aging nervous system
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Aging Nervous System. Neurotrophic Factors Necessary for Maintenance of Neurons. Nerve growth factor Brain-derived neurotrophic factor (BDNF) Neurotrophin 3 (NT3) Neurotrophin 4/5 (NT4,5). Neurotrophin function Play role in development of NS

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neurotrophic factors necessary for maintenance of neurons
Neurotrophic Factors Necessary for Maintenance of Neurons
  • Nerve growth factor
  • Brain-derived neurotrophic factor (BDNF)
  • Neurotrophin 3 (NT3)
  • Neurotrophin 4/5 (NT4,5)
  • Neurotrophin function
    • Play role in development of NS
    • Interact with receptor cells to prolong life of neuron
    • Play role in suppressing apoptosis (death of cell nuclei – programmed cell death)
free radicals and oxidative stress
Free Radicals and Oxidative Stress
  • Free radicals can cause oxidative stress in brain injury and disease and trigger apoptosis
  • Oxidative stress is a secondary complication of many progressive NS disorders
    • Alzheimer’s Disease
    • Parkinson’s Disease
    • Amyotrophic Lateral Sclerosis (ALS)
  • Enhanced antioxidant status associated with reduced risk of some NS diseases
anatomic ns changes with age
Anatomic NS Changes with Age
  • Selective atrophy of brain tissue including glial cells and blood vessels
    • Nerve cell shrinkage may be more significant to function than actual nerve cell loss
  • By 8th decade, mean loss of 15% of velocity in myelinated fibers
  • Blood supply decreases by 10-15%
morphological changes with aging
Morphological Changes with Aging
  • Decreased # of some receptors
  • Decreased concentration of enzymes involved in synthesis of neurotransmitters
    • Decreased synthesis of some neurotransmitters
    • May decrease control of:
      • Visceral function
      • Emotions
      • Attention
  • Serotonin reduced
    • Reduced memory
    • Sleep pattern effects
    • Thermoregulation
  • MAO (monoamine oxidase) increased with age – may contribute to depression
senile plaques
Senile Plaques
  • Neuritic (senile) plaques found outside of neurons with degenerating axons, dendrites, astrocytes
    • extracellular deposits of amyloid (starchlike protein-carbohydrate complex) in the gray matter of the brain
    • Occur most often in cortex and hippocampus=declarative memory
    • Associated with Alzheimer’s and dementia
    • proportion of people with plaques:
      • Age 60 years (10%)
      • Age 80 years (60%)
  • Direct relationship between number of senile plaques and:
    • severity of the clinical impairment
    • decreased neurotransmission of acetylcholine
  • Because acetylcholine is associated with memory loss, it is believed that the senile plaques are a major cause of short term memory loss in Alzheimer’s disease.

Edwardson et al.

neurofibrillary tangles nft
Neurofibrillary Tangles (NFT)
  • pathological accumulation of paired helical filaments composed of abnormally formed tau protein
  • found chiefly in the cytoplasm of nerve cells of the brain and especially the cerebral cortex and hippocampus
  • Found in higher concentration in older adults
  • occurs in Alzheimer\'s disease and other forms of dementia
pns changes
PNS Changes
  • Vestibular system
    • Hair cell receptors decline beginning at age 30
    • Vestibular receptor ganglion cells decrease by age 55-60
    • Myelinated fiber loss in vestibular system is 40%
    • May lead to c/o dizziness
  • Somatosensory system
    • Decreased # of unmyelinated and myelinated fibers
    • Blood vessels become atherosclerotic  loss of blood supply to nerve fibers
      • Major contributor to increased prevalence of peripheral neuropathies in older adults
pns changes1
PNS Changes
  • Autonomic NS
    • Sympathetic control of dermal vasculature is reduced
      • Results in reduced wound repair efficiency
      • In aging animal models, TENS improved vascular response through increasing activity of sympathetic nerves
  • Motor system
    • Loss of motor units remaining motor units become larger which can reduce ability to fine tune motor coordination
    • Signs of re-innervation (space between nodes in myelin was reduced  leads to reduced NCV)
pns changes2
PNS Changes
  • Wallerian degeneration is delayed
  • Regeneration takes longer because secretion of trophic factors is slower than in younger adults
  • Density of regenerated neurons is reduced
  • Less collateral sprouting
  • In PNS, loss of αMN occurs with age.
    • Remaining αMN will innervate the stranded muscle cells
    • Results in larger motor units, which can effectively reduce motor coordination for finely tuned movements
balance changes with aging
Balance Changes with Aging
  • Decreased NCVs for sensory and motor nerves
  • Apparent decrease in ability to integrate senses involved in determining postural responses
  • Functional balance changes
    • With eyes closed single limb stance, balance decreases begin at age 40
    • More co-contraction of muscles during balance responses with aging
    • In some elders, see proximal muscle activation before distal with minor perturbations on solid floor

Choy, Brauer, Nitz, JAGS, 2003

loss of functional reserve
Loss of Functional Reserve
  • Normally, a significant loss of neural tissue can occur before functional change occurs
  • In older adults, there are less redundant neurons to take over the function so functional changes occur more readily
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