T12- CNS Development Flashcards
What happens during primary neurlation
The primary neural tube forms from the neuroectoderm of the neural plate
What happens during secondary neurulation
The secondary neural tube forms from mesodermal remains of the primative streak
What are the steps of primary neurlation
- Induction of neuroectoderm 2. Elevation of the neural folds 3. Conversion, contact, and fusion of the neural folds 4. Differentiation of surface ectoderm
In elevation of the neural folds, (a) what is created? and (b) what importance does the notocord have?
(a) A distinct shape is created with the aid of cell wedging at the median hinge point (b) the notochord controls the position of the median hinge point
When does first fusion of the neural folds occur?
at the 5th somite pair
In which direction does fusion occur
at a cranial+caudal direction
Prior to neuropore closure, the _____________ is in open communication with the ____________ at both cranial and caudal ends
neural canal; amniotic cavity
Remanining mesenchymal cells of the ____________ occupy a midline position within the____________
primative streak, caudal eminence (tail bud)
Where are primative streak mesenchymal cells located in reference to the neuropore
they’re located caudally to the neuropore
What does primative streak mesenchyme condense into during secondary nerulation
the medullary cord
Steps of secondary neurlation
- Formation of medullary cord 2. Mesenchymal cells transition into epithelial cells 3. Canalization of epithelial cells 4. Joining of lumen of medullary cord and neural canal
What are neuroepithelial cells
tall columnar cells found in the ventricular zone of the neural tube
What does rapid proliferation of the neural tube cause?
(a) A psuedostratified appearance on the ventricular zone (b) An overall thickening of the NT wall (c) Change in shape and size of the neural canal
Newly formed neuroepithelial cells differentiate into what
neuroblasts+glioblasts
Where do neuroblasts and glioblasts migrate into
the intermediate zone
Neuroepithelial cells that remain in the ventricular zone transition into what
ependymal cells
Where does the spinal cord begin to develop
from the neural tube caudal to the 4th pair of somites
Neural tube that forms the spinal cord was created by both ___________ and _________ neurulation
primary; secondary
Where does sonic hedgehog influence neuroepithelial cells
in the ventral half of spinal grey matter
What are bone morphogenic protiens (a) produced by? and (b) what do they influence
(a) produced by adjacent ectoderm (b) influence neuroepithelial cells in the dorsal half of spinal grey matter
What does the ventral half of spinal grey matter become?
the basal plate
What is the basal plate associated with?
motor neurons
What does the dorsal half of spinal grey matter become?
the alar plate
What is the alar plate associated with?
sensory neurons
With differentiation of the spinal grey matter, what happens to the neural canal?
The neural canal begins to shrink in size
What does the ventricular zone become?
ependymal cells which line the neural canal
What does the intermediate zone become?
grey matter (nerve cell bodies)
What does the marginal zone become?
white matter (nerve cell axons)
Where is the midline roof plate located?
dorsally
Where is the floor plate located?
ventrally
The midline roof plate and floor plate do not contain __________ and instead serve as pathways for _____________
neuroblasts; crossing fibers
The notochord, which is responsible for secreting ____________ determines where it has the most influence
sonic hedgehog
What happens if there is no notochord
no motor neurons form
What happens if the notochord is transplanted
there would be a formation of an ectopic floor plate with associated motor neurons
How is the spinal cord in the early embryo
it extends the entire length of the vertebral cord and all SC nerve segments lie adjacent to corresponding vertebral segments
What happens in the growing fetus concerning vertebral elongation?
vertebral column elongation occurs faster than that of the SC
Where does the brain begin to develop?
from the neural tube, cranial to the 4th pair of somites
Brain developent is derived from ___________ nerulation only
primary
Closure of the _______ neuropore forms three ________ brain vessicles
cranial; primary
What is the cervical flexure
the point of transition of the spinal cord and the rhombencephalon
Where is the midbrain flexure located?
in the middle of the mesencephalon
What are the three primary brain vessicles
proencephalon, mesencephalon, rhombencephalon
When does transition of primary vessicles to secondary vessicles occur
in the 5th week
Histogenesis of the brain What happens to ependymal cells that migrate to the intermediate zone
They form deep grey matter structures near the ventricles
Histogenesis of the brain What happens to ependymal cells that migrate to the marginal zone
They form the grey matter surounding the white matter in the brain
(a) Telencephalon
(b) Diencephalon
(c) Lateral Ventricles
(d) Thalami
(e) Midbrain
(f) Cerebral Aqueduct
(g) Pons
(h) Cerebellum
(i) Lower part of the 4th ventricle
