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View Diary: Cnidarian Nerve Nets (28 comments)

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  •  This would have to be the blastocyst, which... (1+ / 0-)
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    is undergoing the process of gastrulation.  At this point the embryo implants and the process produces a gastrula with a front and "tail" and a dorsal and ventral.


    •  I think this might be it, the, "Polonaise movemnt" (2+ / 0-)
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      Desert Scientist, RiveroftheWest

      wiki doesn't have much information on it.

      From wiki's entry on the "primitive streak,"

      The presence of the primitive streak will establish bilateral symmetry, determine the site of gastrulation and initiate germ layer formation...  The primitive streak extends through this midline and creates the antero-posterior body axis,[2] becoming the first symmetry-breaking event in the embryo, and marks the beginning of gastrulation.[
      So how does this happen?  Wiki loses a little of its usefulness here.  We do find this:
      The formation of the primitive streak involves the coordinated movement and re-arrangement of cells in the epiblast. Even before the streak is visible, epiblast cells have started to move.[7] Two counter-rotating flows of cells meet at the posterior end, where the streak forms.[7] There is little movement in the center of these flows, while the greatest movement is observed at the periphery of the vortices.[3] The Polonaise Movement is key for the formation of the primitive streak.
      There is no entry on Polonaise Movement at wiki.  Searches for it go back to the primitive streak.  (Or to Chopin, heh.)

      I want to be careful that I don't post bullshit.  Is the Polonaise movement where we lose symmetry, or is that too an extension of a simpler decision point?

      Imagine a pencil standing vertically on its tip.  It can fall either right or left, but once it starts falling that way, it can't change course.  The moment that that commitment happens is when symmetry breaks.  I'd like to know where and when, likewise, the symmetry is first broken and commitment happens in the embryo.  Is the Polonaise Movement that point?  

      Searching more widely, at, I find a movie showing the polonaise movement.  I can hotlink it HERE, but that might get firewalled, so the actual homepage is HERE,, in case that doesn't work.  It's labeled Movie 15.3.  I can't find much information on it.

      I'm hoping to make something much more dumbed down but interesting, tying together symmetry-breaking events.  Like, why is the universe chunky (lots of galaxies) rather than smooth, with matter evenly distributed?  It's a standing question in cosmology, which I can liken to the birth of bilateral symmetry.

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