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Unformatted text preview: www.brain101.info 1 THE LOWER EXTREMITY Musculoskeletal Development Veins, Nerves, Miscellany Hip and Thigh Knee and Leg Ankle and Foot MUSCULOSKELETAL DEVELOPMENT MESENCHYME: Not the same thing as mesoderm. It means loosely organized connective tissue that is pluripotential. It is often derived from mesoderm but may also be derived from Ectoderm Neural Crest, as in (Conus area of heart, branchial arches, area around eyes). MESODERM: The middle germ-layer. SOMITES: They are on the dorsal (back) surface of the embryo. Schlerotome: Medial part, becomes the bone. At this stage it is pluripotential. Dermamyotome: Lateral-Plate Mesoderm -- lateral part, divides into dermatome and myotome to become skin and muscle. BONE DEVELOPMENT: From the pluripotential sclerotome. Osteoblasts: Form bone. Osteoclasts: Break down and reshape bone. Osteocytes: They are osteoblasts, once calcification has already formed around the bone. INTRAMEMBRANOUS OSSIFICATION: Forming bone directly from mesenchymal cells, as they differentiate to osteoblasts with no cartilage intermediate. This happens with flat bones like the skull. ENDOCHONDRAL OSSIFICATION: Forming bones with a Cartilage intermediate. The entry of a periosteal bud into the cartilage is the key stage -- this is what allows the avascular cartilage to form vascular bone. Increase in bone: o WIDTH-INCREASES IN BONE: Occurs by lateral bone-deposition, directly under the collar. The name of this deposited bone is periosteal bone . o LENGTH-INCREASES IN BONE: Occurs by growth at the Metaphyseal Plate, by proliferation of chondrocytes. Ossification centers: o PRIMARY OSSIFICATION CENTER: Periosteal bone development occurs at the primary center prenatally. This is in the middle of a lang bone -- the diaphysis . o SECONDARY OSSIFICATION CENTER: Develops at or after birth. These are located in the epiphysis , or near the ends of the bones. Pretty much all of the bones are present in a fetus already at 13-14 weeks, except for the sesamoid bones -- the tarsals and carpals. AXIAL SKELETON: Spine, skull, sternum, ribs APPENDICULAR SKELETON: Extremities, pectoral girdle (scapula), pelvic girdle www.brain101.info 2 SKELETAL DISORDERS SPINA BIFIDA: o Spina Bifida Occulta: The vertebral arch doesn't form fully. It is innocuous as long as it is localized only to one vertebrae. o Spina Bifida Occulta: More serious. As well as having no closure of the vertebral arch, you have a cyst. If it is just a little sac of meninges, it is called a meningocele and may not be a problem. Meningomyeloceles has both meninges and a piece of spinal chord in the cyst. This is a problem....
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This note was uploaded on 01/30/2011 for the course BIO 210 taught by Professor S during the Spring '10 term at University of Toronto- Toronto.
- Spring '10