Biological aspects of neuroscience: Developmental 2

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What does myelination affect?
PNS and CNS - makes signal more efficient
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Give an example of a condition resulting from a degradation of myelin?
Multiple Sclerosis (affects motor, sensory and integrative systems)
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What is unusual about myelination?
The process lasts for up to 30 yrs
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To what extent is there plasticity postnatally?
1) some neuronal plasticity e.g. cell death, myelination 2) but plasticity is limited e.g. migration: cells can't migrate anywhere!
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Do sensitive periods exist?
Yes, once sensitive period has passed there is a lack of plasticity although extrinsic influences can alter.
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What about adult CNS damage?
Hard to recover from damage BUT have found new neurons in hippocampus
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What is synaptic shedding?
Peaks at 6 yrs (greater than adult levels) then huge shedding before 14 yrs
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Give an example of synaptic shedding
Enriched rats! Diamond et al (87). Enriched input rats had more dendritic connections compared to rats in impoverished environment
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what are three examples of Sensitive Periods of plasticity?
1) Romanian orphans 2) kittens eyes sewn shut 3) lazy eye naturalistic study
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How do the Romanian orphan studies demonstrate sensitive periods of plasticity?
All adopted to other countries and enriched. Tested at 4.5 yrs old. Controls best. But those adopted before 4 mths scored much better than those adopted at 19mths old.
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What is an interaction effect in the case of the Romanian orphans?
Environment and malnutrition.
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What did the kitten experiment find? (Weisel and Hubel 65)
Sew eyes shut for first 4-6 wks then unable to use but sew shut after 6 wks had no affect.
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What is the conclusion from the kitten experiment?
Visual development needs environmental input during critical period for neural development to occur
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when should a lazy eye be surgically corrected?
Before age 7/8
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What studies have found plasticity in the adult human brain?
Taxi driver studies (Eriksson 98) found new neurons in hippocampus compared to other London drivers.
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Would could the enlargement of the hippocampus be due to?
New neurons? Or more dendritic connections? We don't know yet!
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What other plasticity studies are there?
Monkey (sew fingers) and arm amputee: somatosensory cortical map - gives ideas about reorganisation capability of the brain
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Cell development names: day 1, day 16, day 21 and day 26
Zygote, neural plate, neural groove, neural tube
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What does the zygote contain?
Blueprint: 23 pairs of chromosomes, each chromosome contain DNA, each strand contain genes
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What happens in day 16?
Distinctive raised cells: neural plate. N plate is important as it will fold over into groove then tube
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What is day 26 the start of?
Neural tube (birthplace of nervous system) and Encephalisation!
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Why is encephalisation unusual in humans?
Head (cephalic) portions of neural tube grow tremendously and disproportionately.
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26 days: What does the cephalic portion split into?
1) RHOMBencephalon (Hindbrain) 2) MESencephalon 3) PROSencephalon
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What happens at 35 days?
Pros and Rhom split again
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35 days: What does the prosencephalon split into?
TELencephalon (cortex) and DIencephalon (thalamus etc)
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35 days: What does the Rhombencephalon split into?
METencephalon (pons, cerebellum) and MYELencephalon (medulla)
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What can occur during the sensitive period if the neural tube doesn't close?
1) Spina bifida (back of tube) 2) Anencephaly (front, so no brain, fatal)
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What is noticeable at 5 weeks?
Clear flexion/bending of front portions
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Summarise 4-8 week growth
Rapid growth e.g. 2 hemispheres emerge etc
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Summarise 8-26 week growth
Cerebral cortex grows to cover midbrain
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What happens at 28 weeks?
Major structural change begins; cortex expands, becomes wrinkled and folded inside skull and fills with gyro/sulci
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When does neurogenesis occur?
From week 8. By wk 8 structures are in place; after this time amt of tissue is rapidly increasing
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what happens during neurogenesis?
new nerve cells migrate outwards by fibres from glial cells.
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What do later formed cells do?
Migrate further away from their start i.e. brain grows, adding layers like an onion.
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What happens when nerve cells reach their destination?
They take on characteristics specific to that area of the brain. And THEN sprouts axons etc.
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What is synaptogenesis?
synaptic proliferation in the brain and this process continues during a babies first YEAR of life.
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what is synaptic pruning?
Some synapses are eventually removed to make the brain more efficient. Occurs during feral period, infancy, childhood and adolescence.
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What are human brains like at 25 days?
Same as worms!
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What are human brains identifiable as by 40/50 days?
vertebrate
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What are human brains identifiable as by 100 days?
other mammals
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What are human brains identifiable as by 5 mths?
a primate brain
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After 5 mths why do human brains present uniquely as humans?!
Due to cast expanse of forebrain and cerebral cortex.
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Card 2

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Give an example of a condition resulting from a degradation of myelin?

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Multiple Sclerosis (affects motor, sensory and integrative systems)

Card 3

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What is unusual about myelination?

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Preview of the front of card 3

Card 4

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To what extent is there plasticity postnatally?

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Preview of the front of card 4

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Do sensitive periods exist?

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