B6.068 Prework 2: Bone Development and Axial Skeleton Flashcards
axial skeleton component
skull neck vertebral column ribs sternum
2 sections of the skull
neurocranium
viscerocranium
function of neurocranium
protects brain
- membranous part: flat bones, form vault and portion of base of skull
- cartilaginous part: sphenoid, ethmoid, base of occipital bones
function of viscerocranium
forms skeleton of face
- membranous part: largest component
- cartilaginous part: mandibular condyle
sources of head and neck structures
- paraxial mesoderm
- neural crest mesenchyme
- lateral plate mesoderm
head and neck structures formed by paraxial mesoderm
large portion of membranous and cartilaginous components of the neurocranium (skull)
head and neck structures formed by neural crest mesenchyme
face skeleton (viscerocranium) and cartilage parts of membranous and cartilaginous regions of neurocranium
head and neck structures formed by lateral plate mesoderm
laryngeal cartilages
formation of the neurocranium
flat, membranous bones are formed by mesenchyme via intramembranous ossification
needle like bone spicules radiate from primary ossification centers towards the periphery
how do neurocranium bones enlarge
bones enlarge by apposition of new layers on outer surface, and osteoclastic resorption og bone from inside
sutures
narrow seams of connective tissue
temporarily separate flat bones of skull
fontanelles
wide sutures at points where >2 bones meet
anterior fontanelle
where 2 frontal and 2 parietal bones meet - closes at 18 months of age
newborn skull during birth
sutures and fontanelles allow molding - the overlapping of skull bones
newborn skull after birth
membranous bones move back = relatively large and round skull
skull during childhood
sutures and fontanelles allow continued bone growth to accommodate growing brain
what forms the cartilaginous part of the neurocranium
prechordal chondrocranium
chordal chondrocranium
what forms the membranous part of the neurocranium
sutures and fontanelles
prechordal chondrocranium
lies in front of the cranial limit of the notochord
derived from neural crest cells
chordal chondrocranium
lies posterior to cranial limit of notochord
derived from occipital somite sclerotome (paraxial mesoderm)
how do chordal and prechordal chondrocranium connect
fuse and ossify by endochondral ossification
derivation of membranous viscerocranium
mesenchyme from neural crest
formed mainly from 1st two pharyngeal arches
1st arch dorsal (maxillary)
1st arch ventral (mandibular)
maxillary process
gives rise to maxilla, zygomatic bone, part of temporal bone
intramembranous ossification
mandibular process
Meckel cartilage
forms most of mandible (but not condyles)
intramembranous ossification
dorsal tip of mandibular process + 2nd arch
incus, malleus, stapes (middle ear)
what types of cells are vulnerable to teratogens?
neural crest cells
craniofacial birth defects are common for this reason
what is craniosynostosis
improper cell interaction / signaling leading to premature closure of sutures
causes of craniosynostosis
genetic»_space; vit D def, teratogens
what controls the process by which sutures normally grow and close
interactions between neural crest-mesoderm cells at suture boundaries, neural crest cell migration, and regulation of cell signaling
normal components of suture closure
- signaling normally causes cells to repel each other
- neural crest cells normally migrate between parietal bones to form part of sagittal suture
- FGF and FGF receptors regulate cell proliferation, migration, and differentiation
premature closure of sagittal suture
long and narrow head
prominent frontal and occipital region
coronal suture brachycephaly
bilateral premature closure
tall skull, flat frontal and occipital regions
coronal suture plagiocephaly
unilateral premature closure
one side of face looks collapsed
cleidocranial dysostosis
delayed closure of fontanelles
decreased mineralization of the cranial sutures
appearance of cleidocranial dysostosis
enlargement of frontal, parietal, and occipital bones
generalized skeletal dysplasia (osseous and dental issues)
underdeveloped / missing clavicles
microcephaly
brain fails to grow
skull fails to expand
leads to intellectual disabilities
causes of microcephaly
teratogens (alcohol exposure in utero)
herniations of the skull
minor defects in skull through which meninges (meningocele) and brain tissue (meningoencephalocele) herniate
can u survive a skull herniation
babies may survive, but have neuro deficits
anencephaly
cranial neuropore fails to close (neural tube defect)
cranial vault fails to close (cranioschisis)
brain tissue exposed to amniotic fluid and degenerates
cannot survive
when does the axial skeleton start forming
4th week
what forms the vertebrae
sclerotome of somite (paraxial mesoderm)
cells migrate from bilateral somites towards the notochord
components of vertebrae
vertebral arch vertebral foramen (passage of spinal cord) body transverse processes spinous processes
what patterns the shape of vertebrae
HOX genes
what is present in the vertebral column at 4 weeks
sclerotomic segments are separates by less dense intersegmental tissue
myotomes, intersegmental mesenchyme, intersegmental arteries and spinal nerves are present
what is resegmentation
proliferation of the caudal half of one sclerotome proceeds into intersegmental mesenchyme and cranial half of subjacent sclerotome
changes position of arteries and nerves (nerves now at discs and arteries mid somite)
where do intervertebral discs form
between precartilaginous vertebral bodies
nucleus pulposus formation
notochord regresses but persists in the disc region as the nucleus pulposus
what is a mature IV disc composed of
nucleus pulposus plus surrounding annulus fibrosus circular fibers
where are myotomes w reference to the vertebral column
myotomes bridge the IV discs
muscles derived from myotome become attached to 2 adjacent somites across the IV discs and can thus move the IV column
curves of vertebral column
2 primary: when first established -thoracic -sacral 2 secondary -cervical (when child holds up head) -lumbar (when walking begins)
scoliosis
lateral curving of the spine
e.g. 1/2 half of a vertebra is missing
idk if you can fully understand what this is…you’re just not close enough to the situation
Klippel-feil sequence
cervical vertebrae are fused
spina bifida
cleft vertebrae
imperfect fusion of vertebral arches
spina bifida occulta
involved small defects in vertebral arches but spinal cord is relatively intact
few to no neuro defects
skin covers defect
spina bifida meningocele
neural tube fails to close
vertebral arches fail to form
sac of fluid with meninges protrudes through opening and some neuro deficits are observed
spina bifida meningomyelocele
meninges and spinal cord exposed
typically leads to paralysis
detection of neural tube defects
maternal serum AFP elevated
check w amniocentesis
ultrasound
prevention of neural tube defects
folic acid
origin of bony ribs
sclerotome cells that remain in paraxial mesoderm and cells the grow out from costal processes of thoracic vertebrae
origin of costal cartilage of ribs
sclerotome cells that migrate across the lateral somatic frontier adjacent to LPM
origin of sternum
2 sternal bands form in parietal layer of LPM in ventral body wall on either side of midline
later fuse to form cartilaginous models of manubrium, sternebrae, and xiphoid process
extra ribs in lumbar or cervical regions
may impinge on brachial plexus or subclavian artery
cleft sternum
failure of sternal bands to fuse
pectus excavatum / carinatum
abnormal ventral body wall closure or altered formation of the costal cartilages and sternum
