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MSS > MSS29 Development Of The Musculoskeletal System > Flashcards

MSS29 Development Of The Musculoskeletal System Flashcards

1
Q

Mesoderm differentiation

A
  1. Paraxial mesoderm (either side of neural tube)
    - -> Somites
    - -> Dermomyotome (Dermatome + Myotome) + Sclerotome
  2. Intermediate mesoderm
  3. Lateral plate mesoderm
    - -> sternum, limb bone, limb muscle
  4. Diffuse Mesenchyme

by 5th week: 42-44 pairs of somites

  • -> 1st Occipital, last 5-7 coccygeal somites disappear
  • -> final count 35-37 pairs of somites

Dermomyotome (dorsolateral)
Sclerotome (ventromedial)

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2
Q

Sclerotome

A

Sclerotome (ventromedial/入面) migration in 3 directions:

  1. Dorsally –> surround neural tube
    - -> ***Neural arch
  2. Ventromedially –> surround notochord
    - -> **Vertebral body (centrum) + **Annulus fibrosis (notochord –> Nucleus pulposus)
  3. Ventrolaterally
    - -> ***Costal process (rib precursor)

Steps:

  1. Differentiation:
    - differentiate into Chondroblasts
    - -> cartilagneous precursors of axial skeleton (vertebral column, ribs) + bones of cranial base
  2. Condensation:
    - -> surround neural tube (future spinal cord)
    - -> condensation to form vertebral column
  3. Resegmentation:
    - Caudal portion of 1 sclerotome fuse with cranial portion of next sclerotome
    - -> form primordium of vertebral body
    - -> vertebra
  • 中間d窿allow Segmental spinal nerves (from neural tube) grow and innervate myotome through ***Von Ebner’s fissure
  • -> each myotome contains an admixture of motor + sensory fibres
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3
Q

IV disc formation

A
  • Form at segmental levels
  • Notochord –> regresses –> remnant: Nucleus pulposus
  • Sclerotome cells –> Annulus fibrosus
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4
Q

Dermomyotome

A

differentiate into

  • Dermatome (***dermis of skin of back)
  • Myotome (each split into **Epimere + **Hypomere)
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5
Q

Myotome differentiation

A
  • Occipital myotomes x4
  • Cervical myotomes x8
  • Thoracic myotomes x12
  • Lumbar myotomes x5
  • Sacral myotomes x5
  • Coccygeal myotome

Differentiation:
- differentiate into ***Myoblasts

Epimere (dorsal) –> Extensor muscles of spine:

  1. Erector spinae (Intermediate group)
  2. Transversospinalis (Deep group)
    - -> supplied by ***Dorsal primary ramus of spinal nerve

Hypomere (ventral) –>

  1. Hypaxial muscles
  2. Rectus column
    - -> abdominal muscles, strap muscles, intercostal muscles, limb girdle muscles
    - -> supplied by ***Ventral primary ramus of spinal nerve
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6
Q

Development of clavicle and sternum

A

Early mesenchymal stage (6 week)

  • clavicle
  • ribs (sclerotome)
  • suprasternal masses
  • sternal bars (from 2 bands of ***lateral plate mesenchyme, paired mesenchymal condensations) –> fuse starting cranially –> manubrium + body + xiphoid process

Late mesenchyme stage (8 week)

  • Ossification centre for clavicle (7th week)
  • -> differentiate directly from mesenchyme ***without cartilage model
  • -> intramembranous ossification

Cartilage stage (9 week)

  • clavicle (ossifying) –> bone
  • ribs, sternum, others –> cartilage (有cartilage model)

At birth:

  • lateral ribs –> bone
  • central ribs –> costal cartilage
  • ossification centre for Sternebrae (sternal body) appear at 5th-6th month prenatal
  • ossification centre for Xiphoid process appear at 3rd year

Sternal foramen: due to incomplete ossification centre fusion

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7
Q

Limb development (4-8 week)

A

Limb buds: core of mesenchyme from somatopleure of ***lateral plate mesoderm, covered by ectoderm
–> projections from ventrolateral body wall

Upper limb bud: opposite C5-T1 somites
Lower limb bud: opposite L2-S3 somites

  1. **Apical ectodermal ridge (AER) (regulate differentiation of limbs along proximo-distal limb axis)
    5th week:
    - Limb tip **    ectoderm proliferate + thickens
    –> Apical ectodermal ridge (AER)
    –> induce adjacent **mesenchyme to proliferate/condense into an undifferentiated population of cells (cartilage –> endochondral ossification)
    –> Progress zone
    –> causes limb to elongate and develop in **    proximal to distal direction
    –> arms and forearms appear before handplate
  2. **Zone of polarizing activity (ZPA)
    - at Post-axial border near AER
    - regulates **    limb patterning
    - grow in ***cranio-caudal (antero-posterior) direction
    - -> thumb lies on radial (cranial) side (當垂直手板睇)
    - -> little finger on ulnar (caudal) side
  3. Dorso-ventral patterning
    - determined by signals from dorsal ectoderm + ventral ectoderm

