Wednesday, April 30, 2008

The strangeness of neural crest

At last I found, bought, and am busy reading a book that goes into excruciating scientific detail about neural crest, Neural Crest in Development and Evolution (1999), by Brian Hall at Dalhousie, Halifax, Nova Scotia.

Neural crest is considered by Hall as "the fourth germ layer". It makes a large amount of surprising structure in the body and head beside peripheral nerves (sensory and autonomic) and the support cells for them. There is a large amount of info here about ectodermal/mesodermal interaction, what induces what, etc. Hall is careful to point out (see the online lecture linked to below) that what is currently known about neural crest is from work done on chicks, and has only been extrapolated to humans - human neural crest may have some variations to offer up to future investigators.

Because of what we do as manual therapists, I think it's good to understand what this embryonic "layer" does and what it makes. It derives from ectoderm, after the neural tube is already well on its way to forming, and long after mesoderm has already been kicked off by ectoderm and is busily making things out of itself. Like mesoderm, it migrates inwardly, but unlike mesoderm, it makes nerves and a few structures, e.g., connective tissue inside glands, something I never knew about neural crest. I knew it made most of the face including bits of jaw and the teeth.

Apparently (according to Hall) it was neural crest cells which may well have made bony plates inside skin in our ancient finny forbearers. It was mentioned in Your Inner Fish that teeth are bony remnants from long long ago, although the neural crest connection wasn't pointed out specifically. The neural crest cell populations that make teeth have been separate from those that (can, ostensibly) make (dermal) bone for 500 million years.

Hall is now "retired" and working on a revision of Strickberger's Evolution 4th Ed., a textbook on evolution. This is Ch. 1 (18 page pdf).

Other links:
1. Unscrambling the egg
2. Online lecture by Brian Hall on cranial neural crest (as opposed to "truncal" neural crest, which behaves differently in modern mammals and birds). (The slideshow takes frequent rests; patience is advised.
3. Short summary of his achievements (about a third of the way down the page), contributor to the emergence of Evo-Devo
4. The book, Variations, which he co-authored
5. More info on Brian Hall and his work

This, along with reading the Sensory Hand, will no doubt keep me busy for quite awhile.

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