Limb Development

Question 1

paraxial mesoderm branches into ____ -> _____
and ___ –> ____ –> ____
–> ____ –> ____

Answer 1

paraxial mesoderm branches into sclerotome -> axial skeleton

and dermomyotome –> dermatome –> dermis
–> myotome–> axial limb/muscle

Question 2

what initiates limb development

Answer 2

reciprocal induction from lateral plate mesoderm

Question 3

mesenchymal core of ____ and ___ is formed

Answer 3

somatic lateral plate mesoderm: bones/vasculature/connective tissue

somitic mesoderm from myotome: musculature

Question 4

origin of:

sensory axons/Schwann cells
myoblasts
pigment cells
endothelial cells
motor axons

Answer 4

neural crest
somites
neural crest
vessels of the trunk
neural tube

Question 5

progress zone model

Answer 5

maintains underlying mesenchyme as undifferentiated and differentiation occurs proximal to distal

Question 6

early specification model

Answer 6

cell fate decided early, cell populations expand

Question 7

cranial caudal axis development

Answer 7

SHH expressed in caudal Zone of Polarizing Activity (morphogenetic gradient)

Question 8

Dorsal-Ventral axis

Answer 8

dorsal extoederm expresses signaling molecules and ventral has absense of signal

Question 9

steps of segment separation

Answer 9

1) constriction at wrist and elbow
2) flattening at handplate and footplate
3) division of AER (apical ectodermal ridge) and apoptosis b/w digits

Question 10

secondary ossification centers

Answer 10

develop in the epiphysis where there is the secretion of osteocytes to fill the cartilaginous plate with bone

Question 11

interzones form at presumptive _____. _____ form the articular surfaces, and the interzones degenerate to form ________.

Answer 11

joints, hyaline cartilage, synovial cavity

Question 12

dorsal muscles

Answer 12

extensors and supinators of upper limb

extensors and abductors of lower limb

Question 13

ventral muscles

Answer 13

flexors and protonators of upper limb

flexors and adductors of lower limb

Question 14

sensory fibers form from _____ more slowly than motor fibers. From the _____, they can innervate ___/___ or ____/___ muscle.

Answer 14

sensory fibers from DRG form more slowly than motor fibers. From the ventral ramus, they can innervate dorsal/posterior or ventral/anterior muscle.

Question 15

limb rotation; thumbs are ___ while big toes are _____

Answer 15

forelimb and hindlimb rotate 90 degrees. thumb = lateral, big toes = medial