Hands

  • -> Flipper-like UL bud
  • -> Handplate (paddle-shaped end)
  • -> ***Apoptosis divide AER into 5 segments
  • -> permit continued growth for each digit
  • -> Digital rays and notches between digital rays; webbed fingers
  • -> short finger and slightly webbed; elbow and wrist identifiable
  • -> fingers and toes distinct and separate
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8
Q

Rotation of limbs

A

Along longitudinal axis at elbow, knee joints (7-9 weeks):
- before rotation: Flexion creases indicate sites of future joints and flexor aspect of limbs face medially

  • upper limb: rotate 90o laterally (擺去左右)
  • lower limb: rotate 90o medially (向中間)
  • -> Elbow points caudally, original ventral surface becomes cranial surface (上半身)
  • -> Knee points cranially, original ventral surface becomes caudal surface (下半身)
  • dermatome pattern of lower limb becomes distorted
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9
Q

Limb skeleton development

A

Loose mesenchyme (lateral plate mesoderm) with AER (4 week)

  • -> Condensed mesenchyme (5 week)
  • -> Chondrification centres
  • -> Hyaline cartilage models (6 week)
  • -> Ossification begins (7 week)

12 weeks:
Primary ossification centres (in diaphysis) in all long bones
Secondary ossification centres (in epiphysis) appear after birth

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10
Q

Joint development

A

Joints (cartilage, ligaments, capsular elements of joints):

  • develop from ***interzone regions of condensed mesenchyme (lateral plate mesoderm) that form the long bones of limb
  • -> Synovial joint (loose mesenchyme) + Cartilaginous joint + Fibrous joint
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11
Q

***Development of blood supply to limbs

A
  • **7th Cervical + ***5th Lumbar Intersegmental arteries
  • -> extend into upper and lower limb buds as single ***axial artery
  • -> limb buds permeated by anastomosing capillary network
  • -> blood returned to cardinal system by ***marginal veins:
  1. Pre-axial vein (係axial artery上方 / running along cranial border)
    - UL: Cephalic, LL: Great saphenous
  2. Post-axial vein (係axial artery下方 / running caudal border)
    - UL: Basilic, LL: Small saphenous

Developing limb skeleton displaces axial artery –> replacement by new vessels

**UL:
axial artery remnants: Axillary, Brachial, Anterior interosseous arteries
new arteries: **Radial, ***Ulnar arteries

**LL:
axial artery remnants: Inferior Gluteal and Sciatic branch, Popliteal, Peroneal arteries
new arteries: **Femoral, ***Tibial arteries

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12
Q

Development of limb musculature and innervation

A
  • limb muscles develop in situ from local mesenchyme in limb bud (lateral plate mesoderm; NOT from myotome i.e. somite!!!)
  • aggregation of Myoblasts
  • -> large muscle mass
  • -> splits into ventral (flexor) + dorsal (extensor) mass
  • -> both invaded by ***Ventral primary rami of spinal nerves
  • -> flexor: anterior division of ventral primary ramus
  • -> extensor: posterior division of ventral primary ramus
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13
Q

Development of dermatomal patterns of limbs

A
  • as limbs elongate, dermatome migrates along it
  • -> dorsal + ventral axial lines defined (骨方向)
  • -> axial lines separate dermatomes that are supplied by non-adjacent segments of spinal cord
  • -> dermatomal patterns
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14
Q

Developmental anomalies

A

Multifactorial:

  • Genetic
  • Environmental e.g. thalidomide, radiation
  • Mechanical e.g. breech presentation (腳出先)
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15
Q

Spina bifida

A
  • failure of fusion of 2 halves of vertebral ***arch
  • Spina bifida occulta (in cervical, lumbar, sacral region): “closed” spina bifida in which defect is covered by thick, hairy membrane/skin
  • -> quite common, no clinical symptom
  • Spina bifida cystica: severe type involving spinal cord and meninges
  • -> failure to form neural tube / meninges
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16
Q

Club foot

A 
Talipes equinovarus
(Talus=ankle; pes=foot; equinus=plantar flexed; varus=inverted)
1. Varus deformity of the heel
2. Adduction of the forefoot
3. with some degree of plantarflexion
17
Q

Developmental dysplasia of the hip (DDH) / Congenital dislocation of the hip (CDH)

A
  • more common in females, breech presentation
  • abnormal development of acetabulum and head of femur; often associated with abnormal joint laxity
  • Normal: long axis of femur strikes the acetabulum
  • DDH: femur does not strike acetabulum
  • Unilateral CDH: affected side appear slightly shorter
18
Q

Syndactyly, Polydactyly

A

Syndactyly: fused digits, due to lack of differentiation between >=2 digits

Polydactyly: extra digit

19
Q

Read Slides

A

Read Slides

MSS (32 decks)

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