Transcript Neuroplasticity - Bakersfield College

Brain Development
& Neuroplasticity
Neurodevelopment
an ongoing process; the nervous system is
plastic
 A complex process
 Genetics order but experience modifies
 Dire consequences when something goes
wrong
Brain Development
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During dev: 250,000 neurons per minute
At birth..100 billion neurons; 50 trillion to 1
quadrillion synapses
Use it or lose it!
Phases of Development
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Developing neurons accomplish these
things in five phases
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Induction of the neural plate
Neural proliferation
Migration and aggregation
Axon growth and synapse formation
Neuron death and synapse rearrangement
Induction of the Neural Plate
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A patch of tissue on the dorsal surface of the
embryo becomes the neural plate
Visible three weeks after conception
Three layers of embryonic cells
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Ectoderm (outermost)
Mesoderm (middle)
Endoderm (innermost)
Neural Tube Defects
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Neural tube closes about 28 days after
fertilization—WOW!
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Anencephaly-missing or partial dev of cerebral
hemispheres
Spina bifida
Nearly 50-70% can be prevented with folic
acid in diet
Induction of the Neural Plate
(continued)
Neural plate cells are often referred
to as embryonic stem cells
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Have unlimited capacity for self renewal
Can become any kind of mature cell
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Totipotent – earliest cells have the ability to
become any type of body cell
Multipotent – with development, neural plate
cells are limited to becoming one of the range
of mature nervous system cells
How the neural
plate develops into
the neural tube
during the third
and fourth weeks
of human
embryological
development
Neural Proliferation
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Neural plate folds to form the neural groove, which
then fuses to form the neural tube
Inside will be the cerebral ventricles and neural
tube
Neural tube cells proliferate in species-specific ways:
three swellings at the anterior end in humans will
become the forebrain, midbrain, and hindbrain
Proliferation is chemically guided by the organizer
areas – the roof plate and the floor plate
Migration
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Once cells have been created through
cell division in the ventricular zone of the
neural tube, they migrate
Migrating cells are immature, lacking
axons and dendrites
http://www.youtube.com/watch?v=ZRF-gKZHINk
http://www.youtube.com/watch?v=4TwluFDtvvY&feature=related
Somal translocation and glia-mediated migration
Aggregation
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After migration, cells align themselves with
others cells and form structures
Cell-adhesion molecules (CAMs)
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Aid both migration and aggregation
CAMs recognize and adhere to molecules
Axon Growth and Synapse
Formation
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Once migration is complete and structures
have formed (aggregation), axons and
dendrites begin to grow
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Growth cone – at the growing tip of each
extension, extends and retracts filopodia as if
finding its way
http://www.youtube.com/watch?v=n_9YTeEHp
1E&NR=1
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Axon Growth
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A series of chemical signals exist along
the way – attracting and repelling
Such guidance molecules are often
released by glia
Adjacent growing axons also provide
signals
Axon Growth (continued)
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Pioneer growth cones – the first to travel a
route, interact with guidance molecules
Fasciculation – the tendency of developing
axons to grow along the paths established by
preceding axons
Synaptogenesis
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Formation of new synapses (at birth each neuron
has ~2500 synapses; 2-3 years old 15,000)
Depends on presence of glial cells – especially
astrocytes
High levels of cholesterol are needed – supplied by
astrocytes
Chemical signal exchange between pre- and
postsynaptic neurons is needed
Neuron Death and Synapse
Rearrangement
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~50% more neurons than are needed are
produced – death is normal
Neurons die due to failure to compete for
chemicals provided by targets
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The more targets, the fewer cell deaths
Destroying some cells increases survival rate
of remaining cells
Increasing number of innervating axons
decreases the proportion that survives
Life-Preserving Chemicals
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Neurotrophins – promote growth and
survival, guide axons, stimulate
synaptogenesis
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Both passive cell death (necrosis) and
active cell death (apoptosis)
Apoptosis is safer than necrosis – “cleaner”
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Nerve growth factor (NGF)
http://www.youtube.com/watch?v=gYWUTBM8tT
o&feature=related
As we age, old connections are deleted
Neurons must have purpose to survive
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Weak or ineffective connections “pruned”
Plasticityenables process of developing
and pruning connections allowing the brain
to adapt to itself to the environment
Plasticity
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brain changes and adapts
Brain’s ability to reorganize itself by forming
new neural connections
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Allows neurons to compensate for injury or
disease
Allows neurons to adjust to new activities /
change in environment
Plastiticy cont.
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Age-dependent factor
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Young dev brains more plastic
Occurs under two conditions
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Normal development
In response to damage or disease
Hemispherectomy
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Removal of one hemisphere
Last effort to control seizures
http://www.youtube.com/watch?v=TSu9HG
nlMV0
Neuroplastic Responses
 Change
in neurons
Increaed no. of neurons (hippocampus)
 Increased dendritic branching
 Increased efficiency in NT production
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 Increased
neurons
in no. of synapses between
Neurogenesis
 Physical activity and environmental condition affect
proliferation and survival of neurons
 Serotonin believed to play a key role in
neurogenesis
 In lobsters depletion of serotonin reduced
neurogenesis in olfactory areas
 Lab simulation
http://www.wellesley.edu/Biology/Concepts/Simulation/labsimulation.html