Psychology 2220A/B Chapter Notes - Chapter 10: Ataxia, Substantia Nigra, Ovulation

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CAUSES OF BRAIN DAMAGE
Six causes of brain damage: brain tumors, cerebrovascular disorders, closed-head
injuries, infections of the brain, neurotoxins, and genetic factors
Brain Tumors
A tumor, or neoplasm is a mass of cells that grows independently of the rest of the
body
In other words, it is cancer
About 20% of tumors found in the human brain are meningiomas - tumors that
grow between meninges, the three membranes that cover the central nervous
system
All meningiomas are encapsulated tumors - tumors that grow within their own
membrane
They can influence the function of the brain only by the pressure they exert on
surrounding tissue, and they are almost always benign tumors - tumors that are
surgically removable with little risk of further growth in the body
Encapsulation is the exception rather than the rule when it comes to brain tumors
Aside from meningiomas, most brain tumors are infiltrating
Infiltrating tumors are those that grow diffusely through surrounding tissue
They are usually malignants tumors; that is, it is difficult to remove or destroy them
completely, and any cancerous tissue that remains after surgery continues to grow
About 10% of brain tumors do not originate in the brain
They grow from infiltrating cells that are carried to the brain by the bloodstream
from some other part of the body
These tumors are called metastatic tumors; metastasis refers to the transmission
of disease from one organ to another
Cerebrovascular Disorders: Strokes
Strokes are sudden-onset cerebrovascular disorders that cause brain damage
The symptoms of a stroke depend on the area of the brain that is affected, but
common consequences of stroke are amnesia, aphasia, paralysis, and coma
The area of dead or dying tissue produced by a stroke is called an infarct
Surrounding the infarct is a dysfunctional area called the penumbra
The tissue in the penumbra may recover or die, depending on a variety of factors,
and the goal of treatment following stroke is to save it
There are two major types of strokes: those resulting from cerebral hemorrhage
and those resulting from cerebral ischemia
Cerebral Hemorrhage
Cerebral hemorrhage occurs when a cerebral blood vessel ruptures and blood
seeps into the surrounding neural tissue and damages it
Bursting aneurysms are a common cause of intracerebral hemorrhage
An aneurysm is a pathological ballonlike dilation that forms in the wall of an
artery at a point where the elasticity of the artery wall is defective
Aneurysms can be congenital (present at birth) or can result from exposure to
vascular poisons or infection
Cerebral Ischemia
Cerebral ischemia is a disruption of the blood supply to an area of the brain
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The three main causes of cerebral ischemia are thrombosis embolism, and
arteriosclerosis
Thrombosis, a plug called thrombus is formed and blocks blood flow at the site
of its formation
May be composed of a blood clot, fat, oil, and air bubble, tumor cells, or any
combination thereof
Embolism is similar, except that the plug, called an embolus is this case, is
carried by the blood from a larger vessel, where it was formed, to a smaller
one, where it becomes lodged
Arteriosclerosis, the walls of blood vessels thicken and the channels narrow,
usually as the result of fat deposits; this narrowing can eventually lead to
complete blockage of the blood vessels
Much of the brain damage associated with stroke is a consequence of
excessive release of excitatory amino acid neurotransmitters, in particular
glutamate, the brain’s most prevalent excitatory neurotransmitter
After a blood vessel becomes blocked, many of the blood-deprived neurons
becomes blocked, many of the blood-deprived neurons become overactive and
release excessive quantitates of glutamate
The glutamate in turn overactivates glutamate receptors in the membranes of
postsynaptic neurons; the glutamate in turn overactivates glutamate receptors
in the membranes of postsynaptic neurons; the glutamate receptors that are
most involved in this reaction are the NMDA (N-methyl-D-asparate) receptors
As a result, large numbers of Na+ and Ca2+ ions enter the postsynaptic
neurons
The excessive internal concentrations of Na+ and Ca2+ ions affect the
postsynaptic neurons in two ways:
They trigger the release of excessive amounts of glutamate from the
neurons, thus spreading the toxic cascade to yet other neurons
And they trigger a sequence of internal reactions that ultimately kill the
postsynaptic neurons
Ischemia-induced brain damage has three important properties:
First, it takes a while to develop
Second, ischemia-induced brain damage does not occur equally in all parts
of the brain
Third, the mechanisms of ischemia-induced damage vary somewhat from
structure to structure within the brain, and in at least some areas, astrocytes
have been implicated
Closed-Head Injuries
It is not necessary for the skull to be penetrated for the brain to be seriously
damaged
Contusions are closed-head injuries that involve damage to the cerebral circulatory
system
Such damage produces internal hemorrhaging, which results in a hematoma
A hematoma is a localized collection of clotted blood in an organ or tissue
Contusions from closed-head injuries occur when the brain slams against the
inside of the skull
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Blood from such injuries can accumulate in the subdural space and severely distort
the surrounding neural tissue
Contusions frequently occur on the side of the brain opposite the side struck by a
blow
The reason for such so-called contrecoup injuries is that the blow causes the brain
to strike the inside of the skull on the other side of the head
When there is a disturbance of consciousness following a blow to the head and
there is no evidence of a contusion or other structural damage, the diagnosis is
concussion
Evidence that the cognitive, motor, and neurological effects of concussion can last
many years
The punch-drunk syndrome is the dementia and cerebral scarring observed in
boxers and other individuals who experience repeated concussions
Infections of the Brain
An invasion of the brain by microorganisms is a brain infection, and the resulting
inflammation is encephalitis
There are two common types of brain infections:
Bacterial Infections
When bacteria infect the brain, they often lead to the formation of cerebral
abscesses - pockets of pus in the brain
Bacteria are also the major cause of meningitis
Syphilis bacteria are passed from infected to noninfected individuals through
contact with genital sores
The syndrome of insanity and dementia that results from a syphilitic infection is
called general paresis
Viral Infections
There are two types of viral infections of the nervous system:
Those that have a particular affinity for neural tissue
Those that attack neural tissue but have no greater affinity or it than for
other tissues
Rabies is an example of a virus’ affinity for the nervous system
Rabies does not usually attack the brain for at least a month after it has been
contracted, thus allowing time for a preventative vaccination
The mumps and herpes viruses are common viruses that can attack the
nervous system but have no special affinity for it
Neurotoxins
Toxic psychosis - chronic insanity produced by a neurotoxin
Sometimes the very drugs used to treat neurological disorders prove to have toxic
effects
Many of the patients developed a motor disorder termed tardive dyskinesia (TD)
It’s primary symptoms are involuntary smacking and sucking movements of the
lips, thrusting and rolling of the tongue, lateral jaw movements, and puffing of the
cheeks
Some neurotoxins are endogenous (produced by the patients own body)
Genetic Factors
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