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FIGURE 3.22 Chain migration of the rostral migratory stream from the subventricular zone. The cells
normally migrate along complex astrocytic networks that are generally oriented in a rostral-caudal direction.
However, the time-lapse series shows how these cells migrate in chains, by sliding along one another, and
they can do this without any glia present in the cultures. (From Garcia-Verdugo et al., 1998)
Purkinje cells. Figure 3.25 shows what this process
looks like, as originally described by Ramon y Cajal.
Soon after their generation, after their final mitotic
division, the granule cells change from a very round
cell to take on a more horizontal-oriented shape as they
begin to extend axons tangential to the cortical surface.
Next, the cell body extends a large process at right
angles to the axon. As this descending process grows
deep into the cerebellum, the cell body and nucleus
follow, leaving a thin connection to the axon. Mean-
while, the axons have been extending tangentially, and
so the cell assumes a T-shape. The cell body eventually
migrates past the Purkinje cell layer and then begins to
sprout dendrites in the granule cell layer.
The migration of the granule cells is another
example of the importance of radial glia in CNS histo-
genesis. As they migrate, a specialized type of radial
glia, known as the Bergmann glia, guides the granule
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