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Neurology Chapter 17
Blood Supply
| Term | Definition |
|---|---|
| Purpose of blood supply to the brain | -Nutrition to parenchyma (brain cells). -Brain is completely dependent on oxygen supply -No O2 reserves. -No ability to use fat |
| How many minutes without oxygen does it take for irreversible damage to the brain? | 4 to 6 minutes |
| Perfusion | blood flow at the level of capillaries |
| Percentage of oxygen required for body weight | -20% of O2 for 2% of body weight |
| Adequate Cerebral perfusion measured in | measured in mil per 100 grams of tissue per min |
| Adequate Cerebral perfusion in Gray Matter | greater than 60 ml/100gr min-1 |
| Adequate Cerebral perfusion in White Matter | between 40 ml/100gr min and 60 ml/100gr min |
| What happens when perfusion is decreased? | It will cause a gradual death of neurons. |
| How many ml of blood are pumped per min? | 750mL blood |
| Brain relays on what two things? | oxygen and glucose |
| Purpose of blood supply | -Brings oxygen and glucose -Removes carbon dioxide and waste-products from cells |
| Arteries | -carry blood away from the heart |
| Arterioles | - small blood vessels that divide from arteries |
| Capillaries | - smaller blood vessels that divide from arterioles -Exchange of nutrients occurs at this level. |
| Veins | -Carry blood toward the heart |
| Venules | -Carry blood to sinuses on cortical surface -Smallest level -Are connected to capillaries |
| 2 systems for Cerebrovascular Supply | -Carotid System and Vertebral Basilar System -Meet in Circle of Willis |
| Circle of Willis | -Safety Valve of the Brain -Wreath-shaped -located at ventral surface of brain -Connects Carotid and Vertebral Basilar Systems |
| Path of Vertebral and Basilar arteries | two of the arteries enter skull through foramen magnum and go along side the brain stem and go into the basilar artery. Basil artery gives rise to the posterior cerebral arteries. |
| The Common Carotid artery | -Come together with vertebral artery in the Circle of Willis. -Gives rise to anterior and middle cerebral artery -Major source of blood to the brain -Between 80-90% of strokes occur here |
| 2 branches of the Carotoid Artery | 1) External Branch 2) Internal Branch |
| External Branch of the Carotid System | Supplies blood to facial muscles, forehead and oral, nasal and orbital cavities |
| Internal Branch of the Carotid System | -Enters the skull through the carotid foramen -Supplies blood flow to the brain -Before entering the circle of Willis it gives rise to 2 minor arteries: 1)Anterior choroidal artery 2)Ophthalmic artery |
| Anterior choroidal artery | -Part of the Carotoid System -Supplies optic tract, posterior limb of internal capsule, branches to midbrain,and lateral geniculate nucleus). |
| Ophthalmic artery | -Part of the Carotoid System -Supplies blood to the eyeball and ocular muscles |
| What does the Vertebral Basilar System supply blood to? | -Supplies the brainstem and cerebellum |
| Posterior Inferior Cerebellar Artery (PICA) | -vertebral basilar Artery that serves cerebellum |
| If you have an occlusion in the Internal Carotid artery | - despite the circle of Willis you will still have a stroke b/c other branches too small to make up for blood supply. however provides some profusion to prevent total neuron death |
| Cortical (Circumferential) Branches | - Type of artery that supplies the External Brain Structures -Supplies mainly gray matter |
| Central (Penetrating) Branches | -Small type of artery -Penetrate ventral surface to supply internal brain structures -Supplies Mainly white matter |
| Anterior Cerebral Artery | Cortical Artery that supplies Orbital and Medial Surfaces (internal brain)of Frontal and Parietal Lobes |
| Interruption in the Cortical Anterior Cerebral Artery can cause? | -Paralysis of legs and feet -Difficulty in prefrontal lobe functions of cognitive thinking, judgment, motor initiation and self monitoring |
| Middle Cerebral Artery | -Largest cerebral artery in the brain -Direct continuation of internal carotid artery -Branches: 1)Temporal 2)Parietal 3)Frontal -supplies blood to entire lateral surface of brain -Gives rise to Lateral Lenticulostraite Arteries for inner structres |
| What happens most of time to person who has a stroke in the MCA? | Person will have aphasia b/c this artery supplies the language critical areas. |
