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Embryo - Nervous System Development


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Neural tupe formation is induced by ________
Notocord/middle 3rd week
Describe closure of neural tube. When is it complete?
begins in middle , continues anteriorly and posteriorly. Neuropores at both ends.
Completes late in 4th week.
Neural plate developes into 3 zones. What are they? Describe them.
1) Ventricular zone (original cell source)
2) Intermediate zone (cell proliferation and differentiation; future gray matter)
3) Marginal zone (future white matter)
The immediate zone is further divided into
Alar plate (dorsal; sensory)
Basal plate (ventral; motor)
Derivitives of Neuroectoderm
develop directly into ventricular lining cells
nerve cell precursors
differentiates int astroglia and oligodendrocytes
Neural crest Derivitives make up ____ components.
What are the neural crest derivitives?
Name them?
Describe what they make?
PNS components

Ganglion nerve cells (sympathetic, parasympathetic, and unipolar cells)


Adrenal Medulla

Peripheral support cells (schwann cells [neurilemmicytes] & satellite cells)
Formation of Histological Regions
Intermediate zone - parts inside, where cell bodies differentiate, forms gray matter

Marginal- the parts outside, where axons grow and become myelinated, forms white matter

Ventricular - the cells adjacent to central canal and ventricals, which are the initial proliferative cells and which eventially develop into ependyma.
When does Myelination begin, when does it end?
Begins 16-20 weeks intrauterine, complete around 2 yrs
Cytological modification that happens during fetal period.
cell death (timing and percentage of cells depends on site)
Cytological modification that happens during postnatal period.
synapse elimination
Alar plate is located where in the embryo
dorsal and lateral sulcus, sensory areas
Basal plates is located where in the embryo
ventral to lateral sulcus, forms motor areas
Where are somatic regions of alar and basal plates located?
extreme ends: farthest dorsal 1/4 is somatic sensory and farthest ventral 1/4 is somatic motor
Where are visceral regions of alar and basal plates located?
adjacent to lateral sulcus; dorsal part is visceral sensory, ventral part is visceral motor (autonomic
describe sensory/motor organization of spinal cord
most like embryonic pattern.
dorsal horn- snesory
ventral horn-motor
intermediolateral grey column-autonomic motor
describe sensory/motor organization of medulla oblongata
Roof of rhombencephalon is expanded so sensory columns are most lateral, motor columns most medial
describe sensory/motor organization of midbrain
Sensory parts are dorsal to aqueduct, motor parts are ventral to aquaduct
spinal cord fills canal at ___
8 wks
Terminal end of spinal cord is roughly at ____ birth
L3 (+/- 1 vert level)
Spinal cord terminates where in adult?
cause of spinal bifida
spinal cord is the last area to close.
A delay in closure causes the mesoderm to miss it's developmental 'window' in forming the dorsal arch of the vertibrae.
spinal bifida occulta
not conspicuous without close examination
spinal bifida cystica
conspicuous sac
most proximal of the three sections of developing brain.
-Consists of Telencephelon & Diencephelon
Telencephelon describe it's size, when it developes and what it consists of.
Largest and last of the regions to develop.
Consists of:
-Cerebral hemispheres
-Corpus Striatum
-Hippocampus, Amygdala
Diencephelon. What does it connect, what is it's function, and what does it consist of.
Connects the telencephelon to brainstem, involved with significant neural processing

Consists of :
-Epithalamus (pineal)
Midbrain region
-contains several important nuclei, connects to rhombencephalon
Where is it located and what does it consist of?
Most posterior part of brainstem

Consists of:
Metencephelon consists of
Pons - what does it connect and contain
connects medulla w/ midbrain, contains several important nuclei
side-branch; major motor part of brain
Myencephelon consists of
Medulla oblongata
Medula oblongata. What does it connect and contain.
connects brainstem to spinal cord; contains several important nuclei
Flexures are
bends in the brainstem
name and describe
cervical - between spinal cord and myencephalon

cranial - at midbrain
Cortical differentiation
intermediate zone becomes thick. refered to as Germinal matrix. All cells of Cortex differentiate from it.

Cells of cerebral cortex migrate through marginal zone. Three waves of migration: ssecond migrates through the first wave, and the third migrates through the 1st and second waves.

By 34 weeks, this migration is complete and germinal epithelium becomes a series of cortical nuclei adjacent to the ventricals
Anencephaly. What is it What part of brain is typically effected.
Absence of part of skull or brain.
usually only prosencephalic sx affected (generally the telencephalon will always be affected, with more or less involvement of the diencephelon. Brain stem may or may not be affected, or affected only mildly.
inadequate development of brain leading to small size (mult causes)
Cranium bifidum
similar to spinal bifida; a part of the cranium does not develop due to delay in closure of skull
hydrocephalus. What is it? What part of the brain can be crushed? What is most common cause?
Fluid pressure build-up inside ventricle which causes cranium to expand. -will crush telencephalon if left unchecked.
most common cause is blockage of cerebral aqueduct.

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