Brains II

Cutting egg thingy and the early embryo (that’s its name) longways and looking from side we see that the disc had more going on. The backside surface is called ectoderm (the outer derm). We see deep to it a yolk whose membrane against the disc is the endo derm (inner or deep derm). Q: What’s a derm? A: A layer. Isn’t there supposed to be 3 layers? Well some of that infolding slit crawls between the other two layers and gets the name mesoderm (middle layer). It especially crawls between but around a long thin string that runs the whole length between endo & ectoderm. The long string-o-derm? No. The notocord. The notocord behaves like an orchestra conductor telling all cells what they are to become how to behave. Ectoderm, you will be skin and nervous system. ?? Isn’t nervous system supposed to be INSIDE? Yes, but we start with a generality and that development happens a wee bit later. For now just a long longitudinal thin strip is nervous tissue. The rest is skin? No, well, mostly, but where the two touch will be a transitional thin boundary which will eventually connect both. The’neural crest’ will be nerves and things that go from skin to spinal cord to brain. It will also migrate to serve the new middle of the three layers as well.