Lecture 10; Brain development Lecture 2 Flashcards
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?
- Neurogenesis?
- Dendritic branching
- Synaptogenesis–Synaptic elimination
- Gliogenesis / proliferation
- Myelination
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 –SVZ (postnatally) •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
