The phylogenesis of the spinal cord tells about greater development than the brain. The fact is that from the point of view of evolution, it is a more ancient structure. Because of these features of its development much faster than that of the brain.
Starting from the stage of the embryo and ending with the emergence of the individual, the nervous system is a complex path of development.
The ontogenesis of the spinal cord can be divided into the periods of embryonic, prenatal, and postnatal development. Each organ develops, usovershenstvuetsya and gaining the necessary functionality for further development.
The formation of the nervous system
The beginning of the development of the nervous system comes from the formation of its rudiment from ectoderm. This process occurs under the form of a thickening of this ectoderm along the back of the embryo and starts on the 3rd week after conception. Is formed on a certain record. In the future, it forms the neural tube. This occurs by the formation of the neural groove and folds that interlock. Soon, the tube separates from the ectoderm, and continues to develop as a separate body.
At the stage of the formation of the neural tube, its walls consist of one layer of cells. Over time, they are divided into mitotic way. The tube already has 3 layers
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- Internal (ependymal). This layer is the beginning of the development of cells of the Central channel and the walls of the ventricles.
- Intermediate (mantle). Here the neuroblasts generated – sources development of nerve cells, their processes (gray matter of the brain), as well as spongioblast – initiate development of glia.
- The external layer. He is poor on the content of the cells. In the future he forms the white matter of the brain.
The developing brain forms the cords. From the neural crest are formed in the nodal plate. Further they are separated. The cells that are closest to the neural tube in the future develop into sensitive nodes of the cranial and spinal nerves. Cells that were more likely to migrate in the organs, forming the nodes of the autonomic nervous system.
Over time, the neural tube expands at the head end. There begins the development of the brain. A narrower portion becomes the spinal cord.
The embryonic period of development
The spinal cord begins to form from the lateral walls of the neural tube, due to their enhanced growth. Each wall is divided by a border furrow on the bulk and krylnyh plate and intermediate zone. The main furrow is responsible for the motor centers, and krylnyh – sensitive. In the intermediate zone develop Autonomous centers.
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The embryonic period of development
From the motor center out axons, which merge to form the nerve roots. Over time, those growing into the mesoderm and are connected myoblastoma. From sensitive nodes grow bunches of sprouts that soon are going to a sensitive center of the spinal cord. The processes of these neuroblasts grow and converge with motor roots. Thus, on 5-6 week of development formed a spinal nerve.
Formed the nodes of the sympathetic nervous system. The process is due to migration of neuroblasts ganglion plates that form the nodes on the sides of the spine. There are formed connection with the nerve of neuroblasts of the Autonomous centers and front roots. Over time, the migration of cells from these nodes forms a plexus and the other nodes around major vessels.
With the development of the spinal cord, the side walls develop into two symmetrical halves. The Central channel narrows and is filled with cerebrospinal fluid.
Prenatal development of the spinal cord
Development of the spinal cord
In the initial stages of intrauterine growth of the child, the spinal cord fills the entire spinal column. Further, in the third month of development, the spine begins intensive growth in length. Development of the spinal cord begins to lag, as a result, it coccygeal segment moves up. At the time of birth, the lowest point of the spinal cord is at the level of III-IV lumbar vertebra. Segments of the brain are displaced upwards, which is why there is a discrepancy of numbering of vertebral segments. Thus, in the cervical segments are placed above one vertebra, the lumbar parts of the brain lie at the level of XI thoracic vertebra. Sacral and coccygeal segments are at the end of thoracic and early lumbar.
Postnatal development of the spinal cord
The stage of birth in the ontogeny of the spinal cord regains a point when it begins rapid growth. At the time of birth the weight of the spinal cord is 2-6 gr. and the length is 14-15 cm, its end lies at the level II-III lumbar vertebrae. To 5 years supply increases to the widow, and to 20 years in 8-9 times.
