embryo MSK Flashcards
Derivation: Skeleton and voluntary muscle systems are derived from ____
Mesoderm
Notochord →
nucleus pulposus of intervertebral discs
. Paraxial mesoderm →
somites → vertebrae/ribs, muscles (limbs, trunk) skin (limbs, trunk)
Intermediate mesoderm →
urogenital system
Lateral (plate) mesoderm →
limb skeleton
Paraxial mesoderm forms ______ give rise to the ____
somites; segments
The limbs _____ during development, changing the orientation of the dermatomes in the limbs from the original orientation in the embryo.
rotate
Each somite divides into three parts in order to form all the structures in the segment:
Dermatome → dermis
Myotome → skeletal muscle
Sclerotome → cartilage, bone
Lateral plate mesoderm is divided by the coelom (body cavity) into…
______ that forms GI wall and _____ that forms limb skeleton and Anterolateral body wall
An inner splanchnic (visceral) layer ; An outer somatic layer (B,C)
Bones are formed from mesoderm in one of 2 ways:
intramembranous ossification and endochondrial ossification
Intramembranous Ossification are drived from ____ when ______ cells differentiate directly into bone forming cells = ______ that make up ____ bones of the skull
mesoderm; Mesenchymal; osteoblasts; Flat bones of the skull (C)
Starts with cartilage model of a bone. Then must kill the cartilage and replace with bone = _______
endochondral ossification
1st step in forming Endochondral Ossification
Embryonic hyaline cartilage model develops.
2nd step in endochondrial ossification
“Bone collar” forms around cartilage diaphysis. Chondrocytes within die. (B)
3rd step in endochondrial ossification
1.From the periosteum, blood vessels, osteoblasts and osteoclasts invade and form the primary ossification center. Bone formation begins and spreads from here. (C)
4th step in endochondral ossification
4.Secondary ossification centers form in epiphyses → bone formation in each. (D)
•Some begin just before birth, most after birth.
Bone replaces ______ throughout the cartilage model, except the ______ and epiphyseal plates. (E)
hyaline cartilage; articular cartilages
_____ cartilages remain throughout life for joint movement
Articular hyaline
_____ needed for bone growth; remain until adulthood. Then replaced with bone.
Epiphyseal plates (aka growth plates)
limb development begins as limb buds which have begun to gorw by _____
week 4
Each upper & lower limb bud arises as lateral/medial extensions of _____
lateral extension of trunk somites
Upper limb from somites
C5-T1
Lower limb from somites
L2-S2
Initial outgrowth of the limb bud begins with mitosis of ______ in response to mesodermal Fibroblast Growth Factors (FGFs).
New cells are added primarily at the proximal/distal end of the limb bud under the influence of the ______ which produce FGFs coded by FGF gene.
mesoderm cells; distal; apical ectodermal ridge cells
Endochondral ossification. Growth follows _____
Proximal → Distal rule
Limb grows distally by mitosis of cells beneath the _______
apical ectodermal ridge (AER).
Proximal cells then differentiate into ______ and form a hyaline cartilage model of each bone.
chondroblasts (hyaline cartilage)
All cartilage models are formed by end _____
Week 8.
Distal end of each limb forms wide paddle.
Digital rays develop where each digit will form.
____ occurs and separates the individual digits.
Apoptosis
Polydactyly =
Extra digits on hand and/or foot.
Syndactyly = ___
Fused digits
Achondroplasia
Epidemiology:
Etiology:
Pathogenesis:
Clinical:
Epidemiology: common type of dwarfism.
Etiology: AD; ~ 80% are spontaneous …..paternal mutations of FGFR 3 gene
Pathogenesis: decreased endochondral ….ossification in limb bones → short limbs. ….No effect on membranous ossification → ….large head relative to limbs.
Clinical: short limbs with large torso and ….head relative to limbs. Prominent ….forehead and flattened nasal bridge.
As the forelimb/upper limb bud arises as extension of trunk somites, ____extend into the limb bud.
This → Brachial Plexus.
Innervates muscle and skin of upper limb.
ventral rami of C5-T1
As the hindlimb/lower limb bud arises from trunk somites, _______ extend into the limb bud.
This → Lumbosacral Plexus.
Innervates muscle and skin of lower limb.
ventral rami of L2-S2
Limb musculature derived from mesoderm (A)
(paraxial → somite → _____)
Cells of the myotomes ______ migrate into the limb bud. (B)
The myoblasts divide into ______ masses in the limbs. (C)
Spinal nerve ventral rami grow with them for innervation. (C)
myotome; (myoblasts); extensor and flexor muscle
Agenesis and partial development
Muscles may not develop at all or a part may not develop.
The most common muscles include these muscles of the upper limb:
- Palmaris longus
- Part of pectoralis major
- Serratus anterior
Sclerotome cells
(mesoderm → somite → _____) migrate …
toward _____ and _____ medially/laterally
sclerotome; midline notochord and neural tube; laterally
Sclerotome cells surround the neural tube, forming the _____
Notochord becomes _____ of intervertebral discs
vertebrae; nucleus pulposis
Sclerotome cells that migrate laterally form the ___
ribs
_______ Occurs by endochondral ossification (i.e. forms a cartilage model,
kills the cartilage,
replaces with bone).
_____ cells form a cartilage model.
Later, ossification centers develop.
Ossification does not/does continue until adulthood.
vertebra develoment; Sclerotome; does
Vertebral development is complex.
Vertebrae and Spinal nerves develop together.
Each sclerotome forming vertebrae has to divide into _____ parts (along the intrasegmental boundary to allow spinal nerves space to exit vertebral column.
Cranial and caudal parts of adjacent sclerotomes join and create a ______
cranial and caudal; VERTEBRA
Hemivertebra
Lack of formation of part of a vertebra.
Arises from either:
- failure of an ossification center to form properly
- improper subdivision of sclerotomes
The presence of hemivertebra is one cause of scoliosis (lateral curvature of vertebral column).
Neural Tube Defects (NTD)
- Also called Spina bifida (= cleft spine)
- Mild and moderate forms arise from lack of development of dorsal vertebral arch from the sclerotome.
Rib Congenital Anomalies
•Usually small, rudimentary rib immediately above or below the 12 normal ribs.
•Lumbar rib : An extra rib or pair of ribs may develop in the lumbar area from the L1 vertebra. No symptoms.
•Cervical rib : An extra rib or pair of ribs may develop in the cervical area from C7 vertebra. (B) .5-1% of population. May compress brachial plexus +/- subclavian artery (this is one etiology of Thoracic outlet syndrome)
•
Lumbar are more common than cervical
Myotome cells migrate… ventrally/dorsally, to form the intrinsic (deep) back muscles innervated by dorsal rami of spinal nerves. (B,C)
dorsally
Myotome cells migrate… ventrally/dorsally, to form the anterolateral body wall (and limb muscles) innervated by ventral rami of spinal nerves.
ventrally
development of the skull: derived from
mesoderm
skull forms from endochondral/intramembranous ossification
intramembranous ossification
intramembranous ossification process
Begins with mesenchymal cells
↓
Mesenchymal cells differentiate directly into bone forming cells = osteoblasts
NOTE: there is no cartilage model.
↓
These cells make bone matrix (osteoid).
↓
Flat bones of the skull (C)
