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57 Cards in this Set
- Front
- Back
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What are the common carotid arteries?
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Ascend in the neck and divide, just inferior to the angle of the jaw, into the external and internal carotid arteries
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What is the external carotid artery?
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Supplies primarily the face and neck
-also has meningeal branches, particularly the middle meningeal artery, which supply the dura |
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What is the internal carotid artery?
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Supplies much of the anterior portion of the brain (vascular system termed anterior circulation)
-enters skull through carotid canal, passes through cavernous sinus, pierces dura to enter subarachnoid space, and bifurcates into terminal branches |
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Which branches arise from internal carotid before it bifurcates?
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-Opthalmic artery: passes through optic foramen into orbit (supplies eye & orbital contents)
-Posterior communicating artery: courses posteriorly to join the proximal part of the posterior cerebral artery |
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What arteries are the two terminal branches that bifurcate from the internal carotid artery?
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-Anterior cerebral artery: runs medially over optic nerve to the midline where it is joined to its mate by the anterior communicating artery. It then ascends in the longitudinal fissure and bends posteriorly over the genu of the corpus callosum and splits into the pericallosal and callosomarginal arteries.
-Middle cerebral artery: passes laterally to enter the Sylvian fissure. Before entering fissure, gives off the lenticulostriate arteries (examples of end vessels that serve as sole arterioral supply to cerebral tissue). These lenticulostriate arteries supply the striatum, internal capsule, and adjacent structures. |
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What brain regions does the anterior cerebral artery supply?
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-Medial parts of the frontal and parietal lobes, as well as medial portion of the dorsal surface of those lobes
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What brain regions does the middle cerebral artery supply?
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-Most of the lateral aspect of the cerebral hemisphere.
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What does the vertebrobasilar system supply?
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-Also known as the posterior circulation, this system supplies the posterior fossa and much of the posterior portion of the brain
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Where do the vertebral arteries ascend?
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-Posteriorly in the neck and supply much of the posterior fossa. These vessels pierce the dura and enter the subarachnoid space at the level of the foramen magnum.
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What are the branches of the vertebral arteries?
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-Anterior spinal artery: Formed by branches from each vertebral artery; supplies anterior spinal cord
-Posterior spinal arteries (left & right): Formed by branches from the vertebral arterior or from the posterior inferior cerebellar arteries -Posterior inferior cerebellar artery (PICA): Largest branch of the vertebral artery; supplies the posterior cerebellar hemispheres |
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Where do the vertebral arteries terminate?
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-Terminate by uniting beneath the pontomedullary junction to form the basilar artery
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What is the basilar artery?
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-Courses in the midline along the ventral surface of the pons; supplies part of the posterior fossa
-Has several branches: -Anterior inferior cerebellar artery -Internal auditory artery: courses with CN VIII to supply inner ear -Superior cerebellar artery -Pontine arteries: small end vessels that directly penetrate pons along course of basilar artery |
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Where does the basilar artery terminate?
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-By giving rise to the two posterior cerebral arteries at the ventral midbrain; these vessels pass posteriorly around the midbrain to supply the medial occipital lobes, medial and inferior temporal lobes, and adjacent deep structures
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When do arterial anastomoses occur?
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-When vessels of two arterial systems communicate
1. Pial anastomoses: Over the surface of the hemisphere end branches from one system (e.g., MCA) anastomose with end branches of another system (e.g., ACA) 2. Within the Circle of Willis (anterior communicating, anterior cerebral, internal carotid, posterior communicating, posterior cerebral) 3. Connections between internal and external carotid systems (e.g., ophthalmic artery to maxillary artery) |
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What are watershed zones or areas?
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-Border zones between larger arterial territories
-Especially likely to suffer ischemic damage from diffuse cerebral hypoperfusion 1. MCA-ACA watershed is “double-protected” from blockage of a single vessel 2. MCA-ACA watershed maximally susceptible to overall hypotension in the system (decrease pressure in left internal carotid, territories of adequate perfusion of MCA/ACA distributions shrink, may lead to insufficient blood supply along the watershed and result in infarction (stroke) |
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How does venous blood leave the brain?
