Chapter 13: Neural Tube Formation Flashcards
outer germ layer covering late-stage gastrula
ectoderm
3 major components of ectoderm
1) surface ectoderm/epidermis 2) neural plate 3) neural crest
the neural plate is induced by the ___ plate and ___ during gastrulation. The neural plate of the ectoderm forms the ___ ___.
the neural plate is induced by the PRECHORDAL plate and NOTOCHORD during gastrulation. The neural plate of the ectoderm forms the NEURAL TUBE.
The neural crest can be found between the ____ and the ___ ___> Cells of the neurla crest delaminate from these other epithelia at the midline and migrate away between the structures to generate the ___ nervous system
The neural crest can be found between the EPIDERMIS and the NEURAL PLATE. Cells of the neural crest delaminate from these other epithelia at the midline and migrate away between the structures to generate the PERIPHERAL nervous system
the neural crest gives rise to the ___ NS, the neural plate gives rise to the ___ NS.
the neural crest gives rise to the PERIPHERAL NS, the neural plate gives rise to the CENTRAL NS.
Neurulation. When does it happen?
the process by which the three ectodermal regions are actually made distinct from each other. Happens right after gastrulation
Neurula.
an embryo undergoing neurulation.
ectoderm specification is accomplished during gastrulation and before via regulation of _____ gradients. Explain
BMP.
high BMP = epidermis.
Intermediate BMP = neural crest cells
low BMP = neural plate (due to sox expression)
the neural plate is characterized by the expression of ____ transcription factor. What is this TF’s role?
characterized by the expression of SOX1-3. Sox activates genes that specify cells into neural plates. It also inhibits the formation of the epidermis and neural crest by blocking the transcription and signalling of BMPS.
What must neural plate cells do before they can form a nerual tube?
originally, the neural plate cells are still ectoderm, and they lay on the surface of the embryo, but they must migrate inwards so that the CNS is not on the outside of the body lol.
- this migration inwards is accomplished via NEURULATION
OUTLINE the 2 principle modes of neurulation
1) primary neurulation: cells surrounding neural plate directs the neural plate cells to proliferate, invaginate into the body, and separate from the surface ectoderm to form the tube.
2) secondary neurulation: neural tube arises from mesenchymal aggregation into a SOLID CORD that subsequently develops cavities to create a hollow tube.
primary neurulation forms ___ portion of the neural tube, whereas seconday neurulation forms the ___ portion of the neurual tube.
primary neurulation forms ANTERIOR portion of the neural tube, whereas seconday neurulation forms the POSTERIOR portion of the neurual tube.
When does neurulation end?
when the anterior and posterior neural tubes meet in the transition zone in the middle. This middle portion then requires junctional neurulation: combination of primary and secondary neurulation mechanisms.
Primary Neurulation:
After the neural plate forms, the edges thicken and begin to curl up to form ___ ___ and an underlying ___ ___, which divides the further right and left sides of the embryo.
After the neural plate forms (due to sox1-3 TF expression in this region of the ectoderm, resulting in BMP inhibition), the edges thicken and begin to curl up to form neural folds and an underlying neural groove, which divides the further right and left sides of the embryo.
primary neurulation:
The neural folds on the lateral sides of the neural plate migrate towards the midline of the embryo, eventually fusing to form the ___ ___ beneath the overlying ectoderm.
The neural folds on the lateral sides of the neural plate migrate towards the midline of the embryo, eventually fusing to form the NEURAL TUBE beneath the overlying ectoderm.
4 basic stages of primary neurulation (recall 1’ neurulation is the process of cells surounding neural plate cells directing the neural plate cells to proliderate, invaginate into the body, and separate from the surface ectoderm)
1) elongation and folding of the neural plate
2) folding/bending of neural plate
3) convergence of the neural folds
4) closure of the neural tube
In the first stage of 1’ neurulation, elongation and folding of the neural plate occurs. During this stage, cells in the nerual plate ____ in an ___-____ axis manner. What does this allow for?
. During this stage, cells in the nerual plate PROLIFERATE in an ANTERIOR-POSTERIOR axis manner. ALLOWS FOR AXIAL EXTENSION
in the second stage of 1’ neurulation, the neural plate bends and folds. This is due to the formation of hinge points.
- in vertebrates, the cells in the midline of the neural plate forms ___ ___ __, which are anchored to the notochord beneath them, forming a hinge, which allows for formation of ___ ___ . The hinge works through ___ ___ constriction.
in vertebrates, the cells in the midline of the neural plate forms medial hinge point, which are anchored to the notochord (formed by the dorsal mesoderm) beneath them, forming a hinge, which allows for formation of neural groove. The hinge works through actin asymmetrical constriction.
Primary neurulation:
After formation of the medial hinge point, there is a convergence of the neural folds. How does this happen?
there are two dorsolateral hinge points (DLHPS) that form and are attached to the SURFACE ECTODERM (the medial HP is attached to mesodermal-notochord). Each hinge directs the movement of cells around it. Continued convergence of surface ectoderm pushes toward the midline of the embryo, providing another motive force for bending the neural plate, causing the neural folds to converge.
Last stage of primary neurulation:
the neural folds are continued to be brought together by the hinges until they contact each other. The folds adhere to each other, and the nerual and surface ectoderm are now separate from one another. the cells at the ____ of the nerual folds ____ and become _____, ensuring that the nerual tube and outer epidermis are independent structures.
the neural folds are continued to be brought together by the hinges until they contact each other. The folds adhere to each other, and the nerual and surface ectoderm are now separate from one another. the cells at the apex of the nerual folds delaminate and become neural crest cells, ensuring that the nerual tube and outer epidermis are independent structures.
epithelial cells in the MHP and HLDP undergo ___ ___ to become wedge shaped along the apicobasal axis due to contraction fo ____ complexes at the ___ ASPECT of the cell.
epithelial cells in the MHP and HLDP undergo APICAL CONSTRICTION to become wedge shaped along the apicobasal axis due to contraction fo ACTINOMYOSIN complexes at the APICAL apsect of the cell. (the nucleus becomes displaced towards the basal aspect of cells, increasing their volume)
