Adv Anat Embryol Cel
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Adv Anat Embryol Cel · Jan 2000
Review Comparative StudyDevelopment and regenerative capacity of descending supraspinal pathways in tetrapods: a comparative approach.
Throughout tetrapods a basic pattern in the organization of descending supraspinal pathways is present. The most notable difference between nonmammalian tetrapods and mammals is the apparent absence of somatomotor cortical areas giving rise to long descending projections to the spinal cord. The phylogenetic constancy of descending supraspinal pathways, at least of those arising in the brain stem, probably implies a comparable pattern of development, presumably a developmental sequence in the formation of these central motor pathways. ⋯ A special case is presented by anurans which in fact have two motor systems, a primary, transient motor system and a secondary, definitive motor system. Reticulospinal, interstitiospinal and vestibulospinal fibers innervate the spinal cord very early in development, well before the development of the hindlimbs. Rubrospinal fibers in
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Adv Anat Embryol Cel · Jan 1997
ReviewThe projections to the spinal cord of the rat during development: a timetable of descent.
In order to establish a timetable for the developmental descent of supraspinal descending projections in the rat, a retrograde neuronal tracer was injected into the spinal cord of rat fetuses and neonates both at different gestational ages and at different levels of the spinal cord. From the results of these experiments a position interval could be deduced for the leading descending fibers of each spinal-projecting nucleus at each age studied. The chronological series of position intervals of each supraspinal descending projection (the descent pattern) depicts the descent of its fiber front during development and allows for easy comparison between the various projections. ⋯ These results confirm that the generation sequence of the source nuclei is not a prime determinant of descent sequence along the spinal cord. The distance between the source nucleus and the entrance to the target seems of influence only in the most extreme cases (diencephalic source nuclei and the cerebral cortex). Descent velocity of the fiber fronts is not equal between different sources, nor is the descent velocity of specific fiber fronts constant over time. (ABSTRACT TRUNCATED)