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MSK > MSK development 1 > Flashcards

MSK development 1 Flashcards

1
Q

What are the origins of the post-cranial MSK?

A
  • Axial skeleton (vertebrae/ribs) - somites
  • appendicular skeleton (limb digits/girdles) - limb buds
  • Axial muscle (vertebral, thoracic, abdominal) - somites
  • Appendicular muscles (flexors/extensors) - somites
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2
Q

Axial vs Appendicular

A

Axial protects things, appendicular moves things

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3
Q

What are somites?

A

Paraxial mesoderm (either side of axis) that is laid down sequentially cranial to caudal

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4
Q

What are the 4 different differentiated cell populations?

A
  • Sclerotome - vertebrae and ribs (skeleton)
  • Myotome - epimere, hypomere, limb muscles (muscles)
  • Dermatome - dorsal dermis (skin)
  • Syndetome - tendons
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5
Q

What 3 things control somitogenesis and keep it symmetrical?

A
  • Wnt
  • FGF
  • Retinoic acid gradients
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6
Q

What is ossification?

A

Bone formation

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7
Q

What is the process of intramembranous ossification?

A
  • condensation of mesenchyme into soft sheet permeated with capillaries
  • deposition of osteoid tissue by osteoblasts, entrapment of first osteocytes and periosteum formation
  • honeycomb of bony trabeculae formed by mineral deposition + creation of spongy bone
  • surface filled in by bony deposition - converts spongy bone into compact bone
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8
Q

What does intramembranous ossification produce?

A

Flat bones of skull and clavicle

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9
Q

What is endochondral ossification?

A
  • mesenchymal cells in the epiphyses of long bones give rise to hyaline carilage
  • primary ossification centre in shaft of bone provides nutients and growth factors via the nutrient artery
  • osteoblasts start laying down bone
  • medullary cavity is formed by osteoclasts
  • secondary ossification centres are made in the epiphyses
  • articular cartilage and epiphyseal plate is formed
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10
Q

Give an example of a problem that you may have with ossification

A
  • Achondroplastic dwarfism
  • “without cartilage formation”
  • Have a problem with converting the cartilage to bone
  • Results in shortened limb bones as there is premature closure of epiphyseal growth plates
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11
Q

What are the 3 growth axes of limb buds?

A
  • proximal to distal (shoulder to fingers) - need to make limbs long
  • posterior to anterior (little finger to thumb)
  • dorsal to ventral (back to palm of hand)
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12
Q

What happens at week 4 of development?

A
  • limb buds are visible - made from mesenchyme from somatic layer of lateral plate + ectoderm (skin) at distal border of limb forms Apical ectodermal ridge (AER)
  • as limb grows , cells get further away from AER and differentiate into cartilage and muscle
  • limb grows proximally to distally
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13
Q

What happens at week 6?

A
  • terminal portion of limb buds flatten to form hand and foot plates
  • fingers and toes form (posterior to anterior)
  • AER separates into 5 parts due to apoptosis
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14
Q

What is it called when fingers do not separate properly due to the blocking of apoptosis?

A

Syndactyly

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15
Q

What happens at week 7 of development?

A
  • Upper limbs rotate externally (extensors posterior)

- lower limbs rotate internally (extensors anterior)

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16
Q

How is growth regulated at the molecular level?

A
  • HOX genes - regulate the positioning of the limbs proximal-distally
  • BMP - induce formation of AER
  • FGF-10 - initiates outgrowth
  • After the ridge is established FGF-4/8 maintain the progress zone (rapidly proliferating population of mesenchyme cells adjacent to ridge)
  • ZPA - regulates A-P axis
17
Q

What is the zone of polarising activity?

A
  • Cluster of cells at the posterior border of the limb near the flank
  • Limit retinoic acid (Vitamin A)
  • initiates expression of SHH (regulates the A-P axis)
  • As limb grows, ZPA moves distally to remain in proximal to the posterior border of AER
18
Q

Summary of hormone regulation

A

FGFs in the AER activate SSH in ZPA, whilst WNT7a maintains SSH.
- HOX genes regulate types and shapes of bones in the limb

19
Q

Name 4 limb detects

A
  • Polydactyly
  • Cleft hand and foot
  • Club foot
  • Congenital hip dislocation
20
Q

What is polydactyly?

A
  • have extra digits
  • extra digits frequently lack proper muscle connections
  • usually bilateral
21
Q

What is club foot?

A

Sole of foot is supinated

  • usually accompanies syndactyly
  • mainly in males, may be heriditary
22
Q

What is congenital hip dislocation?

A
  • under-development of acetabulum and head of femur
  • dislocation occurs usually after birth - abnormality occur in utero
  • most babies with chd are breech deliveries - may interfere with hip joint development
23
Q

Epaxial vs Hypaxial

A 
Epaxial = transverse --> spinous process
Hypaxial = every other muscle
24
Q

Innervation overview

A
  • signals induce nerve growth from the neural tube
  • nerve grows and splits sclerotome portion of somite into cranial and caudal
  • nerve contacts myotome and dermatome and innervates the segment
  • Spinal nerves pass through the intervertebral foramina
25
Q

What is a dermatome?

A

An area of skin supplied by a single spinal nerve

- Dermatomal stripes are different from embryo to adult

26
Q

Muscle innervation

A
  • nerves innervating segmental muscles divide into dorsal primary ramus (epimere) and ventral primary ramus (hypomere)
  • nerves remain with original muscle segment throughout its migration
27
Q

What is the process of neuromuscular junction formation?

A
  • growth cone of axon approaches muscle fibre, terminates, differentiates and then starts producing cleft
  • multiple axons converge
  • all but one are eliminated - remainder develops a myelin sheath
28
Q

Myotome overview

A
  • small dorsal portion (epimere) formed from dorsomedial cells of somite - forms extensor muscles of vertebral column
  • larger ventral portion (hypomere) formed from dorsolateral cells of somite - gives rise to muscles of limbs and body wall
  • Thorax myoblasts form intercostals
  • Abdomen myoblasts form abdominal muscles and obliques
  • In limbs, dorsal = extensors, ventral = flexors
29
Q

What are the spinal roots for upper and lower limbs?

A
  • Upper limb buds are lower 5 cervical and upper 2 thoracic

- lower limb buds are lower 4 lumbar and upper 2 sacral

30
Q

What is the molecular regulation of muscle development?

A
  • dorsomedial region migrates ventral - MYF5 forms epimeric musculature
  • dorsolateral region of somite expresses MYO-D - forms hypomeric musculature
  • MYOD and MYF5 activate genes myogenin and MRF5 (promotes formation of myotubes and myofibres) - differentiate, fuse and form long multinucleated muscle fibres
31
Q

Muscle regeneration

A
  • Uses muscle stem cells (satellite cells)

- repeats process of embryogenesis

32
Q

Connective tissue connections

A
  • mechanical load also controls skeleton and tendon development
  • the development of a functional MSK depends on regulation of: cartilage morphogenesis, joint formation, bone morphogenesis and tendon homeostasis

MSK (10 decks)

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