Embryology Flashcards
What layer is the musculoskeletal system derived from?
mesoderm
What are the 4 parts of the mesoderm?
notochord
paraxial
intermediate
lateral plate
What does the notochord give rise to?
nucleus pulposus (IV discs)
What does the paraxial mesoderm give rise to?
forms somites
vertebrae/ribs
muscles
skin
What three parts do somites divide into?
dermatomes
myotomes
sclerotome (skeletal)
What two sections is the lateral plate divided into?
splanchnic layer
somatic layer
What does the somatic layer of lateral plate form?
anterolateral body wall
limb skeleton
What are the two ways bones form?
intramembranous (flat skull bones)
endochondral
How does intramembranous ossification work?
mesenchymal cells diff into osteoblasts which make bone matrix within collagen fiber
What are the 4 steps of endochondral ossification?
- hyaline cartilage model develops
- bone collar forms around diaphesis and kill cartilage
- bone cells enter from the periosteum and make matrix (primary ossificatoin center)
- same thing starts in epiphyses
What cartilage survives endochondral ossification?
articular cartilages
epiphysial plates
All 4 limbs have started forming by what week?
week 4
Limb buds form as extensions of what?
somites
Which somites form the upper limb?
C5-T1 (brachial plexus)
What makes the limb buds grow?
mesodermal cells due to Fibroblast Growth Factors (made by apical ectodermal ridge)
How does the hyaline cartilage model form?
proximal cells diff into chondroblasts and form cartilage from proximal to distal
When is the cartilage model finished forming?
week 8
What separates the digits after cartilage is formed?
apoptosis
What is polydactyly?
too many digits
What is syndactyly?
digits that are fused together
What causes achondroplasia?
decreased endochondral ossification leading to shorter bones
due to FGF-receptor mutation
How does muscle form in the limbs?
myotomal myoblasts migrate to limb bud and divide into extensor and flexor masses (forms after bone)
What are the three most common muscles for agenesis and partial development?
palmaris longus
pec major
serratus anterior
The sclerotome is divided into three sections that migrate where?
notochord (nucleus pulposis)
neural tube (vertebrae)
laterally (ribs)
Where are the vertebral ossification centers?
around notochord
pedicles
How do spinal nerves develop?
spinal nerves cut through vertebrae to stay in its somite, so vertebrae split in half and two adjacent bones join between nerves
What is hemivertebra?
malformation of part of a vertebra
due to failure of ossification or improper subdivision of sclerotomes
What is supernumerary rib?
extra rib, either at the top or bottom
What is a complication of a cervical rib?
compression of brachial plexus or subclavian artery
How do the trunk muscles develop?
myotome cells split and migrate dorsally (intrinsic back) and ventrally (all others)