In thickness, the brain grows slowly. Its transverse size is doubled only 12 years of life and further remains almost unchanged. At the time of birth the child has no cervical and lumbar enlargement. Their formation starts for a period of 3 years from the moment of birth. Cervical thickening is developing much faster than the lumbar that justify more rapid development of the upper extremities.
Over time, the marked morphological and histological changes in the brain structure. The front horns develop a little better the rear. The reason is that at an early stage of development of the child takes place the accelerated development of motor skills movements. Kid tries more to coordinate movements of head, hands and feet. Usovershenstvuetsya static and dynamic movement. With the development of the child increases the number of cells in the gray matter, there have been changes in their microstructure.
The autonomic nervous system
The autonomic nervous system
The white matter of the spinal cord grows much faster than gray. With age, its rate of development reaches 14, and gray matter – 5. This is due to the intense myelination of nerve fibers. Fiber the roots of the front and rear horns of the spinal cord are subject to myelination, with a 5-month prenatal age. At the time of birth had already covered most of the nerve fibers. Pyramidal tract is covered by a shell since 6 months of life and ends by 4 years.
At the time of birth the child is already functioning autonomic nervous system. Newborns is dominated by the sympathetic nervous system. Parasympathetic turns on with 2-3 months of life. 3-4 year of life begins to dominate the vagotonia. From 5 to 12 years, these two systems are balanced. In the period of puberty due to hormonal changes can occur dystonia.
A great influence of the sympathetic nervous system may cause cardiac arrhythmia, increased sweating. These phenomena are physiologically normal, so no reason for concern.
Development indicators
An important indicator in the development of the spinal cord is part of the cerebrospinal fluid. In newborns it is a little different from older children and adults.
Indicators | Newborns | Children aged from 1 to 3 months | Children aged 4 to 6 months | Children older than 6 months |
The color and transparency | Xanthochromia, transparent | Colorless, transparent | Colorless, transparent | Colorless, transparent |
Pressure, mm of water column | 50-60 | 50-100 | 50-100 | 80-150 |
Amount of fluid, ml | 5 | 40 | 60 | 100-200 |
The cell count in 1 MKL | 15-20 | 8-10 | 8-10 | 3-5 |
Type of cell | Cells, single neutrophils | Lymphocytes | Lymphocytes | Lymphocytes |
Protein, g/l | 0,35-0,5 | 0,2-0,45 | 0,18-0,35 | 0,16-0,25 |
The Reaction Pandi | + or ++ | + | – or + | – |
Sugar, mmol/l | 1,7-3,9 | 2,2-3,9 | 2,2-4,4 | 2,2-4,4 |
Chlorides, g/l | 7-7,5 | 7-7,5 | 7-7,5 | 7-7,5 |
The total number of cerebrospinal fluid in children less than adults. In newborns is 30-60 ml in children from 1 year – 40-60 ml, older children – up to 150 ml Per day the CSF is updated 6-8 times.
The pressure of the cerebrospinal fluid is also lower in newborns and it does not exceed 80 mm water column. In older children it can reach to the limits 100-120 mm water column. When spinal puncture, the fluid flows in drops with the speed 20-40/min, which is consistent with normal pressure.
Normally, the color of the liquid is colorless. However, newborns may be xanthosis. It is associated with the penetration of bilirubin through the blood-brain barrier, if there is a phenomenon of physiological neonatal jaundice.
Chemical composition is also very different. The protein content in the CSF of the baby more than older children and adults. This explains the positive reaction Pandi (the reaction to the protein). In addition, the spinal fluid has a greater concentration of sugar than those of older people.
Newborns often there is a slight lymphocytosis. Their number can vary in the range of 10-15 lymphocytes per 1 ml. Their content decreases with age. Ranging from 1 year from the moment of birth the number of cells stable – 5 lymphocytes/ml.
All of the above characteristics of the composition of cerebrospinal fluid explain the functional state of the Central nervous system of the child.
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