N2: Embryological Development Flashcards
Gastrulation?
- forms three germ layers
- begins by day 15
- formation of primitive streak on posterior surface of epiblast
- establishes trilaminar disc of cells from epiblast
Gastrulation layers?
ectoderm
- central nervous system (CNS), peripheral nervous system (PNS),
epidermis, connective tissues of head
mesoderm
- muscle tissues, connective tissues of body and limbs, vessels, viscera
endoderm
-epithelium of GI tract, respiratory system,
and urinary bladder
Neurulation?
- begins by day 17
- notochord is located in mesoderm
- notochord induces ectoderm to differentiate into neuroectoderm, neural plate, neural groove, then neural tube
- neural crest arises from ectoderm near neural tube
- neuropores normally close by day 28
If neuropores fail to close:
cranial: anencephaly (absence
of cerebral hemispheres)
caudal: spina bifida (incomplete
vertebral arch)
If neuropores close normally:
cranial (rostral) neuropore closes by day 25
caudal neuropore closes by day 27
What forms the CNS and PNS in neurology?
Neural tube forms CNS.
Neural crest forms PNS.
Neuroblast proliferation?
- neuroblasts are fusiform and have connections to both ventricular and pial surfaces
- nuclei of neuroblasts migrate to pial surface and back to ventricular surface
- neuroblasts lose contact with pial surface in mitosis, but daughter cells regain contact
Neuroblast= still mitotically active
Three layers formed by the neural tube?
ventricular zone – becomes ependymal layer
intermediate zone (mantle) – becomes cerebral cortex and subcortical white matter
marginal zone – becomes marginal layer
“Inside-out” pattern of development?
-neuroblasts migrate outward along radial glial cells and later differentiate
into pyramidal neurons and granule neurons
-first neuroblasts to migrate form deepest layers of neurons in cerebral cortex (layer VI)
-later waves of neuroblasts form more superficial layers of neurons (layer I is last)
-after neuron migration is complete radial glial cells become ependymal cells
Neuron migration in cerebral cortex?
- chief input is from thalamus to layer IV
- chief output is projection fibers from layer V
- thalamus axons arrive at 21-28 weeks of development
- normal EEG patterns occur at 24-30 weeks of development
- perception of sensory stimuli requires functional connections
Primary cortex areas?
primary somatosensory cortex - postcentral gyrus primary somatomotor cortex - precentral gyrus primary visual cortex - cuneus and lingual gyri primary auditory cortex - transverse temporal gyri
Neuron migration in cerebellum?
has similar three layer pattern
ventricular zone – becomes ependymal layer
intermediate zone – becomes most of cerebellar cortex, subcortical white matter, nuclei
marginal zone – becomes molecular layer of cerebellar cortex
internal germinal layer
intermediate zone
some neuroblasts migrate outward (toward the pial surface)
Purkinje cells migrate outward along radial glia cells
external germinal layer
marginal zone
some neuroblasts migrate inward (away from the pial surface)
granule cells migrate inward along radial glia cells
Neural tube derivatives?
CNS neurons
- neurons in brain
- lower motor neurons (LMN)
- autonomic preganglionic neurons
glial cells
- astrocytes
- oligodendrocytes
- ependymal cells
Brain vesicles?
primary brain vesicles
- prosencephalon (forebrain)
- mesencephalon (midbrain)
- rhombencephalon (hindbrain)
secondary brain vesicles
- telencephalon (cerebral hemispheres)
- diencephalon (thalamus and hypothalamus)
- mesencephalon (midbrain)
- metencephalon (pons and cerebellum)
- myelencephalon (medulla)
Neural crest derivatives?
PNS neurons
- posterior root ganglia
- sympathetic prevertebral and paravertebral ganglia
- parasympathetic ganglia for CN III, CN VII, CN IX, CN X
- sensory ganglia for CN V, CN VII, CN VIII, CN IX, CN X
- enteric neurons
non-neuronal elements
- bones of face and skull
- Schwann cells
- melanocytes
