Nervous system – it cos of kupnost nerve structures to ensure coordination of all agencies and communication of an organism with the external environment. She perceives Inform a tion of the external and internal environment of the body, it carries out analysis and provides a response to be involved in the implementation of higher ps and hicheskih human functions and organization of its behavior.
During ontogeny the nervous system undergoes a complex change e Nia. After the merger of the egg with the sperm (fertilization), the new cell begins to divide. After some time, a bubble is formed from these new cells. One invaginates bubble wall inward, and the results s Tate embryo formed, consisting of three layers of cells: the outermost layer – the ectoderm, the inner – endoderm and between – mesoderm. The nervous system develops from the outer germinal layer – the ect of the dermis. In humans, at the end of the 2nd week after fertilization, a section of the primary epithelium is isolated and a neural plate is formed. Its cells begin to divide and differentiate, so that they sharply on tdiffer from neighboring epithelial cells. As a result of cell division, the edges of the neural plate rise and nerve ridges appear. At the end of the third week of pregnancy, the roller edges are closed, mod and Zuya neural tube, which gradually sinks into the mesoderm charge of breathing. Two neuropore (holes) stored at the ends of the tube – re d Nij and rear. By the end of the 4th week, the neuropores are overgrown. The head end of the neural tube expands, and the brain begins to develop from it, and from the rest, the spinal cord. At this stage, the brain is represented by three bubbles. Already on the 3rd – 4th week there are two areas with These neural tube: dorsal (pterygoid plate) and ventral (basal plate). From pterygoid plate developing sensory and Tel’nykh associative elements of the nervous system of a basal – m of the turn. The human forebrain structures develop entirely from the pterygoid plate. During the first 2 months of pregnancy mod and zuetsya core (of the middle) of the brain bending: forebrain and midbrain bent forwards and downwards at a right angle to the straight on the proportion v hydrochloric neural tube axis. Later two more bends are formed: cervical and pavement. In the same period, the first and third brain vesicles section I are additional grooves into secondary bubbles appear here There are 5 brain bubbles. From the first of the half-big bubble formed and brain dence, from the second – diencephalon, which proce with ce of differentiated into thalamus and hypothalamus. From the remaining bubbles form the brain stem and cerebellum. For 5 – 10 minutes n e Delhi development begins growth and differentiation telencephalon: arr and form a cortex and subcortical structures. At this stage of development appears t Xia meninges are formed peripheral autonomic ganglia of the nervous system, adrenal cortical substance. The spinal cord pr and acquires the final structure. In the next 10 – 20 weeks of pregnancy on Since the formation of all parts of the brain is completed, the process of differentiation of brain structures takes place, which ends only with the onset of puberty. Hemispheres become the largest part of the brain. The main lobes are distinguished (frontal, parietal, temporal, and occipital), and convolutions and furrows of the large sex of the sharia are formed. In the spinal cord (cervical and lumbar) formed thickening associated with the innervation of the respective zones course of stey. The final appearance takes the cerebellum. In recent months, b e belt starts myelination (coated nerve fibers spec and -trivial covers) of nerve fibers, which ends after the river on REPRESENTATIONS.
Formation of new crust in the process of individual development of at tributes several processes: division and migration neyrobl and ists, the maturation of the cells and their growth processes, growth check afferen t GOVERNMENTAL fibers from the thalamus and associative cortical fibers, the organization and her synaptic connections and interneuron interaction. In Prenatal s nom ontogenesis processes are especially important division of neuroblasts and their migration. Those neuroblasts, which first formed and migrating on the wali in the future form the deep layers of the cortex, and those who MIGR and last, form more outer layers. The maturation of neurons is expressed in the development and branching processes, growth of the body of the neuron and its nucleus, myelination of axons and the formation of synapses. In postnatal ontogenesis interneuronal connections are formed and synapses mature. Previously identified synapses with round vesicles, and later – with oval s GOVERNMENTAL, which is probably due to the different timing of the formation is excited th boiling and inhibitory synapses. The number of synapses substantially depends on the degree of maturity of a given area of the cortex, and the maturation of different areas of the ne e -cortex is uneven. Aksodendritnyh maturation of synapses proya in The appearance of spines. Increasing the number of spines on the dendrites in ontogeny depends on the level of functional load and connected with straight on cession learning and accumulation of individual experience.
Cerebral CNS. According to the topographical principle, the nervous system can be divided into central (CNS) and peripheral. By the CNS include the brain and spinal cord to the peripheral – Peripheral e skie nerves and ganglia (ganglion), Peripheral nerve plexus and e skie nerve endings. The spinal cord and brain are surrounded by the meninges. There are three shells – hard, arachnoid and soft.
The hard shell is the outermost shell. The arachnoid membrane is a thin, translucent connective tissue of the ovale, devoid of blood vessels. The space between the dura of a span of the arachnoid and in the spinal cord and brain are the nerve roots coming out of the brain. Here they are accompanied by arachnoid and soft shells, which serve as an outer sheath for the nerves. Pautov n Nye brain shell covers only gyrus without entering (as does pia) in brain furrow. In other words, the PA in muddy shell spreads like a bridge from gyrus to izvil and not. Therefore, in places where there is no close contact with the brain, the subarachnoid space is formed. In some places, these spaces have relatively large sizes, and therefore they are called qi with the turn. All subarachnoid cavities of the brain communicate with each other, as well as with the cavity of the IV ventricle, and through this ventricle – with the cavity of the remaining ventricles of the brain. The subarachnoid space is going spinnomo of govaya fluid (CSF) from different parts of the brain. The outflow of fluid from here goes to the lymphatic and venous tracts. Soft shell (vascular about a span of) – the inner membrane of the brain. It envelops the brain and spinal cord and even to be inside the cerebral sulci, passing in itself in e the substance of the brain. Soft shell formed gentle loose connector v hydrochloric cloth. In the thickness of the soft shell lies a large number of cr of venous vessels.