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215 Cards in this Set
- Front
- Back
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Blood supply to brain and meniges from what?
what percentage of total? |
Internal carotids, 2 carotids with derivatives, 90%
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Posterior circulation to brain from what? What percentage total?
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Vertebrals, 2 vertebral arteries w basilar artery, 10%
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What is the direct branch off the aortic arch?
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Left carotid and Left subclavian artery
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Where does the right carotid and right subclavian arise from?
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Innominate or branchiocephalic branch of aorta
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Where does each common carotid divide and into what?
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divides at C4 into internal and external carotid arterities
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What artery supply glands, muscle, bones of head face and dura mater?
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External carotid
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Which artery enters skull through foramen lacerum and carotid canal and crosses cavernous sinus?
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Internal carotid
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When internal carotid occlusion occurs what happens to flow to circle of willis?
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Communication w/ external carotid via facial pathway to opthalamic artery increases casuing retrograde flow to circle of willis
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What are branches from Internal Carotids
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Anterior cerebral artery
opthalamic artery middle cerebral artery posterior communication artery anterior choroidal artery anterior comminicating artery |
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Internal carotids terminate where and divide into what?
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Terminate basal surface of brain and divide into anterior cerebral artery and middle cerebral artery
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What are direct branches of subclavian artery ?
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Vertebral artery
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Where does subclavian artery enter skull?
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Enter transverse foramen at C6 and go up to C1
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Which vertebral artery bigger? Left or right?
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Left
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Vertebral artery give origin to what?
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Posterior inferior cerebeller arteries, anterior spinal artery, 2 posterior spinal arteries
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What forms basiliar artery
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Right and left vertebral arteries
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Pathway between right and left anterior and posterior circulation
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circle of willis
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Connect right and left carotid as well as carotid and vertebrobasilar circulation
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circle of willis
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maintain flow in brain during ischemia
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circle of willis
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Circle of willis formed by?
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anterior and posterior comminicating arteries, proximal portion anterior artery, middle(internal carotid) artery and posterior cerebral artery
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Is there net flow in circle of willis?
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Not net flow unless occlusion due to pressure movements
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How does blood flow in the circle of willis?
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it is a to and fro movement from arterial pulsatile flow
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What compensates for any acute interupption of the circulation to the brain?
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Circle of willis and leptomeningial communication
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Where do all veins of brain terminate?
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in dural sinus
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All veins of brain are classified as?
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internal cerebral vein and external cerebral vein
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Explain the external cerebral vein pathway?
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Vein of trolard(superior) into the vein of Labbe(inferior) into the transverse lateral sinus into the superior saggital sinus medial and superiorly
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Common area epidural hematoma?
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Middle meningeal artery and vein
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Explain pathway for Internal or deep cortical drainage
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Deep gray nuclei along ventricl veins to basal vein to great cerebral vein galen, inferior sagital and straight sinus, superior sagital sinus, to sigmoid sinus into internal jugular that empties into superior vena cava
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Arterial supply spinal cord from
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vertebral arteries and segmental arteries
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Which artery supplies the cervical region of the spinal cord and doesnt supply metabolic demands below the cervical region?
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Vertebral arteries
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Arises as branches off the aorta and enters the cord arterial supply in a variable manner at different levels and supplys spinal cord
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Segmental arteries
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Vertebral arteries give rise to what?
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1 anterior spinal artery and two posterior spinal arteries
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Anterior spinal artery accounts for how much blood supply?
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2/3
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the two posterior spinal arteries account for how much blood supply?
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1/3
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What supplies peripheral portions of spinal cord?
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Pial arterial plexus
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What does the pial arterial plexus arise from?
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Branches off anterior and posterior spinal arteries
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Segmental arteries branch off into what?
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ascending cervial artery, intercostal artery, lumbar artery, sacral artery-all form radicular artery
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What provides main supply to thorasic, lumbar, sacral, and coccygeal spinal cord/
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RADICULAR artery
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What forms artery of adamkiewiz?
