Nervous System

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Nervous System
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Cells of the Nervous System
1. Neurons (Nerve Cell) Motor (Efferent) Sensory
(Afferent) 2. Neuroglia (Glial Cell) 3.
Neurolemmocyte (Oligodendrocyte) (Schwann cells)
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The Action Potential
Excitable cells (nerve and muscle) are polarized
(membrane voltage) resting -70 mV Action
Potential a rapid, transient reversal of
membrane potential, to 40mV all in about 1
msec. Action Potential is all or none (not
graded) Stimulus strength is coded in the
frequency of action potentials
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Cell to Cell Communication
The Chemical Synapse Presynaptic
Cell Postsynaptic Cell Synaptic Cleft (narrow
space 10-20 nm) Neurotransmitter released from
vesicle Binds to Specific Receptor Excitation
- more likely for a.p. Inhibition- less likely
for a.p.
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Neurotransmitters
Acetylcholine Norepinephrine Dopamine Serotonin GA
BA
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Organization of the Nervous System
Peripheral Sensory Motor (Somatic) Autonomic
Sympathetic Parasympathetic
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Organization (cont.)
Central Nervous System Brain Cerebrum Cerbell
um Brain Stem midbrain, pons, medulla
oblongata Spinal Cord Meninges Cerebral Spinal
Fluid
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Age Related Changes

• Gross Structural Changes
• Loss of weight and volume
• 360 g at birth
• 1300 g at age 20
• same at 55
• 1150 g at age 80

• Increase in Ventricular Volume

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Age Related Changes (cont.)

• Microscopic Structural Changes
• Loss in cell number (cerebral cortex)
• est. 10,000 / day (but, most after 55)

• Reduction in number of dendrites and dendritic
  spines
• Functional correlation ?
• Decline in spines in dementia

• Accumulation of lipofuscin

• Neurofibrillary tangles
• Neuritic Plaques

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Age Related Changes (cont.)
Metabolism PET Scan Decreases or stays the
same Mental Ability Cross Sectional vs.
Longitudinal Studies Cross Sectional are age
biased Longitudinal a better measure
(BLSA) Decline in memory (esp.
short-term) Decline in ability to learn BUT,
not so large if given more time.
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Age Related Dysfunction
1. Loss of Reflexes- Knee jerk reflex many loose
by 70, most all by 90 2. Insomnia - awaken
feeling unrested Time spent sleeping varies
little with age Ratio of REM sleep vs. slow wave
(deep) sleep changes. More REM, less deep
sleep in elderly Reticular Activating System
Defect ?
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Age Related Dysfunction
3. Dementia (organic brain syndrome)- serious
decline in memory one other mental
func. Severe 5 under 65, 15 over
85 prevalence increasing with aging
population a) reversible- caused by anemia,
poor nutrition, iatrogenic (prescription meds),
or depression b) irreversible - anatomical
brain deterioration
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Dementia
A. Multi-infarction Dementia transient ischemic
attack (TIA) mini-strokes B. Parkinsons
Disease Incidence - 50,000 /yr. Rigidity,
tremors degeneration of neurons in substantia
nigra axons synapse in basal ganglia
(dopaminergic) C. Cerebrovascular Accident
(CVA) stroke obstruction or rupture of a blood
vessel resulting in ischemia and cell death
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Dementia (cont.)
D. Non Alzheimers dementia appear suddenly, not
progressive, idiopathic E. Alzheimers Disease-
progressive (Alois Alzheimer, 1907) most common
dementia 50-60 of dementia patients 40 of
patients are over 85 20 of all people over 80
are afflicted 100,000 die each year, 4,000,000
affected symptoms memory loss, language
deterioration, impaired visual-spatial skills,
poor judgment, indifferent attitude, but
preserved motor function
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Alzheimers Disease (cont.)
3 defined stages 1) impaired recent memory,
spatial disorientation 2) learning deteriorates,
loose 3 Rs, confusion failure to recognize
familiar persons 3) seizures, loss of
speech Diagnosis symptoms, rule out other
causes, MRI especially of hippocampus verified
at autopsy by senile plaques (Beta-Amyloid),
neurofibrillary tangles (Tau-Protein)
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Alzheimers Disease (cont.)
Causes / Risk Factors genetic component -
familial AD (early onset, FAD) associated with 4
genes on 4 chromosomes mutations - abnormal
proteins chromosome 21- (Downs
Syndrome) APP gene (amyloid precursor
protein) chromosome 14 - presenilin 1
(PS1) chromosome 1 - presenilin 2 (PS2) both
effect handling of APP (secretase) all lead to
increase in Aß1-42/43 (amyloid plaques)
chromosome 19 - ApoE4
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Alzheimers Disease (cont.)
Autosomal dominant (only 1 mutant copy
required) What causes cell death ? Aß1-42/43
induces oxidative damage via a receptor that
mediates neurite outgrowth Sporadic AD (late
onset, SDAT) ApoE4 ? Role of environment ?
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Alzheimers Disease (cont.)
Treatment and Prevention No Cure Treat
Symptoms acetylcholinesterase inhibitors Biomark
ers ? ApoE4 allele sense of smell homocysteine
levels Nun Longitudinal Study Use it or Loose
it
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Age Related Changes (cont.)
Sensory Systems Taste - least affected Smell-
ability to detect and identify odors, declines