L29 - DEVELOPMENT OF THE MUSCULOSKELETAL SYSTEM Flashcards
Define the 3 layers of mesoderm?
- Paraxial mesoderm»_space; somites
- Intermediate mesoderm
- Lateral plate mesoderm»_space; embryonic connective tissue and Notochord
Describe the differentiation of the somites on day 19?
Somites differentiate into:
1) Dermomyotome (dorsolateral)»_space; dermatome (skin) + myotome (muscle)
2) Sclerotome
Define the direction of migration of sclerotome and the specific differentiation in each direction?
- Migrate ventrolaterally: form costal processes = precursor of ribs
- Migrate dorsally: surround notochord to form neural arch
- Migrate ventromedially: surround notochord:
- Condense to form centrum of vertebral body
- Annulus fibrosus of IVD
Differentiation of Sclerotome cells?
Sclerotome cells differentiate into chondroblasts»_space; form the cartilaginous precursors of:
Bones of cranial base
Cartilage of heart
Axial skeleton
Describe the formation of IVD?
1) Notochord in the region of vertebral bodies regresses into nucleus
pulposus
2) Sclerotome cells migrate ventromedially to form vertebral body and Annulus fibrosus
Describe the process of forming primordial vertebral bodies?
Resegmentation of sclerotome:
Caudal portion of one sclerotome fuses with cranial portion of the next sclerotome (below) to form a primordium of vertebral body
each vertebra develops from 2 adjacent sclerotomes
Describe how segmental spinal nerves can grow to innervate myotomes?
Resegmentation of sclerotome = splitting of sclerotomes into cranial and caudal portions = create Von Ebner’s fissures
Spinal segmental nerves grow through the fissures to reach myotomes
Segmental spinal nerves that sprout to reach myotomes are purely motor. T or F?
False
Mixture of sensory and motor
What is the final number of segmented somite myotomes?
42-44 pairs of somite myotomes elaborated
1 occipital and last 5-7coccygeal somites later disappear»_space; final count of 35-37 pairs
4 occipital 8 cervical 12 thoracic 5 lumbar 5 sacral
At which week does the blood supply to limbs develop?
4th week
Describe the formation of arteries that supply the upper limb.
C7 intersegmental artery develop into axial arteries and penetrate limb bud
Axial artery = Brachial artery + Anterior interosseous artery
New arteries = Radial and ulnar artery
Describe the formation of arteries that supply the lower limb.
L5 intersegmental artery develop into axial artery to penetrate limb bud
Axial artery = Sciatic artery (obliterated during development) + popliteal artery + peroneal artery
New arteries = femoral + tibial arteries
Describe how blood supply of limbs and venous drainage connect?
Axial arteries anastomose with pre-axial veins at the cranial border and Post-axial veins at the caudal border
Describe the formation of veins for upper limbs?
Primordial veins = Marginal and Cardinal veins
Along cranial border: pre-axial vein develops into cephalic vein
Along caudal border: post-axial vein develops into Basilic vein
Describe the formation of veins for lower limbs?
Primordial veins = Marginal and Cardinal veins
Along cranial border: pre-axial vein develops into Great saphenous vein
Along caudal border: post-axial vein develops into Small saphenous vein
Define the somites level that develops into the limb buds?
Upper limb buds – opposite the lower cervical (C5-T1) somites
Lower limb buds – opposite the lumbosacral (L2-S3) somites
Which germ layer are limb buds derived from?
Consist of a core of mesenchyme derived from lateral plate mesoderm
Covered by ectoderm
Upper limb and lower limb buds develop in the same rate. T or F?
False
Handplate forms first at 7th week
Lower limb buds develop later at 8th week
Define the growth modalities that determine the proximo-distal, cranial-caudal, and dorso-ventral patterning of limb development?
Apical ectodermal ridge (AER) determines proximo-distal patterning
Zone of polarizing activity (ZPA) determines the cranio-caudal (antero-posterior) patterning
Signals (Wnt7a, Bmpr) from dorsal and ventral ectoderms determine dorso-ventral patterning
Describe the process of proximo-distal patterning in limb development?
