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Dev of Limbs

Development of limbs

Anomalies: Syndactyly Digits (either toes or fingers) are joined together and it is hereditary
What is central ray defect? Rays are missing, disruptions of the pattern for the formation of bones
Describe the somite migration Somite migration and differentitation has to be induced by structures that are located around it. After migration, the scleratome accumulates around the center structures and leave dermatome and myotome behind
What happens at about 5 weeks? The mesencyhme situates around notochord, chondrification takes place and it is bony. There are various islands of cartilage that are developing in the blastema
What happens at about 10 weeks? The vertebral are completely cartilaginous. Enchondral ossification kicks in and there are centers in the cartilage that are going to ossify
True or False: Everything is completely ossified in a newborn False: Almost everything is completely ossified except for the spinous process and head of rib
Where do the scleratomes migrate? Surround the notochord and leave the derma-myotome behind. The top scleratome and the middle scleratome accumulate around the center and separate so that there is a caudal half in each one and a cranial half in each one
Around the foramen magnum developed from what? Somitomeres up in the neck that are less organized but somite-like
What is spina bifida? The neural arch doesn't completely form. The spine is split.
What is a hidden spina bifida called? Spina bifida occulta
Do muscles or nerves migrate first? Muscles migrate first and nerves follow
What do tendons develop from? Resident Mesenchyme
True or False: There is a different ventral muscle mass and dorsal muscle mass True
What does the epimere develop into? Turns into the erector spinae muscles and the transversospinalis group
Where does the hyomere migrate? Towards the belly region and lateral wall. Hypaxial muscles: External, internal and innermost layers between the ribs or in the abdomen
What does the dermatomes become? The dermis of the skin and drags nerves along with it
Describe the dorsal ramus Both afferent and efferent. The efferent is going to the muscles of the back and the cutaneous is coming from the skin
When do we start to see lower limbs develop? At the 4th week. Limb comes out like a little flipper and hugs the body wall
Describe primitively dorsal vs. primitively ventral If muscle is primitively dorsal it extends, if it is primitively ventral it flexes
What runs along the pre and post axial border of the arm? Pre: Cephalic vein. Post: Basilic veain
Where is the apical ectodermal ridge located? On the apex of the developing limb bud and is made of ectoderm
What does the lateral plate mesoderm secrete? A factor that causes the resident mesenchyme to start to develop on the surface
What does the apical ectodermal ridge do? The apical ridge is induced and restricted. It induces the mesoderm underneath it to differentiate
What is progress zone? A region below the apical ectodermal ridge where there is proliferation of the mesenchyme but it doesn't differentiate
How can you tell the difference between dorsal and ventral surface? Dorsal is a little more rounded out and ventral surface is a little more hollowed out
What does the appearance of digits rely on? Apoptosis
Describe the development of the big toe/thumb vs. little toe/pinkie Mesenchyme respons to the orientation of elements such that the further away it is, it will develop into a big toe/thumb and the closer to the zone of proliferation is the structures that will be a pinkie/little toe
What is postaxial polydactyly? Numerus extra-added digits
How do bones develop? From the resident mesenchyme in the limb. they don't migrate, they develop there. It usually relies on the length of time that the mesenchyme is there, exposed to the apical ectodermal ridge. There will be a bone developing into a humerus



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