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neuronal structure develops in what three stages?
cell proliferation, cell migration, and cell differentiation
what are the "five positions" of the cell choreography of cell proliferation?
1. A cell in the ventricular zone extends a process that reaches upward toward the pia.
2. The nucleus of the cell migrates upward from the ventricular surface toward the pial surface; the cell's DNA is copied
3. The nucleus, containing two complete copies of the genetic instructions, settles back to the ventricular surface.
4. The cell retracts its arm from the pial surface
5. The cell divides in two
what is the significance of the terms ventricular zone and marginal zone
very early in development, the walls of the vesicles consist of two layers: the ventricular zone and the marginal zone. The ventricular zone lines the inside of each vesicle, and the marginal zone faces the overlying pia. Within these layers of the telencephalic vesicle, a cellular ballet is performed that gives rise to all the neurons and glia of the visual cortex
when a cell in the ventricular zone divides into two, what is the fate of the two daughter cells?
The fate of the newly formed daughter cells depends on a number of factors. Curiously, a ventricular zone precursor cell that is vertically during division has a different fate than the one that is cleaved horizontally. After vertical cleavage, both daughter cells remain i nthe ventricular zone to divide again and again. This mode of cell division predominates early in development to expand the population of neuronal precursors. Later in development, horzontal cleavage is the rule. in this case, the daughter cell lying farthest away from the ventricular surface migrates away to take up its position in the cortex, where it will never divide again. The other daughter cell remains in the ventricular zone to undergo more divisions.
this pattern is repeated until all the neurons and glia of the cortex have been made
how does the cleavage plane during cell division determine the cell's fate?
Thus, cell fate is regulated y differences in gene expression during development. Gene expression is regulated by cellular proteins called transcription factors. If transcription factors, or the upstream molecules that regulate them, are unevenly distributed within a cell, then the cleavage plane can determine which factors are passed on to the daughter cells. For example, proteins called notch-1 and numb migrate to different poles of ventricular zne precursor cells.
When the neuron divides vertically, the notch-1 and numb proteins are partitioned symmetrically. However, when the cell divides horizontally, notch-1 goes with the daughter that will migrate away, while numb remains with the cell that will divide again.
Research suggests that notch-1, unopposed by numb, activates the gene expression that causes the cell to cease dividing and migrate away from the ventricular zone
true or false? all nervous system cells, of all morphology, neurotransmitter type, etc., arise from the same precursor cell?
true. they all come from neural stem cells
true or false? one of the factors influencing the differentiation of neural stem cell is the environment in which the cell is in.
true. the ultimate fate of the migrating daughter cell is determined by a combination of factors, including the age of the precursor cell, its position within the ventricular zone, and its enviroment at the time of division.
the first cells to migrate away from the dorsal ventricular zone are destined to reside in a layer called the ___________
after the subplate is formed, cells migrate to form which layers of the cortex (and in what order)?
after the subplate is formed, the next cells to divide migrate to become layer VI neurons, followed by trhe neurons of layers V, IV, III, and II.
what are neuroblasts?
the fibers that radiate from the ventricular zone toward the pia are derived from what?
specialized radial glial cells.
true or false? all all migrating cells follow the path provided by the radial glial cells.
false. not all migrating cells follow the path provided by the radial glial cells. About one-third of the neuroblasts wander horizontally on their way to the cortex
neuroblasts destined to become the adult cortex migrate past the subplate and form the what?
the cortical plate
what is meant when it is said that the cortex is said to be assembled inside-out?
each new wave of neuroblasts migrates right past those in the existing cortical plate
where is semaphorin 3A secreted from?
it is secreted by cells of the marginal zone
what is the function of semaphorin 3A?
the protein acts first to repel growing pyramidal cell axons, causing them to stream away from the pial surface, and second to attract growing apical dendrites, causing them to stream toward the brain surface
what is the chronological order to cell differentiation in the brain?
neuronal differentiation occurs first, followed by astrocyte differentiation, which is followed by oligodendrocyte differentiation
what contains the instructions for the "assembly of the cortical quilt"?
the subplate layer seems to contain the instructions for the assembly of the cortical quilt
what is a growth cone?
the growing tip of a neurite
the leading edge of the growth cone consists of flat sheets of membrane called ________ that undulate in rhythmic waves like the wings of a stingray
extending from the lamellipodia are thin spikes called _______, which constantly probe the environment, moving in and out of the lamellipodia.