5th week: limb tip ectoderm proliferates, thickens to form apical ectodermal ridge (AER)
AER induces adjacent mesenchymal cells to proliferate = form progress zone = causes limb to elongate, develop in proximal to distal direction
Describe the process of cranio-caudal patterning in limb development?
Zone of polarizing activity (ZPA) secretes sonic hedgehog
> > higher concentration at caudal (ulnar) end develops little finger first
Selective apoptosis divides AER into 5 segments to form 5 digits
Define the factors that determine the dorso ventral patterning of limbs?
dorsal and ventral ectoderms*** determine dorso-ventral patterning
Dorsal: Wnt7a, Lmx1b
Ventral: bone morphogenic protein (Bmpr), En1
Describe the process of innervating developing limbs?
Limb buds become invaded by ventral primary rami of adjacent spinal nerves
C5-T1»_space; UL
L2-S3»_space; LL
Posterior (dorsal) division = extensor muscle of limb
Anterior (ventral) division = flexor muscle of limb
( Lateral branches = Flexor muscles of spine)
Describe the differentiation lineages of Dermomytome?
1) Dermatome = dermis of skin
2) Myotome = diff. into myoblasts and then skeletal muscles
Further splits into:
a) Epimere = extensor spinal muscles: Erector spinae, Transversospinalis
b) Hypomere = Hypaxial muscles: intercostal, abdominal, strap muscles of neck, limb girdle muscles
Compare the innervation between Epimere and Hypomere?
Epimere muscle derivatives and skin = Dorsal primary ramus
Hypomere muscle derivatives and skin = Ventral primary ramus
Describe the formation of Clavicle and Sternum?
Mesenchymal condensation for development of appendicular skeleton bones:
1) Clavicle = formed by intramembranous ossification
2) Sternum (formed by endochondral ossification):
- 2 bands of lateral plate mesenchyme condense into sternal bars
→ fuse with each other starting cranially into a single piece of cartilage
→ manubrium, body, xiphoid process
→ vertical pairs of ossification centres appear
When does limb rotation occur during limb development?
7th to 9th week
Describe the process of limb rotation in development?
Upper limb rotates laterally = elbow becomes caudal
Lower limb rotates medially = knee becomes cranial
Ventral (flexor): anterior for upper limb
Dorsal (extensor): anterior for lower limb
When does ossification of developing limbs occur? When do secondary ossification centres appear?
Ossification begins in the 7th week
• By 12th week, primary ossification centres present in all long bones
• Most secondary ossification centres appear after birth
Pathogenesis of sternal foramen?
3rd year: Ossification centre for xiphoid process appears
Developmental defect: incomplete ossification centre fusion = sternal foramen
Describe the differentiation and formation of 3 joint types?
Interzone mesenchyme in perichondrium differentiates into cartilage, ligaments, capsular elements of joints:
Cavitation, cavities form synovial cavity in capsule = synovial joint
Fibrocartilage = cartilaginous joint
Fibrous tissue = fibrous joint
Define dermatome axial lines?
Axial lines = Where non-adjacent deratomes meet
Dermatomes become non-segmental and parallel due to elongation of limb buds dragging dermatomes out
Types of spina bifida and pathogenesis?
Defective fusion of 3 primary ossification centres: vertebra does not surround spinal cord, meninges
Spina bifida occulta: no obvious clincial symptom
Spina bifida cystica: neural tube and spine defect
Describe the posture in Talipes equinovarus?
Plantarflexed, inverted foot
“Club foot”
List 4 developmental abnormalities of limbs?
Syndactyly and Polydactyly
Spina bifida
Talipes equinovarus (club foot)
Developmental dysplasia of the hip (DDH) or congenital dislocation of the hip (CDH)
Describe the abnormality in congenital dislocation of the hip?
Affected side is shorter in length
Hip joint not aligned properly»_space; joint laxity means easy dislocation
Which abnormality arises from overexpression of ZPA?
Polydactyly
Which abnormality arises from poor separation of AER into 5 zones?
Syndactyly
Incomplete apoptosis of web between digits
