The ontogeny of man.

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ontogenesis of man is a process of individual development from conception to death.The main characteristics are closely interrelated qualitative and quantitative transformation defined specifically for each stage.

term "ontogeny" was first introduced by Haeckel (German biologist) in 1866.Various representatives of the animal world is inherent in different development.Thus, the ontogeny of insects occurs larval type, followed by metamorphosis.In animals, eggs, individual development occurs predominantly in eggs laid by the external environment.Placental animals, humans tend to develop in utero.In this case, the process is divided into three periods: postembryonic, fetal, proembrionalny.

latter is characterized by the formation and development of male and female sex cells - gametes, which is formed at the confluence of the fertilized egg.

on embryonic human ontogenesis (embryonic) period consists of the stages of the embryo and fetus.

post-embryonic period begins after the resolution of labor.This stage lasts a lifetime, ending in death.Postembryonic human ontogeny is divided into age stage.At each stage, the body undergoes its anatomical and physiological changes.According to experts, the most vulnerable and critical periods are menopause (the time of extinction of sexual function), and adolescence (puberty stage).These are the main features of human ontogenesis.

early stages of fetal life are characterized by the birth of the central nervous system.The ontogeny of the nervous system in humans and continues during the first years after birth.

The dorsal section is formed in the embryo plate.Later, the neural groove, and subsequently - the neural tube.

For the week the embryo is characterized by minor thickening of the tube in the oral department.By the third week in the head region formed three brain vesicles (primary): back, middle, front.Of these, the basic parts of the brain (diamond, middle, end).Later comes a split in the two blisters (front and rear).From the end formed hemispheres of the brain and the nucleus (subcortical).

By the third month of embryonic development are beginning to identify key areas of the central nervous system.These include the cerebral hemispheres, brain ventricles, trunk, spinal cord.By the fifth month highlighted in the cortex (hemispheres) main grooves.Four weeks is determined by the predominance of (functional nature) of the higher parts of the stem, spinal.

nerve cells of the embryo and the newborn are arranged concentrated in the white matter on the surface of the cerebral hemispheres.Due to the increased surface begins migrating cells in the gray matter.

Compared with adults, newborn occipital lobe in the cerebral cortex has a relatively large size.The ontogeny of the human in the first five - six years after the birth has a certain characteristics.During this period, the greatest changes in the topographical location, shape and number of hemispheric gyrus.For fifteen - sixteen noted some similarities with adults.

for postnatal period is characterized by changes in the spinal cord and brain.Newborn it is longer than that of an adult.The spinal cord grows to about twenty years.

newborn nervous system myelinated (coated) is not enough, the location of the bundles of nerve fibers unevenly, and they (beams) are rare.

functioning of the nervous vegetative system begins in humans from birth.In the postpartum period is marked in the merger and the formation of the individual nodes in the nerve plexus of the sympathetic system.