| Dissertation |
Thesis (Ph.D.) --NUI, 2007 at Department of Anatomy, UCC. |
| Summary |
This study investigated the earliest establishment of transitional zone (TZ) loci at the motor exit points (MEPs) and sensory entry zones (SEZs) of various levels of the rat and chick neural tubes. Transverse and parasagittal semithin and ultrathin sections of rat and chick neural tubes from E11 to E13 and E2 to E4 (developmentally corresponding stages), respectively, were taken. The motor rootlets emerge from the neural tube as axon bundles, independent of associated cells or blood vessels. Most of the motor axons converge at one site at the surface of the presumptive grey matter, cross the presumptive white matter as an intramedullary bundle (IMB) and emerge as a ventral rootlet. Peripheral cells contacted the motor rootlets after they had emerged from the neural tube and formed clusters on them at a distance (greater in rat than in chick) from the CNS surface. Boundary cap (BC) cells were abundant at the presumptive SEZ. The notochord differed markedly in size and position between rat and chick. The overall faster development of the chick embryo than the rat embryo could be associated with their classification as atricial and precocial animals, respectively. The growth of white matter within the neural tube begins before the motor rootlet emergence. The number of axons per motor rootlet bundle increased over time. The basal lamina of the CNS surface is continuous with that of the motor rootlets at E12 while it is absent between the CNS surface and the apposing BC cells, at the SEZ. The intraepithelial cells possessed the largest cell volume and the leptomeningeal cells the smallest. The loose network of radial glial cell end feet forming the rat glia limitans at E11 and E12 would facilitate its penetration by outgrowing motor axon bundles. |
| Subject |
Rats -- Nervous system -- Anatomy.
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| Collection |
Theses Ph.D.
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Theses Anatomy Department
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| Description |
2 v. : ill. ; 30 cm. |
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