Neural Development

neural induction

transformation of indifferent ectoderm into neural ectoderm

neurulation

formation of the neural plate into the neural tube

neural proliferation

genesis of neurons

major factory of neurons and glia

neural epithelium at the ventricular surface of the neural tube

neural migration

translocation of neurons from their birth home to permanent home

how do cells find their way to their permanent home

glial cell guides

neural differentiation

electrical, biochemical, morphological transformation of neuroblasts into neurons

axon outgrowth

navigation of the growth cone from the soma to the target cell

synapse formation

changes in the axonal and target cell that lead to a differentiated and functional communication line (synapse) between them

neuronal cell death

large-scale, naturally occurring loss of neurons

synaptic reorganization

refining of synaptic circuitry by eliminating some and strengthening others

day 8 of neural development

gastrulation: emergence of 3 cell lines (ecto/meso/endoderm), emergence of dorsal-ventral axis

function of ectoderm

gives rise to the neural crest and tube and the rest to skin

day 15 of neural development

primitive streak forms that builds the rostral-caudal axis, embryo is egg-shaped

day 18 of neural development

first signs of neurulation, neural plate thickens and sinks in to form a groove, neural folds come up on either side of the groove and merge to form the tube, embryo is pear-shaped

day 22 of neural development

neurulation starts in the middle then zips up caudally and rostrally, embryo is slipper-shaped

day 24 of neural development

cranial (caudal) end closes, neural tube forms the CNS, neural crest forms the PNS, sulcus limitans forms

sulcus limitans

lateral groove that splits the basal and alar plates

day 28 of neural development

3 vesicle stage, cells proliferate quickly and form vesicles, plates flatten out to form ventricles in the brain

broad vesicles of the brain

prosencehpalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain)

characteristics of basal plate

ventral to sulcus limitans, motor information, more medial in the brain

characteristics of the alar plate

dorsal to sulcus limitans, sensory information, more lateral in the brain

day 35 of neural development

5 vesicle stage

divisions of the prosencephalon

telencephalon, diencephalon

what does the telencephalon become

cerebral cortex, basal ganglia, hippocampus, amygdala, olfactory bulb

what does the diencephalon become

thalamus, subthalamus, hypothalamus, retina, optic nerve

divisions of the rhombencephalon

metencephalon, myelencephalon

what does the metencephalon become

pons, cerebellum

what does the myelencephalon become

medulla

formation of the ventricular system

neural tube runs inside along the developing tissues and forms the central canal and ventricles

time it takes for the CNS to be fully recognized

3 months

stages of cellular development

differentiation, proliferation, migration, maturation

path of neural cell migration

ependymal layer → mantle layer → marginal layer

pattern of cortical development

inside-out pattern where new cells must climb past the old ones

long-range cues for axonal growth

chemoattraction and repulsion

short-range cues for axonal growth

contact attraction and repulsion

mechanism of axonal growth

axonal growth cones grow toward their target, grows along glial cells

neuron activity in the first 2 years of life

apoptosis and synapse elimination of inappropriate or less strong connections

how many neurons do we lose within 2-3 years

up to 50%

why does the brain still grow when we lose neurons (in development)

collaterals and synapses grow, pathways are myelinated

critical period

time in development where a specific input is essential for the correct development because the pathway will commit irreversibly

what determines the amount and activity of neurons that are left after a critical period

amount and location of neuronal loss

why is an adult frog not able to compensate after the eye is rotated

the CNS circuits are hard wired after the critical period in development

mechanism of ocular dominance formation

competitive process where neurons die back and form distinct columns of right and left eye information

cause of cortical blindness

an eye is deprived before 6 months and the other becomes more dominant in the ocular dominance columns

types of spina bifida

occulta, meningocele, myelomeningocele, myeloschisis

spina bifida occulta

no vertebrae but skin still overlying the spinal cord

spina bifida meningocele

the dura, arachnoid, and meninges protrude

spina bifida myelomeningocele

neural tissues protrude

spina bifida myeloschisis

the neural tube doesn’t close and the tissue are exposed to the outside

anencephaly

lack of closure on the cranial end causes the brain to fail to develop