The Mammalian Nervous System - University of...
Transcript of The Mammalian Nervous System - University of...
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Timing of embryological development
EventMouse Human
Size (mm)
daySize (mm)
day
Fertilization 1 0.1 - 0.15 1
Implantation of blastocyst 4.5 0.1 - 0.2 7-12
Appearance of primitive streak 7 0.2 13
Gastrulation starts; notochord appears
7.5
0.4 16
Neural plate and groove appear 1.0 – 1.5 18
First (1-3) somites & neuromeres (in hindbrain) appear 8 1.5 – 2.5 20
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Timing of embryological development
EventMouse Human
Size (mm)
daySize (mm)
day
Neural tube starts to close (4-12 somites) 8 2.0 – 3.5 22
Cranial neuropore closes; optic vesicles appear (13-20
somites)
1.2 – 2.59 2.5 – 4.5 24
Caudal neuropore closes (somites; human 21-29; mouse 30-34)
3.3 – 3.9 10
3.0 – 5.0 26
Ventral and dorsal columns start to differentiate in spinal
cord and brain stem. Cranial nerve motor nuclei appear
(>30 somites)
4 – 6 28
Spinal nerves start to sprout, cerebral hemispheres
become visible3.5 – 4.9 10.5 5 – 7 32
Sensory and parasympathetic cranial nerve ganglia begin
to form5 – 6 11 7 – 9 33
Cerebellum starts to form 6 - 7 11.5 11 - 14 41
Gestation lasts 19-21 days for mice and about 266 days for humans
Formation of the yolk sac
8
Definitive yolk sac
Remnants of
primary yolk sac
Germ disk
Aminiotic
cavityAmniotic cavity
9
Week 3
HumanSummary
The primitive streak,
the notochord,
the neural plate and
first somites
Gastrulation.
Primitive streak and the embryonic
mesoderm and endoderm:
Gastrulation
11
The ectoderm, the mesoderm and the
endoderm are all derived from the epiblast
The notochord
12
Cells entering into the mesodermal layer via the
primitive node form a tube (the notochordal process),
which is converted into a solid cylinder (the notochord)
after fusing transiently with the endoderm.
The notochord
The notochord contributes to the development
of the intervertebral discs
The notochord does NOT contribute to the
bone structure of the vertebrae
The notochord does NOT contribute to the
formation of the nervous system.
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The somites
14
Cells entering the mesodermal layer via the primitive
groove and migrating laterally, form the paraxial,
intermediate and lateral plate mesoderms. The two
paraxial mesoderm columns (one on each side of the
midline) develop into somitomeres and then into somites.
Note: the first 7 (cranial) pairs of somatomeres do not form somites
Fates of the somatomeres and somites
Somatomere pairs 1 – 7 (cranial region) Striated muscles of face, jaws & throat
Somite pairs 1 – 4 (occipital region)
(4 pairs)
Occipital bone of the skull, bones around the
nose, eyes and inner ears, extrinsic ocular
muscles and tongue muscles.
Somite pairs 5 – 12 (cervical region)
(8 pairs)
Occipital bone (somite pair 5)
Cervical vertebrae and associated muscles,
part of neck dermis and upper limb muscles
Somite pairs 13 – 24 (thoracic region)
(12 pairs)
Thoracic vertebrae and muscles and bones
of thoracic wall, part of thoracic dermis, part
of abdominal wall and upper limb muscles
Somite pairs 25 – 29 (lumbar region)
(5 pairs)
Lumbar vertebrae, abdominal muscles and
dermis, lower limb muscles.
Somite pairs 30 – 34 (sacral region)
(5 pairs)Sacrum and associated muscles and dermis
Somite pairs 35 – 37 (coccygeal region)
(3 pairs)Coccyx
Somite pairs 38 – 44 (embryonic tail region) Will degenerate later
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Appearance
on
Day 20
~Day 30
From neural plate to neural groove
18
The prechordal plate
and the cranial portion
of the notochordal plate
induce the overlying
epiblast to differentiate
into a thick plate of
columnar, pseudo-
stratified
neuroepithelial cells, or
neurectoderm, called
the neural plate
First somites
appear in
mesodermal layer
Notochordal tube
fuses transiently
with the
endodermal layer
Notochordal
plate
Neurulation
22
The neural tube closes in
a zipper-like manner,
starting in the region of
the first 5 somites and
proceeding
bidirectionally.
Fates of
cells derived
from the
neural crest
26
Ganglion = a cluster of a
large number of neuronal
cell bodies outside of the
brain
Timeline of Spinal cord and
PNS development
27The neural crest plays a major role in PNS development
Formation of peripheral nerves
28
Peripheral nerves are
formed from cells
derived from both the
neural tube and the
neural crest
Sulcus
limitans
Roof plate
Floor
plate
Vertebrae, peripheral nerves & muscles
30
The vertebrae and
skeletal muscles
are derived from the
somites
Glossary
34
Brain regionPrincipal
structuresOther features
Prosencephalon
(forebrain)
TelencephalonCerebral
hemispheres,
Hippocampus
Lateral ventricle, Choroid plexus,
Commissures connecting
hemispheres (e.g. corpus
callosum)
Diencephalon ThalamusThird ventricle, Choroid plexus,
Pituitary gland
Mesencephalon (midbrain)
Relay center between the
forebrain and the hindbrain and
spinal cord. Cerebral aquaduct
(between 3rd & 4th ventricles)
Rhombencephalon
(hindbrain)
MetencephalonCerebellum,
Pons
Pons relays signals between
spinal cord and cerebral and
cerebellar cortices
MyelencephalonMedulla
oblongata
Relay center between spinal
cord and higher brain centers
The brain:
growing & folding
37
26 days
28 days
Future 4th
ventricle
Future pons
Med. Oblongata
cerebrum
Spinal cord
50 days
mes35 days
Midbrain
Future
cerebellum
The brain: growing & folding
39
mes
The cerebellum grows out
of the roof of the future
4th ventricle before it
closes
The telencephalon (future
cerebral hemispheres) grow up,
over and back over the
diencephalon (future [hypo-/epi-]
thalamus)