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Musculoskeletal System > Session 3 - Limb development > Flashcards

Session 3 - Limb development Flashcards

1
Q

What happens to the notochord in development of the embryo?

A

-The remnant of the notochord forms nucleus pulposus of vertebrae as it becomes marooned during vertebral column formation from sclerotome

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2
Q

Where abouts on the embryo do limb buds appear?

A

-Ventero-lateral body

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3
Q

Which limb bud appears first?

A

-Upper limb bud

NB. lower limb bud is about 2 days behind in development

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4
Q

What happens to the distal end of the limb bud after elongation has occured?

A

-It flattens producing the primorida of the hand and feet, ie hand and foot plates

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5
Q

What is a limb bud?

A

-A core of proliferating mesoderm with an ectodermal covering

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6
Q

When do limb buds appear?

A

-By the end of week 4

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7
Q

What is the first step in the development of the limb buds?

A

-Activation and proliferation of somatic lateral mesoderm

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8
Q

What is the apical ectodermal ridge?

A

-A thickened ridge of ectoderm at the apex

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9
Q

What section of mesoderm forms the bones of the upper limb?

A

-Somatic lateral mesoderm

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10
Q

What section of mesoderm makes the musculature of the limbs?

A

-The somites (paraxial mesoderm)

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11
Q

What are the main functions of the AER?

A
  • Drive elongation of the limb bud

- Controls differentiation proximally to distally

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12
Q

How does the AER control elongation and proximal to distal differentiation?

A
  • The AER has an inductive influence on the underlying mesoderm in such a way that it instructs the mesoderm to remain undifferentiated and keep dividing and elongate
  • The proximal mesoderm is too far away to receive signal and thus begins to differentiate
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13
Q

What happens if the AER does not develop?

A

-Elongation of the limb bud will not occur

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14
Q

What happens to the limb bud after it has elongated?

A

-The distal end flattens into the hand and foot plates and the mesenchyme condenses into discrete organisations known as digital rays

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15
Q

What happens to the AER after the hand and foot plates appear?

A

-Organised regression of the AER except over the digital rays

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16
Q

What happens to the digitial rays of hand and foot plates?

A

-Become the bones of the hand/foot through endochondral ossification

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17
Q

What happens to the interdigital spaces between the digital rays?

A

-They become sculped by apoptosis

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18
Q

What happens to the digital rays before ossification?

A

-Elongation driven by the AER

19
Q

Give the postnatal axis of these embryonic axis

i) Anterior
ii) Posterior
iii) Ventral
iiii) Dorsal

A

i) Superior
ii) inferior
iii) Anterior
iv) Posterior

20
Q

What contributes to the formation of the limb buds?

A
  • Somites

- Lateral plate mesoderm

21
Q

What controls dorso-ventral patterning?

A
  • Controlled by the ectoderm

- Dorsal ectoderm produces dorsalising influences whilst ventral ectoderm produces ventralising influences

22
Q

What controls anterioposterior axial development?

A

-The zone of proliferating activity

23
Q

Where is the zone of proliferating activity?

A

-The posterior base of the limb bud

24
Q

What is the function of the zone of prolifeating activity?

A

-Control patterning and maintain the AER

25
Q

Where does ossification begin?

A

-The proximal limb bud

26
Q

Describe endochondral ossification of the limb bud

A
  • Mesoderm condenses and proliferates producing a cartilaginous model of the bone
  • Collar of periosteal bone appears in shaft
  • Central cartilage calcifies and nutrient artery penetrates-> primary ossifcation centre formed
  • Medulla becomes cancellous bone and cartilage forms epiphyseal growth plates
  • Epiphyses develop secondary ossification centres
  • Epiphyses ossify and growth plates continue to move apart, lengthening bone
  • Epiphyseal growth plates replaced by bone
27
Q

Why are epiphyseal growth plates significant in clinical practice?

A

-They can look like fractures on radiographs

28
Q

How is the musculature of the limb bud formed?

A
  • Myogenic precursors migrate from somites into limb buds
  • Precursors coalesce into 2 common muscle masses around the skeleton
  • Split into individual muscles throughout development
29
Q

How does innervation of the limb bud occur?

A
  • The myogenic precursors bring their innervation with them, ie the spinal roots are pulled into the limb bud
  • The nerves grow into the common muscle masses and then are pulled into individual muscles
30
Q

What happens if innervation of the limb bud does not properly develop?

A

-Development of the limb bud stops

31
Q

How are the limbs orientated initially after development?

A
  • Thumb/big toe up

- Elbow/knee out

32
Q

How is the correct anatomical orientation of each limb bud acheived?

A
  • The limb buds rotate as they elongate
  • Upper limb rotate laterally
  • Lower limb rotates medially
33
Q

What is a dermotome?

A

-Strip of skin innervated by a single spinal berve which can be clinically examines

34
Q

What is a myotome?

A

-Muscle or group of muscles innervated by a single spinal nerve which can be clinically examined

35
Q

Which limb buds are more commonly effected by defects?

A

-Upper limb bud

36
Q

How common are limb defects?

A

6/10,000

37
Q

What is the main cause of limb defects?

A

-Usually hereditary but can be teratogen-induced

38
Q

Give an example of a teratogen-induced limb defect

A

-Phocomelia -> interfered with development of AER

39
Q

What is syndactyly?

A

-Fusion of digits (can be by CT or bone)

40
Q

What is polydactyly?

A

-Extra digit

41
Q

What is amelia?

A

-Complete absence of a limb

42
Q

What is meromelia?

A

-Partial absence of one or more limbs

43
Q

Which border of the limb bud is preaxial?

A

-Thumb/big toe

44
Q

Which border of a limb is postaxial?

A

-5th digit

Musculoskeletal System (34 decks)

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