Transcript Airgas template - Morgan Community College

Chapter 36
Disorders of Brain Function
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Hypoxia and Ischemia
• Hypoxia causes ATP depletion or “power failure”
• Aerobic metabolism stops  less ATP is produced
– Na+/K+ ATPase cannot run fast enough
º Cell swells up with water
• Anaerobic metabolism used  lactic acid produced
– Acid damages cell membranes, intracellular
structures, and DNA
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Hypoxia and Ischemia (cont.)
Ischemia also interferes with:
• Delivery of energy stores (e.g., glucose)
• Damage to blood vessels
– Vasomotor paralysis
– Vasoconstriction
• Changes in blood
– Desaturation
– Clotting
– Sludging
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Question
What two substances are needed by the mitochondria in
order to produce ATP?
a. O2 and CO2
b. Glucose and O2
c. Glucose and fatty acids
d. Proteins and monosaccharides
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Answer
b. Glucose and O2
Rationale: Glucose and oxygen are necessary for ATP
production. Without ATP, no physiologic work can be
done—the cells, and eventually the organism, will die.
When oxygen is not available, anaerobic pathways are
used, creating lactic acid that also damages the cell.
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Calcium Cascade
• Ischemia  depolarization
• Depolarization  glutamate
release
• Glutamate  calcium
cascade
• Calcium influx 
depolarization
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Intracranial Pressure (ICP)
• Compartment syndrome in the skull
– Intracranial pressure greater than arterial
blood pressure
– Arteries collapse; blood flow to brain cut off
• Brain swelling
– Vasogenic: extracellular fluid
– Cytotoxic: intracellular fluid
• Hydrocephalus: cerebrospinal fluid
• Tumors
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Brain Herniation
• Increased intracranial
pressure pushes the
brain out of position
• Brain tissue is
compressed into the
center of the brain (2),
against bone (4) or
against rigid folds of
the dura mater
(1, 3)
• Compression of the
oculomotor nerve is an
early sign
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Traumatic Brain Injury
• Primary injuries—due to impact
– Microscopic damage: concussion, diffuse axonal
injury
– Contusions
• Secondary injuries—due to:
– Hemorrhage
– Ischemia
– Infection
– Increased intracranial pressure
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Question
Tell whether the following statement is true or false.
Increased ICP results in primary brain injury.
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Answer
False
Rationale: Increased pressure in the brain leads to
secondary brain injury (there’s nowhere for the pressure
to be released because the brain is encased in bone).
Primary brain injury is caused by trauma.
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Hematoma—Broken
Blood Vessels
• Epidural space: meningeal
arteries
• Rapid bleeding;
unconsciousness may be
followed by brief lucid period
• Dura mater
– Subdural space:
bridging veins
– Slower bleeding;
gradual development
over days or weeks
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Cerebral Blood Flow
Middle cerebral artery
• Internal carotid arteries
branch into:
– Anterior cerebral
arteries
º Medial and superior
surfaces of brain;
frontal lobes
Anterior
cerebral
artery
Brain
(lateral
view)
– Middle cerebral arteries
º Lateral surfaces of
brain: face and arm
motor and sensory
cortexes, optic
radiations, speech
centers
Internal
carotid
artery
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Cerebral Blood Flow (cont.)
• The basilar artery runs
up to the back of the
brain
Posterior
cerebral
artery
– It splits to form the
two posterior
cerebral arteries
º They supply the
medulla, pons,
cerebellum,
midbrain,
occipital lobes,
temporal lobes,
thalamus
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Basilar
artery
Circle of Willis
Brain: ventral view
• Anterior communicating artery
– Connects right and left
anterior cerebral arteries
– Blood from one carotid can
cross over to supply the
other side of the brain
• Posterior communicating arteries
– Connect the posterior and
middle cerebral arteries
– Blood from the basilar
artery can run forward and
supply the front of the brain
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Question
Which of the following blood vessels ensures collateral
circulation in the brain?
a. Internal carotid arteries
b. Cerebral arteries
c. Basilar arteries
d. Circle of Willis
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Answer
d. Circle of Willis
Rationale: The circle of Willis connects the right and left
anterior cerebral arteries and the posterior and middle
cerebral arteries. Blood from one carotid can cross over
to supply the other side of the brain; blood from the
basilar artery can run forward and supply the front of
the brain.
