Transcript Document

Development
of the
Nervous System:
Overview
"It is not birth, marriage, or death, but
gastrulation, which is truly the most important
time in your life."
Lewis Wolpert (1986)
Gastrulation occurs during 3rd week of
gestationin humans
What is an “organizer?”
~19 days
~23 days
Rules for the Birth of
Cells in the CNS
1. Proliferation begins in cervical
segments and proceeds
rostrally and caudally from
there.
2. Large neurons are born first.
3. Motoneurons are born before
sensory neurons.
4. Interneurons last of neurons
born.
5. Glia proliferate after neurons,
with the exception of radial glia.
Ventricular layer = ependymal layer = proliferative zone
birthplace of CNS cells
Mantle layer = newly born, post-proliferative cells
Marginal zone = axonal layer
somites
weeks
3-4
weeks
5-6
Segmental/Genomic Models
Conventional Model
cephalic flexure
cervical flexure
Embryonic stages: conception to 8 wks
Embyronic Images
by
System
http://www.med.unc.edu/embryo_images/
unit-nervous/nerv_htms/nervtoc.htm
University of
New South Wales
Embryology Online
http://php.med.unsw.edu.au/embryology/
index.php?title=Main_Page
Scanning EM
of
Migrating Neurons
http://www.rockefeller.edu/lab
heads/hatten/mechanism.html
Thanks to Aron Workman for finding this
video clip.
Regressive Events in the
Development of the
Nervous System
synapse withdrawal
axon retraction
programmed cell death
(apoptosis)
Animation
of
Neuronal Proliferation
and
Migration in the CNS
http://www.sumanasinc.com/webcontent/animations/
content/neuronal_development.html