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Summary study book Biopsychology [RENTAL EDITION] of John P. J. Pinel, Steven Barnes (Chapters 10-12) - ISBN: 9780135863688 (Chapters 10-12)
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Chapter 10: Brain Damage and NeuroplasticityThe study of human brain damage serves two purposes:
- It increases our understanding of the healthy brain
- It serves as a basis for the development of new treatments.
Causes of Brain Damage
Brain Tumors
→ A tumor, or neoplasm is a mass of cells that grows independently of the rest of the body. About 20 percent
of tumors found in the human brain are meningiomas
- Meningiomas: tumors that grow between the meninges, the three membranes that cover the central
nervous system. All meningiomas are encapsulated tumors which grow within their own membrane.
This makes them easy to identify on a CT scan, as they influence the function of the brain only by the
pressure they exert on surrounding tissue. These are almost always benign tumors where they can be
surgically removed with little risk of further growth in the body
→ Aside from meningiomas, most brain tumors are infiltrating.
- Infiltrating tumors: grow diffusely through surrounding tissue and are usually malignant tumors,
meaning they are difficult to remove or destroy completely. If any cancerous tissue remains after
surgery it usually continues to grow.
- Gliomas: brain tumors that develop from glial cells and are infiltrating, rapidly growing. This is the most
common form of malignant brain tumors
→ About 10 percent 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. Many metastatic brain
tumors originate as cancers of the lungs.
- Currently, the chance of recovering from a cancer that has already attacked two or more separate sites
is slim.
→ Encapsulated tumors that grow on cranial nerve VIII are referred to as acoustic neuromas
- Neuromas are tumors that grow on nerves or tracts
Strokes
→ Strokes are sudden-onset cerebrovascular disorders that cause brain damage.
- In the United States, stroke is the fifth leading cause of death, the major cause of neurological
dysfunction, and a leading cause of adult disability
→ The symptoms of a stroke depend on the area of the brain affected, but common consequences of stroke
are amnesia, aphasia (language difficulties), psychiatric disorders, dementia, 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 in the ensuing days,
depending on a variety of factors. Accordingly, the primary goal of treatment following stroke is to save the
penumbra
→ There are two major types of strokes: those resulting from cerebral hemorrhage and those resulting from
cerebral ischemia…
Cerebral Hemorrhage
→ Cerebral hemorrhage (bleeding in the brain) 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 balloonlike 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
, - Individuals at risk of aneurysms should make every effort to avoid cigarette smoking, alcohol
consumption, and hypertension
Cerebral Ischemia
→ Cerebral ischemia is a disruption of the blood supply to an area of the brain. The three main causes of
cerebral ischemia are…
1. Thrombosis: a plug called a thrombus is formed and blocks blood flow at the site of its formation. This
may be composed of a blood clot, fat, oil, an air bubble, tumor cells, or any combination
2. Embolism: Similar to a thrombosis except that the plug, called an embolus, is carried by the blood from
a larger vessel, where it was formed, to a smaller one, where it becomes lodged. An embolus is just a
thrombus that has taken a trip.
3. 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.
→ Ischemia-induced brain damage has two important properties.
- It takes a while to develop. Soon after a temporary cerebral ischemic episode, there usually is little or
no evidence of brain damage; however, substantial neuron loss can often be detected a day or two
later.
- Ischemia does not occur equally in all parts of the brain. Neurons in certain areas of the hippocampus
are particularly susceptible to ischemia
→ Glutamate, the brain’s most prevalent excitatory neurotransmitter, plays a major role in ischemia-induced
brain damage
- After a blood vessel becomes blocked, many of the blood-deprived neurons
become overactive and release excessive quantities of glutamate.
- The glutamate over-activates glutamate receptors in the membranes of
postsynaptic neurons where NMDA (N-methyl-D-aspartate) receptors are
mostly involved.
- As a result, large numbers of Na+ and Ca2+ ions enter the postsynaptic
neurons. Which affects them in two ways:
- They trigger the release of excessive amounts of glutamate from the
neurons, thus spreading the toxic cascade to yet other neurons
- They trigger a sequence of internal reactions that ultimately kill the
postsynaptic neurons
→ Excessive glutamate release causes much of the brain damage associated with
stroke
- We may be able to prevent stroke-related brain damage by blocking the
glutaminergic cascade.
- Some clinical trials have shown that NMDA-receptor antagonists are effective following acute ischemic
stroke. However, to be effective they need to be administered almost immediately after the stroke.
- This makes them impractical in most human clinical situations
→ Two other sorts of treatments have been shown to be effective for stroke
- The administration of a tissue plasminogen activator - TPA (a drug that breaks down blood clots)
- Endovascular therapy: the surgical removal of a thrombus or embolus from an artery).
→ Administration of these treatments within a few hours after the onset of ischemic stroke can lead to better
recovery
Traumatic Brain Injuries (TBI)
→ About 50–60 million people experience some form of traumatic brain injury (TBI) each year and about 50
percent of us will experience a TBI at least once in our lives
→ For the brain to be seriously damaged by a TBI, it is not necessary for the skull to be penetrated (a
penetrating TBI). Any blow to the head should be treated with extreme caution, particularly when confusion,
,sensorimotor disturbances, or loss of consciousness ensues. Brain injuries produced by blows that do not
penetrate the skull are called closed-head TBIs.
