Embryology Flashcards
From what layer does the nervous system develop?
primitive ectoderm
What happens during week 3 of development?
gastrulation
ectoderm forms neural plate (neural induction- day 16)
rolls up to form neural tube (neurulation)
some neural crest cells migrate out to form PNS
What is the process of neural induction?
Day 16-22, aka end of the 3rd week: axial mesoderm forms the notocord (becomes the nucleus pulposis of intervertebral discs in adults). Notocord secretes factors that induce formation of neuralepithelial cells that become the neural plate.
What is neurulation? What cells are involved?
process by which neural plate rolls up to form the neural tube. neuroblasts, which are precursors to neurons, undergo morphologic changes.
What is primary neurulation? When does it begin and end and what does it form?
begins around day 18 (2.5 wks)
forms brain and spinal cord through the lumbar region
at day 18, neural folds form from thickenin in neural plates. they begin to close in the cervical region and continue closing from that point in a zipper like fashion (both rostral and caudal directions). Neural canal communicates with the amniotic fluid on both sides to form a rostral/anterior neuropore and a caudal/posterior neuropore. The rostral neuropore closes at day 24 and the caudal at day 26.
What is secondary neurulation? When does it begin and end, and what does it form?
begins day 20 and ends day 42.
begins with formation of the caudal eminence, which enlarges and then cavitates. eventually forms the sacral and coccyeal levels
What happens if neurulation doesn’t go well?
dysraphic effects. usually, a neuropore doesn’t close. if it is the anterior neuropore, anencephaly happens; if it is the posterior neuropore, spina bifida happens
What happens during week 4 of development?
closure of nucleopores (day 24 for rostal and day 26 for caudal). Then, formation of primary brain vesicles: prosencehphalon, mesencephalon, rhombencephalon
What are the bends seen in the nervous system at week 4?
cervical flexure between the rhombencephalon and the spinal cord
cephalic flexure in mesencephalic region (between rhombencephalon and mesencephalon)
When do the definitive brain vesicles form? What are theym and from which primary brain vesicles are they derived?
form at week 5. 5 vesicles.
from prosencephalon, telencephalon (bilobed) and diencephalong (2)
from mesencephalon, continued mesencephalon
from rhombencephalong, metencephalon and myelencephalon.
How does the ventricular system develop?
telencephalonic vesicle cavities become lateral ventricles
cavities of the diencephalic vesicle becomes the 3rd ventricle
cavity of the mesencephalon is the cerebral aqueduct
cavity of the rhombencephalon is the 4th ventricle
What is the most common cause of congenital hydrocephalus?
obstruction of CSF flow through the cerebral aqueduct.
What is the basic design of the early neural tube?
3 layers. ventricular zone: source of mitotically active neuroblasts
intermediate zone: location where migrating neuroblasts will eventually come to reside
marginal zone: outer layer; evenually home for neuronal processes like axons
What happens with the dorsal and ventral midline aspects of the neural tube?
form roof plates and floor plates
Describe the process of axonal outgrowth? When does it occur? What structures and factors are important?
axonal outgrowth occurs after neuroblasts finish migrating and stop dividing. extending axons contain distal structures called growth cones, which are guided toward their targets via neuronal growth factors.
