Neurulation


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Neurulation

The process by which the vertebrate neural tube is formed. The primordium of the central nervous system is the neural plate, which arises at the close of gastrulation by inductive action of the chorda-mesoderm on the overlying ectoderm. The axial mesodermal substratum causes the neural ectoderm to thicken into a distinct plate across the dorsal midline and influences both its size and shape. Its shieldlike appearance, broader anteriorly and narrower posteriorly, presages the areas of brain and spinal cord, respectively. The lateral edges of the neural plate then rise as neural folds which meet first at the level of the future midbrain, above the dorsal midline, then fuse anteriorly and posteriorly to form the neural tube. The body ectoderm becomes confluent above the closing neural tube and separates from it. Upon closure, the cells (known as neural crest cells) which occupied the crest of the neural folds leave the roof of the tube and migrate through the mesenchyme to all parts of the embryo, forming diverse structures. The neural tube thus formed gives rise to the brain and about half of the spinal cord. The remainder of the neural tube is added by the tail bud, which proliferates a solid nerve cord that secondarily hollows into a tube. See Nervous system (vertebrate), Neural crest

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Neurulation

 

the embryonic process in chordates and man by which the neural plate emerges and folds to form the neural tube. The embryo undergoing neurulation is said to be in the neurula stage. During neurulation the rudiments of all the organ systems can be discerned in three germ layers.

The external germ layer, or ectoderm, thickens on the dorsal side of the embryo and forms the neural plate; the neural folds arise along the edges of the neural plate. The center of the neural plate deepens, and the crests of the neural folds approach each other and coalesce to form the neural tube, the rudiment of the nervous system. The remaining portion of the ectoderm closes over the neural tube and is transformed into an epithelial covering.

In animals in which the fertilized ovum undergoes total, or holoblastic, cleavage, the innermost germ layer, or endoderm, grows toward the dorsal side of the embryo and completely surrounds the gastrocoele, which thus becomes the primitive digestive cavity of the embryo. In animals with partial, or meroblastic, cleavage of the ovum, the ventral side of the intestine remains open; the intact yolk serves as the intestine’s lower wall.

The middle germ layer, or mesoderm, gives rise to (1) a median, longitudinal, rod-shaped strand of cells—the rudimentary notochord; (2) the somites, or mesodermal segments, that lie on either side of the rudimentary notochord; (3) the nephrotomes, or intermediate cell masses—segmental stalks that extend from the somites; and (4) the lateral plates. By the end of neurulation, the embryo acquires the structural plan of the adult organism: under the epithelium on the dorsal side is the neural tube; under the neural tube, the notochord; and under the notochord, the intestine. The anterior and the posterior segments of the embryonic body are distinguishable.

REFERENCES

See references under EMBRYONIC DEVELOPMENT.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

neurulation

[‚nu̇r·ə′lā·shən]
(embryology)
Differentiation of nerve tissue and formation of the neural tube.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Ptychoderid hemichordate neurulation without a notochord.
Open neural tube defects are NTDs in which the cerebrospinal fluid (CSF) frequently leaks through the present defect, which develops secondary to failed closure of the neural tissue during primary neurulation. Closed NTDs, on the other hand, are abnormalities encountered with a clinical picture of completely closed neural tissue, localized under an epithelialized layer, which occurs because of the failure of secondary neurulation (1, 5).
The process of neurulation in mammals and some other vertebrates is considered discontinuous because it occurs simultaneously at multiple sites along the neuraxis [215-219].
The development of the nervous system can be divided into three stages: gastrulation, primary neurulation and secondary neurulation.
Maintaining the appropriate balance between MMPs and their inhibitors (TIMPs and RECK) is absolutely essential for normal development, and disruption of this balance leads to defects in neurulation, organogenesis, and angiogenesis [4, 5, 8].
Alcohol exposure alters DNA methylation profiles in mouse embryos at early neurulation. Epigenetics 4(7):500-511, 2009.
This is a broad term used to describe a range of conditions that arise owing to errors in the early development of the nervous system, either during closure of the neural tube (also called primary neurulation, from conception to day 28) or subsequent embryological development (or secondary neurulation).
Recent reports demonstrated that alcohol exposure altered DNA methylation profiles in mouse embryos at early neurulation [101] and the patterning of 5-methylcytosine expression during neurogenesis [102].
The neuroectoderm folds dissociate from the superficial ectoderm in a process termed primary neurulation. This process explains the formation of most of the spinal cord.
Neural crest ontogeny during secondary neurulation: a gene expression pattern study in the chick embryo.
Neural tube defects are the result of unsuccessful neural tube closure (neurulation) in early embryonic life.
Arsenic-induced exencephaly in the mouse and associated lesions occurring during neurulation. Teratology, 28(3), 399-411.