→ There are several types of closed-head TBIs.
- Contusions are closed-head TBIs that involve damage to the cerebral circulatory system. Such damage
produces internal hemorrhaging, which in turn produces a localized collection of blood in the brain— a
bruised brain.
→ The hardness of the skull, which protects the brain from penetrating injuries, is the major factor in the
development of contusions.
- Contusions occur when the brain slams against the inside of the skull. Blood from such injuries can
then accumulate in the subdural space (the space between the dura mater and arachnoid membrane)
and severely distort the surrounding neural tissue. Such a “puddle” of blood is known as a subdural
hematoma
- 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 mild TBI (mTBI).
- Most TBIs are mTBIs where they were once called concussions. However, the term “concussion” is no
longer deemed appropriate because it was associated with the mistaken assumption that its effects
involved no long-term damage
- There is now substantial evidence that the effects of mTBIs can last many years and that the effects of
repeated mTBIs can accumulate
→ Chronic traumatic encephalopathy (CTE) is the dementia (general intellectual deterioration) and cerebral
scarring often observed in boxers, rugby players, American football players, and other individuals who have
experienced repeated mTBIs
- For example, there have been reports that most (approximately 90 percent) former American football
players, and many former recreational American football players, meet the diagnostic criteria for
chronic traumatic encephalopathy
Infections of the Brain
→ An invasion of the brain by microorganisms is a brain infection, and the resulting inflammation is called
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 or pockets of pus in
the brain.
- Bacteria are also the major cause of meningitis (inflammation of the meninges), which is fatal in 30
percent of adults
- Penicillin and other antibiotics sometimes eliminate bacterial infections of the brain, but they cannot
reverse brain damage that has already been produced.
→ Syphilis bacteria are passed from infected to noninfected individuals through contact with genital sores.
The infecting bacteria then goes into a dormant stage for several years before they become virulent and
attack many parts of the body, including the brain.
- The syndrome of mental illness 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 for it than for other tissues.
→ Rabies, which is usually transmitted through the bite of a rabid animal, is a well-known example of a virus
that has a particular affinity for the nervous system.
, - The fits of rage caused by the virus’s effects on the brain increase the probability that rabid animals that
normally attack by biting (dogs, cats, raccoons, bats, and mice) will spread the disorder.
- Although the effects of the rabies virus on the brain are almost always lethal, the virus does not usually
attack the brain for at least a month after it has been contracted, thus allowing time for preventive
vaccination.
→ The mumps and herpes viruses are common examples of viruses that can attack the nervous system but
have no special affinity for it. Although these viruses sometimes spread into the brain, they typically attack
other tissues of the body.
→ Viruses may play a far greater role in neuropsychological disorders than is currently thought. Their
involvement in the etiology (cause) of disorders is often difficult to recognize because they can lie dormant for
many years before producing symptoms
Neurotoxins
→ The nervous system can be damaged by exposure to any one of a variety of toxic chemicals
- Chemicals can enter general circulation from the gastrointestinal tract, from the lungs, or through the
skin.
- Heavy metals such as mercury and lead can accumulate in the brain and permanently damage it,
producing a toxic psychosis (chronic mental illness produced by a neurotoxin).
→ Sometimes, the very drugs used to treat neurological or psychiatric disorders prove to be toxic.
- Some of the antipsychotic drugs introduced in the early 1950s produced effects of distressing scope.
By the late 1950s, millions of patients with schizophrenia were being maintained on these drugs.
However, after several years of treatment, about 5 percent of the patients developed a motor disorder
called tardive dyskinesia (TD). Its 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 patient’s own body).
- The body can produce antibodies that attack particular components of the nervous system
- Stress hormones, such as cortisol, are also believed to produce neurotoxic effects
- Glutamate and ischemic stroke, where the excessive release of certain neurotransmitters can also
damage the brain.
Genetic Factors
→ Some neuropsychological diseases of genetic origin are caused by abnormal recessive genes that are
passed from parent to offspring.
→ Inherited neuropsychological disorders are rarely associated with dominant genes because dominant
genes that disturb neuropsychological function tend to be eliminated from the gene pool
- individuals who carry both genes usually have major survival and reproductive disadvantages (PKU)
- In contrast, individuals who inherit one abnormal recessive gene do not develop the disorder, and the
gene is passed on to future generations.
→ Genetic accident is another major cause of neuropsychological disorders of genetic origin.
- Down syndrome, which occurs in about 0.15 percent of births, is such a disorder. The genetic accident
occurs in the mother during ovulation, when an extra chromosome 21 is created in the egg. Thus, when
the egg is fertilized, there are three chromosome 21s, rather than two, in the zygote
- The consequences tend to be characteristic disfigurement, intellectual disability, early-onset
Alzheimer’s disease (a type of dementia), and other troublesome medical complications.
→ There was great optimism among professionals who study and treat neuropsychological disorders when
the human genome was documented at the beginning of this century.
→ Inherited factors play major roles in virtually all neuropsychological disorders, and it seemed that the
offending genes would soon be identified and effective treatments developed to target them. This has not
happened, for two reasons
- Numerous loci on human chromosomes have been associated with each disorder—not just one or two.
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