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52 Cards in this Set

  • Front
  • Back
Human CNS begins to form when the embryo
is
two weeks old
Mass of human brain
1. At birth
2. First year
3. Adult
– at birth: 350 g
– first year: 1000 g
– adult: 1200-1400 g
Proliferation
production of new cells
– primarily early in life
– cells lining the ventricles divide
– stem cells continue to divide
– others turn into neurons or glia that migrate
Migration
movement of neurons and glia to
final locations
– Some reach their destinations in adulthood
– Cells follow chemical paths
(immunoglobins and chemokines)
Differentiation
forming the axon and dendrites into final shape
Differentation occurs in two ways
– neuron tows its axon behind as it moves
• axon terminal stays at source
– projects its axon out to destination
Myelination
glia insulate some axons
Myelination form where?
First forms in spinal cord, then hindbrain,
midbrain, and forebrain
Monday, March
How long does myelination proceed?
– Proceeds gradually for decades
Synaptogenesis
final stage, forming synapses between neurons
– begins before birth
– proceeds throughout the life
– slows later in life
Processes of neuronal development:
1. Proliferation
2. Migration
3. Differentiation
4. Myelination
5. Synaptogenesis
Stem cells
can divide and differentiate into
glia or neurons

– neurons in olfactory receptors continually
divide and replace dead cells
– also stem cells centrally that migrate to
olfactory bulb
Monday, March
Songbirds continually replace neurons in
song nuclei
– lose neurons in fall
– regrow in spring
Pathfinding by Axons
Axons travel greatdistances to
make connections

axons grow to specific target
Axons follow
chemical gradient
At targets axons form
surplus of synapses
Pathfinding axon cell connections
• Strengthen connections with some cells and
eliminate connections with others
• Depends on input from axons
Neural Darwinism:
initially form more neurons
and synapses than needed

• most “successful” neurons/synapses survive
while the others are pruned

• input determines success
What is the number of muscles to the ganglion axon?
Exact match
Rita Levi-Montalcini
muscles do not
determine how many axons form; they
determine how many survive
Nerve growth factor (NGF):
protein released
by muscles that promotes the survival of
nerve cells

• Nerve cells will die without NGF

• Postsynaptic promotion of synapse
Is Cell death is part of normal development and
maturation
– healthy adult nervous system contains no
neurons that failed to make appropriate
connections that can take decades
Why is the Visual cortex is thicker in people born blind
– lack of visual stimuli leads to lack of
pruning
Fetal alcohol syndrome:
children born to mothers who drank heavily
during pregnancy
– Hyperactivity and impulsiveness
– Difficulty maintaining attention
– Varying degrees of mental retardation
– Motor problems and heart defects
– Facial abnormalities
Dendrites in fetal alcohol syndrome:
dendrites short with few branches
The Vulnerable Developing Brain with Fetal Alcohol Syndrome
alcohol suppresses glutamate and enhances
the release of GABA
• many neurons receive less excitation and
undergo cell death
• excessive pruning in fetus
What is Fine-Tuning by Experience
The brain can reorganize in response to experience
– synapses form/retract continuously
– dendrites continually grow new spines

• new connections are
part of learning
What is far transfer and is it supported today?
Once believed that learning one difficult task
would enhance other areas

No support for far transfer
Antisaccade task and its purpose
looking away from a
powerful attention-getter
– a test of inhibition
– gradually improves during the teenage
years
Are adolscents equally impulsive in all
situations?
• Adolescents not equally impulsive in all
situations

• Correlates with decreased PFC activity
Synaptogensis
slows in old age
• Brain structures lose volume (on average)
Closed head injury
blow to the head that
does not puncture the brain
– main cause of brain injury in young adults
– recovery can be slow and incomplete
stroke or cerebrovascular accident
temporary loss of blood flow to the brain
– Common cause of brain damage in elderly
Ischemia
more common, a blood clot or
obstructed artery
– Neurons lose their oxygen and glucose
supply
Hemorrhage
less common, ruptured artery
– Neurons flooded with blood, excess
calcium, oxygen, and other chemicals
Edema
accumulation of fluid in the brain
– basically swelling
– results in increased pressure on the brain
– increasing the risk of further strokes
What does a stroke disrupt in a nerve cell?
Disrupts Na/K pump
Disrupts Na/K pump causes the following:
– accumulation of Na+ inside neurons
– glutamate release
– excites neurons, bringing more Na+ in
– excessive Na+ impairs mitochondria
– cells die
tPA
drug that breaks up clots
Damage Mitigation (3)
• cooling core body temperature (34-35 C)
• cannabinoids decrease glutamate release
• progesterone (experimental)
Damage Mitigation should be done in what time frame?
within 3 hours of stroke: most limiting feature
What happens after swelling subsides?
Functions return
What happens to surviving brain areas?
Surviving brain areas increase or reorganize
Can destroyed cell bodies regrow?
– damaged axons can sometimes grow back
-Destroyed cell bodies cannot be regrown
Paralysis in spinal cord
is relativelypermanent
How do Glia cells react to damage
Glia cells reacting to damage in CNS release
chemicals that inhibit axon growth
Scare Tissue
Scar tissue may form a barrier to axon growth
Collateral sprouts:
new branches by nondamaged axons

• sprouts can be useful, neutral, or harmful
Postsynaptic cells deprived of stimulation
develop increased sensitivity
Denervation supersensitivity
the heightened
sensitivity to a neurotransmitter after the
destruction of an incoming axon

– Can cause consequences such as chronic
pain
Phantom limb
refers to the continuation of perception of an
amputated body part
What does the cortext do after amputation
– cortex reorganizes itself after
amputation
– becomes responsive to other
parts of the body
– because of overlap, stimulating
the new area can lead to feelings
of the old
– artificial limbs can reduce
phantom limb