Download Development of Vertebrae

Development of Vertebrae
&
Intervertebral Discs
Development of the Vertebrae and Intervertebral Discs
Sclerotomal somitic mesoderm surrounds the neural tube and notochord.
Sclerotomal
Somitic
Mesoderm
Roof plate
Alar plate
(sensory)
Sulcus limitans
Basal plate
(motor)
Floor plate
N
Development of the Vertebrae and Intervertebral Discs
A. The vertebrae and annulus fibrosus of the intervertebral discs are derived
from sclerotomal somitic mesoderm
1. A derivative of somitic mesoderm
a. Which is a derivative of paraxial mesoderm
B. The nucleus pulposus of the intervertebral disc is derived from the notochord
Development of the Vertebrae and Intervertebral Discs
Neural Ectoderm
Surface Ectoderm
N
Mesoderm
Endoderm
Development of the Vertebrae and Intervertebral Discs
NE
N
SE
P
I
LP
Endo
NE = neural ectoderm
SE = surface ectoderm
N = notochord
P = paraxial mesoderm
I = intermediate mesoderm
LP = lateral plate mesoderm
Endo = endoderm
The mesoderm segregates into three solid rods of cells paralleling the
notochord: paraxial mesoderm, intermediate mesoderm, and lateral plate
mesoderm
Development of the Vertebrae and Intervertebral Discs
LP
I
L
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P
l
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P
P
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x
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N
N
o
t
o
c
h
o
r
d
X-section
Frontal view
The mesoderm segregates into three solid rods of cells paralleling the notochord: P, I, & LP
Development of the Vertebrae and Intervertebral Discs
X-section
LP
I
L
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m
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P
l
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P
P
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r
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x
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N
N
o
t
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c
h
o
r
d
Frontal view
Frontal
view
(rotated
90o)
X-section
view
(rotated
90o)
Development of the Vertebrae and Intervertebral Discs
Lateral plate mesoderm
Intermediate mesoderm
SE
Endo
Paraxial mesoderm
The paraxial mesoderm begins to migrate around the notochord
near the surface ectoderm and the endoderm.
Development of the Vertebrae and Intervertebral Discs
LP
I
P
N
The paraxial mesoderm begins to migrate around the notochord. There is further
remodeling of intermediate mesoderm and lateral plate mesoderm.
Development of the Vertebrae and Intervertebral Discs
Lateral plate mesoderm
Intermediate mesoderm
SE
Endo
Paraxial mesoderm
Vesicles form within lateral plate mesoderm and then coalesce.
Development of the Vertebrae and Intervertebral Discs
Lateral plate (LP) somatic mesoderm
Intermediate mesoderm
Intraembryonic
coelom
Somitic mesoderm
Lateral plate (LP) splanchnic mesoderm
The paraxial mesoderm differentiates into individual blocks of tissue (somitic
mesoderm) and the lateral plate mesoderm segregates into the LP somatic
mesoderm and LP splanchnic mesoderm with the formation of the intraembryonic
coelom (coalescence of forming vesicles).
Development of the Vertebrae and Intervertebral Discs
The paraxial mesoderm separates into blocks of tissue, called somites.
There are 44 pairs of somites adjacent to the notochord.
N
Frontal view
Somites
Development of the Vertebrae and Intervertebral Discs
Midsagital view = midline (viewing notochord only) and parasagital view = off
midline (viewing somites & notochord)
Ant.
N
Somites
Somites
Post.
Ant.
Parasagital view
Notochord
Midsagital view
Post.
Frontal view
Development of the Vertebrae and Intervertebral Discs
Future-neural tube lies dorsal to notochord/somite complex and endoderm
lies ventral to notochord/somite complex.
Ant.
N
Somites
Surface ectoderm
f-NT
Ant.
Post.
Endoderm
Somite
Notochord
Post.
Frontal view
Parasagital view
Development of the Vertebrae and Intervertebral Discs
Each somite divides into three regions: sclerotome, dermatome, and
myotome.
Ant.
N
Post.
Ant.
Post.
Frontal view
Parasagital view
Development of the Vertebrae and Intervertebral Discs
Each somite divides into three regions: dermatome, sclerotome, and myotome.
Dermatome
Sclerotome
Myotome
Development of the Vertebrae and Intervertebral Discs
Each somite divides into three regions: sclerotome, dermatome, and
myotome.
Ant.
N
The portion of the somite nearest the notochord and
neural tube differentiates into the sclerotome. The
sclerotomal somitic mesoderm will form the bone
(vertebrae), cartilage, tendons, ligaments, annulus
fibrosus of the intervertebral disc, fibrous connective
tissues, and meninges of the axial skeleton.
Post.
Ant.
Post.
Frontal view
Parasagital view
Development of the Vertebrae and Intervertebral Discs
Each somite divides into three regions: dermatome, sclerotome, and myotome.
Sclerotome
The portion of the somite nearest the notochord and neural tube differentiates into
the sclerotome. The sclerotomal somitic mesoderm will form the bone (vertebrae),
cartilage, tendons, ligaments, annulus fibrosus of the intervertebral disc, fibrous
connective tissues, and meninges of the axial skeleton.
Development of the Vertebrae and Intervertebral Discs
Each somite divides into three regions: sclerotome, dermatome, and
myotome.
Ant.
N
The portion of the somite nearest the surface
ectoderm differentiates into the dermatome. The
dermatomal somitic mesoderm will form the dermis
portion of the skin overlying the vertebral column (from
tip of transverse process to tip of transverse process).
Post.
Ant.
Post.
Frontal view
Parasagital view
Development of the Vertebrae and Intervertebral Discs
Each somite divides into three regions: dermatome, sclerotome, and myotome.
