Summary Biopsychology Chapter 5

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




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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