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Intercostal and lumbar artery
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What is brain very sensitive too?
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K, Ca, N, Mg, H ions
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What can cross BBB w/ease?
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H20, C02, 02
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What causes low permeability in BBB?
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tight junctions with no slit pores
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Rapidity w/ substances cross BBB is related to what?
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lipid solubility
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The four properties that govern drug ability to cross BBB is?
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lip solubility, ionization, molecular size, degree protein binding
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BBB surrounds all CNS except what?
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chroid plexus, pineal gland, pituitary gland, parts hypothalamus, arachnoil layer part of BBB
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The major part of the BBB is localized where?
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Walls of brain capillaries
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What tissue layer is a component of the BBB?
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arachnoid layer
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What are the two different cell types of BBB?
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Vascular origin-microvascular endothelial cells lining intraluminal surfaces of capillaries
neural origin-astrocytes |
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What prevents passive movement of most molecules into CNS?
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tight junctions in microvascular endothelium of BBB
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What cells form around the brain cappillaries and secrete a substance to cause formation and maintence of tight junctions-
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Astrocytes
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Astrocytes able to modulate or regulate transfer of substances due to lack of?
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pinocytotic vesciles
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What two ways do molecules penetrate the endothelial cell barrier in BBB?
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passisve diffusion and facilitated diffusion
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the matrix of capillary membrane in BBB composed of?
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protein, phospholipid substance
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What molecules pass easily by simple diffusion down their concentration gradient in the BBB?
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Neutral lipid soluble molecules
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What molecules do not readily cross the BBB?
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polar molecles and electrically charged molecules
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What molecules pass BBB by facilitated diffusion/
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Glucose, ions
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What drugs tend to stay in the blood and are excreted by the kidneys and ionize which limits their crossing BBB?
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Water soluble drugs
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Does water pass BBB?
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yes, due to small molecular size, water rapidly crosses BBB
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How much CSF produced a day?
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150ml adult
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How much CSF in lumbar cistern?
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25-35 ml
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functions to cushion brain within its bony container and to provide optimal physiological fluid environment for nerve function-
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CSF
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Clear, colorless, almost protein-free ultrafiltrate of blood?
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CSF
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Where does CSF form?
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forms in ventricles from hydrostatic pressure through choroid plexus of capillaries and circulates through the subarachnoid space
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Is K, Ca, Bicarb, and glucose concentrations in the CSF lower or higher than plasma?
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lower in CSF
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Is protein concentration in CSF higher or lower plasma?
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lower
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pH of CSF
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7.31, slightly acidic
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pCO2 of CSF
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52mmHg
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specific gravity CSF
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1.003-1.009
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Is Na, Cl, and Mg concentration in CSF higher or lower than plasma?
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higher
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Rate of CSF production?
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0.35-0.40 ml/min or 20-25ml/hr or 500-600ml/day
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Where is CSF produced?
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1/2 to 2/3 from secretion of choroid plexus in ventricles, rest is secreted ependymal surfaces of ventricles, arachnoid membranes and brain itself
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How often CSF turnover?
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four times a day
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Lumbar CSF pressure is?
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10mmHg
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Where is CSF reabsorbed ?
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from subarachnoid space into the venous blood via arachnoid ville that protude into venous sinus
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What are small penetrations of arachnoid tissue that have made small openings in the walls of venous sinus?
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arachnoid villi
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Discribe CSF pathway-
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Formed two lateral ventricles and third ventricle and leaves from the two lateral ventricles via Foramen of Monroe to the third ventricle and from third ventricle via Aqueduct of Sylvius to the fourth ventricle and from the fourth ventricle ivia two lateral exits called Foramen of Luschka and one media exit called Foramen of Magendie into Cisterna Magna . CSF then circulates in subarachnoid space around brain and spinal cord and enters the cerebral venous sinuses and venous blood via arachnoid villi
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Describe flow CSF
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unidirectional b/c of pressure gradient bw source, arterial blood and venous blood
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What the three basic premises of neuroanesthesia?
