Transcript Brain Growth and Neural Development

Brain Growth and Neural
Development
Reflexes
Dynamic Action System
Small changes during development lead to
major changes in structure and functioning
later on
Prenatal and postnatal
Changes attributed to “plasticity”
What does this mean?
Example: ocular dominance
7 Primary Processes in Neural Dev
Neurogenesis (step 1)
 Proliferation of cells/prenatal
 Neurons produced in neural tube during
prenatal development
 Glial cell production starts before birthcontinues beyond birth
 forms a network that the neurons use to
migrate
 Increases efficiency
Migration (2)
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Cells move through passive displacement
(pushed out by newly forming cells)
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Active displacement- along the glial cell
structures
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Plasticity- the degree to which a developing
structure or behavior is modifiable due to
experience.
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Example: cell destined for visual area misses mark
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ends up in auditory area
differentiates
Migration Failure
Axon Growth (3)
 Axons grow toward specific targets
 Guidance occurs as a result of
neurotrophic factors family of proteins - growth and survival of the
neuron
 Chemical attraction or repulsion causes
growth cone of axon to change direction
Maturation (4)
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Neurons are formed and migrating before birth
(by end of 2nd trimester)
Neurons are functional but not optimally (at
adult levels)- we see inconsistent firing patterns
Activity pattern changes with experience to
become more efficient and consistent
See Kaylin video
Synaptogenesis (5)
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Increase in synaptic connections
Dendritic branching begins increasing shortly
before birth
These high levels are associated with infant
relflexes
E.g. visual synapses
 @10% of adult levels @ birth
 @ 8 months, synapses are at max levels
 @ 11-12 years, adult levels (50-60% of max level)
Decrease in # of synapses (6)
 Big increase, then gradually decrease in
number after birth (~8 mo)
 Apoptosis- programmed cell deathpredetermined lifespan of the cell related
to neurotrophic factors
Decrease in # of Synapses (6) -Pruning
Pruning- increased activity in specific
areas associated with a decrease of the
neuronal network.
decrease in density occurs at the same time as
regression of infantile reflexes
acquisition of specific abilities
seems to be a critical mass of synapses
required for onset of specific skills acquisition.
as skills are refined pruning
Myelination (7)
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Responsible for increased wt & size of brain
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Neurons in place after birth- axons become coated with
fatty substance after birth (Glial Cells).
Glial cells
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Taste, smell, touch are myelinated partially or fully at birth
vision- process complete sometime around 5-8 months
language processing pathways
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begin around 12 months
rapid expansion of myelin sheath around 15-18 months- Result?
myelination associated with acquisition of new skillsspeed of transmission
brain growth spurt- last trimester to end of 2nd year
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Additional growth spurt 5-8 years
MRI Studies
Brain Growth
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Size
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Functionally developed at birth
@ birth brain weighs ¾ - 1 lb (25% of adult size)
@ 6 months, 50% of adult size (1.5-2 lbs)
@ 2 years 75% of adult size (2.25-3 lbs)
Fetal Brain Growth
Why such growth?
 What accounts for increased size?
 Addition of glial cellsMyelination of the
axons
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Shape
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As size increases- shape changes
Deeper folds
More convolutions
Increases the surface area