioid-type peptide that inhibits pain effects. The gelatinous substance has an inhibitory effect on the functions of the spinal cord.
The largest neurons of the spinal cord are located in the anterior horns, which have a body diameter of 100-150 microns and form nuclei of considerable volume. This is the same as the neurons of the nuclei of the lateral horns, radicular cells. These nuclei are motor somatic centers. In the anterior horns, the medial and lateral groups of motor cells are most pronounced. The first innervates the muscles of the trunk and is well developed throughout the spinal cord. The second is located in the region of the cervical and lumbar thickenings and innervates the muscles of the limbs.
^ Brain: morphofunctional characteristics.
The brain is enclosed in a reliable shell of the skull. In addition, it is covered with shells of connective tissue - hard, arachnoid and soft.
In the brain, gray and white matter are distinguished, but the distribution of these two components is much more complicated here than in the spinal cord. Most of the gray matter of the brain is located on the surface of the cerebrum and in the cerebellum, forming their cortex. A smaller part forms numerous nuclei of the brain stem.
The brainstem consists of the medulla oblongata, the pons, the cerebellum, and the structures of the midbrain and diencephalon. All nuclei of the gray matter of the brainstem are composed of multipolar neurons. There are nuclei of cranial nerves and switching nuclei.
The medulla oblongata is characterized by the presence of nuclei of the hypoglossal, accessory, vagus, glossopharyngeal, vestibulocochlear nerves. In the central region of the medulla oblongata there is an important coordination apparatus of the brain - the reticular formation.
The bridge is divided into dorsal (tire) and ventral parts. The dorsal part contains fibers of the medulla oblongata, the nuclei of the V-VIII cranial nerves, the reticular formation of the bridge.
The midbrain consists of the roof of the midbrain (the quadrigemina), the tegmentum of the midbrain, the substantia nigra, and the legs of the brain. Substance nigra got its name from the fact that its small spindle-shaped neurons contain melanin.
In the diencephalon, the optic tubercle predominates in volume. Ventral to it is a hypothalamic (hypothalamic) region rich in small nuclei. Nerve impulses to the visual hillock from the brain go along the extrapyramidal motor pathway.
^ Cerebellum: structure and morphofunctional characteristics.
The bulk of the gray matter in the cerebellum is located on the surface and forms its cortex. A smaller part of the gray matter lies deep in the white matter in the form of central nuclei. Three layers are distinguished in the cerebellar cortex: the outer one is the molecular layer, the middle one is the ganglionic layer, and the inner one is the granular one.
The ganglionic layer contains pear-shaped neurons. They have neurites, which, leaving the cerebellar cortex, form the initial link of its efferent inhibitory pathways.
The molecular layer contains two main types of neurons: basket and stellate. Basket neurons are located in the lower third of the molecular layer. These are irregularly shaped small cells about 10-20 microns in size. Their thin long dendrites branch mainly in a plane located transversely to the gyrus. The long neurites of the cells always run across the gyrus and parallel to the surface above the pear-shaped neurons. The activity of the neurites of the basket neurons causes inhibition of the piriform neurons.
The stellate neurons lie above the basket cells and are of two types. Small stellate neurons are equipped with thin short dendrites and weakly branched neurites that form synapses on the dendrites of pear-shaped cells. Large stellate neurons, unlike small ones, have long and highly branched dendrites and neurites.
Basket and stellate neurons of the molecular layer are a single system of intercalary neurons that transmit inhibitory nerve impulses to the dendrites and bodies of pear-shaped cells in a plane transverse to the convolutions. The granular layer is very rich in neurons. The first type of cells in this layer can be considered granular neurons, or granule cells. They have a small volume. The cell has 3-4 short dendrites. The dendrites of granule cells form characteristic structures called cerebellar glomeruli.
The second type of cells in the granular layer of the cerebellum are inhibitory large stellate neurons. There are two types of such cells: with short and long neurites.
The third type of cells are spindle-shaped horizontal cells. They are found predominantly between the granular and ganglionic layers. Afferent fibers entering the cerebellar cortex are represented by two types - mossy and so-called climbing fibers. Mossy fibers are part of the olivocerebellar and cerebellopontine tracts. They end in the glomeruli of the granular layer of the cerebellum, where they come into contact with the dendrites of the granule cells.
