Formation Of Neural Tube Vesicles Figure 122 and Table 121

A. During week 4, the rostral part of the neural tube forms three primary vesicles: the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hind-brain).

B. FGF-8, Wnt-1, En-1, En-2, and Otx-2 appear to play a role in the fundamental patterning of the mesencephalon.

C. The Hox complex and Krox-20 appear to play a role in the fundamental patterning of the rhombencephalon.

Neural plate

Neural groove

Neural groove

Mesoderm

Ectoderm

Mesoderm

Encoderm

Neural Tube Neural Crest

leural crest -Neural tube

Sulcus Limitans

plate

Alar (sensory) plate

Sulcus limitans plate

Figure 12-1. (A-E) Transverse sections of embryos at various stages showing the formation of the neural tube and neural crest cells. (E) The sulcus limitans is a groove in the lumen of the neural tube and is an important anatomic landmark, because it separates the alar (sensory) plate from the basal (motor) plate.

D. During week 6, five secondary vesicles become apparent: telencephalon, dien-cephalon, mesencephalon, metencephalon, and myelencephalon.

A. Neuroblasts arise from neuroectoderm and form all the neurons within the central nervous system (CNS).

B. Glioblasts arise from neuroectoderm and form the supporting cells of the CNS. These supporting cells include:

1. Astrocytes, which contain glial fibrillary acidic protein (GFAP). Astrocytes surround blood capillaries with their vascular feet.

2. Radial glial cells, which are of astrocytic lineage and are GFAP-positive. They provide guidance for migrating neuroblasts.

3. Oligodendrocytes, which produce the myelin of the CNS.

4. Ependymocytes, which line the ventricles and the central canal.

5. Tanycytes, which are located in the wall of the third ventricle. Tanycytes transport substances from the cerebrospinal fluid (CSF) to the hypophyseal portal system.

6. Choroid plexus cells, which produce CSF. These cells are bound together by tight junctions that represent the blood-CSF barrier.

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