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