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Chapter 7

PSYC 280 Chapter Notes - Chapter 7: Radial Glial Cell, Sonic Hedgehog, Neuroglia

4 pages89 viewsSummer 2013

Course Code
PSYC 280
Neil Braganza

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Chapter 7
Recent estimates suggest that there are about 100 billion neurons in the human brain. Neurons
each develop thousands of synapses, and in the end the brain contains a staggering 100 trillion
synaptic connections!
The fertilized egg, or zygote , contains complete genetic blueprints
for the new person in its 46 chromosomes. A period of rapid cell
division follows, and by the end of a week, the cell mass, now known
as a(n) embryo , shows three distinct cell layers. The nervous
system will develop from the ectoderm .
By the end of the 8th week of embryonic life, rudiments of all major
organ systems are apparent, and the head is about 50 % of the total
mass of the embryo. After 10 weeks, the embryo is called a(n) fetus .
The production of nerve cells is called neurogenesis . Although
neurons themselves do not divide, the cells that become neurons
(reproduce) through a process called mitosis and form a closely
packed zone of cells called the ventricular zone
Cells in the ventricular layer of the neural tube undergo division, or
mitosis, giving rise to daughter cells that will eventually leave this
layer and go on to form neurons and glial cells. Neurons themselves
do not divide, and very few are added after birth
In contrast to the situation with invertebrates such as C. elegans,
vertebrate neuronal development is regulated by cellcell
The increasing weight of the brain during postnatal development has
traditionally been attributed to increases in the size of neurons, the
branching of dendrites , the birth of glial cells, and the wrapping of
myelin around axons. However, we now know that neurogenesis also
occurs in humans through adulthood .
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