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MM Test 1 > B6.012 Early Development of the MSK System > Flashcards

B6.012 Early Development of the MSK System Flashcards

1
Q

what are the components of the MSK system

A 
muscles
connective tissue:
-bone
-cartilage
-ligaments
-tendons
-fascia
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2
Q

components of muscle

A

actin and myosin

collagen in endomysium

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3
Q

components of bone

A

collagen and calcium

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4
Q

types of cartilage

A

fibrous- in ligaments, tendons, and joint capsules
hyaline- can provide model for bone formation
both collagen

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5
Q

function and components of ligaments

A

connect bones to bones, enable motion

bands of fibrous connective tissue (collagen) with dense irregular CT sheaths surrounding bundles

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6
Q

function and components of tendons

A

connect muscle to bones, allow joint movement

bands of fibrous CT (collagen), no sheath

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7
Q

function and components of fascia

A

attaches, stabilizes, encloses and separates muscles
allows smooth, unrestricted movement
band or sheet of fibrous connective tissue (collagen)

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8
Q

origin of general muscle tissue

A

mesodermal germ layer

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9
Q

origin of skeletal muscle

A

paraxial mesoderm

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10
Q

origin of smooth muscle

A

splanchnic/visceral lateral plate mesoderm

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11
Q

origin of mammary and sweat gland muscles

A

ectoderm

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12
Q

origin of cardiac muscle

A

splanchnic/visceral LPM

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13
Q

what are the derivatives of the paraxial mesoderm that develop into skeletal muscle

A

somitomeres and somites
transient paired structures
segment cranial-caudal axis

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14
Q

origin of head muscles

A

7 somitomeres in occipital region

partially segments whorls of mesenchymal cells

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15
Q

origin of body wall and limbs muscle

A

somitomeres that undergo epithelialization to form balls of epithelial cells with cavities (somites)
extend from occipital region to tail bud

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16
Q

derivatives of the somite

A

sclerotome
myotome
dermatome
ventrolateral cells (subset)

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17
Q

sclerotome

A

ribs
vertebrae
rib cartilage

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18
Q

myotome

A

muscles of the back, body wall (intercostals), and some limb muscles

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19
Q

dermatome

A

connective tissue of dermis of back

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20
Q

ventrolateral cells (subset of myotome)

A

most of musculature for body wall (obliques, transversus abdominis) and limbs

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21
Q

how is the sclerotome formed from somite

A

ventral region of somite becomes mesenchymal again to form sclerotome

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22
Q

how is dermatome formed from somite

A

dorsal region of somite becomes dermatome and 2 muscle forming regions (dorsomedial and ventrolateral)
cells migrate ventrally

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23
Q

what is the dermamyotome

A

formed from migrating DM and VL muscle cells migrating ventral to dermatome to form the myotome

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24
Q

what happens to a subset o VL muscle cells?

A

migrate into lateral plate mesoderm (parietal layer) to form: infrahyoid, abdominal wall, and limb muscles

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25
Q

what happens to the rest of the myotome cells?

A

form muscles of back, shoulder girdle, and intercostals

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26
Q

what is the lateral somatic frontier (LSF)

A

separates 2 domains of muscle precursor cells (based on origin) into primaxial and abaxial domains

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27
Q

primaxial domain

A

region around neural tube
contains only somite derived cells (paraxial mesoderm)
signaling from neural tube and notocord

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28
Q

abaxial domain

A

parietal layer of LPM plus somite cells from VL region of myotome that migrated across LSF
signaling from LPM

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29
Q

how do skeletal muscle cells form from myoblasts?

