limb embryology Flashcards
(24 cards)
which spinal segments contribute to the brachial plexus?
C5-T1
what is the critical period in embryonic development?
day 24-36
what germ layer are the limbs derived from?
lateral mesoderm —> somatic layer –> lines body wall
limbs arise from body wall
lateral plate mesoderm forms the connective tissue of limbs
what spinal segments contribute to the sacral plexus?
L4-S3
lower limb buds form ____ days later than upper limb buds.
2
limb bud structure:
-mesenchymal core (loose, undifferentiated mesoderm)
-covered in ectoderm
somatopleure layer
what starts the process of limb development?
-activation of mesenchymal cells in the lateral mesoderm
-activation induces the formation of an apical ectodermal ridge (AER)
limb development steps:
-activation of mesenchymal cells in lateral mesoderm
-induces apical ectodermal ridge to form (AER). AKA an ectodermal thickening at apex of limb bud.
-mesenchyme condenses and gives rise to skeleton and connective tissue
role of AER?
has an inductive influence on the mesenchyme
stimulates mesenchyme proliferation
growth and creation of a proximal-distal axis of the limb
when do upper limb buds appear?
day 26-27
when does hand/foot plate formation take place?
week 5
what is a hand and foot plate?
formed when the limb buds enlarge and flatten at the ends
when does digital ray formation take place?
week 6
describe digital ray formation process?
mesenchyme/tissue between digital rays condense and undergoes apoptosis
forms notches which are the primordial digits
what abnormality results from too many digital rays?
polydactyly
during which week do fingers and toes become separated?
week 8
what happens if theres an error during week 8?
syndactyly
mesenchyme fails to undergo apoptosis
describe limb rotation:
initially, extensors are lateral and flexors are medial
upper limbs 90 deg laterally:
-anterior flexors
-posterior extensors
lower limbs 90 degrees medially:
-anterior extensors
-posterior flexors
primary vs secondary ossification centers
primary - shaft, formed during development, allows for osteogenesis (cartilage –> bone) of the long bones during fetal development
secondary - at the epiphyses, formed after birth, at growth plate, ossification of the carpal and tarsal bones (1 year after birth)
what germ layer is the limb musculature derived from?
hypaxial division of myotome (paraxial mesoderm)
describe the timeline for motor and sensory nerve limb bud innevation?
motor neurons arise and enter limb bud around week 5
sensory neurons enter AFTER because they use the motor neurons as a guide
what are the dermatomes created from?
neural crest cells
limb bud arterial supply:
intersegmental arteries that arise from the dorsal aorta
the primordial vascular pattern - primary axial artery and its branches
what is embryonic band syndrome?
tears in the amnion create “amnionic bands” that can wrap around limbs and digits, causing amputations
