MUSCULODEV'T. & LIMB FORMATION Flashcards
Describe how neurulation occurs in embryonic development.
The ectoderm is inducted to form the neural plate which then buckles to form the neural groove and neural folds. The neural folds fuse to make the neural tube which detaches from the surface ectoderm, making the notochord.
Describe the significance neural crest cells.
Neural crest cells migrate to different ectodermal regions of the body. They later become melanocytes in the skin, myenteric plexus in the gut or autonomic ganglia in the PNS.
Describe the significance of the neuroepithelium.
This lines the neural tube in early development. It forms two layers: inner mantle layer (for future spinal cord neurons) and the outer marginal layer (for future myelinated axons).
Describe what occurs in Hirschsprung’s disease.
Congenital megacolon leading to peristalsis and no differentiated gut cells in a portion of the GI system.
Compare the lengths of the spinal cord relative to the vertebral column in development, infants and adults.
Up to the 3rd month of dev’t. The spinal cord extends ALL down the fetal column. In a newborn, it ends at L3/L4, but in an adult it runs until L1/L2. The lower spinal roots exit at inferior levels.
Define the paraxial mesoderm
Differentiates into somites which make myotomes to make skeletal muscles or the tendons, ligaments and bone of the AXIAL skeleton.
Define the lateral plate of the mesoderm.
Differentiates to form the parietal mesoderm which forms the tendons, ligaments and bone of the APPENDICULAR skeleton (think LATERAL limbs).
Describe the two types of folds that occur in embryonic development.
Cranial-caudal folding is the fetal formation at the sagittal view. Lateral folding involves somites that fold towards the ventral body wall at the cross-sectional view. Limb buds extend from the anterior body wall soon after.
Define sclerotome mesenchyme.
A type of mesenchyme that forms the axial bone, cartilage and tendons. In the vertebrae, segments split in half, where the caudal end of the superior vertebra fuses with he cranial end of the inferior segment. This process is called resegmentation.
Define the somatic mesenchyme.
This type of mesenchyme forms the sternum as cartilage bars fuse then ossify. Also important for limb bud formation. Fibroblast growth factors induce its proliferation as limbs grow distally.
Describe endochondrial ossification.
Occurs at long bones as mesenchyme turns into cartilage then ossified into bone. Hardening occurs primarily at the diaphysis (in the middle) then at the epiphysis (at the ends). Leaves behind growth plates.
Explain the significance of growth plates.
These are places at the end of long bones where bone growth occurs, especially when influenced by growth hormones (such as before growth spurts).
Describe intramembranous ossification.
A more direct type of ossification where mesenchyme turns into osteoclasts for bone. A common site are at plates in the skull.
Describe spina bifida cystica.
A severe congenital defect where the meninges protrudes through the vertebral arches and skin.
“Cystic Mew-two”
Describe spina bifida occulta.
A mild congenital defect marked by a tuft of hair and dimple in the lower back. It involves a defect in the fusion of the vertebral arches but without herniation though the skin.