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-By gaining access to the dural sinuses by the bridging veins
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What is the external venous system?
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-Drains the surface of the cerebral hemispheres
-consists of veins that lie in the subarachnoid space on all surfaces of the hemispheres -these veins mostly drain into the superior sagittal, cavernous, and transverse sinuses; they also form the basal vein |
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What is the internal venous system?
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-Drains the central core of the cerebral hemispheres
-The great cerebral vein (of Galen) is about 2 cm in length |
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After the veins drain the brain empty into the dural venous sinuses, where do these empty?
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-Into the jugular veins
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Where is the superior sagittal sinus?
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-Lies along the superior border of the falx cerebri
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Where is the inferior sagittal sinus?
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-Smaller channel that lies along the inferior border of the falx cerebri
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Where is the straight sinus?
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-the inferior sagittal sinus and the great cerebral vein join to form the straight sinus which lies in the attachment of the falx cerebri to the tentorium cerebella
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Where is the confluence of the sinuses?
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-Where the superior sagittal sinus joins with the straight sinus
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What are the two transverse sinuses?
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-These arise from the confluence and course laterally in the attachment of the tentorium
-There course then changes inferiorly toward the jugular foramen and they assume the name of sigmoid sinuses -These sinuses exit the jugular foramen and then are called the jugular veins |
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Where are the cavernous sinuses?
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-located on each side of the sella turcica and receive blood from the ophthalmic veins and some superficial cerebral veins
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Where does the arterial supply of the spinal cord arise from?
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-The spinal (anterior & posterior) arteries and the radicular arteries
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What is the anterior spinal artery?
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-Formed by paired branches of the vertebral arteries
-Descends the length of the spinal cord in the ventral median sulcus -Supplies the ventral and lateral columns as well as all gray matter except the bulk of the dorsal horns |
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What are the paired posterior spinal arteries?
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-Arise from either the vertebral arteries or the PICAs
-Pass down the cord along the line of the attachment of the dorsal spinal roots as a plexiform arterial network -Supplies the dorsal columns and the bulk of the dorsal horns |
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Where are the watershed areas of the spinal arteries?
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-Anterior spinal artery: Often at T1-T4 (esp T4) and L1
-Posterior spinal artery: T1-T4 |
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How much total CBF is there?
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50cc/100g/min
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How much more CBF is in gray matter than white matter?
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4x
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How much oxygen consumption of the brain (CMROs) is there for the whole brain at rest?
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50cc/min
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What happens with occlusion of the blood supply to the brain?
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Hypoxia and produces unconsciousness in about 10 sec
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What is "coupling"?
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In the normal brain, CBF generally is determined by and parallels cerebral glucose and oxygen metabolism
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What is the cerebral arterial pressure regulated by?
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Circulatory reflexes
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What is cerebral perfusion pressure (CPP)?
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aka the pressure gradient (arterial pressure minus internal jugular venous pressure)
-in general, venous pressure is negligible and pressure gradient is determined by arterial pressure |
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What are baroreceptors?
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In the aortic arch and carotid sinuses; help to maintain constant arterial pressure
-If arterial pressure falls below 50-60 mm Hg, baroreceptor mechanism no longer functions (vasomotor neurons then cause sympathetic excitation of cardiovascular system) |
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What is cerebral vascular resistance?
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-A function of blood viscosity and the diameter of of cerebral vessels
(total CBF = CPP/cerebral vascular resistance) |
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What is autoregulation?