| Middle Cerebral Artery supplies blood to entire lateral surface of brain including theses 7 areas | 1) Somatosensory Cortex 2) Motor Cortex 3) Broca's Area 4) Heschl’s Gyrus 5) Wernicke’s 6) basal ganglia 7) diencephalon |
| Water shed region | -where ACA and MCA come together. Neuron in this area will survive the longest b/c it is supplied by both systems. |
| Interruption of the Middle Cerebral Artery can cause | -Contralateral hemiplegia -Impaired sensory systems:Touch,Proprioception, Localization of Pain and temperature -Aphasia -Constructional apraxia -Homonymous hemianopsia -Agraphia and Alexia -Involuntary motor movement b/c of basal ganglia |
| Contralateral hemiplegia | - paralysis of one side of the body - seen in brocas aphasia |
| Agraphia | -acquired writing disorder -usually seen with Aphasia |
| Alexia | -Acquired reading disorder -Usually seen with Aphasia |
| Posterior Cerebral Artery | -two branches -Supply blood to anterior and inferior temporal lobes, uncus, inferior temporal gyri, inferior and medial occipital lobe -Watersheds with middle cerebral artery |
| Posterior Cerebral Artery Interruption can cause | -Homonymous hemianopsia due to interruption of one branch. -Possible total blindness due to bilateral stroke -Cerebellar symptoms |
| Central (Penetrating) Arteries | -Arise from cortical arteries or from Circle of Willis and supply subcortical structures. -Penetrate inferior surface of brain -Can form channels to facilitate blood supply |
| What specific structures do the Central (Penetrating) Arteries supply? | Supplies the: 1) Thalamus 2) Hypothalamus 3) Basal Ganglia 4) Internal capsule 5) Choroid Plexus |
| Collateral Circulation | -Refers to alternative supply when primary supply is lost. -When there is a blockage of an artery, previously closed arteries open up to allow sufficient blood flow. |
| 2 Rules for Collateral Circulation | -Better if blockage is near main trunk b/c closer to trunk you are the more you have of these closed blood vessels. -Better if blockage occurs over a period of time b/c it gives more time for other blood vessels to open. |
| 2 main catergories for strokes | Occlusive and Hemorrhagic |
| Occlusive stroke | Something is blocking the artery causing ischemia (refers to area that is not getting enough blood and is therefore malnourished) |
| 3 Types of Occlusive stroke | 1) Atherosclerosis 2) Embolism 3) Thrombotic |
| Atherosclerosis | -Harding of the arterial wall) -caused from reduced lumen due to lipids, calcium fatty particles etc. |
| Embolism | -blood clot from another part of the body which travels and eventually blocks a smaller artery |
| Thrombosis | -local buildup of fatty substances usually at a bifurcation of artery (where artery splits up). -Happens over a long period of time) |
| Ischemic strokes | -Stroke that causes an area to not get enough blood and is therefore become malnourished. -Embolism and Thrombotic stroke are most common types of theses strokes -Make up between 70 and 80% of strokes in US. |
| Hemorrhagic stroke | -Bleeding from ruptured vessels -accounts for 15 to 30% of all strokes -More common in thalamus and basal ganglia -High blood pressure increases chances -Most people don't survive from this type of stroke |
| 3 Types of Hemorrhagic stroke | Intracerebral, Subdural and Aneurysm |
| Intracerebral Hemorrhagic stroke | bleed in brain itself |
| Subdural Hemorrhagic stroke | Brain bleed below the duramater. Between dura and arachnoid mater |
| Aneurysm | -Caused by a weakening of the arterial wall that causes a ballooning of the artery that eventually burst -can be blocked through surgery by a coil |
| Arteriovenous Malformations or A-V Malformations | - Can lead to a Hemorrhagic stroke - Tangled web of arteries and veins present since birth |
| Regulation of Cerebral Blood Flow | -The vascular system is a closed system under constant pressure -Is Controlled by elasticity of blood vessels, and metabolic needs -Aging can cause less elasticity responsiveness and eveness of flow b/c human arteries harden with age |
| Blood-Brain Barrier | -Tight system that prevents direct contact of all brain tissues with blood. -Blood cannot go outside veins into brain b/c blood that goes through brain is highly toxic -This specialized system extracts needed molecules -May stop medicine entering brain |
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