Dermatome
The portion of the somite nearest the surface ectoderm differentiates into the
dermatome. The dermatomal somitic mesoderm will form the dermis portion
of the skin overlying the vertebral column (from tip of transverse process to tip of
transverse process).
Development of the Vertebrae and Intervertebral Discs
Each somite divides into three regions: sclerotome, dermatome, and
myotome.
Ant.
N
The remaining portion of the somite differentiates
into myotome. The myotomal somitic mesoderm
will form the deep back and neck muscles
associated with the vertebral column. These
particular skeletal muscles are innervated by the
dorsal rami portion of a mixed spinal nerve.
Post.
Ant.
Post.
Frontal view
Parasagital view
Development of the Vertebrae and Intervertebral Discs
Each somite divides into three regions: dermatome, sclerotome, and myotome.
Myotome
The remaining portion of the somite differentiates into myotome. The myotomal
somitic mesoderm will form the deep back and neck muscles associated with
the vertebral column. These particular skeletal muscles are innervated by the
dorsal rami portion of a mixed spinal nerve.
Development of the Vertebrae and Intervertebral Discs
The sclerotomal portion of each somite further differentiates into two
regions: the anterior region is composed of loosely arranged cells, while the
posterior region is composed of densely packed cells.
Ant.
Loosely arranged cells
N
Densely packed cells
SE
f-NT
Post.
Ant.
Post.
Frontal view
Parasagital view
Development of the Vertebrae and Intervertebral Discs
The sclerotomal somitic mesoderm maintains the regional segregation, i.e.,
loosely arranged cranial region and densely packed caudal region, while it
increases in size and begins to surround the notochord and developing
neural tube.
Ant.
SE
N
Post.
Ant.
Post.
Frontal view
Parasagital view
Development of the Vertebrae and Intervertebral Discs
Some densely arranged cells move cranially, where they form the
intervertebral disc between the bodies of the vertebrae.
Ant.
Vertebra
Notochord (seen through
sclerotomal somitic mesoderm)
Ant.
Post.
Intervertebral disc
Post.
Frontal view
Parasagital view
Development of the Vertebrae and Intervertebral Discs
As the vertebral bodies expand, the notochord becomes extremely small. In
contrast, the notochord within the intervetebral disc expands to form its
gelatinous center, the nucleus pulposus.
Ant.
Vertebra
Parasagital view
Post.
Ant.
Intervertebral disc
Vertebral body
Post.
Nucleus pulposis of the IVD
Frontal view
Development of the Vertebrae and Intervertebral Discs
The nucleus pulposis is later surrounded by circularly arranged fibers
constituting the annulus fibrosus of the intervertebral disc. The annulus
fibrosus is formed by sclerotomal somitic mesoderm.
Ant.
Vertebra
Parasagital view
Post.
Ant.
Post.
Frontal view
Vertebral body
Intervertebral disc
Annulus fibrosus
Development of the Vertebrae and Intervertebral Discs
The nucleus pulposis and annulus fibrosus constitute the intervertebral
disc.
Nucleus pulposis of the IVD
Ant.
Vertebra
Parasagital view
Post.
Ant.
Post.
Frontal view
Vertebral body
Intervertebral disc
Annulus fibrosus of the IVD
Development of the Vertebrae and Intervertebral Discs
The sclerotomal somitic mesoderm of the vertebrae surrounding the neural
tube form the vertebral (neural) arch. It is eventually composed of the
pedicles, lamina, transverse processes, and spinous process.
Ant.
Vertebral arch
Post.
Ant.
Post.
Parasagital view
Frontal view
Development of the Vertebrae
The sclerotomal somitic mesoderm of the vertebrae surrounding the neural tube
forms the vertebral (neural) arch. It is eventually composed of the pedicles,
lamina, transverse process, and spinous process.
Vertebral foramen
Vertebral arch
Costal process
Notochord
Centrum
Development of Vertebrae
During the sixth week chondrification centers appear in each vertebra
Vertebral foramen
Chondrification
centers
Centrum
Development of Vertebrae
The two chondrification centers in each centrum fuse at the end of the
embryonic period to form a cartilaginous centrum
Vertebral foramen
Chondrification
centers
Cartilaginous centrum
Development of Vertebrae
Concomitantly, the centers in the vertebral arches fuse with each other
and the centrum.
Vertebral foramen
Cartilaginous
vertebral arch
Cartilaginous centrum
Development of Vertebrae
The spinous process and transverse processes develop from extensions of
chondrification centers of the vertebral arches. Chondrification spreads
until a cartilaginous vertebral column is formed.
Spinous process
Transverse process
Costal process
Development of Vertebrae
Ossification of typical vertebrae begins during the embryonic period and
ends by the twenty-fifth year.
Primary
ossification
centers
Development of Vertebrae
There are two primary ossification centers, dorsal and ventral, for the
centrum.
Primary
ossification
centers
Dorsal
Ventral
Development of Vertebrae
These primary ossification centers for the centrum soon fuse to form one
center.
Primary
ossification
centers
Development of Vertebrae
Three primary ossification centers are present by the end of the embryonic
period:
one in the centrum and
one in each half of the vertebral arch.
Primary
ossification
centers
Development of Vertebrae
Ossification becomes evident in the vertebral arches during the eighth
week. At birth each vertebra consists of three bony parts (vertebral arch,
costal processes, and centrum) connected by cartilage. The bony halves of
the vertebral arches usually fuse during the first 3-5 years.
Development of Vertebrae
Five secondary centers of ossification appear in the vertebrae after puberty:
one at the tip of the spinous process, one at each tip of the transverse
process, and two annular epiphyses, one on the superior and one on the
inferior rim of the vertebral body.
Spinous process
Transverse process
Annular rim of
vertebral body (x 2)