Climbing fibers enter the cerebellar cortex, apparently, along the dorsal-cerebellar and vestibulocerebellar pathways. Climbing fibers transmit excitation directly to piriform neurons.
The cerebellar cortex contains various glial elements. The granular layer contains fibrous and protoplasmic astrocytes. All layers in the cerebellum contain oligodendrocytes. The granular layer and white matter of the cerebellum are especially rich in these cells. Glial cells with dark nuclei lie in the ganglion layer between pear-shaped neurons. Microglia are found in large quantities in the molecular and ganglionic layers.
^ The subject and tasks of human embryology.
In embryogenesis, 3 sections are distinguished: pre-embryonic, embryonic and early post-embryonic.
Actual tasks of embryology are the study of the influence of various endogenous and exogenous factors of the microenvironment on the development and structure of germ cells, tissues, organs and systems.
^ Medical Embryology.
Medical embryology studies the patterns of development of the human embryo. Particular attention in the course of histology with embryology is drawn to the sources and mechanisms of tissue development, metabolic and functional features of the mother-placenta-fetus system, which make it possible to establish the causes of deviations from the norm, which is of great importance for medical practice.
Knowledge of human embryology is necessary for all doctors, especially those working in the field of obstetrics. This helps in diagnosing disorders in the mother-fetus system, identifying the causes of deformities and diseases in children after birth.
Currently, knowledge of human embryology is used to uncover and eliminate the causes of infertility, the birth of "test-tube" children, transplantation of fetal organs, the development and use of contraceptives. In particular, the problems of culturing eggs, in vitro fertilization and implantation of embryos in the uterus have become topical.
The process of human embryonic development is the result of a long evolution and to a certain extent reflects the features of the development of other representatives of the animal world. Therefore, some of the early stages of human development are very similar to similar stages in the embryogenesis of lower organized chordates.
Human embryogenesis is a part of its ontogenesis, including the following main stages: I - fertilization, and the formation of a zygote; II - crushing and formation of the blastula (blastocyst); III - gastrulation - the formation of germ layers and a complex of axial organs; IV - histogenesis and organogenesis of germinal and extra-embryonic organs; V - systemogenesis.
Embryogenesis is closely related to progenesis (development and maturation of germ cells) and the early postembryonic period. Thus, the formation of tissues begins in the embryonic period and continues after the birth of a child.
^ Sex cells: the structure and functions of male and female germ cells, the main stages of their development.
The spermatozoon is covered with a cytolemma, which in the anterior section contains a receptor - glycosyltransferase, which ensures recognition of egg receptors.
The spermatozoon head includes a small dense nucleus with a haploid set of chromosomes containing nucleoprotamines and nucleohistones. The anterior half of the nucleus is covered with a flat sac that forms the cap of the spermatozoon. The acrosome is located in it (from the Greek asgop - top, soma - body). The acrosome contains a set of enzymes, among which an important place belongs to hyaluronidase and proteases. The human sperm nucleus contains 23 chromosomes, one of which is sexual (X or Y), the rest are autosomes. The tail section of the spermatozoon consists of an intermediate, main and terminal parts.
The intermediate part contains 2 central and 9 pairs of peripheral microtubules surrounded by a helical mitochondrion. Paired protrusions, or “handles”, consisting of another protein, dynein, depart from the microtubules. Dynein breaks down ATP.
The main part (pars principalis) of the tail resembles a cilium in structure with a characteristic set of microtubules in the axoneme (9 * 2) + 2, surrounded by circularly oriented fibrils that give elasticity, and a plasma membrane.
The terminal, or final, part of the spermatozoon contains single contractile filaments. The movements of the tail are whip-like, which is due to the successive contraction of microtubules from the first to the ninth pair.
In the study of sperm in clinical practice, various forms of spermatozoa are counted in stained smears, counting their percentage (spermogram).
According to the World Health Organization (WHO), the normal characteristics of human sperm are the following: concentration 20-200 million/ml, content more than 60% of normal forms. Along with normal forms, human sperm always contains abnormal ones - biflagellated, with defective head sizes (macro and microforms), with an amorphous head, with fused heads, immature forms (with remnants of the cytoplasm in the neck and tail), with flagellum defects.