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1.the brain resides in a confined space
2. The brain is metabolically active and has no storage 3. CBF is directly proportional to CMR |
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what are compensatory protective mechanisms for the brain?
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autoregulation, CO2 responsiveness of cerebral vasculature, and anatomy or Circle of willis
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What is the most fragile compensatory mechanism and what most robust?
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Most fragile is autoregulation and most robust is CO2 responsiveness
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Surrounds neurons, oligodendrocytes, schwann cells and microglia-
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glial cells
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What serves as supporting elements that provide firmness and structure of the Cns?
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glial cells
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What insulates the large neuroal axons by formed myelin sheaths?
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glial cells
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What contributes to the formation of the BBB and provide nutrition to neurons?
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glial cells
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What provides re-uptake of neurotransmitters and K ions and serves asscavengers of cellular debris folowwing CNS surgery?
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glial cells
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What two signaling mechanisms enable rapid and precise communication bw neurons?
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electrical synapes and chemical synapses
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What kind of substances act as neurotrasmitters?
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amino acids, amines, purines,and polypeptides
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What is major excitatory neutrasmitter?
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amino acid glutamate
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Stimulation of NMDA recptor induces what?
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influx of Ca, Na, and K
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NMDA receptors can be block by ?
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Mg, phencyclidine and ketamine
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Antagonism of NMDA receptors is useful when?
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following cerebral ischemia and head injury
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Excitatory AA's play a role in what?
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Development of delayed neuronal necrosis after hypoxic or ischemc insult
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Energy depletion after ischemia results in what?
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synaptic accumulation of glutamate and well as failure of its reuptake
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High accumulations of glutamate stimulates what and allows what?
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stimulates glutamate receptors of NMDA subtype which allows for intracellular Ca influx
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Intracellular Ca accumulations activates what and causes what?
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Activates phospholipases with generation of free radicals and destruction of membrane proteins and lipids with eventual neuronal death
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What is the major pre-synaptic inhibitory amino acid?
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GABA
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How does GABA work?
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stabilizes membrane potential via increased permeability of Cl loss. Causes decrease sensitivity of membranes to depolarize
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What kind of drugs potentiate GABA?
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Benzodiazepines, barbiturates, propofol and dialantin
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glyceine is an AA that acts as what?
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direct inhibitor of SC synapes and increase conductance for Cl- ions
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WHat increases conductance for Na ions of nicotinic reectors and increase Ca influx at muscaric receptors?
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Acetylcholine
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What is the neurotransmitter of motor neurons of SC, and all preganglionic and parasympathetic post ganglionic neurons?
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Acetylcholine
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Under physiologic conditions the entire metabolic requirement of CNS is provided by?
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Degradation of glycogen from liver and muscle into glucose which is oxidized to CO2 and H2O in an energy generating process
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The energy store of glycogen whould be exhausted in how much time?
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3 minutes
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In the absence of ketosis the adult brain uses what as its sole metabolic source?
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glucose
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With prolonged starvations what predominates the metabolic substrate in the brain?
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ketone bodies, acetoacetate, and beta hydroxybuterate
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With glucose in anaerobic glycolsis how much ATP formed?
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2 molecules of ATP, not enough energy for energy demands of brain
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In aerobic glycolysis how much ATP is formed?
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total of 38 ATP molecules
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Brain can not live without continous O2 supply and therefore is an?
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obligate aerobe b/c cant store O2
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With glucose in anaerobic glycolsis how much ATP formed?
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2 molecules of ATP, not enough energy for energy demands of brain
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What is high metabolic requirements for O2 in brain?
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3-5ml O2/100g brain tissue/min or
40-70 m; O2/min |
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What percentage of total O2 requirements does the brain have?
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20%
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In aerobic glycolysis how much ATP is formed?
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total of 38 ATP molecules
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With glucose in anaerobic glycolsis how much ATP formed?
