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

The human heart begins to beat late in the third week after fertilization. Before the heart begins
to beat, the nervous system commences to differentiate and change in shape.


Differentiation and growth continue postnatally throughout life as the nervous system is remodeled
through plasticity.


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
neurons and glia
of sensory, symp.
and parasymp nerves

CNS primary vesicles.jpg
Primary brain vesicles


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

Differentiation of the neural tube in the anterior-posterior
axis pattern (rostrocaudal axis) and dorsal-ventral
axis pattern is linked to different transcription factors.
Each somite and its associated spinal cord segment is
integrated into a structural and functional unit consisting
of a spinal nerve, its sensory dermatomal distribution,
and its myotome.

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

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

Neurotrophic factor
families


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

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

Axon guidance



Neurotrophism
Neurotrophic factors


Molecular mechanisms of axonal guidance
q contact adhesion
§ permissive surface (laminin, fibronectin, cell-adhesion
     molecules)
§
q contact inhibition
§ non-permissive surface
§
q fasciculation
q
q chemotropism – attractive molecules

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
§ strengthening 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 proper factors is necessary
     for the next development of the structure
q genetic factors (initial period of development)
q nutritive factors
§ critical period – the 2nd trimester – 1st year
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 to injury 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