It seems that small-bodied primitive organisms could support the development and function of a basic nervous system without glial cells. Longer axons and more complex networks presumably require neuroglia for both development and functioning. I am curious as to which one actually originated first and how long of a timespan passed before the introduction of the other.
Genes for sodium channels evolved first, before the
nervous system and even before multicellularity,
according to this study:
http://phys.org/news/2011-05-sodium-channels-evolved-animals-nervous.html
More on brain evolution:
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000506
http://phys.org/news102328313.html
http://www.eurekalert.org/pub_releases/2008-06/wtsi-oot060508.php
Regards,
Joachim
Genes for sodium channels evolved first, before the
nervous system and even before multicellularity,
according to this study:
http://phys.org/news/2011-05-sodium-channels-evolved-animals-nervous.html
More on brain evolution:
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000506
http://phys.org/news102328313.html
http://www.eurekalert.org/pub_releases/2008-06/wtsi-oot060508.php
Regards,
Joachim
Humans don't have 90% glia, that's an old myth - in the forebrain the ratio is actually close to 1:1 (Azevedo FAC, Carvalho LRB, Grinberg LT, Farfel JM, Ferretti REL, Leite REP, et al. Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain. J Comp Neurol. 2009 Apr 10;513(5):532–41).
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