A
  1. myoblasts fuse and form long, multinucleated muscle fibers, wrapped in CT (endomysium)
  2. myofibrils appear in cytoplasm
  3. cross striations appear at the end of the 3rd month
  4. bundles of myofibers wrapped in CT (epimysium) are called fascicles
  5. partitions of CT (perimysium) form septa
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30
Q

function of CT layer in skeletal muscle fibers

A

contains blood vessels and nerves for muscle

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31
Q

when does cardiac muscle form

A

4th week

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32
Q

what is the origin of cardiac muscle

A

lateral plate (splanchnic/visceral) mesoderm surrounding epithelial heart tube

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33
Q

how do myoblasts of cardiac muscle develop

A
  1. myoblasts adhere to each other by special attachments that develop into intercalated disks
  2. growth of myofibers occurs by formation of new myofilaments
  3. myoblasts DO NOT fuse like in skeletal, myofibers are mono- or bi-nucleated
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34
Q

how do purkinje fibers differ from normal cardiac muscle fibers

A

bundles of muscle cells with irregularly distributed myofibrils and larger cell diameters

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35
Q

origin of smooth muscle cells (SMC) of some blood vessels

A

LPM (splanchnic/visceral)

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36
Q

origin of SMC of coronary arteries

A

proepicardial cells and neural crest

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37
Q

origin of SMC of wall of gut and its derivatives

A

surrounding LPM (splanchnic)

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38
Q

origin of SMC of pupil sphincter and dilator muscles

A

ectoderm

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39
Q

origin of myoepithelial cells in mammary and sweat glands

A

ectoderm

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40
Q

formation of smooth muscle cells

A
  1. differentiation of mesenchymal cells with development of elongated nuclei in spindle shaped myoblasts
  2. myoblasts DO NOT fuse and remain mononucleated
  3. later, more SMC are formed by division of existing myoblasts
  4. filamentous but non sarcomeric contractile elements develop in cytoplasm
  5. some develop into sheets or bundles
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41
Q

origin of axial tendons

A

dorsolateral sclerotome (PA mesoderm) derivatives, lie adjacent to myotomes at anterior and posterior somite borders

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42
Q

origin of limb tendons

A

LPM and dorsolateral sclerotome

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43
Q

origin of deep fascia

A

mesenchymal (mesodermal) undifferentiated CT

present in embryo from week 21

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44
Q

location of deep fascia

A

parallel to skin below subQ adipose tissue
projections extend superficially to organize adipose
projections extend deeply to embed muscle tissue
forms networks in body

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45
Q

factors associated with tendon development

A

SCLERAXIS transcription factor

46
Q

factors associated with muscle development

A

MyoD and MYF5

myogenic regulatory factors

47
Q

factors associated with VL expression of MyoD

A

LPM: BMP4 and FGF
ectoderm: WNT

48
Q

factors associated with DM expression of MYF5

A

ectoderm: BMP4
neural tube: WNT (induced by BMP4)
neural tube floor plate and notochord: SHH (low levels)

49
Q

what controls muscle patterning

A

connective tissue (produced by fibroblasts) into which myoblasts migrate

50
Q

sources of head connective tissue

A

neural crest

51
Q

sources of occipital and cervical connective tissue

A

somitic mesoderm

52
Q

sources of body wall/limb connective tissue

A

LPM (parietal/somatic)

53
Q

when does limb growth and development occur

A

weeks 4-8

54
Q

when are limb buds visible

A

end of 4th week
outpocketings of VL body wall
forelimbs precede hindlimbs by 1-2 days and ongoing forelimb morphogenesis continues to precede hindlimbs

55
Q

components of limb buds

A

a) mesenchymal core (LPM- parietal/somatic) forms bones and CT
b) overlying cuboidal ectoderm (forms apical ectodermal ridge)

56
Q

what is the apical ectodermal ridge (AER)

A

ectoderm at distal border of each limb thickens to for AER
induces adjacent mesenchyme to remain undifferentiated
has role in forming proximal-distal axis

57
Q

what happens to limb development at 6 weeks

A

terminal portion of limb buds

a) flatten to form hand and foot plates
b) become separated from proximal segment by a circular constriction

58
Q

what are hyaline cartilage models

A

as limb grows, cells furthest from AER differentiate into chondrocytes and form cartilage models (6th week)
hyaline cartilage models precede bone

