In this video, we're going to be talking about the specialization of the ectoderm. So as a reminder, the ectoderm is the outer germ layer, and the ectoderm is going to go on to become the majority of the nervous system as well as the sense organs and the epidermis of the skin. And one nice way to remember that last point is that the epidermis is basically the outer layer of our skin and the ectoderm is the outer dermal layer. So those two go together kind of nicely. Now, the first major event of organogenesis is a process called neurulation and this is usually happening around week 3, so very early in development, and neurulation is what forms the nervous system.
We're going to spend the remainder of this video just focusing on neurulation because, you know, the nervous system is kind of a big deal. So, basically, the first event of neurulation is that a portion of the ectoderm is going to begin to thicken and form something called the neural plate. So you can see in image number 1 here we have that blue ectoderm running around along the outer layer there, and then here in the center right above that notochord, so like right center of that embryonic disc, we have these purple cells here and that is representing our neural plate. Okay, so that's happening at about week 3, and then over the next few days, what's going to happen is the neural plate will begin to fold inward. So you can see in image number 2 here how essentially that neural plate is now folding in on itself.
And like I said, that will happen over the course of a couple of days. And then by about week 4, what happens is that the edges of that neural plate fuse into something that is now called the neural tube. Okay. So the neural plate has now fused into the neural tube, and around the same time, something called neural crest cells are going to be forming between the ectoderm and the neural tube. So if you look over here at image number 3, you can see how our neural plate has now formed this circular structure, the neural tube there, and you can see how we now have these green cells here in between our ectoderm and our neural tube.
So those green cells represent our neural crest cells, and the neural tube is going to go on to create the brain and the spinal cord. So that is essentially going to form our central nervous system and then those neural crest cells are going to form the remainder of our nervous system structures. So the peripheral nervous system, the spinal nerves, the cranial nerves, any ganglia that will all be created by those neural crest cells. Alright, so that is the specialization of the ectoderm and I will see you guys in the next one. Bye bye.