Development of the nervous system

Question 1

how many synapses are formed and eliminated during development

Answer 1

~1quadrillion synapses are formed during development, >50% are eliminated again

Question 2

what is the storage capacity of the brain

Answer 2

Estimates of ≥1 petabyte (=1k TB) storage capacity

Question 3

at peak times during development how many nerve cells are added per minute

Answer 3

250,000

Question 4

what does the lumen of the neural tube become

Answer 4

the ventricles (CSF)

Question 5

the patterning along the neural tube is instructed by what

Answer 5

morphogens

Question 6

describe the positions of the axis’ is regards to the neural tube

Answer 6

Anterior/ posterior (rostral/ caudal) along the length of the tube
Dorsal-ventral in cross section

Question 7

what neurological morphology distinguishes humans forms animals

Answer 7

The size of the cortex, particularly the frontal lobe

Question 8

what molecules are higher in the roofplate vs the floorplate

Answer 8

BMPs highest in the roofplate

Shh highest in the floorplate

Question 9

what are hox genes

Answer 9

Family of transcription factors

Establish segmentation along anterior- posterior axis

Question 10

what is synophthalmia (cyclopia)

Answer 10

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

Question 11

what is the difference in division between radial glia and neural precursor cells when building the cortex

Answer 11

Radial glia connect the ventricular and pial surface, divide slowly and symmetrically
Precursors divide asymetrically in the ventricular zone (innermost layer of neural tube)

Question 12

what are transit amplifying cells

Answer 12

an undifferentiated population in transition between SCs and differentiated cells.
(eg neural precursor cells)

Question 13

what does the asymmetric division of neural precursor cells generate when dividing in the ventricular zone

Answer 13

generate new progenitors and post mitotic neuroblasts (will develop into a neuron after a migration phase.)

Question 14

what cells form the venticular zone

Answer 14

Neuroepithelial progenitor cells in neural tube = neural precursor cells

Question 15

why does a neurons location in the cortex reveal its birthdate

Answer 15

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)

Question 16

neuroblasts migrate to the_____surface and form the _________ zone

Answer 16

pial surface and form the marginal zone

Question 17

over time glial blasts do two things to seal their fate, what are they

Answer 17

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)

Question 18

where are cortical interneurons born

Answer 18

ganglionic eminences

Question 19

what are ganglionic eminences

Answer 19

a transitory structure in the development of the nervous system that guides cell and axon migration

Question 20

describe the tangential migration of interneurons

Answer 20

Interneurons migrate tangentially from the ganglionic eminence to the cerebral cortex.
The tangentially migrating interneurons travel perpendicular to the radial glial cells

Question 21

what are the 5 stages of neural cell polarisation where axons and dendrites are established

Answer 21

lamellipodia, minor processes, axonal outgrowth, dendritic outgrowth and maturation

Question 22

what is axonal fasciculation

Answer 22

the process of a growing axon adhering to another, potentially forming groups of axons known as bundles (“fascicles”), which follow similar growth trajectories.

Question 23

how do axons navigate

Answer 23

via intermediate targets and growing along other axons as guides

Question 24

what classes of guidance signals are there

Answer 24

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

Question 25

what are guidance signals interpreted by

Answer 25

the growth cone

Question 26

what is netrin

Answer 26

a long range chemoattractant in axonal guidance

Question 27

what is semaphorin

Answer 27

a long range chemorepulsiant used in axonal guidence

Question 28

what is ephrin

Answer 28

a short range contact mediated repulsiant in axonal guidance

Question 29

what do cadherins do in axonal guidance

Answer 29

contact mediate attraction

Question 30

what are growth cones

Answer 30

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

Question 31

once circuits form what regulates them

Answer 31

the target via continued release of trophic factors and activity
learning and memory
disease

Question 32

why do not all neurons cross

Answer 32

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

Question 33

once direction is determined what is responsible for laying down this axon in its desired direction

Answer 33

microtubular cytoskeletal changes

Question 34

what determines the final pattern of contacts of neurons

Answer 34

neurotrophins and electrical activity

Question 35

what is Hebbs rule

Answer 35

inputs that have correlated activity in time become stabilised

Question 36

what are the adhesion molecules that stabilised formed connections

Answer 36

Presynaptic neurexins: organise the SV docking zone

Postsynaptic neuroligins: recruit PSD

Question 37

Victor Hamburger discovered what

Answer 37

discovered that limb removal results in reduced numbers of motor and sensory neurons in the chick spinal cord (1934)

Question 38

where are radial glia somas and what do they do in the developing brain

Answer 38

in the ventricular zone (projections extending to the marginal)
act as guide wires for the neurones to migrate to the correct place