Development of the nervous system Flashcards
how many synapses are formed and eliminated during development
~1quadrillion synapses are formed during development, >50% are eliminated again
what is the storage capacity of the brain
Estimates of ≥1 petabyte (=1k TB) storage capacity
at peak times during development how many nerve cells are added per minute
250,000
what does the lumen of the neural tube become
the ventricles (CSF)
the patterning along the neural tube is instructed by what
morphogens
describe the positions of the axis’ is regards to the neural tube
Anterior/ posterior (rostral/ caudal) along the length of the tube
Dorsal-ventral in cross section
what neurological morphology distinguishes humans forms animals
The size of the cortex, particularly the frontal lobe
what molecules are higher in the roofplate vs the floorplate
BMPs highest in the roofplate
Shh highest in the floorplate
what are hox genes
Family of transcription factors
Establish segmentation along anterior- posterior axis
what is synophthalmia (cyclopia)
a form of cyclopia, in which some elements of two eyes are fused and form a single eye in the middle region of the forehead
- caused by Shh loss leading to loss of ventral identity that causes optic vesicles to only be generate on the dorsal side
what is the difference in division between radial glia and neural precursor cells when building the cortex
Radial glia connect the ventricular and pial surface, divide slowly and symmetrically
Precursors divide asymetrically in the ventricular zone (innermost layer of neural tube)
what are transit amplifying cells
an undifferentiated population in transition between SCs and differentiated cells.
(eg neural precursor cells)
what does the asymmetric division of neural precursor cells generate when dividing in the ventricular zone
generate new progenitors and post mitotic neuroblasts (will develop into a neuron after a migration phase.)
what cells form the venticular zone
Neuroepithelial progenitor cells in neural tube = neural precursor cells
why does a neurons location in the cortex reveal its birthdate
due to the columnar organisation of the cortex as it is build ‘inside out’ (the youngest neurons on the surface and the oldest ones adjacent to the subcortical white matter)
neuroblasts migrate to the_____surface and form the _________ zone
pial surface and form the marginal zone
over time glial blasts do two things to seal their fate, what are they
glioblasts either remain attached to lumen (of the neural tube) and become ependymal cells (production of CSF)
Or they move to the marginal layer and form astrocytes (maintenance and repair) or oligodendrocytes (myelination)
where are cortical interneurons born
ganglionic eminences
what are ganglionic eminences
a transitory structure in the development of the nervous system that guides cell and axon migration
describe the tangential migration of interneurons
Interneurons migrate tangentially from the ganglionic eminence to the cerebral cortex.
The tangentially migrating interneurons travel perpendicular to the radial glial cells
what are the 5 stages of neural cell polarisation where axons and dendrites are established
lamellipodia, minor processes, axonal outgrowth, dendritic outgrowth and maturation
what is axonal fasciculation
the process of a growing axon adhering to another, potentially forming groups of axons known as bundles (“fascicles”), which follow similar growth trajectories.
how do axons navigate
via intermediate targets and growing along other axons as guides
what classes of guidance signals are there
attractive or repulsive
short range: non diffusible, substrate derived, contact mediated, ECM or target cells - cadherins and ephrins
long range: diffusible, can act as -gradients - netrin, semaphorins
what are guidance signals interpreted by
the growth cone
what is netrin
a long range chemoattractant in axonal guidance
what is semaphorin
a long range chemorepulsiant used in axonal guidence
what is ephrin
a short range contact mediated repulsiant in axonal guidance
what do cadherins do in axonal guidance
contact mediate attraction
what are growth cones
a large actin-supported extension of a developing or regenerating neurite seeking its synaptic target - hand like structures with receptors on the surface at the tip of growing axons and dendrites, senses guidance cues
- first described in 1890 by ramon y cajal
once circuits form what regulates them
the target via continued release of trophic factors and activity
learning and memory
disease
why do not all neurons cross
Netrins are capable of acting as bifunctional cues, attracting some axons to the midline via the DCC receptor and repelling others via the Unc-5 receptor
once direction is determined what is responsible for laying down this axon in its desired direction
microtubular cytoskeletal changes
what determines the final pattern of contacts of neurons
neurotrophins and electrical activity
what is Hebbs rule
inputs that have correlated activity in time become stabilised
what are the adhesion molecules that stabilised formed connections
Presynaptic neurexins: organise the SV docking zone
Postsynaptic neuroligins: recruit PSD
Victor Hamburger discovered what
discovered that limb removal results in reduced numbers of motor and sensory neurons in the chick spinal cord (1934)
where are radial glia somas and what do they do in the developing brain
in the ventricular zone (projections extending to the marginal)
act as guide wires for the neurones to migrate to the correct place