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2 molecules of ATP, not enough energy for energy demands of brain
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Brain can not live without continous O2 supply and therefore is an?
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obligate aerobe b/c cant store O2
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In aerobic glycolysis how much ATP is formed?
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total of 38 ATP molecules
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Brain can not live without continous O2 supply and therefore is an?
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obligate aerobe b/c cant store O2
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What is high metabolic requirements for O2 in brain?
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3-5ml O2/100g brain tissue/min or
40-70 m; O2/min |
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What is high metabolic requirements for O2 in brain?
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3-5ml O2/100g brain tissue/min or
40-70 m; O2/min |
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What percentage of total O2 requirements does the brain have?
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20%
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What percentage of total O2 requirements does the brain have?
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20%
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What is the CMRO2 for brain?
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3.5ml O2/100g/min
avg brain 1300-1400g |
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Average normal CBF
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50ml/100g/min
50 X 13-14 =650-700ml |
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Brain needs how much O2 a min?
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40-70 ml O2/min
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With normal percentage O2 how much oxygen supplied to brain normally? What does the brain need?
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CBF=650-700 ml
O2 20% =130-140ml O2 minimum needed is 130-140 ml, so 3x what needed |
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What are energy utilizing processes in the brain?
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Continous activity of ionic pump, preservation Ca gradients, neurotransmitters, membrane homeostatis, glial functions
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How does the brain conserve energy?
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CNS adjusts expenditure of energy to level of cellular energy, coupling phenomenon so that an increase in CMR02 causes a increase in CBF, difference in the functional and basal activity, save energy if form of phosphocreatine which can be called on in times of ischemia, decrease 60% of energy expenditure by turning off activation metabolism
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The two types of metabolism in brain are?
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activation and basal
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What is portion of metabolism that drives work of the brain, snaptic transmission?
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activation metabolism
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What is portion of metabolism that is necessary to maintain cellular integrity?
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basal metabolism
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What percentage of metabolism is activation?
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60%
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What percentage of metabolim is basal?
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40%
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During critical reductions in cerebral substrate supply, neurons can do what?
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Reduce or shut off their cellular function of activation metabolism and save 60% of energy expenditure.
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Neuronal threshold to compensate for inadequate substrate supply is ?
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low-then function slows or stops
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Utilization of what appears to be the only cellular mechanism by which enrgy can be saved in favor of cellular intregity.
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Phosphocreatine, ketone bodys
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This is a high energy phosphate storage medium and is converted to ATP by what enzyme
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Phosphocreatine converted to ATP by creatine phosphokinase
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The concentration of phosphocreatine is how much compared to ATP? which decreases first?
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Phosphocreatine 3x that of ATP, a decrease in PCR precedes a decrease in ATP, and occurs in high demand states
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What is CO to brain?
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15%
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What is CBF to brain?
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50ml/100g/min
average brain 1300-1400gram |
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What is CBV of brain?
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4-6ml/100g and average brain 1300-1400gram so 70-75ml
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What is CMRO2 of brain?
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3.5ml/100g/min
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CBF is coupled to what?
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CMRO2
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How much total body 02 comsumption is cerebral consumption?
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20%
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What is CBF to cortical area?
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80ml/100g/min
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What is included in cortical area of brain?
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neuron cell bodies, astrocytes, oligodendrocytes, and microglia
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What is blood flow to subcortical area of brain and what is included?
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20ml/100g/min and axon processes of neuron here
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Primary controlling factors of CBF are?
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CO2, O2, CPP
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The most physiologic determinant of CBF is what?
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CO2
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How fast does increases or decreases in CO2 in the brain change cerebrovascular tone?
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less than 1 min
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At normotension, CO2 and CBF are linerally related bw what values?
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20-80 mmHg
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What percentage change in CBF for each 1mmHg change in CO2?
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4% change in CBF, =2ml/100g/min
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Permeability to H ion is low or high?
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low, only O2, CO2, and H2O permeaility
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What mediates the response to PaCO2?
