B7.002 CNS Development and Brain Anatomy Flashcards
when does neural development take place
begins 3 weeks post conception
continues throughout lifetime
after 20 primarily degenerative changes
what starts nervous system development
induction of the neural plate on day 18 by notochord signals
what is spina bifida
failure of the neural tube to close, results in failure of vertebral column to form correctly
can happen anywhere along the spine
nervous system can escape
causes damage to spinal cord and associated peripheral nerves
spina bifida occulta
no external evidence
neuro structures in the correct place, vertebrae just missing
meningocele
meninges escape via outpouching, but spinal cord remains in correct location
myelomeningocele
worst form of spina bifida
cord and meninges exit column resulting in neuro deficits
what is the notochord
structure just ventral to the neural plate
group of mesodermal cells that send chemical signal to the overlying ectoderm cells to begin differentiation into the neural plate (induction)
why do neural folds develop
due to proliferation nd elongation of epithelial cells in the neural plate
neural groove
formed as the neural folds move toward each other
located on the dorsal surface of the embryo
neural tube formation
neural plate cells pinch off to form neural tube, located underneath the ectoderm of the embryo
occurs first in the center of the embryo and extends rostral and caudal
neuropores
openings at each end of the developing neural tube
failure to close caudal one = spina bifida
anencephaly
failure of rostral neuropore closure and tissue differentiation
results in death
epidemiology of spina bifida
1/1000 births
screening for spina bifida
AFP - alpha fetoprotein
ultrasounds
amniocentesis
xray, MRI, or CT of spinal column
treatment / prevention of spina bifida
surgery corrects vertebral and spinal problems
folic acid can reduce incidence (400 mg per day)
neural crest cells
cells that originate lateral to the neural plate
pinched off during formation of the neural tube
migrate between ectoderm and neural tube
examples of neural crest derivatives
dorsal root ganglia
some neurons and all glial cells within the sensory ganglia of V, VII, IX, and X ganglia
sympathetic, parasympathetic, and enteric ganglia
chromaffin cells of adrenal medulla
pia and arachnoid
Schwann cells
melanocytes
what are neurocristopathies
diverse class of pathologies that arise from defects in tissues derived from the embryonic neural crest cell lineage
zones/layers of neural tube
innermost: ventricular zone
intermediate zone (mantle)
outermost: marginal zone
where does mitosis occur in the neural tube
ventricular zone (innermost)
discuss connections to the external and internal limiting membranes of the neural tube during development
most of the time, proliferating cells are connected to both membranes
during M phases, nuclei of dividing cells move toward internal limiting membrane and lose connection with external limiting membrane
this is why mitotic figures are in the ventricular zone
what happens to daughter cells after cell division takes place in the neural tube
move back toward external limiting membrane (interkinetic nuclear migration)
what happens after the last cell division of neurons
migrate out of ventricular layer and come to rest in intermediate (mantle) zone
neuronal birthday
is there neurogenesis in the adult brain
not really
vast majority occurs during embryogenesis in neural tube
effect of Zika virus
targeted developing neurons in pregnant women, causing microcephaly in newborns due to lack of neurons
appearance of neural tube at 4 weeks gestation
3 vesicle stage
- prosencephalon (forebrain)
- mesencephalon (midbrain)
- rhombencephalon (hindbrain)
appearance of neural tube at 5 weeks gestation
5 vesicle stage (rostral and caudal swellings divide into 2) forebrain: -telencephalon (cerebral hemisphere) -diencephalon (thalamus and hypothalamus) mesencephalon (midbrain) hindbrain: -metencephalon (pons) -myelencephalon (medulla)
what genes govern segmentation of the neural tub
homeobox genes
planes of section
horizontal / axial (like looking into feet of a person lying on a table)
coronal (crown like)
sagittal (like drawing back an arrow through the body)
dual meaning of dorsal
in head, superior
in body, posterior
dual meaning of ventral
in head, inferior
in body, anterior
most rostral part of a human adult
forehead region
central sulcus
divides frontal and parietal lobes
precentral gyrus
primary motor cortex
voluntary movement
postcentral gyrus
primary somatosensory cortex
receiver information from sensory receptors in skin
lateral (sylvian) fissue
very deep
separates frontal and temporal lobes
occipital lobe
most caudal lobe
parieto-occipital sulcus
divides parietal and occipital lobes
parts of telencephalon
cerebral hemispheres
- cerebral cortex
- subcortical white matter
- basal ganglia
- basal forebrain nuclei
parts of diencephalon
thalamus
hypothalamus
epithalamus
parts of mesencephalon
cerebral peduncles
midbrain tectum
midbrain tegmentum
parts of metencephalon
pons
cerebellum
parts of myelencephalon
medulla
formation of flexures
occur along the length of the neural tube as proliferation continues
eventually telencephalon expands so that it covers the more caudal derivatives of the neural tube
lumen of neural tube
becomes ventricular system in the adult brain
what influences differentiation into sensory/motor functions
induction factors in specific regions of the neural tube
dorsal = sensory = alar plate
ventral = motor = basal plate
formation of gray matter of spinal cord
post mitotic neurons leave proliferative zone, causing an increase in size of the mantle later
this region becomes the gray matter (dorsal and ventral horns)
formation of white matter of spinal cord
composed of axons of local neurons within gray matter as well as axons from neurons carrying ascending and descending information
stain for neuronal cell bodies
Nissl Stain
ganglion
group of neuronal cell bodies in the periphery
neural crest derivatives
nucleus
group of neuronal cell bodies in the CNS
afferent
information flowing toward the CNS
-sensory axons
efferent
information flowing away from the CNS
-motor axons
ascending
information flow to cerebral cortex (sensory)
descending
information flow toward spinal cortex (motor)
how do pathways develop?
trophic factors
neuronal migration
synapse elimination (plasticity)
maturation of neuronal connection
how do neuron #s match target size
neurons are produced in excess, some die to match the target size
due to production of trophic factors by targets
where does synapse elimination occur
cellular level
competition for innervation
how many layers are present in the gray matter?
6
how do motor and sensory areas of gray matter differ
motor: bigger cells in deeper layer
sensory: more cells in middle region
layer 1
outermost
molecular layer
contains mainly neuropil
layers 2 and 3
2: external granular
3: external pyramidal
generally smaller pyramidal neurons
primarily corticocortical connections
layer 4
internal granular layer
rich in stellate neurons with locally ramifying axons
in the primary sensory cortices, these neurons receive input from the thalamus, the major sensory relay from the periphery
layer 5 and 6
5: ganglionic
6: multiform
contain pyramidal neurons whose axons leave the cortex
prominent in motor areas
function of radial glia in cortex development
neurons use radial glial cells to help with migration into outer layers
chemical cues also help with this
formation of correct connections between groups of neurons
in some cases, neurons make connections early when in close proximity and reel out processes as growth of surrounding structures pushes them apart
in other cases, neurons use cues to grow to a target and synapse on the correct postsynaptic partner
synaptic plasticity
modification of connections between neurons following damage or in the course of learning
maturation of cellular architecture and connectivity of neurons
connections multiply and finalize over a long period of time
