Musculoskeletal Embryology

Question 1

What are the key requirements for joint development?

Answer 1

Genetic regulation of interzonal mesenchyme
TGF-Beta receptor for formation of synovial joint
Fetal movement

Question 2

What is the inter zone?

Answer 2

Undifferentiated mesenchyme between 2 cartilage model

Question 3

What defect is associated with the lack of fetal movement?

Answer 3

Arthrogryposis (1 in 3000)

Question 4

What are the requirements for normal muscle development?

Answer 4

Mesenchymal cells
Genetic signals
CT framework
Fetal movement

Question 5

What is a defect associated with abnormal muscle development?

Answer 5

Poland syndrome(1 in 50,000)- unilateral absence of pectoralis major

Question 6

What are steps of skeletal muscle formation?

Answer 6

Mesenchymal cells differentiate into myogenic cells
Myogenic cells under FGF and TGF-Beta proliferate through mitosis
The unstimulated myogenic cells become satellite cells
MyoD binds to the stimulated myogenic cellls, stops the mitosis and the cells becomes postmitotic myoblast
Postmitotic myoblast are mononucleated and fuse together to form a multinucleated syncytium =myotube
Myotube synthesizes actin and myosin with aggregated into myofibrils and the myotube becomes muscle fiber
Myotube also synthesize troponin, tropomyosin, Titin, nebulin, myomesin and dystrophin

Question 7

How does the myotome differentiate?

Answer 7

Epimere=dorsal
Hypomere= ventral
The non axial comes from the hypomere

Question 8

What are the 2 groups separated by the lateral somatic frontier?

Answer 8

Primaxial=medial

Abaxial=Lateral

Question 9

What are the characteristics of primaxial?

Answer 9

Myogenic cells are from hypomere and epimere
Induced by neural tube and notochord
Innervated by dorsal and ventral rami
CT framework derived from somite

Question 10

What are the characteristics of abaxial?

Answer 10

Myogenic cells from hypomere
Induced by lateral plate mesoderm
Innervated by ventral ramus
CT framework derived from lateral plate

Question 11

What are the origin of the head muscles?

Answer 11

3 populations:
Tongue muscles migrate similar to limb muscles
Extraocular muscles come from 3 condensations in 3 somitomeres then migrate to orbit
Branchial muscle form a very early complex with the neural crest cells

Question 12

What is Duchenne Muscular Dystrophy?

Answer 12

X-linked mutation for a gene that encodes dystrophin
Detected around 3 years of age due to lack strength and coordination in the postural muscles
Progressive muscular wasting leading to death in late teens or early 20s
Milder form=Becker muscular dystrophy

Question 13

When and where does limb formation occur?

Answer 13

Forelimb formed at C5-C8
Hindlimb formed at L3-L5
Limb formation is initiated in the 4th week
Hindlimb formation is initiated 2-5 days later

Question 14

What is the Zone of Polarizing Activity (ZPA)

Answer 14

Mesenchymal cells on the posterior edge of the limb that are in charge of the anterior-posterior axis
Secretes retinoids acid and sonic hedgehog

Question 15

What is a defect associated with the ZPA?

Answer 15

Mirror hand

Polydactyly

Question 16

What is the Apical ectodermal Ridge (AER)?

Answer 16

Ectodermalk cells in charge of the proximal distal axis

Secrete FGF—>progress zone

Question 17

What is a defect associated to the AER?

Answer 17

Truncated limb syndrome

Question 18

What are the steps to hand or foot formation?

Answer 18

By day 32 PZ has spread and flattened to form hand or foot plate
By day 48 AER breaks into 5 distinct ridges and programmed cell death will begin Yao remove tissue and leave 5 digits

Question 19

What are the defects associated with failure of formation of ridges by AER?
Failure of apoptosis?

Answer 19

Cleft hand/foot syndrome
Cutaneous syndactyly
Osseus syndactyly

Question 20

What are the steps of formation of the appendicular skeleton?

Answer 20

Somite specific stage
Gross functional grouping stage
Muscle specific stage
C-met receptor tyrosine kinase
Myogenic determination factors

Question 21

When does limb rotation occur?

Answer 21

Around day 47
Forelimb -lateral rotation
Hindlimb- medial rotation
Club foot-defect associated with incomplete rotation of hindlimb