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ANA 534 Emb Skele

learning objective answers to embryology limb muscle and skeletal development

Describe the different regions of mesoderm. Paraxial - closest to the midline (axis) of the embryo; intermediate - lies directly next to the paraxial; lateral plate - at the lateral edge of the mesoderm mass.
What are the two divisions of the lateral mesoderm and what does each develop into? Somatic (parietal) portion - forms serosa of the body cavities, long bones and connective tissue; splanchnic (visceral) portion - smooth muscle of GI system and serosa of body organs.
What is the space between these two lateral mesodermal plates and with what is it continuous? The space between lateral mesoderm plates is the intraembryonic coelom which is initially continuous with the extraembryonic coelom.
What are somites? What type of mesoderm produces them? This is paraxial mesoderm that becomes segmented along the length of the embryo. The somites are paired, and develop in craniocaudal direction.
Are occipital somites located cranial or caudal to cervical somites? Occipital somites are the most cranial of all – located in the head region, forward of the cervial somites. In fact, the cranial portion of the first cervical somite contributes to the occipital bone along with the occipital somites.
What are the specialized regions within a somite? Dermatome – develops into dermis of skin; Myotome – develops into muscles of the trunk and limb muscles; Sclerotome – develops into vertebral column.
What tissues forms the vertebral bodies? The vertebral arches? Bodies are ventral sclerotome; arches are dorsal sclerotome.
How would loss of the notochord affect vertebral development? notochord induces vertebral body formation development of the neural plate which develops into neural tube which becomes vertebral arches.
Why does spina bifida (an embryological development defect) result in an open vertebral column? Spina bifida is driven by failure of the neural tube to close - which results in a lack of induction of vertebral arch development – thus an open vertebral column.
Why are there only 7 cervical vertebra while there are 8 cervical somites? The cranial portion of cervical somite C1is incorporated into the occipital somites. The caudal segment of C8 is taken into the first thoracic vertebrae. This leaves 7 whole cervical vertebrae.
What does the nucleus pulposus represent? The remnant of the notochord that lies at the center of the intervertebral disc.
How are the ribs derived? Ribs grow out of vertebral arch tissue – so they are derived from sclerotome.
What part of the axial skeleton does the neural crest contribute to? Much of the skull is derived from the neural crest.
How does the derivation of skeletal muscle differ from that of smooth muscle? Skeletal muscles are from myotome mesoderm. Smooth muscle (as well as cardiac) is from the splanchnic mesoderm surrounding the particular organ.
What portion of the myotome are the epaxial muscles derived from? The hypaxial muscles? Epaxial muscles are the dorsal trunk muscles and are from the dorsal (epimere) portion of the myotome. The hypaxial muscles are the ventral trunk muscles & muscles of the limbs and are from the ventral (hypomere) portion of the myotome.
What is the apical ectodermal ridge? The ectodermal surface at the tips of the developing limb buds.
How does it affect limb development? What would happen if the apical ectodermal ridge was removed? It drives the proliferation of the tissue immediately below it, so it is really responsible for the elongation of the limbs. It does not drive differentiation. If the AER is removed the limb will fail to reach it’s expected length.
Created by: wiechartm



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