neural plasticity
Download
Skip this Video
Download Presentation
Neural Plasticity

Loading in 2 Seconds...

play fullscreen
1 / 20

Neural Plasticity - PowerPoint PPT Presentation


  • 248 Views
  • Uploaded on

Neural Plasticity. Damage to the nervous system can induce remodeling of neural pathways Such remodeling reflects plasticity CNS is much more plastic than once believed Plasticity greatest in the developing brain Young child some degree of plasticity remains in the adult brain. Plasticity.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Neural Plasticity' - oya


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
neural plasticity
Neural Plasticity
  • Damage to the nervous system can induce remodeling of neural pathways
  • Such remodeling reflects plasticity
  • CNS is much more plastic than once believed
    • Plasticity greatest in the developing brain
      • Young child
    • some degree of plasticity remains in the adult brain
plasticity
Plasticity
  • Critical period
  • Alteration of connections in visual cortex in visually deprived neonates
  • Amblyopia (reduced visual capacity)
  • Sprouting of new axons does occur in the damaged CNS
neurotrophic factors
Neurotrophic factors
  • Target tissues play a critical role in regulating the # of surviving neurons by secreting a variety of neurotrophic factors
  • Neurotrophin class
    • nerve growth factor (first one discovered)
      • protein with 3 subunits (MW 130,000)
      • beta subunit is biologically active
    • bind to specific receptors
    • promote neuronal survival
neurotrophic factors4
Neurotrophic factors
  • Elimination of neurotrophic factors & their receptors lead to neuronal death
  • sensory and sympathetic neurons require trophic support from neurotrophins secreted by their targets
  • target cells secrete limited amounts of neurotrophic factors
  • deprivation of neurotrophic factors activates a cell death program in neurons
    • apoptosis
apoptosis
Apoptosis
  • Cell death characterised by 4 features
    • cell shrinkage
    • condensation of chromatin
    • cellular fragmentation
    • phagocytosis of cellular remnants
  • Process prevented by neurotrophins
  • The cell death program is the cause of neuronal cell loss that normally occurs in the first year of life
    • Caspase- enzyme that cleaves COOH (protein)
damage in the nervous system
Damage in the nervous system
  • Most injuries involve damage to axons
    • axotomy- transection of the axon
      • dooms the distal segment
      • glial cells degenerate (Wallerian degeneration)
      • proximal portion also affected probably due to lack of trophic factors from target cell
      • postsynaptic neurons can also atrophy and die
      • inputs to injured neuron can withdraw “synaptic stripping” & replaced with Schwann cells (PNS) or Microglia or Astrocytes (CNS)
      • neuronal degeneration can propagate through a circuit in both antro and retrograde directions
regeneration in the nervous system
Regeneration in the nervous system
  • New neural connections can reform following injury
  • Regenerative capacity is
    • > PNS
    • < CNS
  • Axonal Sprouting
  • Chemotropic factors secreted by Schwann cells attract axons to distal stump
pns regeneration
PNS regeneration
  • Once they return to their targets regenerated axons can form functional nerve endings
    • regeneration of neuromuscular junctions
    • re-innervation of glands, blood vessels, & viscera by ANS
    • sensory axons can re-innervate muscle spindles
  • In all three divisions of PNS (motor, sensory & autonomic the effects of axotomy are reversible (but not necessarily perfect)
cns regeneration
CNS regeneration
  • Little regeneration occurs in CNS after injury (short stumps)
  • long distance regeneration of axons is rare
  • may have a latent regenerative capacity that can be exploited via therapeutic interventions
    • environment
    • growth promoting factors (laminin, cell adhesion molecules)
    • central myelin is an inhibitor of axon outgrowth
regeneration cont
Regeneration (cont)
  • Restoration of function requires synaptic regeneration
    • Central axons may retain capacity to form synapses even in adult
minimizing damage in nerve trauma
Minimizing damage in nerve trauma
  • Antioxidants
    • methylprednisone
      • lipid peroxidation
  • Preventing excitotoxicity
    • NMDA receptor antagonists
      • MD 801
regeneration in the nervous system12
Regeneration in the nervous system
  • New neural connections can reform following injury
  • Regenerative capacity is
    • > PNS
    • < CNS
  • Axonal Sprouting
  • Chemotropic factors secreted by Schwann cells attract axons to distal stump
pns regeneration13
PNS regeneration
  • Once they return to their targets regenerated axons can form functional nerve endings
    • regeneration of neuromuscular junctions
    • re-innervation of glands, blood vessels, & viscera by ANS
    • sensory axons can re-innervate muscle spindles
  • In all three divisions of PNS (motor, sensory & autonomic the effects of axotomy are reversible (but not necessarily perfect)
cns regeneration14
CNS regeneration
  • Little regeneration occurs in CNS after injury (short stumps)
  • long distance regeneration of axons is rare
  • may have a latent regenerative capacity that can be exploited via therapeutic interventions
    • environment
    • growth promoting factors (laminin, cell adhesion molecules)
    • central myelin is an inhibitor of axon outgrowth
regeneration cont15
Regeneration (cont)
  • Restoration of function requires synaptic regeneration
    • Central axons may retain capacity to form synapses even in adult
focal hand dystonia
Focal hand dystonia
  • Pt. is unable to independently control digits of the hand.
    • Happens when fingers are moving together at a high rate of activity for long periods of time.
      • Pianists practicing certain pieces for up to 8 hours/day
  • Somatosensory representation in cortex of affected digits are fused
    • In monkeys when two adjacent digits sewn together (sydactyly) the cortical representations of both digits become one
the newborn brain
The newborn brain
  • Contains about 100 billion nerve cells
  • Each neuron connects to anywhere from a few thousand to 100,000 other neurons
  • At birth each neuron averages about 2500 synapses
  • By age 3-4 this has risen to about 15,000 synapses and then you start to lose synapses
    • Process called “pruning”
  • Adult brain 100-1000 trillion synapes
    • Humans have about 35,000 genes
    • So what governs the connections in the brain?
      • NOT THE GENES
plasticity in brain development
Plasticity in Brain Development
  • The final wiring of the brain occurs after birth & is governed by early experience
    • Neurons that fire together wire together
  • A protein called MAP2 ( microtubule-associated protein 2)
    • Map2 molecules form bridges between neurofilaments and microtubules
      • Part of internal skeleton that affects neurons growth and structure
      • May mediate the formation of new neural pathways
      • (Scientific Am, Dec 1988, p56-64.)
plasticity19
Plasticity
  • Even in adults the sensory cortex is constantly remodeling
  • The existence and importance of brain plasticity are no longer in doubt
  • “Some of the most remarkable observations made in recent neuroscience history have been on the capacity of the cerebral cortex to reorganize itself in the face of reduced or enhanced afferent input.” (Edward Jones UCD, center for neuroscience, 2000)
the wiring of the brain
The wiring of the brain
  • Is governed by the neuronal activity
    • Synaptogenesis governed by activity
  • Patterns of stimulation
    • Neurons that wire together fire together
  • Its survival of the busiest
ad