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Chapter 16

Chapter 16 -Neuropsychology :Clinical and Expt Foundations


Department
Psychology
Course Code
PSYB65H3
Professor
Ted Petit
Chapter
16

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Chapter 16 – Recovery of Function
Contrary to what is believed the normal adult brain does produce new neurons and
neural death is a normal part of brain development
16.1 Neural Degeneration, Regeneration, and Reorganization
Autopsy- provides specific information about the life and health of an individual and why
the individual die – but also provides important insights about how various
diseases/conditions affect the body and possible treatments that could be used
Most neurological diseases occur because neurons or glia cells and few people suffer
brain damage due to accidents – important to look at acute and long term effects to
provide proper treatment regimes
Degeneration
Frequent causes of brain damage stroke, tumours, and infection (kill cells and produce
a lesion)
Cells such as neurons die in one of two ways:
(1) Necrosis (homicide) – failure to maintain homeostasis within the neuron causes death
of the neuron, always an abnormal event can be due to inability to produce ATP,
changes in [ion], and damage to organelles
Causes the cell to swell and the membrane of the cell and its organelles and vesicles
to burst
Lysis(bursting) – spills contents of the neuron into the ECF = death of the neuron
Often Associated with damage that occurs rapidly, i.e., mechanical damage (tumour,
blow to the head), disruption to ion channels (ischemia, anoxia), or infections such as
rabies
But can also be associated with damage that occurs more slowly – near stroke areas or
because of neurodegenerative diseases
Ischemia (disruption in blood flow after stroke or CVA) – usually causes necrotic cell
death
Ischemia disrupts energy pathways which can affect ion channels important for
homeostasis
For example, ischemia may cause a reduction or termination of ATP synthesis which
is needed for the Na+/K+ pump to function, therefore the cell cannot maintain these
ion levels following an AP
Disruptions in Na+/K+ pumps also causes disruptions of pumps that maintain Ca2+
and water levels in the neuron – increased internal water levels can lead to swelling
and potential bursting of the membrane – influx of calcium allows release of
neurotransmitters so disruptions in its regulation affects neurotransmitters
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Ca2+ accumulation within cells thought to be responsible for initial ischemic event
damage
TBIs ( acquired injuries), stroke, and neurodegenerative diseases such as
Huntington’s chorea can cause necrotic cell death because they alter the release of
glutamate
Glutamate – excitatory amino acid neurotransmitter used in almost all fast excitatory
events in the nervous system but is toxic to neurons n glia
Excitotoxicity – ability of specific compounds, such as glutamate, to both excite
neurons and kill them
Primary neural death – the death of neurons that occurs immediately following
trauma seems to be associated with glutamate released in excess (leads to more
release of glutamate and excitation of neurons) but also associated with neuron’s
resources being exhausted and overwhelming its homeostatic mechanisms
Secondary neural death(after the primary event) - due to large influx of Ca2+ into the
cell – glutamate regulates these channels – excess glutamate = sustained and
excessive influx of Ca2+
Large [Ca2+] in the ICF triggers many intracellular events changes in second
messengers + production of free radicals = death of neural mitochondria = loss of
energy (ATP) production
Ca2+ can also cause inflammation and membrane breakdown – characteristic of
necrosis
(2)Apoptosis (suicide) – programmed neural death, the neuron uses its own machinery to
ensure its own death
Active process that uses cellular energy to cause death – process regulated by genes
which trigger proteins ‘caspases’ that destruct the neuron
In apoptosis dead cells still have intact membranes and nucleus is condensed into a
tangle of DNA fragments
Is apart of normal development of the neuron – some researchers say that all
neurons will do it
Can be caused by many things such as damage to DNA, free radicals, the removal of
tropic factors needed for development
Presence of nearby necrotic neurons can cause neighbouring neurons to undergo
apoptosis
Can be seen in diseases that cause neural degeneration such as PD or AD and even
acute events such as TBI or stroke
Regeneration (neurogenesis)
Usually in the CNS neural death results in permanent loss of the neuron and regeneration
occurs less frequently
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