development MSK Flashcards
What are the layers of the mesoderm? Medial to lateral
Notochord, Paraxial mesoderm, Intermediate mesoderm, Lateral Plate mesoderm
The somite comes from the paraxial mesoderm.
Name the derivatives of the somite?
What are their functions?
Sclerotome (cartilage) Syndetome (tendons) Myotome (skeletal muscle) Dermatome (dermis, skeletal muscle) Endothelial cells (dorsal aorta)
When does paraxial mesoderm become somites?
End of week 3
How many pairs of somites are there?
Initially 38-39 pairs
After 5 weeks: 42-44
What part of somite does the SCLEROTOME come from?
Ventromedial part (through EMT)
What part of somite does the DERMOMYOTOME come from?
Dorsal part
It eventually splits into dermatome and myotome
What part of somite does the SYNDETOME come from?
Intermediate part
between sclerotome and myotome
What region of the sclerotome does the VERTEBRAL BODY come from?
Ventral Region
makes sense because it is closest to notochord and will wrap around
What region of the sclerotome does the VERTEBRAL ARCH AND SPINE come from?
Dorsal Cells
will surround neural tube
What region of the sclerotome does the TRANSVERSE PROCESS AND RIBS come from?
Lateral cells
How are sclerotomes subdivided in cranial/caudal portions?
Cranial= loose packed
Caudal= densely packed
Divided by intersegmental boundary (aka von Ebner’s fissure)
Due to gene expressivity and cell density
When do sclerotome cells condense around notochord?
End of week 4
How is a centrum formed?
dense (caudal) cells merge with loose (cranial) cells from next caudal sclerotome.
Where do intersegmental arteries lie?
On each side of the vertebral body
Why do we have 8 cervical nerves but only 7 cervical vertibrae?
Because the sclerotome from the occipital bone lies above C1
What becomes part of the nucleus pulposus?
The notochord. If it is not lost by adult, will form a cordoma (cancer)
What forms annulus fibrosis?
the caudal cells forming circular fibers around nucleus pulposis
When/ Where do ribs form?
During week 5. On costal processes of T vertebrae
cartilaginous during embryo, ossify during fetal period
Where do sternal bars arise from?
somatic layer of lateral plate mesoderm
When and in what direction do sternal bars fuse?
10 weeks. ventrolateral and move medially
What axis do Hox genes code for?
cranial-caudal (vertebral identity)
What gene is important at thoracic/ lumbar junction?
Hox10 (stops rib formation)
What can cervical ribs cause?
thoracic outlet syndrom.
Impinge on brachial plexus and/ or subclavian artery –> paresthesia
What is Pectus excavatum?
‘Funnel chest’
Depressed sternum, sunken posteriorly.
From extra cartilage weight
(more common in male)
What is Pectus carinatum?
‘Pigeon chest”
Sternal fusion anomoly
bilateral flattening of chest with anterior protrusion
What is epithelial mesenchymal transformation?
Myotomes become skeletal muscles of trunk and limbs
How do myoblasts form?
elongation of nuclei and bodies of mesenchymal cells (if MYOD expressed)
Product of myoblast fusion?
Myotubes
cylindrical, multinucleated structure
What forms in cytoblasm of myotubes?
myofilaments
Myotome divide into ______ and _______?
epimere and hypomere
Epaxial division forms ____?
extensor muscles of necks and back.
ex: erector spinae and transversospinalis
Hypaxial
Cervical myotomes:
scalene, prevertebral, geniohyoid, diaphram, and infrahyoid muscles
Hypaxial
Thoracic myotomes:
lateral and ventral flexor ms. of vertbral column
Hypaxial
Lumbar myotomes
quatratus lumborum
Hypaxial
Sacrococccygeal myotomes:
pelvic floor ms. striated ms. of anus and sex organs
What innervates epaxial muscles?
Dorsal ramus
What innervates hypaxial muscles?
ventral ramus
What is Poland Syndrome?
absent pec minor, partial pec major
ipsilateral migration
associated with syndactyly or brachydactyly
more in males
What is prune- belly syndrom?
Partial/complete loss of abdominal ms.
distended abdomen
Cryptochidism (testes don’t descend)
Malformation of UT and bladder