59
Q

3 clear components of limbs

A
  1. stylopod (proximal)
  2. zeugopod
  3. autopod (distal)
60
Q

what happens in the 7th week of limb development

A

limbs develop 3 clear components
limbs rotate in opposite directions
upper: 90 degrees laterally
lower: 90 degrees medially

61
Q

how do digits form

A
  1. programmed cell death in AER separates ridge into 5 parts
  2. digit outgrowth continues under influence of 5 ectodermal ridges
  3. mesenchyme condenses to form 5 cartilaginous digital arrays
  4. programmed cell death occurs between digital arrays to form digits
62
Q

brachydactyly

A

shortened digits

63
Q

syndactyly

A

fused soft tissue and/or bones of digits

failure of apoptosis of interdigit mesenchyme

64
Q

polydactyly

A

extra digits

lack proper muscle connections

65
Q

ectrodactyly

A

lack of central digits (cleft hand/foot)

66
Q

cleft hand/foot

A

abnormal cleft between 2nd and 4th metacarpals/tarsals and soft tissues
3rd metacarpal/tarsal absent

67
Q

overview of joint formation

A

weeks 6-8
joints are formed in cartilaginous condensations
chondrogenesis is arrested and a joint interzone is induced

68
Q

3 types of joints

A

fibrous
cartilaginous
synovial

69
Q

fibrous joints

A

joined by fibrous tissue, limited mobility
interzonal mesenchyme between bones differentiates into dense fibrous tissue
ex: sutures of skull

70
Q

cartilaginous joints

A

joined by cartilage, limited mobility
interzonal mesenchyme between bones differentiated into hyaline (costochondral joints) or fibrocartilage (pubis symphysis)

71
Q

synovial joints

A

common joint, most mobile

ex: knee

72
Q

knee joint (synovial) formation

A
  1. cells in interzone increase in number/density and form dense fibrous tissue
  2. fibrous tissue forms articular cartilage, synovial membranes, menisci and ligaments in joint capsule
  3. cell death creates joint cavity
  4. surrounding mesenchymal cells differentiate into a joint capsule
73
Q

discuss innervation of joints

A

innervated by same nerves that innervate the attached muscles and overlying skin
in addition to fibers carrying proprioceptive information, there are abundant pain fibers in the joint

74
Q

arthrogryposis

A

congenital joint contractures

neurological/muscle/joint defects

75
Q

discuss the formation of limb muscles from myotomes (of somites)

A

begin in 7th week
condensation of mesenchyme near base of limb buds form (derivate of DL cells of somites)
initially segmented according to somite origin, but eventually form single muscle
limb patterning based on CT derived from LPM (parietal)

76
Q

when do flexor and extensor compartments emerge

A

with elongation of limb buds

additional splittings and fusions occur

77
Q

Poland sequence

A

absence of pec minor
partial loss of pec major
nipple and areola are absent or displaced
breast development altered
can occur with digital defects on affected side

78
Q

prune belly syndrome

A

partial or complete loss of abdominal muscles
organs visible through thin abdominal wall
urinary tract malformations may be present

79
Q

what are muscular dystrophies

A

inherited muscle diseases that cause progressive muscular wasting and weakness
some caused by mutations in gene for dystrophin

80
Q

what is dystrophin

A

cytoplasmic protein
forms protein complex linking contractile elements to cell membrane
maintains cell structure of myocytes and enables contraction

81
Q

what happens to muscle cells lacking dystrophin

A

degenerate and die
replaced by fibrous tissue
remaining muscle cells hypertrophy

82
Q

Duchenne MD

A 
X-linked recessive, 1 in 4,000 male births
NO functional dystrophin made
early onset < 5 yo
progressive muscle weakness
lifespan ~20 years
83
Q

