11. 2. Differentiation of sclerotomic segments Each segments differentiated into Cephalic part (less condensed) Caudal part (more condensed)
12. 3. Development of intervertebral discs Densely packed cell move cranially to the middle part of each segments Form peripheral part – annulus fibrosus Enclosed notochord expands and undergo mucoid degeneration Form central part –nucleus pulposus
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15. 4. Development of the body of vertebrae Caudal remained part fuse with cephalic part adjacent to it to form mesenchymalcentrum Notochord degenerates and disappears when surrounded by vertebral body
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17. 5. Development of neural arch Sclerotomic tissue migrate backward from both side of centrum and surround neural tube. Neural spine forms at meeting point of neural arch Sclerotomic tissue also extends laterally from both sides of centrum form 2 processes Costal (ventral) Transverse (dorsal)
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19. Stage 2 Stage of formation of cartilaginous vertebral column Time of formation: 6th week
20. Process of chondrification 2 centers of chondrification in each centrum appear Fuse together at the end of embryonic period (8th week) form cartilaginous centrum – Centers of chondrification appear in neural arhes and fuse with each other and centrum – Chondrification spreads until a cartilaginous vertebral column formed
21. Stages of ossification of vertebral column Comprises of 2 stages: 1. primary ossification center 2. secondary ossification center
22. Primary ossification center Time of development: at the end of 8th week Number: 1. 3 ossification centers are present by the end of embryonic period 2. one in the centrum 3. one in the neural arch
23. Process: 1. bony halves of the vertebral arch fuse together during the first 3 to 5 years 2. the arches articulate with the centrum at cartilaginous neurocentral joints 3. these joints dissapear when vertebral arches fuses with the centrum during the 3rd to 6th years
24. Secondary ossification center Time of development: after puberty Number: the 5 secondary ossification center appears at, 1. tip of spinous process 2. tip of each transverse process 3. superior rim of the vertebral body 4. inferior rim of the vertebral body
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26. Fate of notochord Cranial part: merged with basilar part of occipital bone & posterior part of body of sphenoid Notochord located in the vertebra undergo degeneration and disappear The ones located in between undergo mucoid degeneration to form nucleus pulposus
27. Fate of the costal process Costal process results from ventrolateral outgrowth of the caudal, denser half of a sclerotome. In the cervical region: form anterior and lateral boundary of the foramen transversum In the thoracic region: form the ribs In the lumbar region: fuse with the transverse process In the upper sacral region: they unite to form the anterior portion of the ala of sacrum
29. Spina bifida Cause: incomplete fusion of halves of the vertebral arches resulting in midline defect usually in lumbosacral region Feature: It varies, but generally the small bones (vertebrae) that make up the spine don’t form fully and may have gaps between them.
30. Hemivertebra Cause: failure of one of the chondrofication center to appear and subsequent failure of half of vertebra to form Feature: defective vertebra produce scoliosis ( lateral curvature) Most likely to cause neurologic problems
31. Sacralization of 5th lumbar vertebra Cause: 5th lumbar is fused with the sacrum Feature: number of lumbar vertebra is 4 and the sacrum is formed of 6 vertebra
32. Lumbrization of first piece of sacrum to form separate vertebra Cause: separation of first piece of sacrum to form separate vertebra Feature: number of lumbar vertebra is 6 and the sacrum is only formed of 4 sacral vertebra
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