The growth of the human brain during the embryonic period proper

Abstract

Linear axes of the brain were measured in 143 human embryos from Carnegie stages 11 to 23 (3 1/2-8 postovulatory weeks). The embryos ranged from 3 to 30 mm in C.-R. length. Both Born reconstructions and serial sections of the central nervous system were used. The brain axes included were the fronto-occipital diameter, bitemporal diameter, and length and width of both the mesencephalon and cerebellum. A least squares line was fitted to the set of data points corresponding to each brain axis measured, and a t test verified that a linear model was an appropriate representation of the data. Based on these linear measurements it can be concluded that for forebrain grows more rapidly than the rest of the brain at the onset of tubular brain enlargement. Furthermore, as seen by comparing growth along two dimensions, the forebrain and midbrain grow at the same rate, whereas the cerebellum grows at different rates along the length and height axes. In addition, the cerebellum begins to grow later than the rostral part of the brain. Covariance analysis of the data points of the embryonic brain axes with data points of identical brain axes of the fetus showed that the measurements from the embryonic and fetal brain axes cannot be represented by a single regression line.

Morphology and morphometry of the human embryonic brain: A three-dimensional analysis

“…Jenkins (1921) measured the relative weight and volume of the component parts of the brain in 10 samples at different stages of development, including three samples from the embryonic period. With regard to the embryonic period proper, Desmond and O'Rahilly (1981) measured the major axes of the three embryonic brain vesicles and showed that the rates of growth of all three embryonic brain vesicles were much greater than the growth of the corresponding vesicles during the fetal period. Levitan and Desmond (2009) measured the areas of median sections two dimensionally to describe the growth of the three primary brain vesicles and to determine the change in the ratio of tissue area to cavity area.…”

Taspase1-dependent TFIIA cleavage coordinates head morphogenesis by limiting Cdkn2a locus transcription

“…Upon neurulation, the anterior neural plate forms a neural tube that subdivides into 3 vesicles: the prosen cephalon (forebrain), mesencephalon (midbrain), and rhomben cephalon (hindbrain) (9). When neural progenitor cells increase in population, the brain vesicles experience robust size expansion, with a cell cycle time of 7 hours in the prosencephalon and 8.5 hours in more caudal regions (10,11). Importantly, cell proliferation is tightly controlled during brain expansion (12,13).…”

The Longitudinal Growth of the Neuromeres and the Resulting Brain in the Human Embryo

“…The following three are used in vivo: transverse cerebellar diameter (in either an axial or a coronal plane); vermian craniocaudal diameter (height, but termed length by Dunn [1921]), and vermian anteroposterior diameter (termed height by Dunn [1921]!). The growth of the cerebellum is complicated and differs from that of the remainder of the brain in the fetal period [Dunn, 1921;Noback and Moss, 1956] and possibly also in the embryonic period [Desmond and O'Rahilly, 1981].…”

“…Jenkins, 1921]. Exceptionally a detailed study that includes the important bitemporal diameter in staged embryos was published [Desmond and O'Rahilly, 1981]. The neuromeres considered individually, however, were not a part of that study, nor were the complexities of the telencephalon, and the definitions of segments measured are in need of much greater precision.…”