Kuehn - neurulation and fate of mesoderm Flashcards
what is neurulation
process of neural tube formation (differentiates from ectoderm overlying the notochord)
what thickens into the neural plate
the receptive area (oval patch stretching from oral plate to primitive node)
what is expressed by notochord to activate the folding of the neural tube
SHH (sonic hedgehog)
what contracts inducing the neural plate to fold
actin filaments at apical surface contract until edges fuse together = neural groove -> neural tube
what are the edges of the neural folding called
neural fold
after the neural folds fuse together, what forms around the neural tube
ectoderm
what happens at 20 days
folds begin to form at center of embryo and somites form on either side
what happens at 22 days
center folds have fused - zippering from center to edges
what day are there 2 small connections/openings between the amnion and neural tube
day 23
what day does the rostral neuropore close at
day 25
what happens at day 27
the caudal neuropore closes
what happens if the rostral neuropore has a delay in closing
exencephaly - failure to develop occipital/parietal bones -> dural and brain herniation
what is spina bifida
if there is a delay in the caudal neuropore closing - failure of formation of lamina and spine in lower thoracic/upper lumbar vertebral column
what develops between the two neuropores at the proximal part of the neural tube
brain and brainstem (prosencephalon, mesencephalon, and rhombencephalon)
what is primary neurulation
period of time where there is neural folding
what is secondary neurulation
neural tube (lower sacral) forms by development of medullary core - cannulates and joins with rest of neural tube
what 2 things does the umbilicus arise from
umbilical vesicle and connecting stalk
when is the umbilicus detached
at 6 weeks
what is the fate of the ectoderm
skin, epidermal glands, hair, nails, eye (lens and corneal epithelium), inner ear labyrinth, anterior pituitary, and tooth enamel
what is neuroectoderm
specialized ectoderm
what arises from neuroectoderm
brain, brainstem, spinal cord, eye (retina, pigmented epithelium, optic nerve, part of iris) and pars nervosa of pituitary gland
what is continuous with the endoderm
yolk sac membrane (extra-embryonic mesoderm, yolk-sac epithelium)
what is the original endoderm (hypoblast) replaced with
mesodermal cells
what epithelia arises from endoderm
epithelium of alimentary canal, parenchyma of pancreas and liver, thyroid, parathyroid, thymus, lung, trachea, middle ear epithelium, urinary bladder, urethral epithelia, and vaginal epithelium
what is the septum transversum
it migrates with heart during folding - separates throrax from abdomen and then participates in venous cardiac development
what does the intermediate mesoderm give rise to
kidney, ureter, ductus deferens and gonads
where does the neural crest layer come from
the neural folds
what does the neural crest layer give rise to
melanocytes, PNS, adrenal medulla, bulbar ridges of heart- semilunar valves, meninges, and near head can form- bone, cartilage and other connective tissue of pharyngeal arches, odontoblasts and ear ossicles
what 2 types of mesoderm come from the lateral plate mesoderm
somatic mesoderm (somatopleure) and splanchinic mesoderm (splanchonopleure)
what 2 layers does the somatic mesoderm differentiate into
dermomyotome and sclerotome
what does the somatic mesoderm give rise to
bones, cartilage, fascia, and other connective tissue around periphery of body
what does the dermomyotome give rise to
dermis of skin and muscles
what does the sclerotome give rise to
vertebral bones and intervertebral disks
what does the splanchinic mesoderm give rise to
visceral smooth muscle, fascia, and connective tissue of viscera and associated vasculature
when does the mesenchymal migration occur for endochondral bone development
4th-5th week
what happens in the 5th-6th week for endochondral bone development
condensation of mesoderm
what happens at the beginning of the 6th week for endochondral bone development
chondrification
what happens weeks 7-12 for endochondral bone development
primary ossification
what happens from birth - 9th year for endochondral bone formation
secondary ossification
when do the epiphyseal plates fuse together
years 18-25
From what do vertebra develop
arise from sclerotome - each segment is derived from 2 seperate somites - come together to form single vertebra
From what are intervertebral disks formed
mesoderm remaining behind after mesodermal migration
what are the steps for muscle formation starting at the 15th week
migrating myoblasts - fusion of myoblasts - primary myotube - myotube growing - secondary myotube - mature skeletal muscle fiber
how do the upper and lower limbs grow
with middle joint facing laterally and ventral surfaces facing medially
