Key processes that develop the body plan

Gastrulation

• A process that forms of the 3 primary germ layers
• initially, you have the bilaminar disc which is the Epiblast and Hyopblast. A faint line then forms down the middle, on top of the Epiblast. This is called the Primitive Streak.
• As the primitive streak starts to furrow and invaginate it displaces the hypoblast layer beneath which leads to:
• - Endoderm (epiblast layer)
• - Mesoderm (epiblast cells in the primitive streak)
• - Endoderm (epiblast that displaces the hypoblast)
• 

Notochord

• Mesodermal cells cluster and form a rod straight down the midline of the embryo
• Defines the left and right axis --> forms the bilateral symmetry
• Initiates the Neuraltion
• Forms the Nuclei Pulposi
• 
• Caption: The Notochord

Neuralation

• The presence of the notochord initiates the cell division if the upper layer of ectoderm above it. The weight of the cells causes this ectoderm to buckle and invaginate, forming a neural groove. The 2 neural crests have neural crest cells in them and they merge at the midline. This tube pinches off and zips close both directions and the NCCs get trapped under the ectoderm layer.
• If cranial pore doesn't close = Anencephaly
• If caudal pore doesn't close = Spina Bifida - prevent with folate