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Ch. 7 Study Questions

Terms in this set (47)

1. neurogenesis, production of new cells
- some progenitor cells in ventricular zone migrate short distance to formulate subventricular zone by symmetrical division
- later (~7 wks in humans) cells in ventricular zone start dividing by asymmetrical division, first into radial glia, then asymmetrically into ongoing progenitor cells and precursors of non-dividing neuroblasts and glioblasts
- rate and timing varies from one region of tube to another over developmental time
- 3 swellings at anterior pole by 24-40 days

2. migration, movement to final location
- radial glia extend temporary network of projections from ventricular zone to pial surface to guide outward migration in CNS
- provides scaffold for migration into columnar organization of cortex
- migration occurs in waves
1) preplate zone (PP) established by wave of migration from ventricular zone (VZ)
2) second wave migrates through intermediate zone (IZ) to split preplate into marginal zone (MZ) and subplate (SP)
3) successive waves migrate out to expand cortical plate (CP) in inside-out manner (layers 1-6-5-4-3-2)

3. differentiation, modifications to neuronal/glial type
- dividing pluripotent precursor cells differentiate into non-dividing neuroblasts and glioblasts that further mature into specialized neuronal and glial cell types
- remaining ventricular zone cells differentiate into ependymal cells, forming the linings of the ventricles and spinal column

4. synaptogenesis, growth of axons/dendrites/synapses
- extension and contraction of filopodial structures from the growth cone
- chemoaffinity: postsynaptic target releases chemical label that attracts growing axon
- netrins identified- dissociated neurons can innervate appropriate targets in vitro
- regrowing frog retinal ganglion cells will innervate original targets
- reversal of spinal cord in chick embryo does not alter target innervation
- extension and contraction of filopodial structures from the growth cone
- fasciculation: stereotyped axonal pathfinding wherein pioneer growth cones interact with NCAMs that guide along the length of the path, and subsequent neurons follow this blazed trail
- helps to explain complex paths followed by some growth cones
- destruction of pioneer axons in fish spinal cord disrupted subsequent axon pathfinding

5. apoptosis, programmed cell death
- early exuberant proliferation, then apoptosis (including termination of progenitors)
- cells that do not reach appropriate target undergo apoptosis
- cells shrink, chromatin irreversibly condenses, cytoplasm and nucleus break up into membrane bound apoptotic bodies that are phagocytized
- phagocytosis triggered by surface expression of death signals
- since phagocytosis prevents release of individual cellular contents , immune response is not elicited
- recent finding, progenitor cells still exist in some parts of adult human brain
- in surviving cell, Bcl-2 family of proteins inhibits release of Diablo from mitochondria
- inhibitor of apoptosis proteins (IAPs) inhibit caspases
- in apoptotic cell, lack of growth factor inhibits expression of Bcl-2- Ca2+ influx / intracellular Ca2+ release activates mitochondrial release of Diablo
- lack of Bcl-2 inhibition of Diablo allows Diablo to bind to IAPs, preventing inhibition of caspases
- caspases activate endonucleases (fragmenting nuclear DNA), and breakdown of cytoskeleton
- apoptosis initiated by lack of growth factor, loss of growth factor, DNA damage, protein misfolding, specific chemical signaling through death receptors6. synaptic rearrangement, fine tuning
- neurons that fire together, wire together (Hebb, 1949)
- open spaces on postsynaptic neurons are filled in by sprouting axon terminals of surviving neurons
- diffuse pattern of synaptic contact is characteristic of early stages of development
- more focused pattern of synaptic contact is present after synapse rearrangement
- synaptic density peaks at about 1 year
- topographic gradients: integrity of neuronal map is maintained from source to target
- adjustments made as source and target grow at different rates
- organized by chemical gradients
- when half retina lesioned and optic nerve cut, RGCs from remaining retina projected systematically over tectum
- when half optic tectum lesioned and optic nerve cut, RGCs projected systematically over remaining tectumretina optic tectum
- gradient-based organization of inputs- explained by spontaneous waves of activity across electrically-coupled cells

7. myelination, formation of myelin sheath (not all neurons)
- commences around 24 weeks after conception
- commences in spinal cord, and spreads successively to hindbrain, midbrain and forebrain
- intense phase of myelination in the early postnatal period