Flashcards in Lecture 10; Brain development Lecture 2 Deck (39):
Describe post natal brain growth;
•At birth, brain ~25% of adult volume
•By end 1st year, ~75%
- 6-7 years of age ~adult volume
What happens during development if the there is an insult;
Insults during this rapid development can be very critical and life long
What can happen post natally in brain development?
•Gliogenesis / proliferation
Does post natal neurogenesis occur?
•Markedly reduction postnatally compared to prenatally
•Two main postnatal proliferative zones
Continue to adult life, but produce very small % of population
What are the two main proliferative zones ?
- Sub ventricular zone
- Sub granular zone
Describe the sub ventricular zone;
–Lining of the lateral ventricles
–Neuroblasts migrate to olfactory bulb via the RMS
Describe the sub granular zone;
–Dentate gyrus of hippocampus
–Neuroblasts migrate from subgranular layer to nearby granular layer
Why does neurogenesis occur continue post natally?
–Functional relevance unclear
–Learning and memory?
Altered in adult neurodegenerative disorders?
What is the evidence in rhodents of continue post natal neurogenesis?
- If this neuroblast genesis is stopped in rhodents then learning and memory is impaired
- It is also found that neurogenesis is impaired in neurodegeneration
What is the evidence of neurogenesis in humans?
–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
What is aboration?
Dendritic spine formation
What dendritic spine formation ocurs post natally;
•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
Does synpatogenesis occur post natally?
•Postnatally, marked production of synapses up to 3-4 years–
~40,000 synapses per second!
What happens to synapses later in development?
•Synapses eliminated–By adolescence synaptic density is ~60% of maximum density at age 2–Critical for fine tuning of brain circuits
What is a key thing that happens in brain development as a adolescent?
Best circuits are refined, others are removed
- Peak synapse formation associates with key sensory systems development
- Synapse removal enhances these circuits
When does glial genesis occur?
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
What glial cells are generated the same time as neurogenesis?
•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
What % brain volume do astrocytes take up? and thier shape?
•20-50% brain volume
•Process-bearing cells in nervous system–Lack axons and dendrites
•‘Astro’ - star-shape
Describe ologiodendrocyte genesis;
•OPC produced in two waves
–Ganglionic eminence (prenatally)
•Tangential migration into WM
•Radial migration into cortex
What do oligiodendrocytes do?
•Differentiation into myelin producing state begins once reach destination–Follows axogenesis
What is the function of myelon?
•Myelinated axons, signal can travel in excess of 100m/s.
•Unmyelinated axons, signal conducted at less than 1m/s
How long does myelination occur for?
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!
What is astrocyte function?
Critical for synapse formation, regulation and function
What does the timing of myelination events relate to?
Timing of these events relates to the onset of different behaviours+functions
What is brain plasticity?
The ability of the brain to remodel
When is a key time brain plasticity is beneficial?
From birth, adolescence, adulthood – marked improvements in perceptual,language, and cognitive abilities
What is the key events of brain plasticity?
–Development and refinement offunctional brain networks(plasticity)
–Postnatal events (e.g. synaptogenesis/pruning, dendritic growth, circuit connectivity etc.) are altered by experience (plasticity)
- 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
What drives brain change?
Whats example 1 of environmental enrichment?
Pet rats performed better on problem solving tests than caged ones
Whats an example of how environmental enrichment can improve brain injury outcomes in rodents?
Enrichment after H-I brain injury in P7 rats improves memory/hippocampal synaptogenesis
What does enrichment do
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
Whats example two of environmental enrichment?
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
Whats example three of environmental enrichment?
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
What does input deprivation lead to?
Whats example one of input deprivation?
(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
What is example two of input deprivation?
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)
What is example three of input deprivation?
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
What are the methods for studying assessing CNS structure?
- post mortem examination