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changes in H ion in the extracellular fluid, pH
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Is respiratory acidosis or metabolic acidosis change cerebrovascular tone?
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respiratory acidosis due to increase in CO2
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CO2 levels greater than what abolishes autoregulation and have maximal dilation-
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greater than 80mmHg
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Maximul vasoconstriction with little decrease in CBF and can actually casuse issues at what CO2 levels ?
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less than 25mmHg
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When CO2 levels are less than 25mmHg what happens to the oxygen dissociative curve?
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Shift to left thus limiting off loading of O2 tissue at the tissue capillary level.
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When CBF goes up what happens to CBV?
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CBV goes up
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Increase CBF if increased ICP means what?
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increase in CBV which further increases ICP
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For each 1mmHg change in PaCO2, how much change in CBV?
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CBV 0.049/100g,
6.4 ml for a 10mmHg increase if brain 1300g brain |
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Cerebral autoregulation maintains a CBF relatively constant between a CPP of ?
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50-150mmHg
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A normal CPP coresponds to a map of what?
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bw 60-160mmHg
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When on lower level of CPP a progressive decrease in BP or increase in ICP will do what?
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if less than CPP of 50, the CBF will be totally dependent on MAP b/c when less than this there is no more further dilation. Therefore there is a decrease in CBF in a pressure passive fashion
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CPP=
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MAP-ICP
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Progressive increases in BP or decrease in ICP with CPP greater than 180 cause what?
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Increases beyond autoregulation dilate the cerebral vasculature in a pressure passive fashion and in turn increase CBF, induce cerebral hyperemia, disruption BBB, vasogenic edema, called breakthough
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What happens as a result in a rightward shift in the autoregulatory curve?
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chronic hypertension, maximal dilation and constriction occurs at higher than average MAP or CPP
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Do not decrease MAP more than what percent from normal values?
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greater than 20%
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How are vascular changes and autoregulation shifts modified?
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by long term antihypertensive therapy with the degree of reversal being related to length of treatment
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Normal resting hemispheric CBF increases or decreases with increasing age.
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increases
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The cerebral vasoconstrictive response to hypocabia increases or decreases with age.
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decreases
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The CBF in elderly is higher or lower?
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significantly lower so limit hyperventilation b/c easier to vasoconstrict and decrease CBF to ischemic thresholds
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Control of autoregulation is dependent on what time of controls?
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Myogenic control-increase in pressure results in vasoconstriction and decrease in pressure produce vasodilation
Metabolic control- as cerebral metabolim increase, CBF increase as a result of cerebovasodilation and as cerebral metabolism decreases CBF decrease due to vasoconstriction Neurogenic control- Sympathetic stimulation causes cerebrovascular constriction and decrease CPP is less tolerated |
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Is there parasympathetic innervation to the basal cerebrovascular tone or CBF regulation?
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very little contribution
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With higher sympathetic tone it takes less or more CBF to maintain a given CPP
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less CBF
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With lower sympathetic tone it requires less or more CBF to maintain a given CPP?
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more CBF
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Factors that can impair or abolish autoregulation are?
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cerebral insults, cerebral hypoxia or ischemia, hypertension, intracranial tumors, hypothermia to 30 degrees, hypercapnia, subarachnoid hemorrhage, volatile anesthetics agent in dose dependent fashion
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Patients presenting for intracranial surgery probably possess what in the area of pathology?
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non or impaired autoregulating areas
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When autoregulation is impaired, and increase in CPP can lead to what?
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increase CBV and possibly increase ICP
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Within physiologic ranges, PaO2 does or doesnt affect CBF?
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doesnt
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Hypoxia is a potent stimulus for what?
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arterior dilation due to tissue hypoxia and lactic acidosis
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CBF begins to increase at a PaO2 of what and doubles at a PaO2 of what?
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increase at PaO2 of 50mmHg and doubles at PaO2 of 30mmHg
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Hyperoxia can increase or decrease CBF?
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decrease
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Flow through the cerebral microcirculation is called?
