Olfactory Structures in Staged Human Embryos

Abstract

The olfactory region was investigated in 303 serially sectioned human embryos, 23 of which were controlled by precise graphic reconstructions. The following findings in the embryonic period are new for the human. (1) The nasal plates arise at the neurosomatic junction, as do also the otic placodes. (2) Crest comes from the nasal plates later (stage 13) than the maximum production in the neural folds (stage 10). (3) The crest arises and migrates during a much longer time (at least until the end of the embryonic period) than the neural crest of the head, where origin and migration end at stage 12. (4) Olfactory nerve fibres enter the brain at stage 17, the vomeronasal fibres and those of the nervus terminalis at stages 17 and 18. (5) Fibre connections between the olfactory tubercle and the olfactory bulb, as well as those to the amygdaloid nuclei, forebrain septum, and hippocampus, develop during and after stage 17. (6) Mitral cells appear late in the embryonic period. (7) Localized, although incomplete, lamination of the olfactory bulb is detectable at the embryonic/fetal transition. (8) Tangential migratory streams of neurons, from stage 22 to the early fetal period, proceed from the subventricular zone of the olfactory bulb towards the future claustrum; they remain within the insular region but are separated from the cortical plate. (9) In future cebocephaly morphological indications may be visible as early as stage 13. The various findings are integrated by means of staging, and current information for the fetal period is tabulated from the literature.

Evolution of the base of the brain in highly encephalized human species

“…Evolutionary changes at the cribriform plate and the associated olfactory bulbs 11,42 and other endocranial parts we report here can implicate changes to the olfactory system that appear unique to modern humans. It is clear, however, that cognitive functions are incommensurable even with the most sophisticated measurement of brain impressions in endocranial casts.…”

“…5 ). Th e size of the cribriform plate is driven by the size of the olfactory bulbs due to coordinated embryological development 9,11 . Adult morphology of the cribriform plate is achieved early in ontogeny (4 years in humans 9 and probably even earlier in Neanderthals due to faster maturation rates 31 ).…”

“…Th erefore, the ca. 12 % larger cribriform plates and associated larger olfactory bulbs in modern humans may be suggestive of improved olfactory function 11,42,43 , although caution is warranted because of the small Neanderthal sample.…”

Rapid recovery of segmental neurological function in a tetraplegic patient following transplantation of fetal olfactory bulb-derived cells

“…31,32 We do not find such strong GFAP labeling in human OEG cultures and suggest that the observed cells may be astrocytes. It should be noted that it is not known with certainty at what developmental stage the human fetal OB becomes populated by OEGs 12,33,34 and the spectrum of cell types that are present in the primary cultures has not been published. Nor is known at what developmental stage conventional OEG markers begin to be identifiable.…”

“…10,11 However, it is not known at what developmental stage the human OB becomes populated by OEGs although it has been proposed that this may occur as early as 6.5 weeks of embryonic development. 12 Currently, a small-scale phase one clinical trial is exploring the safety and efficacy of transplanting adult nasal-derived putative OEGs into the chronically injured spinal cord, 13 but the number of patients treated with fetal cell preparations in China exceeds 500. The first and third authors of this case report acted as observers of this transplant series 14 over a 12-day period and wrote this report.…”