Development of vertebral column
Stages in the development of vertebral column
i. Stage of formation of mesenchymal vertebral column
ii. Stage of formation cartilaginous vertebral column
iii. Stage of ossification of vertebral column
1.migration of the sclerotomes
1.Stage of formation of mesenchymal vertebral The cell of the sclerotomes migrate ventromedially
column to surround the spinal cord and notochord, thus
Time of development : during the 4th week forming a long mesenchymal column. This column
retains its segmental origin as the scleromotic
segments are separated by less dense areas
containing the intersegmental arteries.
2.Differentation of the sclerotomic segment
Each sclerotomic segment is differentiated into:
a-Less condensed cephalic part.
b-More condensed caudal part.
3.The development of the intervetebral disc
Mesenchymal cells between cephalic and caudal
parts o f the original sclerotome segment do not
proliferate but ﬁll the space between two
precartilaginous vertebral bodies. The notochord
persists and undergoes mucoid degeneration in
this region and forms the nucleus pulposus,
which is later surrounded by circular ﬁbers of the
4.The development of the body (the centrum) of
The remaining caudal condensed part of each
sclerotomic segment joins the cephalic less
condensed part of the sclerotomic segment caudal
to it to form the mesenchymal centrum, the
primordium of the body of a vertebrae.
The notochord degenerates and disappears.
N.B: The body of each vertebrae develops from
two sclerotomic segments and so it becomes an
5.The development of the neural arch
Sclerotomic tissue migrates backwards from both
sides of the centrum of the vertebrae to surround
the neural tube (two pedicles and two lamina).
The neural spine forms at the point of meeting of
the neural arch, posteriorly.
Sclerotomic tissue ,also, extends laterally from
both sides of the centrum to form two processes:
a-Costal process ventrally
b-Transverse process dorsally
2.Stage of formation of cartilaginous vertebral Process of chondrofication:
column -Two centers of chodrofication appear in the
Time of appearance of the chondrofication centrum of the vertebrae. They fused together at
centers: during the 6th week. the end of the embryonic period (8th week)
-Centers of chondrofication appear in the neural
arches. They fuse with each other and with the
-The spinous and transverse processes develop
from extensions of chondrofication centers in the
3.Stage of ossification of vertebral column i. The primary ossification centers:
Time of development: At the end of the 8th week.
-Three primary ossification centers are present by
the end of the embryonic period
-One in the centrum
-One in each half of the neural arch.
Process of Ossification:
-At birth each vertebrae consists of three bony
parts connected by cartilages.
-The bony halves of the vertebral arch fuse
together during the first 3 to 5 years.
-The arches articulate with the centrum at
cartilaginous neurocentral joints. These joints
disappear when the vertebral arch fuses with the
centrum during the third to sixth year.
ii.The secondary ossification centers:
Time of development: after puberty
Five secondary ossification centers appear:
1.One for the tip of the spinous process.
2.One for the tip of each tranverse process.
3.One for the superior rim of the vertebral body.
4.One for the inferior rim of the vertebral body.
Fate of notochord:
1.The most cranial part
3.The part of the
of the notochord is
incorporated in the
2.The parts of the the bodies of the
basilar part of occipital
notochord in the bodies vertebrae undergo
bone and the posterior
of the vertebrae undergo mucoid degeneration to
part of body of sphenoid
degeneration and form the nucleus
1.In the cervical Fate of costal processes: 4.In the upper sacral
region: They form region: They unite to
the anterior and form the anterior
lateral boundary of 2.In the 3.In the portion of the ala of
the foramen thoracic lumbar region: sacrum.
transversum region: They fuse with
They form the
the ribs. transverses
Anomalies of the vertebral column
1)The spina bifida Cause : non-fusion of the embryonic halves of the
2)Hemivertebrae Cause: failure of one of the chondrofication centers
to appear and subsequent failure of half of the
vertebrae to form.
Feature: These defective vertebrae produce
scoliosis (lateral curvature)
3)Sacralization of the fifth lumbar vertebrae Cause: The 5th lumbar vertebrae is fused with the
Feature: Number of lumbar vertebrae is 4 and the
sacrum is formed of 6 vertebrae.
4)Lumbrization of the first piece of the sacrum to Cause: Separation of the first piece of the sacrum
form a separate vertebrae to form a separate vertebrae.
Feature: Number of lumbar vertebrae is 6 and the
sacrum is only formed of 4 sacral vertebrae.
5)Congenital kyphosis Feature: abnormality increased convexity in
curvature of the thoracic spine as viewed from side
6)Congenital scoliosis Feature: Lateral curvature of the vertebral column