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rheology
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Physiologic or pharmacologic challenges exert their effects on CBF by either changing what two factors?
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pressure or resistance
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Resistance is related to what?
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viscosity and Hct is major determinant
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A decrease in Hct is related in an increase in what?
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CBF and CBV
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Optimal O2 delivery is thought to be obtained with a Hct of what?
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30-34%
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When cerebral vessel dilation is prevented by vessel spasm or stenosis, CBF may be enhanced by what?
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decreased blood viscosity with hemodilution
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For each 1 degree C decrease in temp, CMRO2 decreases by what?
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7%
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Temperatures below what require cardiopulmonary by-pass to sustain CO and CBF due to heart fibrillation
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below 30 degrees
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Cerebral metabolism increase as temp gets to what?
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above 40-42 degree C
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CMRO2 increases by what percent per degree C
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increase 5% by degree C
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What is very metabolically active and result in dramatic increase CBF due to increase CMRO2?
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seizures
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Seizures increases CBF by what percent? What happens to brain?
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400% Cerebral acidosis
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Hypoperfusion leads to what?
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ischemia
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At point where EEG becomes flat, what is abolished?
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activation metabolism
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What is the CBF needed to maintain basal metabolism?
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15-20 ml/100g/min
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CBF less than waht leads to membrane failure?
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CBF values<10ml/100g/min
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what are two low fow states that can exist wherby if flow is re established function will return?
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penlucida, penumbra
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Tissue recovers function irrespective of ischemic time, receives flow between 18-23ml/100g/min
tissue is functionally inactive but function can be restored at any time with reinstitution of increased perfusion |
penlucida
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Tissue is salvageable only is flow is restored within a certain time, flow has to be restored to adequate perfustion before time for infarction
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Penumbra
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at what CBF do neurons die within mins, membrane failure
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CBF<10ml/100g/min
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At what CBF does electrical failure occur, loss of EEG, neurons don't immediately die, but remain in penumbra state
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CBF<20ml/100g/min
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Max O2 extraction at what CBF, starting to see cerebral ischemia, nausea somnlence, impaired mentation, EEG present but depressed
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CBF=20-25ml/100g/min
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Decrease in flow to ischemic areas of the brain caused by blood vessels dilating in non-ischemic areas
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Cerebral steal
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What can induce cerebral steal?
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hypercapnia, volatile anesthetic agens, sodium nitroprusside, hydralazine, nitroglycerin
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Vasocontriction in the normal areas of the brain which may result in the redistribution of blood to ischemic areas, barbiturates and hyperventilation are said to result in these things
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Inverse steal or Robin Hood phenomenon
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potent cerebral vasodilator in the absence of other interventions and may cause increased CBF, ICP, CMRO2
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Nitrous oxide
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Initially, all volatile agents produce what with CBF/CMRO2?
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an uncoupling, CMRO2 is depressed and the increase in CBF is due to direct potent vasodilating effect of agent
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Of anesthetic gases the least potent vasodilator and most potent depressant of CMRO2 is?
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Isoflurane
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all anesthetic gases do what to ICP, CBF, and CMRO2?
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modest increase ICP, all increase CBF, decrease CMRO2
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The order of vasodilating potency from most to least is?
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halothane>enflurane>isoflurane=sevoflurane=desflurane
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Dose dependent decrease CMRO2 and CBF until isoelectric EEG, cerebral vasocontrictors, hemodynamic issues
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barbiturates, maintain coupling CBF and CMRO2
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Cause decrease CBF and CMRO2, minimal hemodynamic suppression
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Etomidate
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How does etomidate enhance the risk of cerebral ischemic injury?
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Creates vasoconstriction in the already marginally perfused areas so makes ischemic areas worse
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What is propofols affect on CMRO2, CBF, and ICP?
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decrease CBF secondarily to decrease in CMRO2, is dose related fashion, may possess neuroprotective affects
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narcotics affects of CMRO2, CBF, and ICP are?
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variable, may have a small decrease in ICP
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