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What occurs during week 1 of embryonic
development?
pre-embryonic period (0-2 wks)the zygote develops TERM 2
What happens during zygote development?
DEFINITION 2 A series of mytotic divisions yields a ball of cells (morula).The intercellular spaces consolidate to form a cavity, the inner cells move to one pole (embryoblast), and the outer cells form the epithelial wall of the blastocyst.The blastocyst attaches to the uterine wall. TERM 3
What occurs during week 2 of embryonic
development?
DEFINITION 3 Bilaminar Germ Disc formation: TERM 4
What happens during bilaminar germ disc
formation?
DEFINITION 4 Uteroplacental circulation is establishedThe inner cell mass differentiates into two layers TERM 5
What two layers does the inner cell mass
differentiate into?
DEFINITION 5 Epiblast amniotic cavity develops within this layer.Hypoblast
- contributes to formation of exocoelomic cavity within surrounding mesoderm and later produces cells that form the smaller definitive yolk sac.
What is significant of the embryonic
period?
(3-8 wks)The embryonic period is the period of greatest susceptibility to teratogenesis. TERM 7
What occurs during week 3 of embryonic
development?
DEFINITION 7 Trilaminar Germ Disc formation: TERM 8
What occurs during trilaminar germ disc
formation?
DEFINITION 8 Gastrulation occurs 3 germ layer are established Primitive streak forms on surface of epiblast A slightly elevated area, the primitive node, surrounding a pit forms at the p. streaks cephalic end Epiblast cells invaginate in the primitive pit and travel rostrally to ultimately form the definitive notochord. Forms in the midline. The notochord serves as basis for the axial skeleton. TERM 9
How are the 3 germ layers
established?
DEFINITION 9 Epiblast cells migrate through the streak to form endoderm and mesoderm. Cells that remain in the epiblast form the ectoderm. All the tissue of the body are formed from these 3 germ layers. This process continues through the 4th week. TERM 10
What occurs during weeks 3-8 of embryonic
development?
DEFINITION 10 Period of organogenesis where ectoderm, mesoderm, and endoderm give rise to specific tissues and organs, establishing major features of body form.
Ectoderm gives rise to what?
Gives rise to structures that maintain contact with the outside world.EpidermisSensory epithelium of eye, ear, and noseCNS and PNS TERM 17
What occurs in NS formation during weeks 3-
DEFINITION 17 Neural Tube Formation (neurulation)Ectoderm dorsal to the notochord thickens to form the Neural Plate.The lateral edges thicken more rapidly forming neural folds with the depressed midregion forming the neural groove.Neural crest cells appear along edge of neural folds give rise to important PNS structures. TERM 18
Neural crest cells migrate and differentiate
into what?
DEFINITION 18 Dorsal root and cranial nerve sensory ganglia neuronsPost ganglionic and enteric visceromotor neuronsSchwann cells responsible for myelination of axons in PNSChromaffin cells of adrenal medullaMelanocyte pigment cellsPia and Arachnoid mater TERM 19
How do neural folds fuse in the midline?
DEFINITION 19 Begins in the future cervical region (5th somite)Proceeds cranially and caudally in a zipper-like fashionForms the neural tube TERM 20
what happens to the unfused ends of the
neural tube?
DEFINITION 20 called neuroporesclose up Anterior neuropore closure days 24- Posterior neuropore closure days 25-
What is folic acid important
for?
Folic acid is important for neural tube closure;prescribed for pregnant women to prevent neural tube defects (dysraphic effects) TERM 22
Where do dysraphic effects normally occur?
DEFINITION 22 aka neural tube defectsoften occur at the anterior or posterior neuropore. TERM 23
what is arnold-chiari malformation?
DEFINITION 23 Subtle defect involving anterior neuroporeCerebellar vermis herniates through the foramen magnum compressing the medulla and cervical spinal cordHydrocephalus (blockage of CSF flow) and syringomyelia (cavitation of the spinal cord) are also associated with this condition TERM 24
what is spina bifida?
DEFINITION 24 May affect both spinal cord and surrounding tissues (in the future lumbar region).Verebral arch fails to form completely and fuse TERM 25
Defects involving closure of the posterior
neuropore are referred to as what?
DEFINITION 25 myeloschisis
Cell mass (caudal eminence) appears where?
caudal to neural tube, expands and cavitates.Caudal eminence joins neural tube. TERM 32
tethered cord syndrome
DEFINITION 32 The bottom of the spinal cord and filum terminale are abnormally fixed to the defective vertebral columnProgressive disorder may manifest early or in adulthood (sports, pregnancy). TERM 33
tethered cord syndrome is a form of what?
DEFINITION 33 Form of myelodysplasia defect of secondary neurulation TERM 34
Tension on the spinal cord results in what?
DEFINITION 34 weakness of the lower limb, sensory deficits, pain, and loss of bladder control. TERM 35
how is tethered cord syndrome treated?
DEFINITION 35 surgically
Differentiation of the neural tube is guided by
what?
morphogen signals secreted by centers derived from surrounding germ layers TERM 37
When does the formation of brain vesicles
occur?
DEFINITION 37 week 4- TERM 38
describe the formation of brain
vesicles
DEFINITION 38 The cephalic end of the neural tube expandsDifferential growth result in formation of 3 cavities, the primary brain vesicles. Prosencephalon forebrain Mesencephalon midbrain Rhombencephalon hindbrain TERM 39
How do the vesicles further
differentiate?
DEFINITION 39 Vesicles further differentiate into 5 vesicles (secondary brain vesicles), which ultimately develop to form the structures of the brain.The caudal end of the neural tube undergoes less changes, developing into the spinal cord TERM 40
the wall of the neural tube early on consists of
what?
DEFINITION 40 neuroepithelial cells forming a pseudostratified epithelium
How do neurons migrate during
development?
Neurons migrate from their site of origin to their destination where they mature and develop connections TERM 47
Neuronal maturation includes what?
DEFINITION 47 Maturation includes axonal growth, dendrite development and synaptogenisis TERM 48
What guides growth and pruning of dendritic
arbors?
DEFINITION 48 Patterns of acitivty of inputs guide growth and pruning of dendritic arbors TERM 49
Synaptic connections are also strengthened
or removed based on what?
DEFINITION 49 activityThis allows for significant recovery of function with damage to the early postnatal period. TERM 50
Gliablast differentiate into what?
DEFINITION 50 astrocytes, oligodendrocytes, and ependymal cells
Radial glia are present when?
during development but ultimately differentiate into astrocytes.They provide a scaffold that is critical for guiding migration of immature neurons during the formation of the cerebral cortex. TERM 52
Cellular Events continuing
postnatally
DEFINITION 52 Considerable development of the nervous system occur over the perinatal period and into early childhood.Three important parameters: Neuronal density Neuronal process branching and myelination Pattern of synaptic contacts TERM 53
Development begins when?
DEFINITION 53 Development begins around the 6th month of gestation.Remodeling of synaptic connections continues throughout life.
