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Formation of the Primitive Streak – Skull and Brain Development

by John McLachlan, PhD
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    00:01 Hello, and welcome to this lecture on the development of the brain, and the influence that has on the skull. And we’ll also look at some abnormalities that will develop.

    00:10 I should advise you that towards the end of this presentation, there are some photographs of babies with significant abnormalities, and this may be something you wish to bear in mind. So, the plan that we’re going to follow is that we’ll look at the early development and flexion of the brain, and then how the brain regionalizes into different regions, and then how that influences the development of the skull. Inevitably, there are some abnormalities that may arise from things going wrong during these processes. So we’ll touch in them towards the end of the lecture. As so often as the case, we’ll have to go back to the very beginning to look at the very early stages of development and the formation of the neural tube. So in the top image, we have the amniotic cavity, and below that, we have the yolk sac.

    00:56 In between the two is the bilaminar disk. If you’re in the amniotic cavity looking down, you could see the primitive streak which establishes the main body axis. Along the line of this streak, the ectoderm will begin to roll up on either side to form the neural tube. And of course, the neural tube will later become the spinal cord in the adult.

    01:19 That rolling up process begins round about the central part of the body axis at this time. We can see it coming together in the right-hand diagram, and it will fuse at this point, and then the line of fusion will extend towards the head and towards the tail.

    01:36 So, a little later in the process, we can see this zipping up process, as it were, moving towards the head and moving towards the tail. On either side of the neural tube, which is derived from ectoderm, as we’ve said, there are square such structures which are known as the somites, and these are in the mesoderm. Later, they will give rise to the vertebrae among other things. In the right-hand picture, we can see that the posterior part of the neural tube has almost completely closed. But the anterior part towards the head end is still open. We can also see that this is enlarged as beginning to form structure, which will be recognizable in time as the brain. In this image, a scanning electron micrograph image of a real human embryo, we can see that this fusion process is almost completed at the head and tail end. We can follow this spinal cord down and mark the somites surrounding it on each side. Now, let’s look at that process from the side. We can see the developing


    About the Lecture

    The lecture Formation of the Primitive Streak – Skull and Brain Development by John McLachlan, PhD is from the course System-Specific Embryology with John McLachlan.


    Author of lecture Formation of the Primitive Streak – Skull and Brain Development

     John McLachlan, PhD

    John McLachlan, PhD


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