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Development of the human face
By Lynda Kohn
My writing on beauty is going to be very basic. Its going to be how the face is formed. By this I mea the facial bone structure. I am not only referring to the human face. This is true of the face of every vertebrate from fishes on up It is a fact that every animal with a vertebrae ‘s bone formation of the face is a pretty straight forward process. That is the development consistently follows a certain order. Thee are cells that form nearly at the beginning of conception called neural crest cells. That are so named because they are formed from cells that will become the nervous system. They are derived from the neural tube. The neural tube is responsible for brain and vertebrae formation. This is why anacephaly, born without the higher structures of the brain and spina bifida are considered neural tube defects. In humans neural crest cells start forming in the embryo at as early as two weeks from conception. They are derived from ectodermal tissue. Specifically their origin is from the crest of the neural tube. Hence the nane neural crest. More specifically there are three separate tissue layers. Ectoderm on the outside, in the middle the mesoderm and finally furthest in, the endoderm. By the 19th day the ectoderm interacting wth the mesoderm forms the neural place. This is the beginning of the human central nervous system.
Bordering these three layers of cells is the epidermal that forms the deepest layers of one’s skin. Plus from these endothermal, ectodermal and mesodermal cells all other cells are formed. The endothermal cells form the skin, the mesodermal are precursors to the muscles and lastly the ectodermal is reposnsible for our nervous system and the cranial nerves. Rather basically the neural crest cells interact with other nearby cells to create the bony structure of the human face. It is a complicated yet straight forward process. The neural crest cells work with the skin and bone cells to create the forehead, the nose, the cheeks, the mouth and the chin. The first structure to form is the mouth. Then from bottom to top, the chin, the philtrum (space between the upper lip and nose) , the nose and finally the forehead is formed. Then the cheeks are created going in the dirfection from top to down. Finally the chin is created. Particularly The cranial neural crest cells make cells that form the bone structure of our human faces . By the time the developing embryo becomes a a fetus at eight weeks from conception, if developing normally, a primitive, yet recognizable face should begin to be visible. At a very early stage, the development of the very of the human face is now begun. . More specifically from these different layers of ecotermal, mesodermal and endodermal tissues and their derivatives, what looks to be knobby protrusions are formed. They are called branchial arches. I think they are named as such because they look like they are branching out from the aforementioned cell types and each of these protrusions form an arch. From the first and second branchial arch the human face is created. The normal time table for forming the face is as follows. At 28 days the lower jaw and nostrils begin to be formed. Day 31 both eyes can be seen Day 33 the nostrils move to their normal position. Now the ears are there but they lower than the position they will be at birth. Day 35 further refinement of the nostrils, nose and eyes. Day 40 the eyelids appear. From now on the facial features are further developed and their positions to where they will be at birth continues to develop. It’s a pattern of development that will continue until birth. The pragmatic value of knowing how the neural crest cells are quite responsible for facial development may shed light on certain defects such a harelips, cleft lips, cleft palace and other physical defects. One genetic syndrome that is classified as a neural crest derived malformation is Treachers-Collikns syndrome. Juliana Wetmore of FL is known to possess the worst case. She was the girl who was “born without a face.” Her progress in her plastic surgery and her life in general can be seen at www.julianawetmore.net. However its not been updated since December 2009. In other words its updates are not that regular. Treachers Collins is usually characterized in much less severe cases as downward slanting eyes, drooping eyelids, poorly formed, barely there cheeks. It is theorized that it is the result of a person whose face was in arrested development from the sixth to eighth week of prenatal development. On a personal note there is a keen interest in neural crest cells since I inherited f rom my father a genetic facial syndrome that is caused by abnormal neural crest cell development. It is Waardenberg syndrome. Its true my nose is small, upturned and I possess Cupid Bow lips and if you get close enough quite striking blue and hazel eyes. Yet knowing my facial features are the result of a hereditary error makes me feel self-conscience. In the professional edition of the Merck manual Waardenburg syndrome is listed in the index as a craniofacial disorder.
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Thanks Lynda for all that great information.
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This intel was contributed by mugwort
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May, 2012
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