MID 3-NEUROGENESIS

by the end of neurulation there is…

fully formed neural tube

in fully formed neural tube cells produced proteins that…

coated outer surface of neural tube

• basal lamins

in fully formed neural tube, single layer of…

multipotent neural progenitors

• bipolar

in fully formed neural tube soma migrates..

back and forth between ventricular and outer surfaces

making neurons

while migrating, neural progenitors proliferate

when making neurons, cytokinesis occurs only…

when soma are near ventricular surface

• ventricular zone

when making neurons, cells enter rest phase of mitosis…

near outer surface

• marginal zone

why are neural tube cells pseudostratified

they take on a stratified appearance but still are only a single layer

• combination of migrating soma and massive proliferation

3 neurogenesis phases

1. expansion

2. neurogenic

3. late neurogenesis

expansion phase of neurogenesis

symmetric division only

• prelude to true neurogeneiss

• neural tube thickenig

neurogenic phase of neuogenesis

sym + asym division

• true neurogenesis

• asym division = 1 progentior + 1 transiently amplifying neuron

• TA neuron = neuron precurosr

late neurogenesis phase

messy (sym + asymm + direct conversion)

• neuroglial cell generation

• direction conversion: progenitor stops dividing and fully differentiates into a neuroglial cell

during neurogenic phase, what happens with daughter cell

asymmetric division so 1 daughter cell ont bipolar

• wraps around marginal zone process of progenitor cell and ‘climb’ toward marginal zone

neural tube changes in neurogenic phase

along tube, regional differentiation in cell division rates and types of daughter cells

• produce regions of CNS in anterior posterior pattern

neural tube changes in neurogenic phase: as neurons leave intermediate zone…

the differentiate and become post mitotic

• gets more crowded, new cohorts of neurons must migrate further out

• forms layers of cortex— no longer pseudo stratified

post natal neurogenesis in endotherms

rare in endotherms

• little evidence of neurogenesis beyond sexual maturity

• restricted to hippocampus, subventricular zone of later ventricle with migration to olfactory bulb

post natal neurogenesis exceptions in birds

occurs in birds in seasonal, dramatic changes in behavior

• neurogenesis in hippocampus:

  • song acquisition and performance

  • migration

  • caching

post natal neurogenesis exceptions in rodents

occurs in rodents during olfactory memory formation

• neurogenesis in forebrain with migration to olfactory bulb

• neurogenesis in hippocampus possible throughout life