Development of Muscular System Flashcards
What does sclerotome become?
mesenchyme –> bone either through intramembranous ossification or endochondral ossification
What does the sternum develop from?
somatic lateral plate mesoderm –> sternal bars –> sternum
What part of the sclerotome do all the processes of a vertebra come from?
caudal dense part
What are the hypaxial divisions?
cervical myotomes
thoracic myotomes
lumbar myotome
sacrococcygeal myotome
What do thoracic myotomes form?
lateral and ventral flexor muscles of vertebral column
What is prune-belly syndrome?
What is it due to?
partial or complete absence of abdominal musculature; primarly in males; associated w/ failure of testes to descend and malformation of urinary tract and bladder
due to absence/abnormality of hypomere migration
As you go superior to inferior/cranial to caudal, what happens to hox genes?
go up in number
What is the basic process of hyaline cartilage formation?
chondrification centers –> prechondrocytes –> chondroblasts –> chondrocytes
What is pectus excavatum?
What causes it?
“funnel chest”; causes SOB, exercise intolerance, can shift heart
unknown cause
What part of the mesoderm becomes the somites?
paraxial mesoderm
What is a cervical rib and what is its clinical significance?
extra rib(s) that form on cervical vertebrae; can compress brachial plexus which can cause pain
What does the hypomere become?
hypaxial muscles = all muscles besides true back muscles
innervated by ventral rami
What do cervical myotomes form? (4)
scalene, prevertebral, geniohyoid, and infrahyoid muscles
What part of the somite becomes sclerotome?
Where does it migrate?
ventromedial somite –> migrates around notochord and neural tube –> becomes vertebrae
What does the dorsolateral part of a somite become?
myotome and dermatome
become muscle and dermis, respectively
What happens in a gain of function mutation of a hox gene (expressed where it is not supposed to be)?
caudalization of area where it is newly expressed
What does the annulus fibrosus form from?
sclerotome –> fibrocartilage –> annulus fibrosis
What is endochondral ossification?
What bones do this?
mesenchyme –> hyaline cartilage –> bone
long bones, most bones except flat ones of skull and face
What does the epimere become?
epaxial muscles = true back muscles
innervated by dorsal rami
What happens in a loss of function mutation of a hox gene?
cranialization
area will look like whatever is superior to it
What is intramembraneous ossification?
What bones do this?
mesencyme –> directly to bone
flat bones of skull, face, mandible, clavicle
What do Hox genes do?
control the body plan along a cranio-caudal axis
In what direction does the cephalic loose side of the sclerotome migrate?
superior/cephalic–> fuses with dense part of sclerotome above –> vertebra
What are the two parts of the myotome?
epimere
hypomere
What do ribs form from?
sclerotome cells that grow out of costal processes on early vertebrae
costal cartilage also comes from sclerotome
What side of the sclerotome is the loose part?
cephalic/head side
What is pectus carnatum?
what causes it?
“pigeon chest” usually causes no symptoms; pts remove for aesthetic purposes
unknown cause
What does the nucleus pulposus form from?
notochord
What side of the sclerotome is the dense part?
caudal/tail side
What is poland syndrome?
What is it due to?
absence of pectoralis major and minor
sometimes absence of ribs
due to absence/abnormality of hypomere migration
What does the sacrococcygeal myotome form?
pelvic diaphragm
What does the lumbar myotome form?
quadratus lumborum
In what direction does the caudal dense part of the sclerotome migrate?
caudal/inferior –> fuses with the loose part of the sclerotome above –> vertebra
