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  • 1
    Electronic Resource
    Electronic Resource
    The development of the human brain and the closure of the rostral neuropore at stage 11 (1986)
    Springer
    Anatomy and embryology 175 (1986), S. 205-222 
    Details
    ISSN: 1432-0568
    Keywords: Human embryo ; Human brain ; Neural tube ; Rostral neuropore ; Neural crest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Twenty embryos of stage 11 (24 days) were studied in detail and graphic reconstructions of twelve of them were prepared. The characteristic feature of this stage is 13–20 pairs of somites. The notochord sensu stricto appears first during this stage, and its rostral and caudal parts differ in origin. Rostrally, the notochordal plate is being transformed into the notochord in a caudorostral direction. The caudal part, however, arises from the axial condensation in the caudal eminence in a rostrocaudal direction. The caudal eminence (or end bud) represents the former primitive streak. The somites are increasing in number at a mean rate of 6.6 h per pair. The rostral neuropore closes towards the end of stage 11. The closure is basically bidirectional, being more rapid in the roof region and producing the embryonic lamina terminalis and future commissural plate in the basal region. The caudal neuropore is constantly open. The brain comprises telencephalon medium (represented by the embryonic lamina terminalis) and a series of neuromeres: 2 for the forebrain (D1 and D2), 1 for the midbrain, and 6–7 for the hindbrain (RhA-C; Rh D is not clearly delineated). The forebrain still occupies a small proportion of the total brain, whereas the spinal part of the neural tube is lengthening rapidly. Some occlusion of the lumen of the neural tube was noted in 4 embryos, all of which had an open rostral neuropore. Hence there is at present no evidence that occlusion plays a role in expansion of the human brain. The marginal (primordial plexiform) layer is appearing, particularly in rhombomere D and in the spinal portion of the neural tube. The neural crest is still forming from both the (open) neural groove and the (closed) neural tube, and exclusively from both neural (including optic) and (mainly) otic ectoderm. The optic sulcus is now prominent, and its wall becomes transformed into the optic vesicle towards the end of stage 11. At this time also, an optic sheath derived from mesencephalic crest and optic crest is present. The mitotic figures of the optic neural crest are exceptional in being situated in the external part of the neural epithelium. The otic pit is becoming deeper, and its wall is giving rise to neural crest that is partly added to the faciovestibulocochlear ganglion and partly forms an otic sheath. The nasal plate does not yet give off neural crest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00389597
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The first appearance of the neural tube and optic primordium in the human embryo at stage 10 (1985)
    Springer
    Anatomy and embryology 172 (1985), S. 157-169 
    Details
    ISSN: 1432-0568
    Keywords: Human embryo ; Human brain ; Neural tube ; Neural crest ; Optic primordium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Thirteen embryos of stage 10 (22 days) were studied in detail and graphic reconstructions of most of them were prepared. The characteristic feature of this stage is 4–12 pairs of somites. Constantly present are the prechordal and notochordal plates (the notochord sensu stricto is not yet apparent), the neurenteric canal or at least its site, the thyroid primordium, probably the mesencephalic and rhombencephalic neural crest and the adenohypophysial primordium. During this stage, the following features appear: terminal notch, optic sulcus, initial formation of neural tube, oropharyngeal membrane, pulmonary primordium, cardiac loop, aortic arches 1–3, intersegmental arteries, and laryngotracheal groove. The primitive streak is still an important feature. Graphic reconstructions have permitted the detection of the telencephalic portion of the forebrain, for the first time at such an early stage. It is proposed that the remainder of the forebrain comprises two subdivisions: D1, which becomes largely the optic primordium during stage 10, and D2, which is the future thalamic region. The optic sulcus is found in D1 but does not extent into D2, as has been claimed in the literature. An indication of invagionation of the otic disc appears towards the end of the stage. As compared with the previous stage, the prosencephalon has increased in length, the mesencephalon has remained the same, the rhombencephalon has decreased, and the spinal part of the neural plate has increased fivefold in length. The site of the initial closure of the neural groove is rhombencephalic, upper cervical, or both. The neural plate extends caudally beyond the site of the neurenteric canal. Cytoplasmic inclusions believed to indicate locations of great activity were always detected in the forebrain (especially in the optic primordium), and also in the rhombencephalon, spmal part, and mesencephalon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00319598
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    Paper (German National Licenses)
    Fulltext
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