5. Neurogenesis also occurs in adult life
• In adult life neurogenesis occurs in only two
areas of the brain:
• in the dentate nucleus of the hyppocampus
and in the olfactory bulb.
7. Synapse loss and restoration
• Stress, aging and neurodegeneration can
cause loss of the synapse with or without
neuronal loss.
• Learning, exercise, growth factors,
antidepressants and psychotherapy cause
restoration of the synapse and of neurons.
• Transplantation of stem cells is another way to
restore the neurons or the synapses.
9. Necrosis vs. Apoptosis
• In necrosis neurons are being destroyed by
suffocation or toxins/poisons(neuronal
assassination).
• In apoptosis neurons are being destroyed by
the activation of a gene inside the cell’s
DNA(neuronal suicide).
11. Neurodevelopment
• During neurodevelopment, neurons are
formed in excess (some are normal and some
are defective) then they are selected for
performing their duties.
• The defective neurons are eliminated.
• In developmental disorders the defective
neurons may be selected leading to a
neurologic or psychiatric condition.
13. Neuronal Migration
• After neurons are selected, they must migrate to
the right parts of the brain.
• In order to migrate, neurons trace either glial
cells or the neurons that already migrated.
• Migration is helped by adhesion molecules on the
neuronal surfaces and complementary molecules
on the glia.
• If migration is successful, the neurons are
properly aligned to grow, develop and form
synapses.
16. Synaptogenesis
• Synaptogenesis is directed by neurotrophins.
• Neurotrophins are molecules that cause neurons
to sprout an axonal growth cone.
• Once the growth cone is formed the neurons and
glia in the area make recognition molecules that
can be ATTRACTIVE or REPULSIVE.
• Repulsive neurotrophins cause the neurons to
grow away from them, while attractive
neurotrophins cause the neurons to grow
towards them.
21. Formation of a Synapse
• Presynaptic axons contain some of the
molecular components necessary to form a
synaptic connection even before making
contact with a postsynaptic site.
• A synapse is formed in stages:
27. Long term potentiation
Frequent utilization of synapse leads to:
• increased flexibility of the postsynaptic site,
• Increased neurotransmitter release
• postsynaptic receptors increase in number
• surface area of the postsynaptic neuron
increases
• adjacent postsynaptic sites form
31. Dendritic pruning
The dendritic tree is constantly changing
throughout life, it can:
• sprout new branches, grow and establish
synaptic connections when necessary
• trims, alter or destroy synaptic connections
when necessary (pruning)
36. Competitive Elimination
• Between birth and age 6 synapses are formed
at an accelerated rate
• During adolescence competitive elimination
(pruning) occurs destroying about 50% of the
synapses.
