DEVELOPMENT

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DEVELOPMENT OF THE MUSCULOSKELETON
SYSTEM N.S. Vasan, D.V.M., Ph.D.
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The musculoskeletal system develops from both the
mesodermal and Neural crest cells.
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• DIFFERNTIATION
• OF SOMITE
• Dermatome-(dorsolateral)
• Myotome-(dorsolateral)
• Sclerotome-(ventromedial)

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Muscle develops from the cells of the myotome.
with exception.
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BONE DEVELOPS IN MESENCHYME BY Intramebranous
Endochondral Ossification
Ossification Mesenchymal Condensation Mesenchymal
condensation Highly Vascularized Cartilage
formation Mineralization Mineralization Bone
formation Bone formation Flat bones
(Skull,Hip) Long bones (Limb,Vertebra)
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• PRIMARY OSSIFICATION CENTER
• Perichondrium deposits bone matrix at the
  periphery.
• Bone lengthen at the growth plate.
• At birth, diaphysis is mostly ossified, but
  epiphysis remains cartilaginous.

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• PRIMARY OSSIFICATION
• CENTER
• Appears during late embryonic
• period.
• Begin in long bones in the
• diaphysis (shaft).
• Expands towards Epiphysis
• (end of bone).

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• PRIMARY OSSIFICATION
• CENTER (continued)
• Perichondrium deposits bone matrix at the
  periphery.
• Bone lengthen at the growth plate.
• At birth, diaphysis is mostly
  ossified, but epiphysis remains cartilaginous.

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• SECONDARY OSSIFICATION CENTER
• Appears during the first few years of life.
• Appears in the Epiphysis.
• Spread in all directions.
• Growth plate remains cartilaginous until 20
  years.
• Growth plate becomes spongy bone fuse with
  epiphysis.
• This stops further elongation of bone.
• Pediatricians on X-ray use growth plate line to
  judge growth.

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• SECONDARY OSSIFICATION
• CENTER
• Appears during the first few
• years of life.
• Appears in the Epiphysis.
• Spread in all directions.

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• SECONDARY OSSIFICATION
• CENTER (continued)
• Growth plate remains cartilaginous until 20
  years.
• Growth plate becomes spongy bone fuse with
  epiphysis.
• This stops further elongation of bone.
• Pediatricians on X-ray use
• growth plate line to judge growth.

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• DEVELOPMENT OF JOINTS
• Joints provide mobility.
• Synovial joint.
• Cartilagenous joint.
• Fibrous joint.

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SYNOVIAL JOINT
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CARTILAGENOUS JOINT
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FIBROUS JOINT
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• DEVELOPMENT
• OF
• AXIAL SKELETON
• Vertebral column.
• Sternum.
• Ribs.
• Skull.

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The Vertebra, Rib Sternum develops from the
Sclerotomal Cells first a cartilaginous
primordia is formed, which later ossify.
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• The sclerotomal cells that
• Surrounds the notochord (N) give rise to the body
  of the vertebra.

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• The sclerotomal cells that
• Surrounds the neural tube (NT) give rise to
  vertebral arch - i.e Pedicle, Lamina, Transverse
  process, Spine.

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SCOLIOSIS
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Spina bifida occulta
Meningocele
Meningomyelocele
Rachischisis
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DEVELOPMENT OF STERNUM RIBS
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DEVELOPMENT OF STERNUM RIBS

• STERNAL BARS, FUSE OSSIFY.
• COSTAL PROCESSESS FORM RIBS.

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SCOLIOSIS
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• OMPHALOCELE.
• ECTOPIA CORDIS.

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WHAT HAPPENS TO THE NOTOCHORD?
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DEVELOPMENT OF THE SKULL Skull develops from the
mesenchyme around the developing
brain. Neurocranium-Protects the
brain. Viscerocranium-forms the skeleton of the
Jaw/Face. MOSTLY THROUGH INTRAMEMBRANOUS
OSSIFICATION.
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FIBROUS JOINT FONTANELLES
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CRANIOSYNOSTOSIS
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• NEW BORN SKULL
• Skull is large in proportion to face.
• Absence of paranasal air sinuses.
• Under development of facial bones.

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APPENDICULAR SKELETON Upper limb-Pectoral
girdle Lower limb-Pelvic girdle.

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LIMB DEVELOPMENT
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Proximo-distal development.
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• LIMB DEVELOPMENT points to remember.
• Limb develops from the lateral plate mesoderm.
• Induced by the adjacent somites.
• Through a series of Tissue Interaction.
• Number of Gene gene products are expressed
  differentially.
• Bones form by Endochondral Ossification.
• Musculature of limbs arise from Myotome of
  adjacent somites.
• Bones, Cartilages, Blood vessels, Connective
  tissues all develops from the lateral plate
  mesoderm.
• Develops Proximo-distal.