by day 16 the embryo consists of three layers endoderm mesoderm and ectoderm ectoderm develops into the nervous system and the first phase of this process is known as neural ation around day 18 part of the ectoderm begins to thicken this portion is known as the neural plate in dark blue between the cranial end of the embryo and the primitive node new relation is the process of neural plate becoming neural tube got a schematic animation here to try to illustrate that process we'll break this down day-by-day throughout the rest of the video on day 19 the neural plate begins to buckle in the midline we call this dip the neural groove and the mounds either side the neural folds these folds progress toward each other and begin to fuse around day 21 where they have fused they form a hollow cylinder which is the neural tube fusion then continues in synchrony toward caudal and cranial ends the as-yet unfused portions are known respectively as the cranial Naropa and chordal Naropa poor literally means minut opening the minut opening at the cranial end closes around day 24 and the chordal end closes around day 26 a particular group of cells resided the peaks of the neural fault these are the neural crest cells which form a layer over the top of the closed and neural tube these develop into most of the peripheral nervous system to sum up new relation is the process of neural plate becoming neural tube the closure of the neural folds begins in the centre and zips up towards either end the central nervous system is developed from the neural tube it's worth mentioning the by this gestational age the embryo has started curving into the fetal position we've kept the ectoderm flat to keep our schematic version really simple but these pictures from Grey's Anatomy accurately show the embryo at around 21 and 31 days the neural tube curves through the back of them like so that's it for now hit subscribe if you like this video thanks for watching and we will see you next time [Music]