Transcript Temporal Aspects of Visual Extinction

Chapter 17: Blood Supply
 Chris Rorden
University of South Carolina
Norman J. Arnold School of Public Health
Department of Communication Sciences and Disorders
University of South Carolina
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Role of Blood Supply
 Nutrition to parenchyma (functional parts of organ = brain cells).
– Brain is completely dependent on oxygen supply - No O2 reserves.
 Irreversible damage in 4-6 minutes if no oxygen
 Brain requires 20% of O2 for 2% of body weight.
– Brain requires glucose for energy
 No ability to use fat
 Remove carbon dioxide and waste-products from cells
 Cerebral perfusion
– > 60 ml/100gr min-1 in Gray matter
– 40 < X < 60 in White matter
– 750mL blood pumped per minute and circulated blood
returned for reoxygenation
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Vascular Network
Network of arteries and veins
– Arteries carry blood away from the heart
– Arteries divide into smaller vessels called:
arterioles
– Arterioles divide further into capillaries
Vascular Network
– Veins carry blood toward the heart
– Smallest level are venules that are connected to
capillaries
– Venules Carry blood to sinuses on cortical surface
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Local blood flow
Arteries
Arterioles
Capillaries
Venules
Sinuses
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Cerebrovascular Supply
Two Systems
– Carotid System
– Vertebral Basilar System
Meet in Circle of Willis
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Vertebral / Basilar Arteries
Brain stem
– Basilar Artery
– Vertebral Arteries
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Vertebral Basilar System
Two Vertebral Arteries enter skull through Foramen
Magnum
Join to form the Basilar Artery and then Circle of Willis
Numerous small branches
Supplies the brainstem and cerebellum
Cerebellum:
•Superior Cerebellar Artery
•Anterior Inferior Cerebellar Artery
•Posterior Inferior Cerebellar
Artery
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Carotid Arteries
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Carotid System
 Common Carotid Artery
 Divides into two branches
– External Branch
 Supply blood to facial muscles, forehead and oral, nasal and orbital
cavities
– Internal Branch (enters the skull through the carotid foramen)
 Anterior choroidal artery (supplies optic tract, posterior limb of internal
capsule, branches to midbrain,and lateral geniculate nucleus).
 Ophthalmic artery (Supplies blood to the eyeball and ocular muscles)
– Major source of blood to the brain
– After joining Circle of Willis becomes anterior cerebral and
middle cerebral arteries
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Circle of Willis
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Circle of Willis
Wreath-shaped circle of Willis located at
ventral surface of brain
Connects Carotid and Vertebral Basilar
Systems
– Middle and Anterior Cerebral Arteries
– Anterior Communicating Artery
– Posterior Cerebral Artery
– Posterior Communicating Artery
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Cortical Blood Supply
–
–
–
–
ACA: Medial Frontal Perfusion
MCA: Lateral Perfusion
PCA: Posterior medial Perfusion, cerebellum
Watershed Areas: overlap between major arteries
Major Arteries
 Carotid
 Anterior Cerebral
 Middle Cerebral
Posterior Cerebral
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Two Types of Arteries
Cortical (Circumferential) Branches
– Supply External Brain Structures
Central (Penetrating) Branches
– Small
– Penetrate ventral surface to supply internal brain
structures
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Anterior Cerebral Artery
 Supplies Orbital and Medial
Surfaces of Frontal and Parietal
Lobes
 Interruption causes
– Cortical Arteries
– Paralysis of legs and feet
– Difficulty in prefrontal lobe functions of
cognitive thinking, judgment, motor
initiation and self monitoring
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Middle Cerebral Artery
Direct continuation of carotid artery
Cortical Branches
– Temporal
– Parietal
– Frontal
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MCA: Cortical Branches
Supplies blood to entire lateral surface of brain
– Somatosensory Cortex
– Motor Cortex
– Broca's Area
– Heschl’s Gyrus
– Wernicke’s Area
Therefore, symptoms include
– Aphasia
– Motor deficits
– Neglect (right hemisphere)
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MCA – Penetrating Arteries
Supplies basal ganglia
and diencephalon
Interruption causes
– Contralateral hemiplegia
– Impaired sensory systems
– Touch
– Pain and temperature
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Central Penetrating Arteries
 Arise from cortical arteries or from Circle of Willis
 Penetrate inferior surface of brain
 Can form channels to facilitate blood supply
 Central (Penetrating) Arteries
 Supply
–
–
–
–
–
Thalamus
Hypothalamus
Basal Ganglia
Internal capsule
Choroid Plexus
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Posterior Cerebral Artery
Supplies blood to anterior and inferior temporal
lobes, uncus, inferior temporal gyri, inferior and
medial occipital lobe
Watersheds with middle cerebral artery
Interruption causes
– Homonymous hemianopsia
– Possible total blindness
– Cerebellar symptoms
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Collateral Circulation
Redundant arteries provide alternative supply when
primary supply is lost
Small, normally closed arteries open up after
occlusion, connecting two larger arteries or different
parts of the same artery.
Dependent on location and severity of blockage
– Better collateral circulation if blockage is near main trunk
– Better if blockage occurs gradually
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Vascular Pathologies
Occlusive (Something is blocked causing
ischemia). 80% of strokes are ischemic
– Embolism: object from another part of the body which
travels through artery until it gets stuck.
– Thrombosis: object originating within a blood vessel:
local buildup of fatty substances usually at a bifurcation
of artery, these can rupture leading to catastrophic
blockage
Hemorrhagic (Bleed). 20% of strokes are due to
arteries rupturing.
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Risk factor for ischemic stroke
 Atherosclerosis from
reduced lumen due to
lipids, calcium fatty particles
etc. (‘Athera’ = porridge in
Greek)
 A form of Arteriosclerosis: a
general term describing any
hardening (and loss of
elasticity) of arteries.
 Leads to stenosis (narrowing) of
the artery, gradually leading to
insufficient blood supply
 Plaques can rupture, creating a
thrombus in blood supply
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Vascular Pathologies - Bleeds
Hemorrhagic
Bleeding from ruptured vessels
Types
– Intracerebral: More common in thalamus and basal
ganglia
– Subdural
– Aneurysm
Aneurysm
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Haemorrhages
 20% of strokes are bleeds
 Typically, due to ruptured aneurysm
CT of recent haemorrhage
– An aneurysm is a sac-like protrusion of an artery caused by a
weakened area within the vessel wall.
– Introspectively, the worst headache of your life.
– http://www.microvent.com/
– Surgery to clip aneurysm can save patients life.
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Arteriovenous Malformations
 AVMs can cause hemorrhagic strokes
 Tangled web of arteries and veins present since birth
 ~3 percent of all AVMs hemorrhage
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Venous Sinus System
Blood returns to lungs for
oxygen
Drain into Sinus System
Dural Sinuses
– Superior Sagittal Sinus
– Inferior Sagittal Sinus
– Straight Sinus
– Transverse Sinus
– Cavernous Sinus
– Petrosal Sinuses
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Notes
 Regulation of Cerebral Blood Flow
– Closed system under constant pressure
– Controlled by elasticity of blood vessels, and metabolic
needs
– Aging can cause less elasticity responsiveness and
eveness of flow
 Blood-Brain Barrier
– Tight system does not allow direct contact of all brain
tissues with blood
– Specialized system to extract needed molecules
– May impede medicine entering the brain
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