Becker MD

A 
X-linked recessive
dystrophin of altered MW is made
some dystrophin in muscles (milder presentation)
onset around puberty
lifespan ~40-50
84
Q

motor innervation of developing musculature

A

due to vertebral level from which muscle cells originate

85
Q

limb muscle innervation

A

innervated by primary ventral rami of spinal nerves from its spinal segment
divide to form dorsal and ventral branches to compartments
branches unite to form larger nerves
contact between nerves and muscle cells necessary for differentiation

86
Q

sensory innervation of musculature

A

spinal nerves
reflects embryological origin and innervation of skin dermatomes (NOT somite dermatome)
dermatome pattern changes with growth and rotations of extremities; but retains segmental pattern

87
Q

blood supply to the limbs

A

supplies by branches of intersegmental arteries from the aorta
primary axial artery and its branches form in limbs, vascular pattern progresses via angiogenesis to form vessels of upper and lower limbs

88
Q

molecular regulation of proximal-distal limb development

A

outgrowth from body wall: FGF10 from LPM
formation of AER: BMPs in ventral ectoderm
restriction of AER to distal limb tip: SER2 from RADICAL FRINGE in dorsal limb ectoderm
establishment of AER: SER2 at border we ENGRAILED-1

89
Q

what factors does AER express

A

FGF4 and 8

maintain progress zone/undifferentiated zone of proliferating mesenchyme near AER

90
Q

what induces patterning of 3 limb segments

A

depends on relative distance from signals
retinoic acid - stylopod
SHH - zeugopod
FGF stops - autopod

91
Q

what is anterior to posterior limb development

A

thumb to pinky development

92
Q

how is anterior to posterior limb development regulated

A

zone of polarizing activity (ZPA)- cluster of mesenchymal cells at posterior border of limb, near AER

93
Q

what is the function of ZPA

A

produced retinoic acid which leads to expression of SHH
contributes to specification of posterior in AP axis
as limb grows, ZPA moves distal in proximity to posterior border of AER

94
Q

what happens if anterior to posterior limb development is dysregulated

A

abnormal expression of SHH by ZPA misplaced to anterior border leads to duplication of ZPA and SHH
signaling
results in mirror duplication of posterior limb structures (little fingers)

95
Q

function of HOX gene

A

gene expression in limbs that correspond to 3 limb segments

regulates types and shapes of bones

96
Q

molecular regulation of dorsal-ventral limb development

A

BMPs in ventral ectoderm induce EN1
WNT7 in dorsal ectoderm induce LMX1
EN1 repressed WNT7 (act antagonistically)

97
Q

amelia

A

complete absence of upper and/or lower limbs

98
Q

meromelia

A

partial absence of limbs

99
Q

phucomelia

A

long bones absent; rudimentary hands/feet attached to trunk

100
Q

micromelia

A

all segments of limb present, but short

101
Q

effects of thalidomide on limb development

A

when taken by pregnant women, leads to defects
absence or gross deformities of long bones
intestinal and cardiac abnormalities as cell
4th and 5th weeks of development are most sensitive for teratogens

102
Q

origin of teeth

A

arise from interactions between oral epithelium and neural crest derived mesenchyme
NOT bones
harder than bones due to dentine

103
Q

structure of bones

A

composed of minerals but are mostly collagen
exterior lined by periosteum w/ osteoblasts
interior BM produces RBCs and WBCs

104
Q

structure of teeth

A

composed of minerals
exterior is enamel (non regenerative)
interior dental pulp does not produce blood cells

105
Q

when does tooth development occur

A

3 months

106
Q

overview of tooth development

A

buds for permanent teeth form and lie on lingual aspect of milk teeth
buds remain dormant until age 6
buds grow and push against milk teeth
milk teeth lost

107
Q

what happens as permanent teeth grow

A

root of overlying deciduous tooth is resorbed by osteoclasts

108
Q

natal teeth

A

premature baby teeth present in newborns

may or may not survive

109
Q

hypodontia

A

6 or fewer permanent teeth missing

110
Q

oligodontia

A

more than 6 permanent teeth missing

111
Q

when should you have your first dental visit

A

by 1 year of age

MM Test 1 (20 decks)

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