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MSK Exam 1 > Development of the MSK > Flashcards

Development of the MSK Flashcards

1
Q

What cells form the paraxial mesoderm?

A

Cells derived from the primitive node

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2
Q

Paraxial Mesoderm

A

Thick, bilateral longitudinal columns of cells along the developing NT

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3
Q

Each column of paraxial mesoderm is continuous with ___ mesoderm which gradually thins into a layer of ___ mesoderm

A
  • Intermediate
  • Lateral (plate)
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4
Q

Lateral (plate) mesoderm is continuous with ____ mesoderm

A

Extraembryonic

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5
Q

Extraembryonic mesoderm covers the:

A

Umbilical Vesicle & Amnion

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6
Q

What mesoderm type forms on either side of the notochord?

A

Paraxial mesoderm (next is intermediate mesoderm then lateral plate mesoderm)

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7
Q

When do the paraxial mesoderm differentiate, condense and form paired somites (form in head to tail/craniocaudal fashion)?

A

End of the 3rd week

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8
Q

Where do the fist somites form?

A

In the future occipital region

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9
Q

How many somites develop initially?

A

38-39 pairs

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10
Q

How many somite pairs form by the end of the 5th week?

A

42-44 pairs

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11
Q

Shortly after forming, each somite pair separates into __

A

subdivisions

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12
Q

Ventromedial part of somite undergoes EMT and forms the:

A

Sclerotome

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13
Q

Dorsal part of somite forms __ which further divides into __ and __

A
  • Dermamyotome
  • Dermatome & Myotome
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14
Q

Intermediate part of somite forms ___

A

Syndetome (located between sclerotome and myotome)

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15
Q

Central Sclerotome:

A
  • Pedicles
  • Ventral parts of neural arches
  • Transverse processes
  • Proximal ribs
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16
Q

Ventral Sclerotome:

A

Vertebral body

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17
Q

Dorsal Sclerotome:

A
  • Vertebral arch
  • Vertebral spine (spinous process)
  • Lamina of the vertebral arch
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18
Q

Lateral Sclerotome:

A

Distal ribs

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19
Q

What are the two parts of a sclerotome that divide? Which parts of the divided sclerotome combine?

A
  • Cranial and caudal parts with a intersegmental boundary between (somitocoele cells, von ebners fissure)
  • The caudal part of the superior sclerotome combines with the cranial part of the inferior sclerotome to produce vertebrae
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20
Q

How are the cells organized in the cranial part of the sclerotome? Caudal part?

A
  • Cranial portion contains loosely packed cells
  • Caudal portion contains tight/densely packed cells
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21
Q

Where is the nerve initially trying to grow out before sclerotome resegmentation occurs?

A

At the intrasegmental boundary

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22
Q

Why does the sclerotome undergo resegmentation? What does resegmentation this explain?

A
  • Because the migrating NCC and axons of the motor neurons can only migrate towards the cranial portion of the sclerotome; allows us to have the range of muscle actions that we do for many of our vertebral muscles
  • This explains why there are 8 cervical nerves but only 7 vertebrae, and also why the C1 nerve comes out above its cervical vertebrae
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23
Q

What mediates resegmentation?

A

Protein signaling

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24
Q

What contributes to formation of the occipital bone of the skull?

A

Cranial half of the C1 sclerotome fuses with the sclerotome superior

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25
Q

How many vertebrae do muscle masses span?

A

2

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26
Q

What do ribs develop from?

A

Costal Processes of the thoracic vertebrae

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27
Q

Ribs are cartilaginous during the ___ period and go through endochondrial ossification during the ___ period

A
  • Embryo
  • Fetal
28
Q

What part of the sternum is the last to ossify and sometimes remains cartilaginous for entire lifetime?

A

Xiphoid Process

29
Q

When do ribs start forming?

A

35 days / 5th week of development

30
Q

Paired sternal bars arise in the body wall from somatic layer of ___ ___ ___

A

Lateral Plate Mesoderm

31
Q

Sternum Development

A

(1) Paired sternal bars arise in body wall from lateral plate mesoderm
(2) Originally ventrolateral but move medially
(3) Fuse in a cranial-caudal manner to form cartilaginous models of the manubrium, sternebrae, and xiphoid process

32
Q

What ribs grow faster, true ribs or false/floating ribs?

A

True ribs

33
Q

What gene codes for vertebrae identity?

A

Hox genes

34
Q

What gene is important at the thoracic/lumbar boundary?

A

Hox10 (presence of this gene leads to the loss of ribs that is seen in the lumbar region, not the thoracic region)

35
Q

Hox Genes

A
  • Different Hox gene families expressed in different segments of the vertebrae
  • Family members have nested pattern of expression boundaries along cranial-caudal axis
  • Boundaries correspond to changes in vertebral shape – changes in expression causes transformations of vertebrae
36
Q

What happens if there is a loss of Hox10 paralogs?

A

Leads to presence of thoracic vertebrae/ribs growing in the lumbar and sacral region

37
Q

What happens if there is a gain of Hox10 paralogs?

A

Leads to loss of ribs in the thoracic region; what was supposed to be thoracic vertebrae is now lumbar vertebrae

38
Q

Where do intervertebral discs develop?

