Download The Mammalian Nervous System

The Mammalian Nervous
System
Development
1
Timing of embryological development
Mouse
Event
Size
(mm)
Fertilization
Implantation of blastocyst
Appearance of primitive streak
Human
day
Size
(mm)
day
1
0.1 - 0.15
1
4.5
0.1 - 0.2
7-12
7
0.2
13
0.4
16
1.0 – 1.5
18
1.5 – 2.5
20
Gastrulation starts; notochord appears
7.5
Neural plate and groove appear
First (1-3) somites & neuromeres (in hindbrain) appear
8
2
Timing of embryological development
Mouse
Event
Size
(mm)
Neural tube starts to close (4-12 somites)
Cranial neuropore closes; optic vesicles appear (13-20
somites)
1.2 – 2.5
Human
day
Spinal nerves start to sprout, cerebral hemispheres
become visible
3.3 – 3.9
(mm)
day
8
2.0 – 3.5
22
9
2.5 – 4.5
24
3.0 – 5.0
26
4–6
28
Caudal neuropore closes (somites; human 21-29; mouse 30-34)
Ventral and dorsal columns start to differentiate in spinal
cord and brain stem. Cranial nerve motor nuclei appear
(>30 somites)
Size
10
3.5 – 4.9
10.5
5–7
32
Sensory and parasympathetic cranial nerve ganglia begin
to form
5–6
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
3
Fertilization
4
Formation of the blastocyst
Week 1: human
5
Week 2
Human
Summary
Implantation and
formation of the
embryo
6
Implantation of the blastocyst
Germ disk
7
Formation of the yolk sac
Definitive yolk sac
Aminiotic
Amniotic cavity
cavity
Germ disk
Remnants of
primary yolk sac
8
Week 3
Human
Summary
Gastrulation.
The primitive streak,
the notochord,
the neural plate and
first somites
9
Appearance of the
primitive streak
10
Primitive streak and the embryonic
mesoderm and endoderm:
Gastrulation
The ectoderm, the mesoderm and the
endoderm are all derived from the epiblast
11
The notochord
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.
12
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.
13
The somites
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
14
Scanning electron microscopy
somites
Notocord & somites
Remove ectoderm
Days 19 - 20
15
Fates of the somatomeres and somites
Somatomere pairs 1 – 7 (cranial region)
Appearance
on
Day 20
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)
~Day 30
Striated muscles of face, jaws & throat
Somite pairs 38 – 44 (embryonic tail region)
Coccyx
Will degenerate later
16
Development of the nervous
system
17
From neural plate to neural groove
The prechordal plate
and the cranial portion
of the notochordal plate
induce the overlying
epiblast to differentiate
into a thick plate of
columnar, pseudostratified
neuroepithelial cells, or
neurectoderm, called
Notochordal
plate
Notochordal tube
fuses transiently
with the
endodermal layer
the neural plate
First somites
appear in
mesodermal layer
18
Scanning electron microscopy
Neural plate & groove
Day 19 - 20
19
Weeks 4 & 5
Human
20
Neurulation
Neural crest
Neural crest
Neural tube
notocord
21
Neurulation
The neural tube closes in
a zipper-like manner,
starting in the region of
the first 5 somites and
proceeding
bidirectionally.
22
Cellular structure of the
neural tube
23
Cells derived
from the
neural tube
Central canal
24
Fates of cells from the neural crest
25
Fates of
cells derived
from the
neural crest
Ganglion = a cluster of a
large number of neuronal
cell bodies outside of the
brain
26
Timeline of Spinal cord and
PNS development
The neural crest plays a major role in PNS development
27
Formation of peripheral nerves
Peripheral nerves are
formed from cells
derived from both the
neural tube and the
neural crest
Roof plate
Floor
plate
Sulcus
limitans
28
Spinal nerve formation
29
Spinal nerve
Vertebrae, peripheral nerves & muscles
The vertebrae and
skeletal muscles
are derived from the
somites
30
The notocord,
sclerotomes & the
vertebral column
31
Spinal cord
32
Timeline of brain development
pituitary
cerebellum
33
Glossary
Principal
structures
Other features
Telencephalon
Cerebral
hemispheres,
Hippocampus
Lateral ventricle, Choroid plexus,
Commissures connecting
hemispheres (e.g. corpus
callosum)
Diencephalon
Thalamus
Brain region
Prosencephalon
(forebrain)
Relay center between the
forebrain and the hindbrain and
spinal cord. Cerebral aquaduct
(between 3rd & 4th ventricles)
Mesencephalon (midbrain)
Metencephalon
Cerebellum,
Pons
Myelencephalon
Medulla
oblongata
Rhombencephalon
(hindbrain)
Third ventricle, Choroid plexus,
Pituitary gland
Pons relays signals between
spinal cord and cerebral and
cerebellar cortices
Relay center between spinal
cord and higher brain centers
34
The Neural Plate
& Neurulation
35
The brain: growing & folding
36
The brain:
growing & folding
26 days
28 days
35 days
mes
50 days
Midbrain
Future
cerebellum
Future 4th
ventricle
cerebrum
Future pons
Med. Oblongata
Spinal cord
37
40 days
Development of the
cerebellum
60 days
90 days
150 days
120 days
38
The brain: growing & folding
mes
The telencephalon (future
cerebral hemispheres) grow up,
over and back over the
diencephalon (future [hypo-/epi-]
thalamus)
The cerebellum grows out
of the roof of the future
4th ventricle before it
closes
39
The brain and the embryo
40
41
Sources
• Human embryology. W. J. Larsen, 2nd edition,
1997 (publ. Churchill Livinstone Inc)
• An introduction to embryology. B. I. Balinski,
2nd edition,1970 (publ. W.B. Saunders Company)
• The house mouse: atlas of embryonic
development. K. Theiler, 1989 (publ. Springer-Verlag)
42