NS 1: Development of NS Flashcards
When does the CNS begin development?
at the beginning of the 3rd wk as the neural plate= an ectodermal thickening in the mid-dorsal region, in front of the primitive node.
what regulates notochord formation?
the primitive node= elevated region around cranial end of primitive streak.
what is the primitive streak?
groove formed in the epiblast at the caudal end of the embryo at the bilaminar germ disc stage through which epiblast cells migrate to form endoderm and mesoderm during gastrulation- formation of trilaminar disc from bilaminar disc.
what is the remnant of the notochord in the adult?
the nucleus pulposus= central gelatinous portion of IV disc.
how is the notochord formed?
by prenotochordal cells migrating through the primitive pit (depression in primitive node) to form a solid cord of cells..
what does the definitive notochord serve as the basis of?
midline
axial skeleton
neural tube
describe the formation of the neural tube
signalling molecules from the notochord cause thickening of neuroectoderm to form the neural plate, whose lateral edges soon elevate to form the neural folds. These continue to elevate with further development, approach each other in midline and fuse to form the neural tube.
Fusion starts in cervical region and then proceeds both cranially and caudally.
name given to depressed midregion in neural tube formation?
neural groove
how long does it take for the neural tube to be completely closed?
10 days
name given to openings of neural tube formed during fusion that communicate with the amniotic cavity?
anterior and posterior neuropores
when do the anterior and posterior neuropores close?
anterior= day 25 posterior= day 28
what happens if the anterior neuropore fails to close?
anencephaly- absent brain and calvaria
what happens if neural tube fails to close caudally?
spina bifida
what can the mother take to prevent NT defects in pregnancy?
folic acid- for 3 months pre-conceptually and for the 1st trimester
what can be measured in the maternal serum to assess for neural tube defects?
how else can NTDs be assessed for?
alpha-fetoprotein, if increased may signify NT defect
USS- by 12 wks defects in closure of vertebral arches ca be detected.
what is the vertebral arch?
the region of the vertebra comprising the pedicle (between the VB and the transverse process) and the lamina (between the transverse process and the spinous process).
what is spina bifida occulta?
neural tube defect where abnormal closure of neural folds in caudal region produces defect in vertebral arches (lack of fusion) covered by skin, and DOES NOT normally involve neural tissue.
patch of hair may overly affected region
may be incidental finding on back X-ray
define spina bifida
all neural tube defects affecting the spinal region, producing a defect as the bony arch of 1 or more vertebrae has failed to fuse dorsal to the SC.
name given to NTD where only fluid-filled meinges protrude through defect in vertebral arches and skin?
meningocele