Compléter Gastrulation and NeurulationVersion en ligne Use this activity to revise these two very important concepts. par Natalia Bilton 1 fertilization node three spinal gastrulation endoderm primitive neurulation edges invaginated third systems notochord bones develop brain notochordal ectoderm tube mesoderm trilaminar fold plate invagination tube skin endoderm neural gastrulation bilaminar left hypoblast cylinder The first major event of the week of development , , occurs about 15 days after . In this process , the embryonic disc , consisting of epiblast and , transformes into a embryonic disc consisting of primary germ layers ( from the outside in ) these are : the , mesoderm , and . The primary germs layers are the tissues from which all of the organs of the body . The first evidence of is the formation of the streak , which establishes the head , tail , as well as the right and sides of the embryo . At the head end of the primitive streak , a group of cells form a rounded structure called the primitive . Following formation of the primitive streak , cells of the epiblast move inward below the primitive streak and detach from the epiblast in a process called . Once the cells have , some of them displace the hypobast , forming the . Other cells remain between the epiblast and newly formed endoderm to form the . Cells that remain in the epiblast form the ectoderm . As the embryo develops , the endoderm becomes the epithelial lining of multiple . The mesoderm gives rise to muscles , and other connective tissues . The ectoderm develops in to the and nervous system . About 16 days after fertilization , cells from the primitive node migrate toward the head of the embryo and form a hollow of cells in the midline called the process . By days 22 - 24 , the notochordal process becomes a solid of cells called the . The notochord induces the cells laying over it to form the neural . By the end of the third week , the lateral of the neural plate become more elevated and form the neural . Generally , the folds approach each other and fuse , thus converting the neural plate into the neural . Neural tube cells go on to become the and cord . The process by which the neural plate , neural folds and neural tube form is called .
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