L6 - Cellular mechanisms of neural development and sense organs

Question 1

histogenesis of the neural tube

Answer 1

early neural tube = cells form pseudostratified columnar epithelium

nuclei migrate between the ventricular and marinal surface

nuceli are near the marginal surface - DNA synthesis

ventricular side - cell division

as the neural tube matures
cells leave cell cycle and differentiate
into neurones + glia

epithelial cells keep dividing in the ventricular layer

newly formed neurones form mantle layer = grey matter

axons sent towards the marginal surface = marginal layer = white matter

Question 2

neural differentiation - neurogenesis

Answer 2

from progenitors to neurones

first they are all alike and express Sox2

2. neurogenic regions are defined = just ready to differentiate
   Neuro
3. within neurogenic regions cells are selcted to diffferentiate
   NeuroD

fgf signllling restricts neurogenic region in the caudal diencephelon

Question 3

lateral inhibition to control cell differentiation

Answer 3

selection of neuronal precursors from grooup of neuroectodermal cells with neurogenic potential

involves recirpcal signalling which enhances random differences between cells

regulation of number and distribution of neurones

notch receptor - delta ligand
will activate Hes
Ascl, nerogenin proneural

at first contigous neural plate cells express neurgenin, delta and notch

with time one cell expresses more delta develops into a neuroblast and inhibits the neighbouring cells from following a neural fate

Question 4

fate of neural progenitor cells

Answer 4

neuroepithelial cells develop into radial glia

can undergo asymmetric cell division =1 stem cell + cell differentiates

neurones
glia astrocytes oligo

Question 5

adult neurogenesis

Answer 5

neurogenesis continues in distinct areas in the adult brain
subventricular zone of lateral ventricles
neurones migrate to offactory bulb via rostral migratory stream

neural progenitors transit amplifying cells are located in stem cell nice associated with brain capillaries

Question 6

developmental anatomy of the telencephalon

Answer 6

dorsal = pallium
cerebral cortex + hippocampus

ventral = subpallium
lateral ganglionic eminance
striatum
medial ganglionic eminence
pallidum

Question 7

radial and tangential migraation

Answer 7

radial migration
perpendicular to brain surface
pyramidal projection neurones in the cortex migrate radially

tangential migration - along surface of the brain

cortical interneurones migrate from subpallium to neocortex

Question 8

axon outgrowth

Answer 8

when a neuron. is born it will start growing neurites

axon growth must be controlled to ensure correct innervation of the target

Question 9

axon guidance

Answer 9

axons grow at the distal end growth cone

controlled by extrinsic signals
repellents - cell adhesion molecules and attractants - semaphorin, ephrin and ecm molecules

midline cells secrete Netrin - gradient sensed by commissural axons

expression levels detected by ephrinA ligands gradient in tectum

Question 10

why do axons of medial longitudinal fasicle MLF grow away from forebrain

Answer 10

Sema3 is expressed rostral to MLF causing growth cone to collapse invitro

sema inhibits mlf axon growth and repels mlf axons from forebrain

Question 11

how are synapses formed in development

Answer 11

neuromusclar junction - motor axons and skeletal muscle
larger than cns synapses
AChr label

once the growth cone reaches its target cell growth stops
a thight junction is formed between neuron and target cell
the differentiation of the synapse must ensure functional signal transition
matching neurotransmitter receptor interaction

presynaptic: whole apparatus involved in neurotransmission release is assembled
postsynaptically: the receptor system is established

Question 12

CNS synapses

Answer 12

initial contact through cell adhesion molecules
CAMs Neurexin-Neuroligin

presynaptic assembly of active zone machinery for neurotransmitter release

postsynaptic recruitment of neurotransmitter receptors

Question 13

cephalisation

Answer 13

mouthand sense orgains around it

brain to recieve and process sensory input

find and assess food

Question 14

the role placodes play in sense organ development

Answer 14

contribute to sense organs offactory epithelium lens otic epithelium
cranial ganglia

offactory 
lens
trigeminal
epibranchial
otic precursors

Question 15

fate determination of placodes

Answer 15

precursors of diff placodesare intermingles
progenitors w diff fate segregate at diff regions

the early pre placodal region has presumptive lens preference

subsequent signalling inhibits lens formation specifying other placode fates

a cell that has both fate option and has fgf offactory will dominate

Question 16

development of the inner ear

Answer 16

otic placode origin
inuced by fgf19 from adjacent mesendoderm

form a pit = invagination to form the otic vesicle
dorsal = vesitbular semicircluar canals

ventral = cochlear cochlea

close like with pharyngeal cleft

Question 17

development of the eye

Answer 17

optic region retina deriverd from diencephalon = neural tube

neurons in the retina are orgainsed into functional layers = the light sensing part is away from the light
primary - connection with photoreceptors
secondary - axons into optic nerve - ganglia

lens derived from optic placode

Question 18

retina cell fates

Answer 18

retinal ganglion cellsfirst

photoreceptors cones + rods

muller glia last

Question 19

olfactory sense organ

Answer 19

epithelium develops from nasal placode

invagination to form nasal pit
dual origin of olfactory sensory neurones
most from olfactory epithelium but some from neural crest

most rostral of the placodes

located in close connection to mouth and maxillary

Question 20

sensor = processor = effector

Answer 20

mechano chemo light or electrical receptors sample info from environment

info sent to CNS to be interpretwd = effect

Question 21

how can the neurons in the CNS know which of the many sensory neurons in the sense organ has received a signal

Answer 21

topographic representation =
afferents (sensory axons) to the CNS visual system =
WHERE spatial info
olfactory = WHAT odorant specificity

Question 22

light perception

Answer 22

photoreceptors in neural retina

signals transmitted by retinal ganglion

the axons of ganglion cells that form the optic nerve = brain
- tectum in midbrain

nasal retina = posterior optic tectum

temporal retina project to the anterior tectum

Question 23

Chemical sense

Answer 23

olfactory sense neurons are in olfactory epithelium

project cells to the olfactory bulb

transmit info to other brain areas

Question 24

olfactory axons into 1 glomerulus

Answer 24

knock out of LacZ into gene of odorant receotir

axons from all olfactory sensory neurons expressing this receptor converge on just one glomerulus

Question 25

olfactory epithelium organisation

Answer 25

sensory neurones only express one olfactory receptor

scattred distribution of receptors in the olfactory epithelium

Question 26

development of the nervous system

Answer 26

lateral inhibition and asymmetric cell division are key processes during neurogenesis
migration of neurones contributes to the organisation of the nervous system
for the formation of the nervous system
for the formation of functional circuits axons must be guided by extrinsic signals to their targets
at the target reciprocal interaction between neurone and target cell establishes the synapse
chemical signalling is the basis for topographic mapping in vision and smell