4. The Gastrula

The embryo next enters the gastrulation stage, marked by morphogenesis (i.e., systematic cell movement). In our embryonic life cycle schematic, we are now looking at the last "blobs," blobs 6 to 9:

It's easiest to understand gastrulation in motion. This quick clip below may help:

So what's happening here? First, the mesoderm cells at the dorsal lip of the embryo starts migrating INTO the embryo in a counterclockwise manner (blob 6). Next, the mesoderm leads the remaining outer layer of cells into the embryo, lining the embryo's inner perimeter (blob 7). This creates an embryo with multiple layers of cells (bonus note: over time, these cells will rearrange to become a single layer). By the end of gastrulation, the embryo elongates, and the head-tail axis (the anterior-posterior axis) is formed. This formation is called the neurula (blob 8 for overhead view, blob 9 for mid-section view).

The neurula contains all stem cells needed to form the central nervous system, which contains the brain and spinal cord. Here's what the neurula looks like in real life:

The highlighted central portion of the neurula is called the neural plate, which we will discuss in more detail in the neurulation lecture.

As always, I hope you learned something new (even if it is a factoid) and are finding developmental neurobiology interesting (even if just a little bit more). Hope to see you back.

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