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Stroke
• Stroke = “brain attack”
• Ischemic stroke
– Large vessel (thrombotic)
– Small vessel (lacunar infarct)
– Cardiogenic embolic
• Hemorrhagic stroke
• Transient ischemic attacks (“brain angina”)
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Excitotoxicity
• Neuron firing releases
glutamate
• Causes neighboring
neurons to fire
• Spreading injury
across the ischemic
area
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Discussion
Mr. X has cor pulmonale. Mr. Y has a left
ventricular aneurysm.
Questions:
• Which of them is more likely to have a stroke?
• Which is more likely to have a pulmonary
embolism?
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Aneurysmal Subarachnoid Hemorrhage
• Aneurysm
– Sudden-onset headache with nausea, vomiting,
dizziness
• Hemorrhage
– Sudden severe headache, neck stiffness,
photophobia, vision and motor problems
• Complications
– Rebleeding, vasospasm and ischemia, hydrocephalus,
hypothalamus dysfunction, seizures
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Brain Tumors
• Focal disturbances
– Dysfunction of particular brain areas
– Seizures, hallucinations, weakness or
palsies in specific areas, sensory deficits
• Generalized disturbances
– Increased intracranial pressure: headache,
vomiting, visual problems
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Seizures
• Spontaneous nerve firing
• Provoked seizures
– Fever
– Electrolyte imbalances (hypocalcemia, alkalosis)
– Hypoglycemia
– CNS infection or damage
• Unprovoked seizures: cause unknown
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Epileptic Syndromes
• Partial seizures
– Begin in one cerebral hemisphere
• Secondarily generalized seizures
– Begin in one hemisphere and spread to other
• Generalized seizures
– Involve both hemispheres
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Kinds of Seizures
• Absence (petit mal): disturbances in
consciousness
• Atonic: loss of muscle tone
• Myoclonic: muscles contract
• Tonic-clonic (grand mal): muscle contraction
and loss of consciousness
• Generalized convulsive status epilepticus:
seizures continue without recovery between
them
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Question
Which type of seizure affects only one cerebral
hemisphere?
a. Partial
b. Secondarily generalized
c. Generalized
d. All of the above
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Answer
a. Partial
Rationale: Partial seizures affect one cerebral hemisphere;
secondarily generalized seizures begin in one
hemisphere and then spread to the other side;
generalized seizures involve both hemispheres.
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Dementias
• Many dementias are associated with
abnormal inclusions in the brain
• Alzheimer disease: amyloid plaques
• Pick disease: Pick bodies
• Prion diseases: prion proteins
– Creutzfeldt-Jakob disease
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Alzheimer Disease
• Amyloid-beta protein-forming plaques
• Neurofibrillary tangles
• Decreased acetylcholine production
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amyloid
precursor
protein
Alzheimer
Disease
normally
soluble
protein
fragments
cleared
away
in
Alzheimer disease
amyloid b
stick together
to form fibrils
amyloid
plaques
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Stages of Alzheimer Disease
• First: short-term memory loss
• Second: confusional stage
– Disorientation, lack of insight, impaired
hygiene and language use, sundown
syndrome
• Third: incontinence, inability to recognize
family and friends
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Other Causes of Dementia
• Microinfarcts: vascular dementia
• Vitamin B12 deficiency: Wernicke-Korsakoff
syndrome
• Inherited atrophy of brain structure:
Huntington disease
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Question
Which cause of dementia is vascular in nature?
a. Alzheimer
b. Microinfarcts
c. Vitamin B12 deficiency
d. Inherited
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Answer
b. Microinfarcts
Rationale: Small infarctions cause blood flow to be cut off
to certain areas of the brain, causing tissue death.
Depending on the extent of the infarctions, the
dementia may be more or less severe.
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