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29 Cards in this Set
- Front
- Back
Where are the somites located?
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On either side of the notochord/ neural tube region
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How many pairs of somites are formed? Where do most of them disappear from?
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44 - a lot disappear from the rostra somites (occipital region) and a large number in the coccygeal region dissapear
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When do somites form? It what direction do they form? When do they finish forming?
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Start forming by day 20 end at day 30 - formed from rostal to caudal
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What are the 3 regions of the somite from inner to outer? what do they form?
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the sclerotome - future axial
myotome- future skeletal muscles dermatome - future dermis of skin in axial regions |
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In what direction does the sclerotome migrate?
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Cells along its medial side begin to migrate towards the notochord and neural tube
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What creates the vertebral arch?
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the dorsally migrating sclerotome cells that pass posterior to the neural tube
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What creates teh vertebral body?
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The ventrally migrating sclerotome cells
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Why does the migrated sclerotome undergo programmed cell death?
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To shape the sclerotome into a primitive form of the vertebral body and neural arch
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Which somites makes up the vertebral body?
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A rostral and a cadual part of two different numbered somites
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Which somites does the spinal nerves go through?
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the same ones
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What does the first cervical somite form?
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rostal half - fuses with the lower occipital somites -- occipital bone
caudal - helps from the C1 vertebra |
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In what direction does the dermatome migrate?
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migrates from the lateral part of the somite
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What does the dermatome help form?
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the dermis of the skin everywhere except the head
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When does the myotome start migrating? What direction?
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Week 4 -- Ventraly and dorsally
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What does the ventrally migrating myotome form? The dorsal? what do they give rise to?
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Ventral - hypomere - muscles of body and limbs
Dorsal - Epimere - true back muscles |
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When do limb buds start to form? Where?
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end of the 4th week
Upper - C4-T1 Lower- L3-S3/4 |
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What are the limb buds mostly made out of at the end of 4th week?
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mostly somatic lateral plate mesoderm
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Why do the limb buds form?
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Apical ectodermal ridge --the overylying ectoderm a result of inductive influence
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What does the hypomere split into?
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ventral muscle mass -flexors, pronators, and adductors
Dorsal muscle mass - extensors, supinators, and abductors |
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What goes first into a limb bud? What follows
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the myotome and dermatome go first and the spinal nerves follow
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What do bones in the limbs develop from?
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somatic lateral mesoderm mesenchyme
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When does limb development start to occur? end?
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Day 24 for upper limb adn day 28 for lower
ends by the 8th week |
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When is the most sensitive time for limb development?
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during week 4-5
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How long does limb development last?
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5 weeks
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What is each limb bud composed of?
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a surface of ectoderm and a core of somatic mesoderm
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How is AER induced? what does it do?
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Apical ectodermal ridge --starts by the somatic mesoderm inducing the ectoderm to get thicker
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What does the AER signal to happen?
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Induces the mesoderm to continue to divide and results in the lengthening of the limbs
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What creates the digits?
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The AER is turned off between the future digits and now undergoes apoptosis
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Meromelia-
Amelia- Syndactyly - Phocomelia |
Meromelia- absence of part of a limb
Amelia- absence of 1 or more limbs Syndactyly -- webbing between digits Phocomelia- short, poorly formed limbs |