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Human Neurobiology 910.217
Development of the CNS
Prof. Stuart Bunt Semester 2 2004
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Make yourself a brain
• The brain is probably the most
complex structure in the
universe for its size (putting
little green men aside).
• However, not only is it an
amazing structure, it is also self
assembling.
• When development goes wrong
it causes great problems as,
unlike for example cardiac
problems it does not always lead
to death. (1.3% of total births
have some abnormality)
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Formation of Ectoderm
• The environment of a cell
plus its genes and
developmental history
determine what a cell will
become
• Cells on the “inside” form
the embryo
• Cells next to the
blastoceol form the
endoderm
• Cells next to the amniotic
cavity form the ectoderm
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Neural plate
• One of the first signs of polarity
is the blostopore
• This may be laid down by
polarity in the egg following
fertilisation
• Much of developmental
complexity results from two
tissues getting together induce
the formation of a third
• This gives rise to the notocord
• The notocord induces formation
of the neural plate
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Species Variations
• Much experimental
neuroembryology done on
other species
• The invertebrates develop
differently
• Their neural cords are
ventral
• Blastopore at their mouths
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Determinate vs regulative
development
• Development determinate,
not regulative
• Half the cells leads to half
an embryo in invertebrates
• Not mammals
• Not man
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Neural plate forms the neural tube
• Cell movement and
contraction makes it form
a tube
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Anterior neuropore
• These close over time
• If anterior pore does not
close leads to anencephaly
(1:1000 births)
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Posterior neuropore
• Closure of this is complex
• partially due to “rolling”
• addition of a solid cord
posteriorly
• problems can occur if
these two parts do not join
• problems occur if the
neural tube fails to close
• problems if the
surrounding mesoderm
does not form complete
vertebrae.
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Lumbar cistern
• At 3 months cord runs the
length of the vertebrae
• As the vertebrae grow and
the spinal cord does not
• At birth stops at L3
• In the adult at L2
• use this space for epidural
anaesthesia
• lumbar puncture
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Spina bifida
• All these problems can lead
to varying severities of spina
bifida
– rachischisis
– spina bifida 1-4/1000
• occulta
• meningocele
• meningomyelocele
• from some hair over the base
of the spine
• to open spinal cord with total
paralysis below that point
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Arnold-Chiari malformation
• when the cord is
tethered by spinal
bifida it can be
pulled down
through the
foramen magnum
as the vertebrae
lengthen.
• More common in
the UK.
• In US isolated so
drain CSF in utero
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Detection
• can be detected by ultrasound
• samples of amniotic fluid can
confirm this
• looking for alpha fetal protein
released by the spinal cord
• older mothers - higher risk
• all pregnant women in Australia
given folic acid
• reduces incidence
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Neural Crest derivatives
• cells migrate out
• follow set paths
• differentiate into many
tissues
• dorsal root ganglia
• schwann cells (peripheral
nerve glia)
• facial muscles
• adrenal medulla
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Neuroepithelial cells “bounce” up
and down
Prof Stuart Bunt
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Human Neurobiology 910.217
Neural tube
• formation of basal and alar
plates
Prof Stuart Bunt
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Human Neurobiology 910.217
Brain section from spinal cord
Prof Stuart Bunt
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Human Neurobiology 910.217
Formation of
dilations
• forebrain prosencephalon
• midbrain mesencephalon
– cephalic flexure
• hindbrain rhombencephalon
– cervical flexure
• spinal cord
Prof Stuart Bunt
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Human Neurobiology 910.217
Telencephalon
• vesicles
• cortex and contents in a
“C” shape
• basal ganglia
• shaped growth (not a
simple folded sheet)
• diencephalon
– thalami
– hypothalamus half
from endoderm
• Rathke’s pouch from
roof of mouth
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Mesencephalon
• tectum (superior and
inferior colliculi)
• cerebral peduncles
Prof Stuart Bunt
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Human Neurobiology 910.217
Brain section from mesencephalon
Prof Stuart Bunt
[email protected]
Human Neurobiology 910.217
Rhombic flexure
• fourth
ventricle
• somatic
and
visceral
nuclei
Prof Stuart Bunt
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Human Neurobiology 910.217
Rhombencephalon
• metencephalon
– pons and
cerebellum
• myelencephalon
– brainstem/SC
junction
Prof Stuart Bunt
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Human Neurobiology 910.217
Brain section from rhombencephalon
Prof Stuart Bunt
[email protected]