Developmentof 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

3. Motoneurons are born before sensory neurons.

2. Large neurons are born first.

5. Glia proliferate after neurons, with the exception of radial glia.

4. Interneurons last of neurons born.

1. Proliferation begins in cervical segments and proceeds

rostrally and caudally from there.

Ventricular layer = ependymal layer = proliferative zonebirthplace of CNS cells

Mantle layer = newly born, post-proliferative cellsMarginal zone = axonal layer

weeks3-4

weeks5-6

somites

Segmental/Genomic Models

Conventional Model

cervical flexure

cephalic flexure

Embryonic stages: conception to 8 wks

http://www.med.unc.edu/embryo_images/unit-nervous/nerv_htms/nervtoc.htm

http://php.med.unsw.edu.au/embryology/index.php?title=Main_Page

Embyronic Imagesby

System

University of New South WalesEmbryology Online

http://www.rockefeller.edu/labheads/hatten/mechanism.html

Thanks to Aron Workman for finding this video clip.

Scanning EMof

Migrating Neurons

synapse withdrawal

axon retraction

programmed cell death(apoptosis)

Regressive Events in the Development of the

Nervous System

http://www.sumanasinc.com/webcontent/animations/content/neuronal_development.html

Animationof

Neuronal Proliferationand

Migration in the CNS