Development of MSK Flashcards
What do cells derived from the primitive node create bilaterally along the neural tube?
Paraxial mesoderm, intermediate mesoderm, lateral plate mesoderm
What does the notochord form?
Nucleus pulposus
What does the paraxial mesoderm form?
Head and somites
somites form: Sclerotome, myotome, dermatome, syndetome, endothelial cells
What does the intermediate mesoderm form?
Kidney and gonads
What does the lateral plate mesoderm form?
Splanchic (circulatory system), somatic (limb bones, body cavity, pelvis), extraembryonic
At what stage in development does the paraxial mesoderm differentiate and form bilateral somite pairs?
At the end of the 3rd week
In what sequential fashion to somites form?
Cranial to caudal
By the end of the 5th week, how many somite pairs have formed?
42-44
What do the somites create?
Sclerotome, myotome, dermatome
Shortly after forming, each somite separates into subdivisions, what are those subdivisions?
Ventromedial, dorsal, intermediate
What does the ventromedial subdivision of the somite create?
Sclerotome
What does the dorsal subdivision of the somite create?
Dermamyotome – dermatome and myotome eventually
What does the intermediate subdivision of the somite create?
Syndetome = tendons of the vertebral column
The sclerotome will then further migrate and differentiate, what regions will it form?
Ventral, dorsal and lateral migrations
Where does the ventral sclerotome go and what will it form?
To surround the notochord to form the vertebral bodies
Where does the dorsal sclerotome go and what will it form?
To surround the neural tube to form the vertebral arch and spine
Where does the lateral sclerotome go and what will it form?
Out laterally to form the transverse processes and ribs
How does the neural tube and notochord become fully enclosed in sclerotome?
Because the somites are BILATERAL pairs
Sclerotomes are then divided cranial and caudal subdivisions due to what?
Gene expression and cell density
Cranial = loosely packed cells
Caudal = densely packed cells
What divides the cranial and caudal subdivisions of one sclerotome?
Intrasegmental boundary (von ebner’s fissure)
What cells help to form the IV disc?
Caudal cells
The remaining caudal cells then fuse with what?
Cranial cells adjacent to them to form the centrum
The notochord expands to form the nucleus pulposus and the caudal cells that migrated there do what?
Surround the notochord to form the annulus fibrosis
At what day in development do ribs begin to extend?
Day 35
Paired sternal bars arise form what layer?
Somatic layer of the lateral plate mesoderm
What gene codes for vertebral identity?
Hox
If Hox10 is removed, what vertebrae will form?
Thoracic
If Hox10 is added to another layer it is not commonly found, what vertebrae will form?
Lumbar
Pectus excavatum
Depressed sternum
Pectus carinatum
Anteriorly protruding sternum
“pigeon chest”
Describe myogenesis
Mesenchymal cells become myoblasts
myoblasts fuse to form myotubes
Myofilaments form in cytoplasm of myotubes
When is most skeletal muscle developed?
Before birth and by 1 year of age
What does the myotome divide into?
Epimere and hypomere
What will the epimere become?
Epaxial muscles of the neck and back
What will the hypomere become?
Hypaxial muscles everywhere else
What innervates epaxial muscles?
Dorsal rami
What innervates hypaxial muscles?
Ventral rami
What is poland syndrome?
Absence of pectoralis minor and partial loss of pectoralis major
Ipsilateral breast hypoplasia
More frequent in males
What is prune belly syndrome?
Loss of abdominal musculature; fluid accumulates that distends the abdomen
Can also result in cryptorchidism - failure of 1 or both testes to descend
What myotome division is responsible for poland syndrome and prune belly syndrome?
Hypomere