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the capacity of a tissue to regulate its own blood flow (responsible for adjusting cerebral vascular resistance to maintain proper CBF)
-2 methods: Local myogenic factor, local metabolic factor |
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Describe the local myogenic factor of autoregulation
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-Purpose: Maintain CBF at a constant value when there is a change in arterial pressure
-Consists of contraction of smooth muscles in arteries in reaction to increases in arterial pressure (also arteries dilate in reaction to decreased arterial pressure) -This vasoconstriction caused increased resistance allowing CBF to remain constant |
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Why is it important that we have the myogenic factor to keep CBF constant?
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-If CBF increased with increased BP wouldn't hurt to have increased glucose or oxygen, but would get increased CO2 leaving the brain and that would change brain pH
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Describe the two local metabolic factors of autoregulation
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-Local metabolic factors maintain homeostasis by increasing or decreasing CBF following a change in cerebral metabolism cause
1) Increase in local metabolism leads to increase of CO2 which leads to increased PCO2 which produces increased local CBF. The increased local CBF carries away the excess CO2 to maintain homeostasis. 2) PO2 gets very low before see an increase in CBF |
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What is neural regulation?
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-sympathetic adrenergic innervation of blood vessels
-may be important in protecting brain against severe hypertension |
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What is thought to be the key agent in coupling neuronal activity to local CBF?
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nitric oxide
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What is ischemia?
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Deficiency of blood due to decreased flow to a region of brain
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What happens to the CBF versus Mean Arterial Pressure curve in individuals with chronic hypertension?
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It is right-shifted centering around the individual's "normal" mean arterial pressure
-If a person has a stroke and presents to ER with MAP of 150, it would be bad to lower it to a "normal" 80 (CBF would decrease and extend infarct). Presume curve will gradually left shift with treatment of HBP and so gradually control the BP after the stroke has been stable for a couple of weeks. |
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What is an infarct or infarction?
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An area of cell death in the brain due to local ischemia
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What happens during hyperventilation?
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-Decreased pCO2 which leads to decreased CBF and O2.
-helpful in ER because the decreased CBF can help stave off herniation -helpful in EEG because mild hypoxia brings out EEG abnormalities |
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What is ischemic penumbra?
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Dysfunctioning, but not dead, brain tissue that is in jeopardy of dying if CBF is not restored in hours (around an area of brain infarction)
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What is hypoxia?
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Decreased O2 to tissue
-Ischemic: decreased blood flow (most common form of hypoxia) -Hypoxic: decreased pO2 (altitude , lung disease) -Anemic: decreased Hg (anemia, CO poisoning) -Histotoxic: can't use O2 (cyanide) |
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What does the term passive bed refer to?
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Injured territory following a cerebral insult that causes CBF to vary linearly with mean arterial pressure and causes response to pCO2 and pO2 to be abolished or blunted
-patients with loss of autoregulation need strict BP control and fixed head elevation to preserve CBF |
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What is anoxia?
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May refer to a total lack of tissue oxygen, but often used to mean clinically significant hypoxia
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What is asphyxia?
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aka suffocation, occurs when respiration stops
-leads to hypoxia and hypercarbia |
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Why is the brain particularly vulnerable to hypoxia?
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Because of its high metabolic rate, low capillary density, low carbohydrate reserve, and meager high energy phosphate pool
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What is the major brain response to hypoxia?
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Elevation of CBF, up to 3-4 times normal
-if this cannot correct for tissue hypoxia, permanent brain damage is likely -Below PO2 of 40 mm Hg, brain lactate increases, phosphocreatine falls -Below PO2 of 20 mm Hg, levels of ATP are reduced -There are well-defined behavioral responses to different degrees of cerebral hypoxia |
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What does global ischemia lead to?
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-6-8 sec: LOC
-10-20 sec: loss of corneal reflex -40-90: loss of respiration *Resuscitation may be successful following delay of 4-10 min |
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Which brain areas are selectively vulnerable to effects of ischemia and hypoxia?
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-Neurons more vulnerable than glia or endothelial cells
-Hippocampus -Purkinje cell layer of cerebellum -Layers 3/5 of cerebral cortex -Globus pallidus *these areas contain large numbers of glutamate receptors |
