🚀 go-pugleaf

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)