A

At the intrasegmental boundary (between cranial and caudal segments of the sclerotomes that make the vertebrae)

39
Q

What is the core of each intervertebral disc composed of?

A

Notochordal cells that produce the Nucleus Pulposus

40
Q

What does the annulus fibrosis (surrounds the nucleus pulposus) develop from?

A

Somitocoele cells

41
Q

Notochord DOES NOT directly contribute to the vertebrae but remnants can give rise to rare tumors called:

A

Chordomas

42
Q

What is myogenesis?

A

The process where myogenic precursors (myotomes) undergo EMT to form skeletal muscle of the trunk and limbs

43
Q

List the steps of Myogenesis

A

(1) Elongation of nuclei and cell bodies of mesenchymal cells -> differentiate into myoblasts
(2) Myoblasts fuse to form myotubes (elongated, multinucleated, cyndrical structures)
(4) During/after fusion, myofilaments develop in the cytoplasm of the myotubes – become invested with connective tissue to produce fasicles

44
Q

Genes expressed when myogenic precursors are in quiescence

A
  • PAX7
  • PAX3
  • MYF5
45
Q

Genes expressed when myogenesis is activated

A
  • MYOD1
  • MYF5
  • PAX 3/7
46
Q

Genes expressed during the differentiation phase of myogenesis

A
  • MYOD1
  • MYOG
  • MYF6
47
Q

Most skeletal muscles develop before __

A

Birth (almost all remaining muscles are formed by the end of the first year)

48
Q

Where are myotomes located?

A

Along each segment of the trunk, cranial-to-caudal (occipital, cervical, thoracic, lumbar, ect)

49
Q

What are the 2 segments the myotome divides into?

A
  • Epimere (dorsal/posterior)
  • Hypomere (ventral/anterior)
50
Q

What does the Epaxial division form?

A
  • Extensor muscles of neck and vertebral column (erector spinae, transverse spinalis muscles)
51
Q

What does the Hypoaxial division form?

A
  • Hypaxial muscles of the lateral and ventral walls in the thorax and abdomen
  • Limb muslces
52
Q

What are the 4 different myotomes of the Hypaxial Division?

A
  • Cervical myotomes: scalene, prevertebral geniohyoid and infrahyoid muscles
  • Thoracic myotomes: lateral and ventral flexor muscles of the vertebral column
  • Lumbar myotomes: quadratus lumborum
  • Sacrococcygeal myotomes: pelvic floor musculature, striated muscles of anus and sex organs
53
Q

Developing spinal nerves divide into what 2 ramus to innervate trunk musculature? What muscles do they supply?

A
  • Dorsal ramus: supplies epaxial muscles
  • Ventral ramus: supplies hypaxial muscles
54
Q

Tendons connecting muscle and vertebrae arise from the:

A

Syndetome (region of somite between developing sclerotome and myotome)

55
Q

What forms primitive axons and enters skeletal muscle of the body wall?

A

Motor neuroblasts

56
Q

What day does the myotome split into two different segments?

A

Day 40

57
Q

When is the layout of the myotomes complete?

A

Day 50

58
Q

Dermatome Definition

A
  • Area of skin innervated by one single spinal nerve or spinal segment
  • Associated with posterior root
59
Q

Myotome Definition

A
  • Muscles innervated by one single spinal nerve or spinal segment
  • Associated with anterior root
60
Q

What are the 5 skeletal wall malformations?

A
  • Cervical ribs
  • Pectus Excavatum
  • Pectus Carinatum
  • Poland Syndrome
  • Prune-Belly Syndrome
61
Q

Cervical Ribs

A
  • Typically attached to C7
  • 1% of population
  • May impinge on brachial plexus and/or subclavian artery (thoracic outlet syndrome)
62
Q

Pectus Excavatum

A
  • 1/300 to 1/400 births
  • Depressed sternum, sunken posteriorly
  • “Funnel chest”
  • Can impinge on lung function
63
Q

Pectus Carinatum

A
  • 1/1500 to 1/2000 births
  • Protrusion of the sternum and costal cartilages
  • “Pigeon chest”
64
Q

Poland Syndrome

A
  • 1/10,000 to 1/100,000 live births
  • Encompass a constellation of anomalies
  • Partial (28%) or complete (72%) absence of pectoral muscles
  • Most commonly unilateral
  • Associated anomalies include: Aplasia/hypoplasia of other chest wall muscles/breast/nipple, absense of teh costal cartilages of ribs 2-4 or 3-5, high-riding scapula (Sprengel deformity), digital anomalies
65
Q

Prune Belly Syndrome

A
  • Congenital disorder defined by a characteristic clinical triad:
    (1) partial or complete absence of abdominal musculature (mesodermal malformation)
    (2) Cryptorchidism (failure of one/both testes to descend)
    (3) Malformation of urinary tract and bladder/urethral obstruction
  • fluid accumulation distends the abdomen causing muscle atrophy, display concomitant cardiopulmonary, GI and MSK anomalies
  • very rare
  • 20% of children are stillborn and 50% do not survive to 2yrs

MSK Exam 1 (6 decks)

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