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Chapter 9

PSYC 370 Chapter Notes - Chapter 9: Cell Potency, Hindbrain, Apoptosis

Course Code
PSYC 370

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PSYC370 Chapter 9: Development of the Nervous System
9.1 Phases of Neurodevelopment
- Neurodevelopment beings with a zygote. Zygote = ovum + sperm
- 3 things other than cell replication occur in the development process:
oCell differentiation muscle cells, neurons, glial cells, etc.
oCells relocate and align themselves with other cells to form particular
oCells establish appropriate functional relations with other cells
- all 3 tasks are accomplished through 5 phases: induction of neural plate, neural
proliferation, migration & aggregation, axon growth & synapse formation, and
neuron death & synapse rearrangement
- 1. Induction of the Neural Plate
o3 weeks after conception, neural plate forms (the basis of the human
nervous system)
Neural Plate: a small patch of ectodermal tissue on the dorsal
surface of the vertebrate embryo, from which the neural groove,
the neural tube, and, ultimately, the mature nervous system
Neural plate formation is started by chemical signaling from the
underlying mesoderm layer – also called ‘the organizer’
extracting parts of mesoderm layer and injecting them into another
surface of the embryo starts a second neural plate.
Ectoderm = outermost layer of embryonic cells – ectoderm,
mesoderm, endoderm
oCells starts off totipotent, but as neural plate develops become more
specialized  multipotent or stem cells
Totipotent: capable of developing into any type of mature body
oStem Cells: developing cells that have an unlimited capacity for self-
renewal and the potential to develop into various types of mature cells
Can keep recreating because when it divides, forms 2 cells:
daughter cell that matures into a body cell and another stem cell.
Doesn’t continue forever though because eventually errors
accumulate and the self-renewal comes to a halt.
oAs neural plate begins to form into neural tube, cells begin to specialize
and become glial stem cells & neural stem cells
o18 days - Neural plate  21 days – neural groove  24 days – neural tube
oBrain formation: Inside of neural tube eventually becomes cerebral
ventricles & spinal canal; by 40 days neural tube swells in 3 places that
eventually become forebrain, midbrain & hindbrain
- 2. Neural Proliferation:
oNeural Proliferation: the rapid increase in the number of neurons that
follows the formation of the neural tube

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oIncrease in neurons doesn’t occur equally or simultaneously throughout.
Most occurs in the ventricular zone – region adjacent to ventricle (fluid
filled center of the tube).
oDistinct brain shapes of different species are due to neural proliferation.
Different parts of the neural tube proliferate at different sequences,
causing swelling in distinct areas and distinct brain shapes
oSequences of proliferation controlled by chemical messages sent from the
2 organizers in the neural tube: the floor plate (tube anterior) & roof plate
(dorsal side of tube)
- 3. Migration and Aggregation:
oMigration: the movement of cells from their site of creation in the
ventricular zone of the neural tube to their ultimate location in the mature
nervous system. Note: cells are still immature when migrate.
o2 factors govern migration: time & location
o2 types of migration:
Radial Migration: proceeds in straight line from ventricular zone
to outer wall of tube
Tangential Migration: occurs at a right angle to radial migration –
parallel to the tube’s walls.
Most cells use both radial & tangential migration to get to their
target destination
o2 methods to migration:
Somal Translocation: an extension grows out from the
undeveloped neuron and heads in the direction of migration. Drags
the cell body behind it and eventually body draw up into it.
Glia-Mediated Migration: immature neurons move out from the
central canal along radial glial cells. Radial glial cells exist in the
neural tube only during migration period and form a network along
which neurons travel.
Inside-out Pattern: the pattern of cortical development in which
migrations progress from deeper to more superficial layers
oPattern of proliferation & migration different for different areas of the
oChemicals guide migration by attracting/repelling neurons.
oNeural Crest: located just above neural tube. Formed from cells breaking
off from the neural tube as it is being formed. Develops into the peripheral
nervous system  neurons & glials from here must migrate long distances
oAggregation: the alignment of cells after migration, forming various
Migration & aggregation both mediated by CAMs
Cell-Adhesion Molecules (CAMs): molecules on the surface of
cells that have the ability to recognize specific molecules on the
surface of other cells and bind to them
CAM abnormalities may cause neurological disorders
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