Modules are like legos, interactions are the different ways you can snap them together • various different ways things can fit together and “work” ← ← Selection can then act on this variation ← ← since development is hierarchical w/ many stages/units/interactions great opportunity for change (descent w/ modification) ← ← Origins of Muscles
• the mesoderm along the central axis: segmented into somites by homeobox ( Hox ) genes • somites (paraxial mesodermal swellings) differentiate o dermomyotome: on dorsal side muscle, inner dermis myotome: differentiates later to become muscle dermotome: differentiates later to become inner dermis o sclerotome: on ventral side bone cartilage • ALSO, the notochord below and ectoderm above the neural tube induce the neural tube to send out branches of cells o upper (dorsal) cells sensory neurons o lower (ventral) cells motor neurons • in each somite, the myotome cells migrate laterally bring w/ them their bundle of sensory and motor nerves muscles and nerves are integrated as they migrate! ← ← How are muscles and nerves connected to the skeleton? • sclerotomes = vertebral cells; connected tissue precursor cells o condese around notochord and neural tube • sclerotome in each segment becomes a vertebra around the notochord (which remains a gelatinous substance in the intervertebral discs ← ← For each segment of the body we have: • a vertebra • myotome to make muscles • sensory and motor nerves ←
← myotome and sensory & motor nerves all travel together •
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- Spring '08
- Developmental Biology, Neural tube