Oocytes, or oocytes (from Latin ovum - egg), mature in an immeasurably smaller amount than spermatozoa. In a woman during the sexual cycle B4-28 days), as a rule, one egg matures. Thus, during the childbearing period, about 400 mature eggs are formed.
The release of an oocyte from the ovary is called ovulation. The oocyte that comes out of the ovary is surrounded by a crown of follicular cells, the number of which reaches 3-4 thousand. It is picked up by the fringes of the fallopian tube (oviduct) and moves along it. Here the maturation of the germ cell ends. The egg cell has a spherical shape, a larger cytoplasmic volume than that of a sperm cell, and does not have the ability to move independently.
The classification of eggs is based on the signs of the presence, quantity and distribution of the yolk (lecithos), which is a protein-lipid inclusion in the cytoplasm used to nourish the embryo.
There are yolkless (alecital), low yolk (oligolecital), medium yolk (mesolecithal), multiyolk (polylecital) eggs.
In humans, the presence of a small amount of yolk in the egg is due to the development of the embryo in the mother's body.
Structure. The human egg has a diameter of about 130 microns. Adjacent to the cytolemma is a shiny, or transparent, zone (zona pellucida - Zp) and then a layer of follicular cells. The nucleus of the female germ cell has a haploid set of chromosomes with an X-sex chromosome, a well-defined nucleolus, and there are many pore complexes in the karyolemma. During the period of oocyte growth, intensive processes of mRNA and rRNA synthesis take place in the nucleus.
In the cytoplasm, the protein synthesis apparatus (endoplasmic reticulum, ribosomes) and the Golgi apparatus are developed. The number of mitochondria is moderate, they are located near the yolk nucleus, where there is an intensive synthesis of the yolk, the cell center is absent. The Golgi apparatus in the early stages of development is located near the nucleus, and in the process of maturation of the egg, it shifts to the periphery of the cytoplasm. Here are the derivatives of this complex - cortical granules, the number of which reaches about 4000, and the size is 1 micron. They contain glycosaminoglycans and various enzymes (including proteolytic), participate in the cortical reaction, protecting the egg from polyspermy.
The transparent, or shiny, zone (zona pellucida - Zp) consists of glycoproteins and glycosaminoglycans. The shiny zone contains tens of millions of Zp3 glycoprotein molecules, each of which has more than 400 amino acid residues connected to many oligosaccharide branches. Follicular cells take part in the formation of this zone: the processes of follicular cells penetrate through the transparent zone, heading towards the cytolemma of the egg. The cytolemma of the egg has microvilli located between the processes of the follicular cells. Follicular cells perform trophic and protective functions.
The spinal cord is the most ancient formation of the central nervous system; it first appears in the lancelet
A characteristic feature of the organization of the spinal cord is the periodicity of its structure in the form of segments with inputs in the form of posterior roots, a cell mass of neurons (gray matter) and outputs in the form of anterior roots.
The human spinal cord has 31-33 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1-3 coccygeal.
Morphological boundaries between segments of the spinal cord do not exist. Each segment innervates three metameres of the body through its roots and also receives information from three metameres of the body. As a result, each metamere of the body is innervated by three segments and transmits signals to three segments of the spinal cord.
The posterior roots are afferent, sensory, centripetal, and the anterior roots are efferent, motor, centrifugal (Bell-Magendie law).
Afferent inputs to the spinal cord are organized by the axons of the spinal ganglia, which lie outside the spinal cord, and by the axons of the sympathetic and parasympathetic divisions of the autonomic nervous system.
The first group of afferent inputs of the spinal cord is formed by sensory fibers coming from muscle receptors, tendon receptors, periosteum, and joint membranes. This group of receptors forms the beginning of the so-called proprioceptive sensitivity.
The second group of afferent inputs of the spinal cord starts from skin receptors: pain, temperature, tactile, pressure.
The third group of afferent inputs of the spinal cord is represented by fibers from visceral organs, this is the viscero-receptive system.
