Ontogenetic development
= individual development of
the organism from the fertilized egg
to its mature form and finally death

Development of a neuron:
1)genetic level
    a) transciption (DNA → RNA)
    b) translation (RNA → polypeptides)
2)epigenetic level
     neurotropic and neurotrophic molecules

•Target field theory



http://what-when-how.com/wp-content/uploads/2012/04/tmp1411.jpg
Development of
the NS

https://upload.wikimedia.org/wikipedia/commons/thumb/6/67/Development_of_nervous_system.svg/2000px-
Development_of_nervous_system.svg.png
Development of the NS

CNS primary vesicles.jpg
Primary brain vesicles


Human Stage14 neural02.jpg
Secondary vesicles
and cranial nerves
1 mm

General principles of the ontogenetic
development of the CNS
q segmentation of NS (somitogenesis)
§  control by genes
q fate of neurons (death or survival) based on epigenetic
     factors, migration and interaction of neurons –
     neurotrophic molecules
§neuronal differentiation and survival molecules
q navigation of neurons towards the target structures –
     neurotropism
q end-differentiation of neurons

Neurotrophic factor
families


Trophic relationships in the NS
Neurons have trophic effect on periferal tissues
Periferal tissues have trophic effect on neurons

https://mbi-figure.storage.googleapis.com/figure/1384241728804.jpg
Growth cone
http://www.ucl.ac.uk/~ucbzwdr/teaching/b250-99/axons_files/growthcone.jpg

Axon guidance



Reduction of redundant axons



Neurotrophism
Neurotrophic factors


Molecular mechanisms of axonal guidance
q contact adhesion
§ permissive surface
§
q contact inhibition
§ non-permissive surface
§
q fasciculation
q
q chemotropism – attractive molecules

Axon guidance
http://www.mdpi.com/polymers/polymers-05-00254/article_deploy/html/images/polymers-05-00254-g001-10
24.png

Contact adhesion and inhibition



Fasciculation
http://www.frontiersin.org/files/Articles/91599/fnana-09-00051-r2/image_m/fnana-09-00051-g004.jpg


https://resources.rndsystems.com/images/site/2004-mr-axon-fig-1_960.png
Chemotropism


Neural plasticity
qdevelopmental plasticity
§neuroanatomical and neurophysiological changes
qchemical plasticity
§fast or slow turnover
qneurotrophic-derived plasticity
§neurons are not irrevocably genetically programmed
       to produce one transmitter
q
qneuronal plasticity
§ capability of generating new branches and synapses
q
qsynaptic plasticity
§ strenthening or weakening of synapses
q
q
q

Reciprocal Schwann cell-axon interactions



Apoptosis






Critical factors and periods in
development of the CNS
q critical period in development of the CNS
§ influence of the developmental factors is necessary
     for the next development of the structure
q genetic factors (initial period of development)
q nutritive factors
§ critical period – the 3rd trimester – reduction in amount of
     neurons
q hormonal factors
q factors of afferent pathways

Reaction of neurons to injury
q loss of function
q influence of duration of the damaging agent
q reaction of processes differs in neurons of CNS and PNS
q CNS neurons - atrophy and death due to great decline
     of RNA synthesis
q PNS neurons – anabolic processes depending on
§type of injury
§distance of the injury site from the body
§age of the organism
§localization and function of neurons

http://lh4.ggpht.com/_RIjx_Mg4ZVM/TNv76QN3M0I/AAAAAAAAC3A/HP_UZI1eTfg/image_thumb5.png?imgmax=800



https://static-content.springer.com/image/prt%3A978-3-642-28753-4%2F23/MediaObjects/978-3-642-28753
-4_23_Part_Fig1-4855_HTML.jpg
Wallerian degeneration

http://missinglink.ucsf.edu/lm/ids_104_cns_injury/Response%20_to_Injury/Injury_Images/PNSWallerDeg.
jpg
Peripheral nerve transection

http://missinglink.ucsf.edu/lm/ids_104_cns_injury/Response%20_to_Injury/Injury_Images/WallerDegCNS.
jpg
Spinal cord trauma

Illustrations were copied from:
Neuroscience Online, the Open-Access Neuroscience
Electronic Textbook
Department of Neurobiology and Anatomy
University of Texas Medical School at Houston