Development Of Vertebral Column Group 1


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Development Of Vertebral Column Group 1

  1. 1. Group 1 – SEM IV – 2010 The Development Of The Vertebral Column A. Stage of formation of mesenchymal vertebral column.  Time development : during 4th week 1) Migration of sclerotomes : the sclerotomes migrate ventromedially to surround the spinal cord and notochord forming long mesenchymal column this column retains its segmental origin as the sclerotomic segments are separated by less dense areas containing the intersegmental arteries 2) Differentiation of sclerotomic segment : -Each sclerotome segment is differentiated into : a. less densed cephalic part b. more condensed caudal part 3) The development of intervertebral disc : Mesenchymal cells between the cranial and caudal parts of each sclerotomic segment do not proliferate and give rise to the intervertebral discs The peripheral part of which will form rings of fibrous tissue and is called annulus fibrosus that surround the notochord the enclosed notochord expands and undergoes nucoid degeneratiom and form the central soft part of intervertebral disc called nucleus pulposus So in the intervertebrae disc there are two regions, the inner region is nucleus pulposus and the outer region is annulus fibrosus. 1 By : Khalida , Yasmin & Abrar
  2. 2. Group 1 – SEM IV – 2010 4) The development of the body (the centrum) of the vertebra : The remaining caudal condensed part of each scelorotomic segment joins the cephalic less condensed part of scelorotomic segment caudal Form mesenchymal centrum ( the primordium of the body of vertebra) The notochord degenerates and disappears 5) The development of neural arch : Scelorotomic tissue migrates backwards from both sides of the centrum of vertebra to surround the neural tube The neural spine forms at the point of meeting of neural arch,posteriorly. Sclerotomic tissue also extends laterally from both sides of the centrum to form 2 processes (costal process ventrally, transverse process dorsally) B. Stage of formation of cartilaginous vertebral column  Time of appearance of chondrofication centres : during 6th week  Process of chondrofication : 2 centres of chondrofication appear in centrum of vertebra They fused together at the end of embryonic period (8th week) Centres of chondrofication appear in neural arches They fuse with each other and with the centrum The spinous and transverse processes develop from extension of chondrofication centres in the neural arch 2 By : Khalida , Yasmin & Abrar
  3. 3. Group 1 – SEM IV – 2010 C. Stage of ossification of vertebral column Primary ossification centers Secondary ossification centers End of 8th week Time of After puberty development 3 primary ossification centers Number 5 secondary ossifation cernters i. 1 in the centrum i. 1 for the tip of the spinous ii. 1 in each half of neural arch process ii. 1 for the tip of each transverse process iii. 1 for the superior rim of the vertebral body iv. 1 for inferior rim of the vertebral body Process of ossification: Fate of notochord:  At birth each vertebra consists 1. The most cranial part of the of 3 bony parts connected by notochord is incorporated in the cartilages. basilar part of the occipital bone  The bony halves of the vertebral ant the posterior part of body of arch fuse together during the 1st sphenoid bone. 3 to 5 years. 2. The parts of the notochord in the  The arches articulate with the bodies of the vertebrae centrum at cartilaginous degeneration and disappear. neurocentral joints. 3. The parts of the notochord in  These joints disappear when the between the bodies of the vertebral arch fuses with the vertebrae undergo mucoid centrum during the 3rd to 6th degeneration to form the nucleus year. pulposus. Fate of costal processes: 1. In cervical region  they form the anterior and lateral boundary of the foramen transversum. 2. In thoracic region they form the ribs. 3. In lumbar region they fuse with the transverse processes. 4. In upper sacral region  they unite tgether to form the anterior portion of the ala of sacrum. 3 By : Khalida , Yasmin & Abrar
  4. 4. Group 1 – SEM IV – 2010 Curvature of the vertebral column 1. Primary curvature  In the fetus the entire vertebral column is flexed anteriorly like a "C"  anterior concavity  maintained at birth  seen in the thoracic and sacral regions. 2. Secondary curvatures  develop after birth  seen in the cervical and lumbar region  appears at the 3rd to 6th month when the child holds its head up and the lumbar curvature in the 6th month to 2 year range when the child sits up Anomalies of vertebral column 1. Spina bifida  Incomplete fusion of the halves of the vertebral arches resulting in a midline defect usually in the lumbosacral region  Types : a) Spina bifida occulta( closed): 20% b) Spina bifida manifesta (open): 80% -Meningocele: CSF only -Meningomyelocele( CSF+ Nerve fibers) 2. Hemivertebra  Failure of one of the chondrofication centres to appear and subsequent failure of half of the vertebra to form producing scoliosis. 3. Scralization of the fifth lumbar vertebra  5th lumbar vertebra is fused with the sacrum and as a result the number of lumbar vertebrae is 4 and the sacrum is formed of 6 vertebrae. 4. Lumbrization of the first piece of sacrum  Separation of the first piece of the sacrum to form a separate vertebra so the number of lumbar vertebrae is 6 and the sacrum is only formed of 4 sacral vertebrae. 5. Congenital Kyphosis  due to either failure of segmentation or defect in formation of vertebral body elements. N/B : For pictures, please refer to group 1 student presentation. 4 By : Khalida , Yasmin & Abrar