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52 Cards in this Set
- Front
- Back
Human CNS begins to form when the embryo
is |
two weeks old
|
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Mass of human brain
1. At birth 2. First year 3. Adult |
– at birth: 350 g
– first year: 1000 g – adult: 1200-1400 g |
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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 |
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Migration
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movement of neurons and glia to
final locations – Some reach their destinations in adulthood – Cells follow chemical paths (immunoglobins and chemokines) |
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Differentiation
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forming the axon and dendrites into final shape
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Differentation occurs in two ways
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– neuron tows its axon behind as it moves
• axon terminal stays at source – projects its axon out to destination |
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Myelination
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glia insulate some axons
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Myelination form where?
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First forms in spinal cord, then hindbrain,
midbrain, and forebrain Monday, March |
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How long does myelination proceed?
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– Proceeds gradually for decades
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Synaptogenesis
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final stage, forming synapses between neurons
– begins before birth – proceeds throughout the life – slows later in life |
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Processes of neuronal development:
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1. Proliferation
2. Migration 3. Differentiation 4. Myelination 5. Synaptogenesis |
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Stem cells
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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 |
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Pathfinding by Axons
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Axons travel greatdistances to
make connections axons grow to specific target |
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Axons follow
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chemical gradient
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At targets axons form
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surplus of synapses
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Pathfinding axon cell connections
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• Strengthen connections with some cells and
eliminate connections with others • Depends on input from axons |
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Neural Darwinism:
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initially form more neurons
and synapses than needed • most “successful” neurons/synapses survive while the others are pruned • input determines success |
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What is the number of muscles to the ganglion axon?
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Exact match
|
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Rita Levi-Montalcini
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muscles do not
determine how many axons form; they determine how many survive |
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Nerve growth factor (NGF):
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protein released
by muscles that promotes the survival of nerve cells • Nerve cells will die without NGF • Postsynaptic promotion of synapse |
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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 |
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Why is the Visual cortex is thicker in people born blind
|
– lack of visual stimuli leads to lack of
pruning |
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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 |
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Dendrites in fetal alcohol syndrome:
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dendrites short with few branches
|
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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 |
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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 |
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What is far transfer and is it supported today?
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Once believed that learning one difficult task
would enhance other areas No support for far transfer |
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Antisaccade task and its purpose
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looking away from a
powerful attention-getter – a test of inhibition – gradually improves during the teenage years |
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Are adolscents equally impulsive in all
situations? |
• Adolescents not equally impulsive in all
situations • Correlates with decreased PFC activity |
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Synaptogensis
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slows in old age
• Brain structures lose volume (on average) |
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Closed head injury
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blow to the head that
does not puncture the brain – main cause of brain injury in young adults – recovery can be slow and incomplete |
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stroke or cerebrovascular accident
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temporary loss of blood flow to the brain
– Common cause of brain damage in elderly |
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Ischemia
|
more common, a blood clot or
obstructed artery – Neurons lose their oxygen and glucose supply |
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Hemorrhage
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less common, ruptured artery
– Neurons flooded with blood, excess calcium, oxygen, and other chemicals |
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Edema
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accumulation of fluid in the brain
– basically swelling – results in increased pressure on the brain – increasing the risk of further strokes |
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What does a stroke disrupt in a nerve cell?
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Disrupts Na/K pump
|
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Disrupts Na/K pump causes the following:
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– accumulation of Na+ inside neurons
– glutamate release – excites neurons, bringing more Na+ in – excessive Na+ impairs mitochondria – cells die |
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tPA
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drug that breaks up clots
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Damage Mitigation (3)
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• cooling core body temperature (34-35 C)
• cannabinoids decrease glutamate release • progesterone (experimental) |
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Damage Mitigation should be done in what time frame?
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within 3 hours of stroke: most limiting feature
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What happens after swelling subsides?
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Functions return
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What happens to surviving brain areas?
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Surviving brain areas increase or reorganize
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Can destroyed cell bodies regrow?
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– damaged axons can sometimes grow back
-Destroyed cell bodies cannot be regrown |
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Paralysis in spinal cord
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is relativelypermanent
|
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How do Glia cells react to damage
|
Glia cells reacting to damage in CNS release
chemicals that inhibit axon growth |
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Scare Tissue
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Scar tissue may form a barrier to axon growth
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Collateral sprouts:
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new branches by nondamaged axons
• sprouts can be useful, neutral, or harmful |
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Postsynaptic cells deprived of stimulation
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develop increased sensitivity
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Denervation supersensitivity
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the heightened
sensitivity to a neurotransmitter after the destruction of an incoming axon – Can cause consequences such as chronic pain |
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Phantom limb
|
refers to the continuation of perception of an
amputated body part |
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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 |