LEC41: Early Limb Development and the Musculoskeletal System Flashcards Preview

Structures: Part Deux > LEC41: Early Limb Development and the Musculoskeletal System > Flashcards

Flashcards in LEC41: Early Limb Development and the Musculoskeletal System Deck (67):
1

where does limb development begin?

upper extremity

2

when does limb development begin?

end of week 3 - when heart starting to beat

3

when do upper limb buds appear?

day 26-27

4

when do lower limb buds appear?

day 28-29

5

what do limb buds develop from?

proliferation of somatic layer of lateral mesoderm into surface ectoderm

6

where do upper extremities form?

cervical region of embryo

7

where do lower extremities form?

lumbar/sacral region of embryo

8

how does AER form

apical ectodermal ridge, formed by mesenchyme pushing into ectoderm, induces it to thicken at apex

9

what is AER

dense ridge of tissue that'll form the limb

10

function of SHH

sonic hedgehog tissue factor - differentiates limb bud from symmetrical structure to distinct fingers

11

how does SHH work

gradient across mesenchymal growth area; most dense in zone of polarizing activity which gives hands diff poles

12

without SHH how would hand appear?

paddle, no fingers

13

what is zone behind AER called?

progress zone

14

function of progress zone

proliferates rapidly, causing mechanical growth of AER

15

what does AER induce

tissue, transcription factors to feed back on mesodermal core (mesenchyme) and become musculoskeletal (bone, muscle) components

16

when does upper limb > hand develop

finished by end of week 6

17

how do fingers form

apoptosis in region of upper limb paddle

18

digital rays

outgrowths from hand/foot paddles that become fingers, toes; each has AER (apical ecotodermal ridge, growth area) at its tip

19

when do foot plates finish forming

week 7

20

how do toes for m

apoptosis in region of lower limb paddle

21

what is endochondral ossification

mesenchyme remodels into cartilage remodels into bone

22

when does bone ossification occur

begins week 7, finishes after birth

23

end of week 6, what is make up of limb skeleton?

all cartilage

24

where is growth plate of long bone?

epiphyseal cartilage plate

25

where in bone does primary ossification occur?

diathesis

26

what is direction of bone ossification?

primary ossification in diathesis; bone grows toward secondary ossification centers at ends of bone, the growth plates

27

how can you visualize ossification centers

ultrasound

28

when and how does growth plate become obliterated?

at/after puberty; diaphysis-epiphysis fuse, long bone growth stops (or earlier if have something like radiation)

29

limb muscle muscle type

skeletal, for movement

30

what are somites derived from

paraxial mesoderm laid down during gastrulation, right next to notochord

31

what do somites differentiate into?

dermomyotome, sclerotome

32

what do dermomyotomes become

dermatomes (dermis), myotomes (muscle)

33

what do sclerotomes become?

vertebrae, ribs

34

which somite derivative is more dense?

dermomyotome (outer layer) is more dense than sclerotome (inner layer)

35

what are myoblasts, where are they derived from?

from myotome region of somites; give rise to muscle fibers

36

what do neural crest cells become?

pigment cells (melanocytes), nerve sheaths, insulators

37

what migrates to end of limb bud/hand?

myogenic precursors from myotomes & major blood vessels, nerves, muscle fibers (flexors, extensors)

38

what do myoblasts form from

myogenic precursors

39

which muscle compartment forms from aggregate of dorsal myloblasts

extensor

40

which muscle compartment forms from aggregate of ventral myloblasts

flexor

41

how do muscles elongate

as limb grows outward

42

what does limb bud mesenchyme give rise to?

loose CT > tendons, ligaments, blood vessels that attach to bone

43

what controls limb muscles

motor nerve axons, arise from spinal cord; grow into both dorsal and ventral muscle masses

44

when does motor innervation of limbs occur

week 5

45

what provides cutaneous innervation of the limbs?

neural crest cells

46

which nerves mostly supply cutaneous innervation of upper limb?

C6, 7, 8

47

spinal cord transsection where would allow upper limbs to still work?

C8-T1

48

what nerve root values mostly involved with lower extremity?

L3, 4, 5

49

what is root value for dermatomal innervation for anterior aspect for arm?

T1, T2

50

how do upper limbs rotate, what is the result?

laterally 90o; elbow becomes dorsal

51

how do lower limbs rotate, what is the result?

medially 90o, knee becomes ventral

52

when did thalidomide impact embryo

critical period of limb development, days 24-36

53

process by which vertebral column forms?

endochondral ossification: mesenchymal models of vertebrae made; transform into cartilage; cartilage, w/ osteoplasts & osteoblasts, become ossified, elongated bone

54

what makes bony encasement of spinal cord, and when?

sclerotomes from somites surround neural tube; embryonic week 4-5

55

what occurs during mesenchymal stage of vertebral development?

sclerotomal cells "migrate to"
1) notocord
2) neural tube
3) body wall

56

what is centrome, how does it form?

body of vertebra, neural arches on sides of vertebral bodies; forms when cranial portion of 1 sclerotome joins w/ caudal portion of adjacent sclerotome

57

action of intersegmental nerves?

grow between 2 portions of sclerotomes, toward myotomes

58

what does centrum formation create?

space for intervertebral disc

59

hypaxial dermomyotome becomes

flexor muscles

60

epaxial dermomyotome becomes

extensor muscles

61

what happens to notochord during vertebral development?

degenerates within vertebral bodies; forms nucleus pulposis of IV discs

62

when and where are chondrification centers re: vertebral development?

week 6
formation of cartilagenous vertebral column

63

when is cartilaginous stage of vertebral development?

week 6

64

when is bony stage of vertebral development?

week 7

65

where are ossification centers during bony stage of vertebral development?

3 primary ossification centers in vertebra:
1) body of vertebra
2) 1 in each neural arch, to 2 others

continue to ossify until age 25 - long bones to grow!

66

what is kyphoscoliosis

when sclerotomes split and nerves grow between, one of them doesn't split correctly or disproportionate split, etc. - anything to make hemivertebrae not form - get klyphoscholiosis of the spine

67

what causes kyphoscoliosis

hemivertebra (1 or more)