MSK embryology
Terms
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- How many somites do we have?
- 42-44
- How many of each type of somite do we have?
-
4 occipital
8 cervical
12 thoracic
5 lumbar
5 sacral
8-10 coccygeal - what are the 3 parts of a somite?
-
Dermatome (dermis of skin)
Myotome (skeletal muscle)
Sclerotome (bone) - the myotomes in the thorax and abdomen are split into 2 regions called:
-
-the epaxial division (back and neck muscles)
-the hypaxial division (trunk and limb muscles) - the epaxial division of the trunk and abdominal somites is innervated by...
- the dorsal rami
- the hypaxial division of the trunk and abdominal somites is innervated by...
- the ventral rami
- Does vertebral column undergo intramembranous or endochondral ossification?
- endochondral
- at what week does muscle differentiation begin? i.e. what week do myoblasts form?
- week 4-5 (myoblasts form)
- at what week do limbs begin to develop?
- week 4
- what is the apical ectodermal ridge?
- a region of thickenined epithelium at the tip of a limb bud
- which determines the form and feather distribution: mesoderm or ectoderm?
- mesoderm
- which determines the feather type: mesoderm or ectoderm?
- ectoderm
- define amelia
- failure to develop a limb
- define meromelia
- development of a partial limb
- limb bud development is controlled by the homeobox genes. T/F?
- T
- What is the role of retinoic acid and morphogenetic proteins? If they fail to perform their role, what happens?
-
They determine the pattern of limb development and programmed cell death.
If they fail to perform their role, either polydactyly (too many digits) or syndactyly (fused digits) occurs. - at what week do nerves grow out to innervate developping muscles?
- week 5 (right when the myoblasts are forming)!
-
fill in the blanks.
When the nerve cord develops, it as _____ (more/less) neurons than it needs. If a given neuron finds a target it will _____ (die/survive). Else it will (die/survive) - more. survive. die.
- How many arteries to each somite?
- 1 (segmental artery)
-
of the 3 limb axes, what is the order in which they develop?
ant/post axis
proximal/distal axis
ventral/dorsal axis -
1. ant post
2. dorso-vental is determined 2nd
3. proximal-distal is determined last