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Chapter 10

PSY290H5 Chapter Notes - Chapter 10: Axotomy, Brain Ischemia, Dementia


Department
Psychology
Course Code
PSY290H5
Professor
Brett Beston
Chapter
10

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Chapter 10
Tumor = neoplasm = mass of cells that grows independently of the rest of the body
20% of brain tumors are meningiomas (tumors that grow between menginges)
oAll meningiomas are encapsulated tumors: they grow within their own
membrane. They are almost always benign as well and can be removed without
much risk.
Aside from meningiomas, most brain tumors are infiltrating tumors: grow diffusely
through surrounding tissue and therefore are malignant
10% of tumors are metastatically derived via the bloodstream from other parts of the
body
oMany originate as cancers of the lungs
Dr. Pinel had an encapsulated tumor on CN VIII, referred to as acoustic neuroma
Neuromas are tumors that grow on nerves or tracts
Strokes:
Infarct is the area of dead or dying tissue produced by a stroke
Penumbra is the dysfunctional area surrounding the infarct
othis tissue may recover or die
There are two major types of strokes:
Cerebral hemorrhage (bleeding of the brain) occurs when a cerebral blood vessel
ruptures and blood seeps into the surrounding neural tissue and damages it
oBursting aneurysms (balloonlike dilation of an artery) are common causes of
intracerebral hemorrhage. Aneurysms can be congenital (present at birth) or due
to poisons or infections
Cerebral ischemia is a disruption of the blood supply to an area of the brain. Three main
cause:
oThrombosis: a plug (thrombus) is formed and blocks blood flow at the site of its
formation
oEmbolism: a plug (embolus) is carried by the blood from a larger vessel (where it
was formed) to a smaller one where it becomes lodged
oArteriosclerosis: walls of blood vessels thicken and the channels narrow, usually
due to fat deposition. This can lead to eventual blockage.
Much of the brain damage associated with stroke is a consequence of excessive release of
excitatory amino acid neurotransmitters (particularly glutamate).
Mechanism: blockage of blood vessels leads to blood-deprived neurons that become
overactive and release excessive quantities of glutamate. This overactivates glutamate
receptors in postsynaptic neurons (particularly NMDA in this situation), resulting in Na+
and Ca2+ influxes in the postsynaptic neurons. This Ca2+ and Na+ influx has two
effects:
oTrigger the release of more glutamate (spreading toxic cascade to other neurons)

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oTrigger sequence of internal reactions that ultimately kill postsynaptic neuron
Ischemia-induced brain damage has three important properties:
1. Takes a while to develop
Even though a temporary cerebral ischemica episode may last 10 minutes, there is
usually little evidence of brain damage, but substantial neuron loss can often be
detected a day or two later
2. Does not occur equally in all parts of the brain
Neurons of the hippocampus are particularly susceptible
3. Mechanisms of ischemia-induced damage vary somewhat from brain structure to brain
structure
Closed-head injuries: injuries by blows that do not penetrate the skull
Contusions involve damage to the cerebral circulatory system and produces internal
hemorrhaging, which results in a hematoma
oHematoma is a localized collection of clotted blood in an organ or tissue (bruise).
This blood can accumulate in the subdural space (between dura mater and
arachnoid membrane) and distort surrounding neural tissue
oContusions occur when the brain slams against the inside of the skull, on the
opposite side struck by the blow: contrecoup injuries
Concussion is a disturbance of consciousness following a blow to the head without
evidence of contusion or structural damage
oPunch-drunk syndrome is the dementia and cerebral scarring observed in
individuals who experience repeated concussions
Brain infections: cerebral abscesses (pockets of bus in the brain) can be a result of bacterial
infection.
Bacteria are the major cause of meningitis (inflammation of the meninges)
Syphilis bacteria attack the brain, resulting in a syndrome of insanity and dementia
known as general paresis
Viral infections: there are two types- those that have affinity for brain tissue or those that attack
neural tissue but do not have a preferential affinity for it (relative to other tissues)
Rabies is a virus that has an affinity for the nevous system. Although lethal, it does not
manifest for months
Mumps and Herpes: attack nervous system but have no special affinity for it
Neurotoxins:
Heavy metals such as lead and mercury can accumulate in the brain and permenantly
damage it, producing toxic psychosis
Genetic factors:
Down syndrome is a result of an extra chromosome 21 (3 copies instead of 2)
Programmed cell death: apoptosis
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