Efferent (motor) neurons are located in the anterior horns of the spinal cord, and their fibers innervate the entire skeletal muscles.
Features of the neural organization of the spinal cord
The neurons of the spinal cord form its gray matter in the form of symmetrically located two anterior and two posterior horns. the nuclei, elongated along the length of the spinal cord, and on the transverse section are located in the shape of the letter H. In the thoracic region, the spinal cord has, in addition to those mentioned, also lateral horns.
The posterior horns perform mainly sensory functions; signals are transmitted from them to the overlying centers, to the structures of the opposite side, or to the anterior horns of the spinal cord.
In the anterior horns are neurons that give their axons to the muscles. All descending pathways of the central nervous system that cause motor responses end at the neurons of the anterior horns. In this regard, Sherrington called them "the common final path".
In the lateral horns, starting from the 1st thoracic segment of the spinal cord and up to the first lumbar segments, there are neurons of the sympathetic, and in the sacral - of the parasympathetic division of the autonomic nervous system.
The human spinal cord contains about 13 million neurons, of which 3% are motor neurons, and 97% are intercalary. Functionally, spinal cord neurons can be divided into 4 main groups:
1) motor neurons, or motor, - cells of the anterior horns, the axons of which form the anterior roots;
2) interneurons - neurons that receive information from the spinal ganglia and are located in the posterior horns. These neurons respond to pain, temperature, tactile, vibrational, proprioceptive stimuli;
3) sympathetic, parasympathetic neurons are located mainly in the lateral horns. The axons of these neurons exit the spinal cord as part of the anterior roots;
4) associative cells - neurons of the spinal cord's own apparatus, establishing connections within and between segments.
In the middle zone of the gray matter (between the posterior and anterior horns) of the spinal cord there is an intermediate nucleus (Cajal nucleus) with cells whose axons go up or down by 1-2 segments and give collaterals to the neurons of the ipsi- and contralateral side, forming a network. There is a similar network at the top of the posterior horn of the spinal cord - this network forms the so-called gelatinous substance (Roland's gelatinous substance) and performs the functions of the reticular formation of the spinal cord. , between the cells of its anterior and posterior horns.
Motoneurons. The axon of a motor neuron innervates hundreds of muscle fibers with its terminals, forming a motor neuron unit. Several motor neurons can innervate one muscle, in which case they form the so-called motor neuron pool. The excitability of motor neurons is different, therefore, with different intensity of stimulation, a different number of fibers of one muscle is involved in contraction. With the optimal strength of irritation, all fibers of this muscle are reduced; in this case, the maximum contraction develops. Motor neurons can generate impulses with a frequency of up to 200 per second.
Interneurons. These intermediate neurons, generating impulses with a frequency of up to 1000 per second, are background-active and have up to 500 synapses on their dendrites. The function of interneurons is to organize connections between the structures of the spinal cord and ensure the influence of ascending and descending pathways on the cells of individual segments of the spinal cord. A very important function of interneurons is the inhibition of neuron activity, which ensures the preservation of the direction of the excitation pathway. Excitation of interneurons associated with motor cells has an inhibitory effect on antagonist muscles.
The neurons of the sympathetic division of the autonomic nervous system are located in the lateral horns of the thoracic spinal cord, have a rare impulse frequency (3-5 per second), parasympathetic neurons are localized in the sacral spinal cord.
With irritation or lesions of the posterior roots, girdle pains are observed at the level of the metamer of the affected segment, sensitivity decreases, reflexes disappear or weaken. If an isolated lesion of the posterior horn occurs, pain and temperature sensitivity on the side of the injury is lost, while tactile and proprioceptive sensations are preserved, since axons of temperature and pain sensitivity go from the posterior root to the posterior horn, and axons of tactile and proprioceptive - directly to the posterior column and along the conductive paths rise up.
The defeat of the anterior horn and the anterior root of the spinal cord leads to paralysis of the muscles, which lose their tone, atrophy, and the reflexes associated with the affected segment disappear.
The defeat of the lateral horns of the spinal cord is accompanied by the disappearance of skin vascular reflexes, impaired sweating, trophic changes in the skin and nails. Bilateral damage to the parasympathetic department at the level of the sacrum leads to impaired defecation and urination.
