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NSC 2201 (16)
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NSC 2201 Chapter Article: Diseases of the Brain

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NSC 2201

DISEASES OF THE BRAIN INTRO • Mrs. Schwartz is 86 and suffered stroke • Kept alive by machines and costs taxpayers a $1000 a day • Debates about her degree of consciousness STATES OF CONSCIOUSNESS • Spectrum of states of awareness ALERT CONSCIOUSNESS • Consciousness made of two qualitatively different components: wakefulness and awareness COMA AND ALTERED STATES • Coma: most unconscious state with impairment of consciousness and loss of wakefulness • Degree of lasting impairments is proportional to size of the brain lesion • Selective impairments may happen if specific areas of the brain are injured o Carbon monoxide poisoning selectively damages globus pallidus more so victims can have normal mental capacity but have exhibit same movement disorder as cerebral palsy • Coma is induced either by widespread interruption of neuronal function or small lesions in brain stem which lead to metabolic derangement of neuronal function • Show no response to stimuli except primitive posturing reflexes • Coma lasts for only two to four weeks • Degree of recovery is variable • Depending on level, area, and size of brain lesion, brain injury may effect a patient’s degree of awareness in entirely different manners CHRONIC VEGETATIVE STATE • Chronic vegetative state: awareness stops at level of brainstem • Can only perform most primitive reflexes (e.g. sucking and chewing) • Body can still maintain vegetative functions (e.g. maintain blood pressure) DEMENTIA • Dementia: wakeful state of coma • Irreversible loss of memories and cognitive function • Patient’s reaction to stimuli is no longer appropriate BRAIN DEATH • Brain death: irreversible cessation of all brain function of entire brain, including the brainstem • Body temperature must be above a certain point since hypothermia is known to result in brain-dead-like coma but patients generally recover when body reaches a certain temperature • Drug levels must be below a certain point as drugs can induce a temporary brain-dead-like state • Two issues of cost and transplantation: o Millions of taxpayer money spent every year to sustain the lives of people who will never regain cognitive function o Transplantation is an issue since organ function deteriorates rapidly in brain dead patients, but since patient isn’t brain dead, organs aren’t taken and given to those who need them DISEASES OF THE BRAIN • Brain is particularly vulnerable to disease because: o Neuron is post-mitotic cell so it sacrifices reproduction, regeneration, and motility of its axon o Brain is non-homogeneous and each area is specialized with destruction of each specific ability when a particular area is destroyed o “articulate organ” since no regions are silent o Brain has unique blood supply from four major arteries: two carotids and two vertebral arteries ▪ Internal carotids carry 65% to 75% of blood to brain, mainly to cerebral hemispheres via Anterior and Middle Cerebral Arteries ▪ Two vertebral arteries supply the other third of blood to brain to life-sustaining vegetative centers located in brainstem ▪ These four arteries are thin-walled (one smooth muscle layer, not two) and are very vulnerable to atherosclerosis o Physical location of the brain makes it vulnerable to brain swelling ▪ Cranial brain case (skull) is unyielding ▪ Initial effort to get more space for brain if there is inflammation or other object is to reduce CSF in ventricles ▪ Ventricular compression can only compensate for mild swelling ▪ Eventually brain is squeezed out of any opening in the skull ▪ Foramen magnum is largest opening in cranium through which spinal cord exits into spinal canal in vertebrae ▪ Herniation of brain causes extensive and usually irreversible damage to compressed parts of midbrain, pons, and medulla ▪ Can be squeezed to half their volume before brain decompensates completely ▪ Combined with bleeding in the brainstem, this pathological state leads to decerebrate rigidity, coma, and death ▪ When brain swells and compresses the third nerve of the oculomotor nerve, the pupil on that side stays dilated • Symptoms range from mild headache to coma to pain to weakness to abnormal movement VASCULAR DISEASES OF THE BRAIN • Stroke: o Embolism: traveling clot that obstructs blood flow o Ischemia: brain tissue deprived of oxygen o Transient ischemic attack (TIA) is warning that blood vessels are being blocked o Secondary effect of ischemia is edema (swelling) o Stroke > edema causes neurons to stop firing (to become chromatolytic) > edema recedes > some function returns as sick neurons become healthy again o After sroke there is fluid-filled cystic space left in brain after tissue is removed by glia • Cerebral hemorrhage: rupture of brain artery (AKA apoplexy) o Leading cause of death due to brain disease o Associated with hypertension o 50-100mL of blood accumulated can cause profound coma in 30-40 sconds and death in a little more than a day o Brain is pushed down through foramen magnum o Blood supply in brainstem is compromised or “embarrassed” as structures are squeezed • Aneurism: o Third type of stroke is bursting of aneurism o Aneurism: thinning of arterial wall due to developmental defect which leaves artery ballooning under pressure of circulating blood o Brain arteries are thin and vulnerable to this o Death within hours with no apparent symptoms o Most common symptom is headache o Treatment is CT scan and surgery to remove aneurism • Trauma to skull: o Can cause surface bleeding in cortical tissue o Can result in area of abnormal electrical excitability called epileptic focus o Epidural hematoma: hemorrhage in potential space between inside of skull and dura o Many fractures occur in frontal region o Infectious agents can enter brain from frontal sinuses after skull fracture to cause inflammation of the meninges or meningitis o Fracture of lateral region of calvarium causes bleeding from middle meningial artery into innner surface of cranial bone; puts pressure on brain and leads to brain herniations and effects similar to tumor o Subdural hemorrhage or hematoma: venous bleeding between dura and arachnoid meninges, causes headache, memory loss, and sleepiness, then coma and death BRAIN TUMORS • Meningioma: most common benign tumor from connective tissue of dura mater • Astrocytoma: other common intracranial tumors come from astrocytes • Only 1% of brain tumors ar
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