MSK Embryology Flashcards
nucleus pulposus of IV discs derived from
notochord
vertebrae, ribs, muscles of limbs and trunk, skin derived from
paraxial mesoderm, somites
limb skeleton derived from
lateral plate mesoderm
paraxial mesoderm forms ____ which then give rise to ____
somites; segments
each body “segment” contains what
skin or dermatome, underlying muscle, skeleton, blood vessels
somites divide into 3 divisions…
dermatome- dermis
myotome- skeletal muscle
sclerotome- cartilage and bone
two types of mesoderm divided by coelom
two parts of lateral plate mesoderm
inner splanchnic layer forms GI wall
outer somatic layer forms limb skeleton and anterolateral body wall
two ways mesoderm forms bone
intramembranous ossification- flat bones of skull
endochondral ossification- rest of bones
osteoblasts derive from
mesenchymal cells
osteoblasts fn
make bone matrix or osteoid, creates flat bones of skull directly w/o cartilage matrix
outline 4 steps of endochondral ossification
- embryonic hyaline cartilage model develops
- bone collar forms around cartilage diaphysis, chondrocytes w/i die
- vessels, osteoblasts, and osteoclasts invade from periosteum and form primary ossification center, begin bone formation
- secondary ossification centers form in epiphyses, mostly after birth
exceptions for bone replacement of hyaline cartilage
articular hyaline cartilage- remain for life for joint movement
epiphyseal plates- aka growth plates, needed for bone growth but are replace w/ bone at adulthood
all 4 limb buds have begun to form by…
week 4
upper and lower limb buds arise as..
lateral extensions of trunk somites- upper from somites C5-T1
lower limb from L2-S2
molecules initiating mesoderm mitosis and limb bud outgrowth
Fibroblast Growth Factors- produced by apical ectodermal ridge cells at the distal end of the limb bud
how are hyaline cartilage models made for limb
proximal cells differentiate into chondroblasts, progresssively add distal elements progressively
all models formed by week 8
development of digits
distal end of limb forms wide paddle, forms digital rays
apoptosis separates the digits
polydactyly vs syndactyly
poly- extra digits
syn- fused digits
achondroplasia pathogenesis
less endochondral ossification in limb bones cause short limbs
no effect on membranous ossification, large head relative to limbs
achondroplasia epi and etiology
epi- common type of dwarfism
etiology- AD, most are spontaneous paternal mutations of FGFR 3 genes (for FGF receptor)
most common muscles of upper limb affected by agenesis and partial development
palmaris longus
part of pectoralis major
serratus anterior
describe migration of sclerotome cells for axial development
toward midline notochord (becomes nucleus pulposis) and neural tube- vertebral
laterally- ribs
vertebral cartilage model formed by..
sclerotome cells, later followed by ossification centers (cont til adulthoods)
how do sclerotomes allow spinal nerves to exit vertebral column?
sclerotomes divide into cranial and caudal parts, provide space for spinal nerves along intersegmental boundary
initially the neural tube and vertebral column develop in parallel w/o nerves passing thru laterally
final vertebra are formed from __ and ___ sclerotomes
cranial; caudal
half of adjacent sclerotomes form vertebrae
hemivertebra
lack of formation of part of vertebra
from either ossification center failure or improper subdivision of sclerotomes
cause of scoliosis
neural tube defects
aka spina bifida
lack of development of dorsal vertebral arch from sclerotome, spinal chord elements protrude out of vertebral column
supernumary/ accessory ribs
small rudimentary rib in addition to nl 12
typical location/sx of supernumary ribs
lumbar- extra from area of L1 vertebra, asx (more common)
cervical- area of C7, can compress brachial plexus and sometimes subclavian
dorsal vs ventral migration of myotomes
dorsally- intrinsic back muscles innervated by dorsal rami
ventrally- anterolateral body wall and limbs, innervated by ventral rami
