SKULL and BRAIN DEVELOPMENT (and EVOLUTION)

I am interested in the development of the brain. I have designed an experimental protocole by which you can follow in vivo the "neurulation" of vertebrates (a chicken actually). During neurulation, it is observed that the epiblast (or ectoderm) rolls up, and the two lips of the epiblast collide against each other.


This movement can be understood on the basis of simple hydrodynamic flow. The tisue behaves as a visco-elastic sheet. The two halves of the embryo flow towards each other and collide along the median axis.

I have therefore studied in great detail the speed of the tissue, point by point, in the rostral area, at the exact moment of collision.


The image here shows the neural folds, just before the collision, and just after

I have employed the PIV method to extract the tissue speed during the collision, a few minutes before the collision,a dn a few minutes after.


The image here to the right shows the speeds, oriented towatds the midline, just prior to the collision.
And here the speeds just after the collision.

We witness a change from a dipolar situation, associated to an engulfment along the fold, which corresponds to a free condition for the flow along the fold.

To a quadrupolar situation, after the collision corresponding to a mirror symmetry condition or reflection condition along the median axis, after the collision. This is the true origin of the brain and of the cephalic features of craniates.

After this collision has occurred, the tissue recirculates in a quadrupolar fashion, which opens the foremost area, and allows it to expand and form a head. The position of teh eyes on either side of the head is some sort of a trail, or a wake of tissue following a quadrupolar movement in a limited space.

La citation de la page : "Lorsque vous avez éliminé l'impossible, ce qui reste, si improbable soit-il, est nécessairement la vérité", Arthur Conan Doyle.
Suite sur le cerveau, vu par ses vaisseaux sanguins SUITE
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