LEC41: Early Limb Development and the Musculoskeletal System

Question 1

where does limb development begin?

Answer 1

upper extremity

Question 2

when does limb development begin?

Answer 2

end of week 3 - when heart starting to beat

Question 3

when do upper limb buds appear?

Answer 3

day 26-27

Question 4

when do lower limb buds appear?

Answer 4

day 28-29

Question 5

what do limb buds develop from?

Answer 5

proliferation of somatic layer of lateral mesoderm into surface ectoderm

Question 6

where do upper extremities form?

Answer 6

cervical region of embryo

Question 7

where do lower extremities form?

Answer 7

lumbar/sacral region of embryo

Question 8

how does AER form

Answer 8

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

Question 9

what is AER

Answer 9

dense ridge of tissue that’ll form the limb

Question 10

function of SHH

Answer 10

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

Question 11

how does SHH work

Answer 11

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

Question 12

without SHH how would hand appear?

Answer 12

paddle, no fingers

Question 13

what is zone behind AER called?

Answer 13

progress zone

Question 14

function of progress zone

Answer 14

proliferates rapidly, causing mechanical growth of AER

Question 15

what does AER induce

Answer 15

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

Question 16

when does upper limb > hand develop

Answer 16

finished by end of week 6

Question 17

how do fingers form

Answer 17

apoptosis in region of upper limb paddle

Question 18

digital rays

Answer 18

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

Question 19

when do foot plates finish forming

Answer 19

week 7

Question 20

how do toes for m

Answer 20

apoptosis in region of lower limb paddle

Question 21

what is endochondral ossification

Answer 21

mesenchyme remodels into cartilage remodels into bone

Question 22

when does bone ossification occur

Answer 22

begins week 7, finishes after birth

Question 23

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

Answer 23

all cartilage

Question 24

where is growth plate of long bone?

Answer 24

epiphyseal cartilage plate

Question 25

where in bone does primary ossification occur?

Answer 25

diathesis

Question 26

what is direction of bone ossification?

Answer 26

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

Question 27

how can you visualize ossification centers

Answer 27

ultrasound

Question 28

when and how does growth plate become obliterated?

Answer 28

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

Question 29

limb muscle muscle type

Answer 29

skeletal, for movement

Question 30

what are somites derived from

Answer 30

paraxial mesoderm laid down during gastrulation, right next to notochord

Question 31

what do somites differentiate into?

Answer 31

dermomyotome, sclerotome

Question 32

what do dermomyotomes become

Answer 32

dermatomes (dermis), myotomes (muscle)

Question 33

what do sclerotomes become?

Answer 33

vertebrae, ribs

Question 34

which somite derivative is more dense?

Answer 34

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

Question 35

what are myoblasts, where are they derived from?

Answer 35

from myotome region of somites; give rise to muscle fibers

Question 36

what do neural crest cells become?

Answer 36

pigment cells (melanocytes), nerve sheaths, insulators

Question 37

what migrates to end of limb bud/hand?

Answer 37

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

Question 38

what do myoblasts form from

Answer 38

myogenic precursors

Question 39

which muscle compartment forms from aggregate of dorsal myloblasts

Answer 39

extensor

Question 40

which muscle compartment forms from aggregate of ventral myloblasts

Answer 40

flexor

Question 41

how do muscles elongate

Answer 41

as limb grows outward

Question 42

what does limb bud mesenchyme give rise to?

Answer 42

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

Question 43

what controls limb muscles

Answer 43

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

Question 44

when does motor innervation of limbs occur

Answer 44

week 5

Question 45

what provides cutaneous innervation of the limbs?

Answer 45

neural crest cells

Question 46

which nerves mostly supply cutaneous innervation of upper limb?

Answer 46

C6, 7, 8

Question 47

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

Answer 47

C8-T1

Question 48

what nerve root values mostly involved with lower extremity?

Answer 48

L3, 4, 5

Question 49

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

Answer 49

T1, T2

Question 50

how do upper limbs rotate, what is the result?

Answer 50

laterally 90o; elbow becomes dorsal

Question 51

how do lower limbs rotate, what is the result?

Answer 51

medially 90o, knee becomes ventral

Question 52

when did thalidomide impact embryo

Answer 52

critical period of limb development, days 24-36

Question 53

process by which vertebral column forms?

Answer 53

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

Question 54

what makes bony encasement of spinal cord, and when?

Answer 54

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

Question 55

what occurs during mesenchymal stage of vertebral development?

Answer 55

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

Question 56

what is centrome, how does it form?

Answer 56

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

Question 57

action of intersegmental nerves?

Answer 57

grow between 2 portions of sclerotomes, toward myotomes

Question 58

what does centrum formation create?

Answer 58

space for intervertebral disc

Question 59

hypaxial dermomyotome becomes

Answer 59

flexor muscles

Question 60

epaxial dermomyotome becomes

Answer 60

extensor muscles

Question 61

what happens to notochord during vertebral development?

Answer 61

degenerates within vertebral bodies; forms nucleus pulposis of IV discs

Question 62

when and where are chondrification centers re: vertebral development?

Answer 62

week 6 | formation of cartilagenous vertebral column

Question 63

when is cartilaginous stage of vertebral development?

Answer 63

week 6

Question 64

when is bony stage of vertebral development?

Answer 64

week 7

Question 65

where are ossification centers during bony stage of vertebral development?

Answer 65

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!

Question 66

what is kyphoscoliosis

Answer 66

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

Question 67

what causes kyphoscoliosis

Answer 67

hemivertebra (1 or more)