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Summary Biopsychology Chapter 5
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Bio Psychology – Chapter 5 “Development and Plasticity of the Brain” Maturation of the vertebrate brain
o The human central nervous system begins to form when the embryo
is approximately two weeks old
The dorsal surface thickens forming a neural tube surrounding
a fluid filled cavity
The forward end enlarges and differentiates into the
hindbrain, midbrain, and forebrain
The rest of the neural tube becomes the spinal cord
o
o
o The fluid-filled cavity becomes the central canal of the spinal cord
and the four ventricles of the brain
The fluid is the cerebrospinal fluid
o At birth, the human brain weighs approximately 350 grams
o By the first year, the brain weighs approximately 1000 grams
o The adult brain weighs 1200-1400 grams
o The development of neurons in the brain involves the following
processes:
Proliferation
The production of new cells/ neurons in the brain
primarily occurring early in life
Early in development, the cells lining the ventricles
divide
Some cells become stem cells that continue to divide
Others remain where they are or become neurons or
glia that migrate to other locations
Migration
, The movement of the newly formed neurons and glia to
their eventual locations
Some don’t reach their destinations until adulthood
Occurs in a variety of directions throughout the brain
Occurs via cells following chemical paths in the brain of
immunoglobins and chemokines
Differentiation
The forming of the axon and dendrite that gives the
neuron its distinctive shape
The axon grows first either during migration or once it
has reached its target and is followed by the
development of the dendrites
Myelination
The process by which glia produce the fatty sheath that
covers the axons of some neurons
Myelin speeds up the transmission of neural impulses
First occurs in the spinal cord and then in the hindbrain,
midbrain and forebrain
Occurs gradually for decades
Synaptogenesis
The final stage of neural development and refers to the
formation of the synapses between neurons
Occurs throughout the life as neurons are constantly
forming new connections and discarding old ones
Slows significantly later in the lifetime
o Originally believed that no new neurons were formed after early
development
o Later research suggests otherwise:
Stem cells are undifferentiated cells found in the interior of
the brain that generate “daughter cells” that can transform
into glia or neurons
New olfactory receptors also continually replace dying ones
o Development of new neurons also occurs in other brain regions
Example: songbirds have a steady replacement of new
neurons in the singing area of the brain
o Stem cells differentiate into new neurons in the adult hippocampus
of mammals and facilitate learning
o Different cells have different average life spans
o Skin cells are the newest; most are under a year old
o Heart cells, on the other hand, tend to be as old as the person
o Mammalian cerebral cortexes form few or no new neurons after birth
Pathfinding by axons
o Axons must travel great distances across the brain to form the
correct connections
o Sperry’s (1954) research with newts indicated that axons follow a
chemical trial to reach their appropriate target
o Growing axons reach their target area by following a gradient of
chemicals in which they are attracted by some chemicals and
repelled by others
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