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MBBS II MSS > L29 - DEVELOPMENT OF THE MUSCULOSKELETAL SYSTEM > Flashcards

L29 - DEVELOPMENT OF THE MUSCULOSKELETAL SYSTEM Flashcards

1
Q

Define the 3 layers of mesoderm?

A
  1. Paraxial mesoderm&raquo_space; somites
  2. Intermediate mesoderm
  3. Lateral plate mesoderm&raquo_space; embryonic connective tissue and Notochord
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2
Q

Describe the differentiation of the somites on day 19?

A

Somites differentiate into:

1) Dermomyotome (dorsolateral)&raquo_space; dermatome (skin) + myotome (muscle)
2) Sclerotome

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3
Q

Define the direction of migration of sclerotome and the specific differentiation in each direction?

A
  1. Migrate ventrolaterally: form costal processes = precursor of ribs
  2. Migrate dorsally: surround notochord to form neural arch
  3. Migrate ventromedially: surround notochord:
    - Condense to form centrum of vertebral body
    - Annulus fibrosus of IVD
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4
Q

Differentiation of Sclerotome cells?

A

Sclerotome cells differentiate into chondroblasts&raquo_space; form the cartilaginous precursors of:
 Bones of cranial base
 Cartilage of heart
 Axial skeleton

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5
Q

Describe the formation of IVD?

A

1) Notochord in the region of vertebral bodies regresses into nucleus
pulposus

2) Sclerotome cells migrate ventromedially to form vertebral body and Annulus fibrosus

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6
Q

Describe the process of forming primordial vertebral bodies?

A

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

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7
Q

Describe how segmental spinal nerves can grow to innervate myotomes?

A

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

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8
Q

Segmental spinal nerves that sprout to reach myotomes are purely motor. T or F?

A

False

Mixture of sensory and motor

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9
Q

What is the final number of segmented somite myotomes?

A

42-44 pairs of somite myotomes elaborated

1 occipital and last 5-7coccygeal somites later disappear&raquo_space; final count of 35-37 pairs

 4 occipital  8 cervical  12 thoracic  5 lumbar  5 sacral

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10
Q

At which week does the blood supply to limbs develop?

A

4th week

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11
Q

Describe the formation of arteries that supply the upper limb.

A

C7 intersegmental artery develop into axial arteries and penetrate limb bud

Axial artery = Brachial artery + Anterior interosseous artery

New arteries = Radial and ulnar artery

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12
Q

Describe the formation of arteries that supply the lower limb.

A

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

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13
Q

Describe how blood supply of limbs and venous drainage connect?

A

Axial arteries anastomose with pre-axial veins at the cranial border and Post-axial veins at the caudal border

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14
Q

Describe the formation of veins for upper limbs?

A

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

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15
Q

Describe the formation of veins for lower limbs?

A

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

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16
Q

Define the somites level that develops into the limb buds?

A

 Upper limb buds – opposite the lower cervical (C5-T1) somites

 Lower limb buds – opposite the lumbosacral (L2-S3) somites

17
Q

Which germ layer are limb buds derived from?

A

 Consist of a core of mesenchyme derived from lateral plate mesoderm

 Covered by ectoderm

18
Q

Upper limb and lower limb buds develop in the same rate. T or F?

A

False

Handplate forms first at 7th week
Lower limb buds develop later at 8th week

19
Q

Define the growth modalities that determine the proximo-distal, cranial-caudal, and dorso-ventral patterning of limb development?

A

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

20
Q

Describe the process of proximo-distal patterning in limb development?

A

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

21
Q

Describe the process of cranio-caudal patterning in limb development?

A

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

22
Q

Define the factors that determine the dorso ventral patterning of limbs?

A

dorsal and ventral ectoderms*** determine dorso-ventral patterning

 Dorsal: Wnt7a, Lmx1b
 Ventral: bone morphogenic protein (Bmpr), En1

23
Q

Describe the process of innervating developing limbs?

A

Limb buds become invaded by ventral primary rami of adjacent spinal nerves

C5-T1&raquo_space; UL
L2-S3&raquo_space; LL

 Posterior (dorsal) division = extensor muscle of limb
 Anterior (ventral) division = flexor muscle of limb

( Lateral branches = Flexor muscles of spine)

24
Q

Describe the differentiation lineages of Dermomytome?

A

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

25
Q

Compare the innervation between Epimere and Hypomere?

A

Epimere muscle derivatives and skin = Dorsal primary ramus

Hypomere muscle derivatives and skin = Ventral primary ramus

26
Q

Describe the formation of Clavicle and Sternum?

A

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

27
Q

When does limb rotation occur during limb development?

A

7th to 9th week

28
Q

Describe the process of limb rotation in development?

A

 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

29
Q

When does ossification of developing limbs occur? When do secondary ossification centres appear?

A

Ossification begins in the 7th week
• By 12th week, primary ossification centres present in all long bones
• Most secondary ossification centres appear after birth

30
Q

Pathogenesis of sternal foramen?

A

3rd year: Ossification centre for xiphoid process appears

Developmental defect: incomplete ossification centre fusion = sternal foramen

31
Q

Describe the differentiation and formation of 3 joint types?

A

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

32
Q

Define dermatome axial lines?

A

Axial lines = Where non-adjacent deratomes meet

Dermatomes become non-segmental and parallel due to elongation of limb buds dragging dermatomes out

33
Q

Types of spina bifida and pathogenesis?

A

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

34
Q

Describe the posture in Talipes equinovarus?

A

Plantarflexed, inverted foot

“Club foot”

35
Q

List 4 developmental abnormalities of limbs?

A

Syndactyly and Polydactyly
Spina bifida
Talipes equinovarus (club foot)
Developmental dysplasia of the hip (DDH) or congenital dislocation of the hip (CDH)

36
Q

Describe the abnormality in congenital dislocation of the hip?

A

Affected side is shorter in length

Hip joint not aligned properly&raquo_space; joint laxity means easy dislocation

37
Q

Which abnormality arises from overexpression of ZPA?

A

Polydactyly

38
Q

Which abnormality arises from poor separation of AER into 5 zones?

A

Syndactyly

Incomplete apoptosis of web between digits

MBBS II MSS (31 decks)

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