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MSK embryology


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How many somites do we have?
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?
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?
which determines the feather type: mesoderm or 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?
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

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