Movie - Central Nervous System 3D stage 22
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| <Flowplayer height="415" width="400" autoplay="true">Stage22 CNS.flv</Flowplayer> | 3 Dimensional Reconstruction
Based upon a serial reconstruction from individual embryo slice images (27 mm Human embryo, Carnegie Stage 22 approximate day 56).
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Central Nervous System
During Week 5, as the neural tube continues to enlarge, the prosencephalon and rhombencephalon subdivide, while the mesencephalon expands. This gives rise to five secondary brain vesicles:
From the Prosencephalon:
- Telencephlon – forms the cerebral hemispheres
- Diencephlon – forms the thalamus and hypothalamus
Mesencephlon (doesn’t subdivide, expands) – forms the tectum and tegmentum
From the Rhombencephlon:
- Metencephlon – forms the pons and the cerebellum
- Myelencephlon – forms the medulla oblongata
In each of these areas, the central canal running through the CNS enlarges and forms the ventricular system within the adult brain.
As the tube grows in diameter, it also bends due to the rapid proliferation and ventral folding of the embryo. The resulting flexures that occur in the brain are called primary brain flexures. Three flexures occur:
- cervical flexure occurs between the brain and the spinal cord.
- cephalic flexure pushes the mesencephalon upwards
- pontine flexure occurs in the opposite direction from the other two; it generates the 4th ventricle
