bredy@serum.kodak.com (Dan Bredy (x37360)) (06/28/91)
Hi all! I wonder if anyone has any information on human fetal development (particularly, at what stages brain appears, brain starts functioning i.e. brain waves appear, when mylienation occurs)? I would really, really, really, appreciate it!!! Thanks all! Dan E-mail me if you think this information would not be of interest to the group.
rowe@pender.ee.upenn.edu (Mickey Rowe) (06/28/91)
In article <1991Jun28.114219.3025@ssd.kodak.com> bredy@serum.kodak.com (Dan Bredy (x37360)) writes: >Hi all! > >I wonder if anyone has any information on human fetal development >(particularly, at what stages brain appears, brain starts functioning i.e. >brain waves appear, when mylienation occurs)? I would really, really, really, >appreciate it!!! Thanks all! The nervous system begins developing at the outset. You cannot study the development of nervous systems in isolation from overall development, because they are intricately linked. As for when brain waves appear, it's probably not possible to measure in utero, but the connections between neurons and the ion channels necessary for them to function as neurons are created more or less as the neurons are created (though some connections are made much later). All of the processes involved overlap in time, and flow pretty much fluidly. If you could watch the brain develop with time-lapse photography, you'd have a pretty difficult time deciding when it was a brain. It would be like trying to decide when a boy becomes a man; you can define it as the time that he kills his first lion or wolf or something like that, but does that transition really have a meaning? Stepping back to look at development again--Cells typically are "born" (read an undifferentiated cell undergoes mitosis), specialize (read express certain proteins which cause them to behave in a certain way and have a particular shape), and migrate to a new location in roughly that order. Neurons also send out axons, which may reach their targets some time after the cell has reached its destination. All of these events are occurring from fertilization to some point *after* birth. Myelination begins to occur fairly early on (first trimester ?) but continues (in humans) for several *years* after birth. I hope you're not planning to use information such as this to reach (or buttress) a stance about abortion. My feeling is that biology does not give answers to the type of questions that you would want to raise in deciding the ethics of such an act. I'm willing to discuss it if you'd like, though. >Dan Mickey Rowe (rowe@pender.ee.upenn.edu)