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The triple layered arrangement seen in the spinal cord (ependymal, mantle and marginal layers) continues into the caudal portion of the brain (the medulla oblongata), but becomes more complex cranially. In the brain, the neuronal cell bodies comprising the grey matter become clustered into groups called nuclei (singular - nucleus). Nuclei in the central nervous system are analogous to ganglia in the peripheral nervous system. A nucleus is composed of clusters of neuronal cell bodies and should not be confused with the nucleus contained within each cell (it's the same word referring to two different things again - what a world, what a world...). In the some parts of the brain, neurons and neuroglia differentiating from the mantle layer of the original neural tube migrate outwards through the white matter (myelinated axons) of the marginal layer where they form a peripheral, multi-layered covering of grey matter. This outer covering of grey matter on the cerebral hemispheres is called the cerebral cortex (cortex means "bark" in Latin, inferring the peripheral grey matter covers the exterior of the cerebral hemispheres as bark covers the exterior of a tree - knock on wood?!). The cerebellum also has a cerebellar cortex which develops in a similar way. NOTE: Be careful not to get cerebrum (or cerebral) and cerebellum (or cerebellar) mixed up, either while you are reading this or when you are answering test questions. This is very easy to do and can lead to a lot of confusion (as well as lost marks for answers you knew...).
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These coloured diagrams that follow show the developed
brain in the frog (amphibian), bird (avian) and cat (mammal). The various
areas have been coloured to give you an idea of the differences and similarities
between the species. Note that all vertebrates have the same basic brain
structure. The differences seen between species results from the differences
in the degree of development of the five embryonic subdivisions. Different
parts of the brain may be specialized in different vertebrate classes.
The relative growth of regions may be considerably different leading to
one region overgrowing another region. (Name the five subdivisions, including
the three primary divisions they developed from, and what they become
in the adult brain. Answer - use your
browsers "Back" button to return to this page). To get a feel for this,
please an animation of brain development.
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| Frog brain:
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| Bird brain(!):
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| Cat brain:
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View an Animation of Brain Development
View a Chart of Brain Development
View a Schematic of Brain Development
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Here we see a sagittal section through
a mouse cerebellum. The outer portion is composed of grey matter in two
layers: the molecular layer (outer, lighter) and the granular layer (inner,
dark). The white matter is seen in the middle of the cerebellum. Note
the many convolutions of the cerebellum, which increase cerebellar cortical
(surface) area, as did the convolutions in the cerebral hemispheres. The
tissue seen below the cerebellum is the medulla oblongata (M) and the
space between the medulla oblongata and the cerebellum is the 4th
ventricle (V). Anterior is to the right in this picture.
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This is a high power image of the cortical
area seen in the magenta box on the image to the left. From left to right
we see the outer molecular layer (ML), the single row of Purkinje cells
(P), the inner granular layer (GL) and a thin strip of the white matter
(WM) occupying the central portion of the cerebellum. Purkinje cells are
large neuronal cells with numerous dendrites which are characteristic
of the cerebellar cortex.
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| Top of the Page |
| Review Development and Differentiation of the Neural Tube |
| Back to the Histology II index |
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Special thanks to Hans Christoffersen for the preparation of this page.
Send comments to:
Sandra K. Ackerley (),
Department of Zoology, University of Guelph, Guelph, Ontario,
Canada N1G 2W1.
