Lecture 3 Flashcards
what forms somites along the spinal cord and somitomeres in the head?
paraxial mesoderm
3 components of a somite
dermatome (skin)
myotome (muscle)
sclerotome (bone)
tissues derived from the mesodermal germ layer
mesoderm
any loose connective tissue regardless of origin
Ex: neural crest cells
mesenchyme
2 parts of neurocranium
- membranous: flat bones, intramembranous ossification
2. chondocranium: formed cartilage model first then ossification: bones of the base
the prechordal portion of the chondrocranium (part of neurocranium) is derived from the ______
neural crest (cranial to pituitary)
everything on the chondrocranium (part of the neurocranium) except the prechordal portion is derived from the _______
paraxial mesoderm
narrow seams of connective tissue that separate the flat bones of the skull allowing molding of the skull through the birth canal and growth and expansion as the brain grows
Ex: coronal, sagittal, etc.
suture
larger spaces between the bones of the skull
“soft spots” in babies
fontanelles
early fusion of the sutures of the skull in babies
abnormal skull
many defects result from mutations in fibroblast growth factor receptors (FGFRs)
craniosynostosis
facial part of the skull
mostly from the frontonasal prominence and the 1st and 2nd pharyngeal arches
formed from neural crest cells
viscerocranium
first pharyngeal arch portion of viscerocranium
maxilla
mandible
malleus
incus
second pharyngeal arch portion of viscerocranium
stapes
part of hyoid bone
limb buds form furing 4th and 5th weeks
positions specified by ________
HOX genes
gene that specifies forelimb structures
TBX5 gene
gene that specifies hindlimb structures
TBX4 gene
layer of thickened ectoderm at the distal tip of the limb that controls outgrowth of the limb by maintaining a rapidly proliferating population of adjacent mesoderm cells
FGFs maintain a rapidly proliferating population of cells adjacent to the ridge
“progress zone”
apical ectodermal ridge (AER)
occurrence that allows formation of digits
separates each finger
cell death (apoptosis) in the ridge
cranial to caudal (anterior-posterior) patterning
thumb to little finger
zone of polarizing activity (ZPA)
two morphogens that control the zone of polarizing activity (ZPA)
sonic hedgehog (SHH) and retinoic acid
genes that control bone patterning
HOX genes
defect that causes no limbs
Amelia
defect that causes short limbs
partial absence of a limb
Meromelia
anti-nausea drug that causes limb defects in newborns
now an anti-cancer, anti-AIDS drug
seeing limb defects again
Thalidomide
defect that causes too many digits
polydactyly
defect that causes fused digits
syndactyly
defect that causes short digits
barchydactyly
from what two things is the vertebral column derived from?
somites (sclerotome)
notochord (nucleus pulposus of intervertebral disc)
when forming the vertebral column, what allows for movement between vertebra?
caudal part of one sclerotome fuses with cranial part of another
intersegmental so that muscles bridge the vertebra to act on them
intersegmental fusion of sclerotome with cranial part of another
muscles bridge the vertebra to act on them and allow movement
resegmentation
epithelial balls of cells formed in segmental pairs along the neural tube from paraxial mesoderm
differentiate into vertebrae, muscles of the back and body wall, and dermis of the skin
somites
loosely organized segmented collections of paraxial mesoderm in the cranial region
form muscles and bones of the face and skull
somitomeres
secreted protein that acts as a morphogen in several emybryonic sites: limbs, somites, guy formation, and establishment of the id-line in the CNS
sonic hedgehog (SHH)
shaft of the long bone
diaphysis
end of long bone
epiphysis
proliferating population of mesenchyme cells immediately beneath the apical ectodermal ridge (AER)
by signaling through FGFs, the AER maintains this and promotes proximodistal growth of the limb
progress zone
