exam 2 Flashcards
which layer of tissue of the embryo produces the nervous system?
ectoderm
six stages of neural development
neurogenesis, cell migration, differentiation, synaptogenesis, neuronal cell death, synapse rearrangement
neurogenesis
– proliferation of precursors of neurons and glial cells
– marginal zone, intermediate zone, ventricular zone (top, middle, bottom)
– stems cells – undifferentiated cells that can become any type of neuron or glia
neurogenesis in adult brain
– possible adult learning and memory
– decline of neurogenesis associated with cognitive decline
– multiple reserves help resist loss of function
brain changes in healthy aging
– medial temporal lobe areas involved with memory
– executive pathways connecting basal ganglia and frontal lobes
cell migration
radial glia as a “scaffolding”
what regulates migration?
cell adhesion molecules, expressed by migrating neuron and radial glia (n-cadherin)
differentiation
cells begin to express specific genes
synaptogenesis
– synapses form rapidly on dendritic spines of dendrites
– growth of cones regulated by chemical signals (chemoattractants and chemorepellants)
– continues throughout life
– spines proliferate after birth
– cell bodies increase in size
neuronal cell death
– apoptosis is the death of cells which occurs as a normal controlled part of development
– access to neurotrophins influences neuronal survival
synapse rearrangement
– elimination of extraneous connections and maintenance of functional connections
– also known as synaptic remodeling
Explain the process of neuronal precursor proliferation in the ventricular zone.
a small number of precursor cells divide in two; then, in another cycle, each precursor cell divides again, perhaps several more times
What is the role of radial glia in the cell migration stage of neural development?
act as a physical scaffold, providing a pathway for newly generated neurons to migrate from the ventricular zone to their final destination in the cortex by extending long, radial fibers that guide the neurons along their journey, essentially acting as “guide rails” for cell migration
Compare & contrast the 2 triggers of cell differentiation that occurs in the 3rd stage of neural development.
– Cell autonomous (w/o instructions)
– Driven by genes
– Intrinsic organization seen in vitro
– Induction
– One set of cells determines the fate of nearby cells
– Only occurs in vivo
What regulates the outgrowth of axons & dendrites in the first phase of synaptogenesis?
Intrinsic factors (genetics)
Extrinsic factors (environment)
Explain when synaptogenesis starts and when it stops.
Synaptogenesis, the process of forming new synapses between neurons, begins shortly after conception during prenatal development and continues throughout life, although it occurs most rapidly during infancy and adolescence, with the peak rate of synapse formation happening in early childhood; it essentially “stops” when the brain reaches maturity and has established its adult number of synapses, which happens gradually throughout the later stages of development and into early adulthood
Describe how death genes regulate apoptosis.
– By activating a series of events that leaf to cell death
– In normal cells, there are: caspases
– Are proteases that cut up proteins and DNA
– Are normally inhibited by inhibitors of apoptosis proteins (IAPs)
– Initiating apoptosis
– Starts with a Ca2+ influx
– Ca2+ releases Diablo from mitochondrion
– Diablo binds to inhibitors of apoptosis proteins (IAPs)
– Releases brake on caspases
What are the primary factors that influence apoptosis?
– Making adequate number of synapses
– Chemical signals from the targets
– Neurotrophic factors (aka neurotrophins)
– A target derived chemical that acts as if it “feeds” neurons to keep them alive
– Taken up by the axons of innervating neurons
Ex.
– Nerve growth factor (NGF) – regulated sympathetic nervous system growth
– Brain derived neurotrophic factor (BDNF) – involved in guiding synaptic rearrangement
What is the purpose of the 6th stage of neural development, synapse rearrangement?
to refine the neural circuitry by selectively strengthening certain synaptic connections while weakening others
Radial Glia:
Location: Found in the developing nervous system, particularly in the neural tube.
Role in Cell Migration: Serve as scaffolding for migrating neurons during development. Neurons use radial glia to navigate to their appropriate locations.
Signals for Cell Migration: Key signals include neurotransmitters and guidance cues like netrins and slits, which help guide the migrating cells along the radial glia.
