development of the nervous system Flashcards
what features are involved at the beginning of the development of the spinal chord *
neural plate ectoderm mesoderm endoderm - internally
how does the neural tube develop *
the ectoderm over the trilaminar embryonic disk thickens to form the nerual plate
the neural plate folds in on itself to form the CNS, first becoming the neural fold - this forms the neural canal
the neural tube is lined by neuroepithelial cells
the neural crest tissue forms alomng either side of the neural tube
what do neuroepithelial cells form *
the CNS
what are neural crest cells *
they are cells either side of the neural tube that develop into the peripheral NS
- sensory neurons of the dorsal root ganglia and cranial ganglia
- postganglionic autonomic neurons
- schwann cells
- non-neuronal derivitives eg melanocytes
describe the differentiation of neuroepithelium *
it ahs to make lots of different cell types including neuroblasts, glioblasts and ependymal cells
describe neuroblasts *
they are of developmental origen turn into neurons with cell bodies in CNS
describe glioblasts *
developmental they form astrocytes, oligodendrocytes
describe astrocytes *
involved in neurotransmission support neurons involved in the blood brain barrier
describe oligodendrocytes *
wrap around neurons - myelination
describe ependymal cells *
line the ventricles and central canal of spinal cord
descrinbe the differentiation of the neural crest cells *
form the sensory neurons - cell bodies sit in the dorsal root ganglia form ganglia in the periphery - postganglionic autonomic neurons form shwann cells form non-neuronal derivitives eg melanocytes
where does proliferation of the neuroepithelium occur *
cell division happens at the inside of the neural tube
describe the formation of the layers in the neural tube *
ependymal cells stay at the inner membrane - germinal layer
neuroblasts migrate away from the inner membrane to the grey matter layer - the mantle layer
the neurobast axons are directed out to form the white matter layer - marginal layer
glioblasts migrate to both the white and grey matter
describe the layers of the neural tube *
at the dorsal side - roof plate
at the ventral - floor plate
ependymal/germinal layer lines the canal
grey matter/mantle layer
white matter/marginal layer
in brain, grey outside and white beneath
what controls neural differentiation *
sequential secretion of different selective signalling molecules that interact with recpetors on neuroblasts that determine how far, where and what the blast cells differentiate to they control migration and axonal growth by attraction and repulsion (atrophic and inhibitory factors) depends on the conc gradient and timing of secretion of signalling molcules
summarise the developing spinal cord *
the grey matter layer differentiates into the alar plates dorsally and the basal plates ventrally
alar plates develop into dorsal horns
basal plates develop into ventral horns
the neural crest develops into the dorsal root ganglia (sensory)
ventral neurons are motor neurons and interneurons - in the ventral grey matter
neurons in the dorsal grey matter are the interneurons
sensory info comes from the dorsal root ganglia and synapse on the interneurons in the dorsal horns and the information goes up to the brain.
describe a simple reflex pathway *
the sensory info goes into the dorsal horn and then there is a single synsapse between the dorsal and ventral neurons - then the motor neurons take the signal away via ventral root and the spinal nerve
describe the developing brainstem *
the ventral/motor nuclei are more medial, the dorsal/sensory are more lateral because the neural plate hasn’t folded properly (because of the presence of the 4th ventricle) - this dictates the pattern of the cranial nerve nuclei in the brainstem
there is the 4th ventricle - large just under the cerebellum, this is formed becasue of lateral proliferation of teh root plate
describe the dorsal view of an embryo brain at 4wks - dorsal view of embryo *
it is the anterior part of the neural tube there is the future forebrain - PROSENCEPHALON the future midbrain (brainstem) - MESENCEPHALON the future hindbrain (cerebellum) - RHOMBENCEPHALON future spinal cord
describe the developing brain at 5 weeks - dorsal view of embryo *
the forebrain (cortex) has the telencephalon and the diencephalon - thalamus and hypothalamus midbrain - brainstem pons - brainstem medulla - brainstem
describe the developing brain at 8wks - dorsal view of embryo *
neural tube forms ventricles - lateral ventricles (forebrain) drain into 3rd ventricle in the forebrain there are developing hemispheres midbrain - aqueduct drains into 4th ventricle hind - developing cerebellum, behind this - have the 4th ventricle
explain how flexures in the brain give rise to development of the mature brain *
at 4wks there are - cephalic flexure, pontine flexure (level of pons) and cervical flexure (develop spinal cord below) 5wk - increase in flexures 8wk - have the cortex, diencephalon subcortically, and the cerebellum in hind brain term - still growth - myelination and formation of pathways
summarise how the cotical layers form from the neuroepithelium *
in the subventricular zone there are developmental cells - even in adult in ventricular zone there are vertically orientated radial glial cells - astrocytes which scaffold from ventricle to pia surface using growth and inhibitory factors, neurons migrate along radial glia - ultimately end with 6 layers - layer 1 is just fibres
what are the zones in the cortex *
ventricular zone subventricular zone intermiediate zone ???
what does the normal developmet depend on *
proliferation, differentiation, migration, axon growth and synapse formation
how can things go wrong in development
genetics and environment, - lifestyle, diet, teratogens can interfere with processes
describe cranioachischisis
completely open brain and spinal cord
describe anencephaly
open brain and lack of skull vault anterior portion of neural tube hasn’t fused and brain hasn’t developed
describe encephalocele
herniation of the meninges and brain - brain develop out of the cranial cavity
describe iniencephaly
extreme retroflexion of the head
describve meningocele
meninges bulging out of defect of skull/spine - filled with CSF
describe closed spine dysraphism
deficiency of at least 2 vertebral arches - covered by lipoma - hernia
describe spina bifida occulata
closed asymptomatic, some of the vertebrae are not completely closed no closure of the base of the spinal tube
describe myelomeningocele
open spinal cord - externally visible
what is a neural tube defect
defecit at top of bottom of neural tube can be prevented by folic acid in pregnancy
describe neuronal stem cells and their use for regeneration *
in development many are lost by apoptosis some are left behind - especially in the hippocampus in degenerative diseases you can’t regenerate nerve cells - if we can access progenitor cells we might be able to treat
summarise how developmental neurobiology can be used in the repair of the nervous system *
stem cells
use axonal guidance mechanisms to induce regeneration of the CNS
