Lecture 10; Brain development Lecture 2

Question 1

Describe post natal brain growth;

Answer 1

• At birth, brain ~25% of adult volume
• By end 1st year, ~75%
• 6-7 years of age ~adult volume

Question 2

What happens during development if the there is an insult;

Answer 2

Insults during this rapid development can be very critical and life long

Question 3

What can happen post natally in brain development?

Answer 3

• Neurogenesis?
• Dendritic branching
• Synaptogenesis–Synaptic elimination
• Gliogenesis / proliferation
• Myelination

Question 4

Does post natal neurogenesis occur?

Answer 4

• Markedly reduction postnatally compared to prenatally
• Two main postnatal proliferative zones

Continue to adult life, but produce very small % of population

Question 5

What are the two main proliferative zones ?

Answer 5

• Sub ventricular zone

- Sub granular zone

Question 6

Describe the sub ventricular zone;

Answer 6

–Lining of the lateral ventricles

–Neuroblasts migrate to olfactory bulb via the RMS

Question 7

Describe the sub granular zone;

Answer 7

–Dentate gyrus of hippocampus

–Neuroblasts migrate from subgranular layer to nearby granular layer

Question 8

Why does neurogenesis occur continue post natally?

Answer 8

–Functional relevance unclear
–Learning and memory?

Altered in adult neurodegenerative disorders?

Question 9

What is the evidence in rhodents of continue post natal neurogenesis?

Answer 9

• If this neuroblast genesis is stopped in rhodents then learning and memory is impaired
• It is also found that neurogenesis is impaired in neurodegeneration

Question 10

What is the evidence of neurogenesis in humans?

Answer 10

–Much greater in newborns (6-18 months), than children and adults
–Thus, early postnatally, may have greater contribution to brain development/plasticity

Therefore maybe children recover better trauma b/c better neurogenesis

Question 11

What is aboration?

Answer 11

Dendritic spine formation

Question 12

What dendritic spine formation ocurs post natally;

Answer 12

•Aborisation of both pyramidal neurons and GABAergic inter-neurons continues postnatally (integration of neurons to create circuits)

–Marked elaboration of spines in first 1-2 years
–Drives postnatal expansion of the cerebral cortex and other GM structures

Question 13

Does synpatogenesis occur post natally?

Answer 13

•Postnatally, marked production of synapses up to 3-4 years–

~40,000 synapses per second!

Question 14

What happens to synapses later in development?

Answer 14

•Synapses eliminated–By adolescence synaptic density is ~60% of maximum density at age 2–Critical for fine tuning of brain circuits

Question 15

What is a key thing that happens in brain development as a adolescent?

Answer 15

Best circuits are refined, others are removed

• Peak synapse formation associates with key sensory systems development
• Synapse removal enhances these circuits

Question 16

When does glial genesis occur?

Answer 16

Astrocytes and oligodendrocytes progenitors develop well after initial neurogenesis

–Glial progenitors genesis, migration, and differentiation starts prenatally, but predominately postnatal process
–Unlike neurons, glial progenitors continue to proliferate as they migrate and at final destination

Question 17

What glial cells are generated the same time as neurogenesis?

Answer 17

• Radial glial – scaffolding for neuronal migration
• Microglia – clean up cell debris after apoptosis

–Genesis of radial glia and microglia occurs in parallel with neurogenesis prenatally

Question 18

What % brain volume do astrocytes take up? and thier shape?

Answer 18

• 20-50% brain volume
• Process-bearing cells in nervous system–Lack axons and dendrites
• ‘Astro’ - star-shape

Question 19

Describe ologiodendrocyte genesis;

Answer 19

•OPC produced in two waves
–Ganglionic eminence (prenatally)
•Tangential migration into WM
–SVZ (postnatally)
•Radial migration into cortex

Question 20

What do oligiodendrocytes do?

Answer 20

•Differentiation into myelin producing state begins once reach destination–Follows axogenesis

Question 21

What is the function of myelon?

Answer 21

• Myelinated axons, signal can travel in excess of 100m/s.

* Unmyelinated axons, signal conducted at less than 1m/s

Question 22

How long does myelination occur for?

Answer 22

Axonal myelination begins (around 6 months gestation), but not completed until adolescence
–Sensory pathways myelinate prior to motor pathways
–Postnatal motor development linked to myelination

Can last up to 30 years!

Question 23

What is astrocyte function?

Answer 23

Critical for synapse formation, regulation and function

Question 24

What does the timing of myelination events relate to?

Answer 24

Timing of these events relates to the onset of different behaviours+functions

Question 25

What is brain plasticity?

Answer 25

The ability of the brain to remodel

Question 26

When is a key time brain plasticity is beneficial?

Answer 26

From birth, adolescence, adulthood – marked improvements in perceptual,language, and cognitive abilities

Question 27

What is the key events of brain plasticity?

Answer 27

–Development and refinement offunctional brain networks(plasticity)
–Postnatal events (e.g. synaptogenesis/pruning, dendritic growth, circuit connectivity etc.) are altered by experience (plasticity)

E.g.,
- Correct development of visual and auditory circuits requires correct visual and auditory input, at correct time!
–Incorrect and lacking input can alter correct circuit formation

Question 28

What drives brain change?

Answer 28

Environmental enrichment

Question 29

Whats example 1 of environmental enrichment?

Answer 29

Pet rats performed better on problem solving tests than caged ones

Question 30

Whats an example of how environmental enrichment can improve brain injury outcomes in rodents?

Answer 30

Enrichment after H-I brain injury in P7 rats improves memory/hippocampal synaptogenesis

Question 31

What does enrichment do

?

Answer 31

Environmental enrichment in lab rodents increases:–synaptic density (~25%), dendritic arborization, glial cell numbers, neurogenesis, cortical thickness, and learning and memory–Both neonatal (greatest) and adult plasticity

Question 32

Whats example two of environmental enrichment?

Answer 32

Somatosensory cortex remodeling

• In string instrument players, volume of cortical region devoted to left hand (string hand)
• Cortical representation of left hand of string players was larger than non-players
• Increase correlated with age at which began to play, rather than amount practice

Question 33

Whats example three of environmental enrichment?

Answer 33

Structural brain changes with learning

• In medical students intensively studying for medical examination (3 months), MRI used to assess parietal cortex volume
• Significant increase in volume in bilateral parietal cortex after 3 months study
• No change at 3 months after exam

Question 34

What does input deprivation lead to?

Answer 34

Detrimental effects

Question 35

Whats example one of input deprivation?

Answer 35

(in kittens) Eye effectively ‘blind’ – functionally disconnected from visual cortex (cortical blindness or ‘amblyopia)

The brain does not develop for that eye, no cortical activation for the deprived eye

•Visual experience in early life determines wiring of visual cortex

Question 36

What is example two of input deprivation?

Answer 36

Human infants with dense cataracts

• Failure to correct congenital cataracts by 4-6 months of age produces irreversible impairments in the visual system
• Patterned visual input necessary for postnatal development of visual acuity (focus)

Question 37

What is example three of input deprivation?

Answer 37

Orphans raised in very poor quality romanian institutions

–Severe impairments in cognition, language, comprehension
–Developmental disorders e.g. ADHD, Autistic traits (by 4-years; synaptic deficits?)
–Reduced cortical volumes
–Reduced brain electrical activity and abnormal brain connectivity

Question 38

What are the methods for studying assessing CNS structure?

Answer 38

• post mortem examination
• MRI
• fMRI
• PET
• EEG
• DWI

Question 39

Note; Go back and recover the imaging techniques, he said not examinable for mid term but in exam yes

Answer 39

Now