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
Development of
the NS
Development of the NS
General principles of the ontogenetic
development of the CNS
 segmentation of NS (somitogenesis)
 control by genes
 fate of neurons (death or survival) based on epigenetic
factors, migration and interaction of neurons –
neurotrophic molecules
 neuronal differentiation and survival molecules
 navigation of neurons towards the target structures –
neurotropism
 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
Growth cone
Axon guidance
Reduction of redundant axons
Axon guidance
Molecular mechanisms of axonal guidance
 contact adhesion
 permissive surface
 contact inhibition
 non-permissive surface
 fasciculation
 chemotropism – attractive molecules
Contact adhesion and inhibition
Fasciculation
Chemotropism
Neural plasticity
 developmental plasticity
 neuroanatomical and neurophysiological changes
 chemical plasticity
 fast or slow turnover
 neurotrophic-derived plasticity
 neurons are not irrevocably genetically programmed
to produce one transmitter
 neuronal plasticity
 capability of generating new branches and synapses
 synaptic plasticity
 strenthening or weakening of synapses
Reciprocal Schwann cell-axon interactions
Apoptosis
Critical factors and periods in
development of the CNS
 critical period in development of the CNS
 influence of the developmental factors is necessary
for the next development of the structure
 genetic factors (initial period of development)
 nutritive factors
 critical period – the 3rd trimester – reduction in amount of
neurons
 hormonal factors
 factors of afferent pathways
Reaction of neurons to injury
 loss of function
 influence of duration of the damaging agent
 reaction of processes differs in neurons of CNS and PNS
 CNS neurons - atrophy and death due to great decline
of RNA synthesis
 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
Wallerian degeneration
Peripheral nerve transection
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