cranial blood supply

blood flow determines

which neural systems remain functional

brain cant effectively store

oxygen or glucose

continuous perfusion is required to

sustain neuronal signaling

the cerebral cortex is especially vulnerable to

hypoxia

right and left internal carotid arteries

anterior circulation

right and left vertebral arteries, which join to form the basilar artery

posterior circulation

anterior and posterior circulation systems communicate through the

circle of willis

vertebral arteries ascend and supply the

spinal cord and medulla

vertebral arteries give rise to

posterior inferior cerebellar arteries

vertebral arteries joint to form the

basilar artery

basilar branches supply the

pons and cerebellum

basilar artery divides into the

anterior inferior cerebellar and superior cerebellar arteries, posterior cerebral arteries

internal carotid arteries supply most of the

cerebral hemispheres

major branches of internal carotid artery

anterior cerebral aa., middle cerebral aa., anterior choroidal artery

anterior communicating artery connects the

2 ACAs

anterior circulation of the brain

internal carotid arteries

middle cerebral aa

anterior cerebral aa

posterior circulation of brain

vertebrobasilar aa

posterior cerebral aa

components of circle of willis

Posterior cerebral arteries, posterior communicating arteries, internal carotid arteries, anterior cerebral arteries, anterior communicating artery

circle of willis supplies

cerebral hemispheres

allows blood to reach tissue through alternative routes over time

circle of willis

connected by posterior communicating arteries

PCA and internal carotid

3 things you need to know when blood flow in brain is impaired

-how quickly it happened

-size of lesion (how much blood flow is cut off)

-collateral circulation?

brief focal neurologic dysfunction w/ full recovery w/in 24 hours, typically due to ischemia; medical emergency even though symptoms resolve; pt education, stroke prevention intervention

transient ischemic attack

deficits persist for longer than 1 day and are stable

completed stroke

deficits worsen intermittently b/c of continuing thrombosis or repeated emboli

progressive stroke

mini stroke, silent stroke, or temporary clot or amyloid cells

TIA

obstruction of blood flow to the brain

ischemic stroke

rupture of flow of blood to the brain and preventing BF to the brain

hemorrhagic stroke

increased BP means more

stress on arterial wall

80% of strokes

ischemic

-can be thrombotic or emboli

vessel rupture causes loss of downstream perfusion plus pressure from extravascular blood

hemorrhagic

Types of Hemorrhagic Stroke

intracerebral and subarachnoid (aneurysm- barry or saccular)

clot forms elsewhere, travels, and abruptly occludes a cerebral vessel

embolus

clot forms at the site of vascular disease; onset may be abrupt or progressive

thrombus

clinical deficits reflect the

tissue deprived of blood (stroke)

small vessel lesions

lacunar infarcts

occlusion of small, deep arteries creates small cavities after necrotic tissue is cleared

lacunar infarcts

common locations of lacunar infarcts

basal ganglia, internal capsule, thalamus, and brainstem

findings are often purely sensory or purely motor

lacunar infarcts

blood outside vessel compresses surrounding brain tissue

hemorrhagic stroke

deficits may be severe at onset and change as edema evolves

hemorrhagic stroke

sudden, excruciating headache

subarachnoid hem.

possible brief loss of consciousness

subarachnoid hem.

initial findings may be nonfocal

subarachnoid hem.

complications of subarachnoid hem. include

continued bleeding, vasospasm, infarction, and hydrocephalus

bleeding into CSF-filled subarachnoid space, often w sudden severe headache

subarachnoid hem.

sequence to localize stroke

artery

tissue supplied

disrupted function

movement and examination findings

produces massive infarction in both MCA and ACA arteries

ICA

supplies the entire lateral aspect of the cerebral hemispheres (frontal, temporal, and parietal lobes) and subcortical structures

MCA

supplies the medial aspect of the cerebral hemispheres (frontal and parietal lobes) and subcortical structures including basal ganglia

ACA

supplies the cerebellum and medulla (vertebral artery) as well as pons, internal ear and cerebellum (basilar artery)

VBA

supplies the corresponding occipital lobe and medial and inferior temporal lobe, upper brainstem, midbrain, posterior diencephalons, and most of thalamus

PCA

homunclus

how much brain space dedicated to each body part

post central gyrus

parietal lobe

precentral gyrus

frontal lobe

central sulcus

lies b/t the post central and pre central gyri

2 parts of homunclus

somatosensory cortex and motor cortex

ACA supplies

medial frontal and parietal lobes

contralateral weakness and fine touch loss are greater in the lower limb than the upper limb or face

ACA

possible personality change, impulsiveness, perseveration, and gait apraxia

ACA

supplies most of the lateral cerebral hemispheres and parts of the basal ganglia/internal capsule

MCA

contralateral face and upper limb weakness and sensory loss are often greater than lower limb involvement

MCA

optic radiation involvement can cause contralateral homonymous hemianopia

MCA

occipital involvement: contralateral visual-field loss or cortical blindness

PCA

secondary visual cortex involvement: visual agnosia

PCA

thalamic involvement:

hemisensory loss and possible severe pain (PCA)

hippocampal involvement:

declarative memory impairment (PCA)

supplies brainstem/cerebellum

VBA

cranial nerve involvement, equilibrium disturbances, possibility of locked in syndrome

VBA

lie between distal branches of major cerebral arteries

watershed regions

systemic hypotension can reduce perfusion to

watershed areas

upper limb weakness and paresthesias may occur when

ACA-MCA border areas are affected (watershed areas)

abnormal vascular formation, arteries connect to veins through abnormal thin-walled vessels rather than normal capillaries

arteriovenous malformation

may stay silent till rupture

AVM

rupture can cause hemorrhage, loss of perfusion, and mass effect; presents like stroke

AVM

dilation of wall of artery or vein

aneurysm

swollen area has thin walls- prone to rupture

aneurysm

most common, outpouching of vessel wall

saccular (berry) aneurysm

small sac connected by a thin connection to the artery increases the risk for bleeding

saccular aneursym

treatment via clipping or coiling

saccular aneurysm

common sites of berry aneurysm

at bifurcations of vessels

specialized permeable barrier b/w the capillary endothelium of CNS and extracellular space

BBB

assists in preventing many pathogens from entering the CNS

BBB

blocks certain drugs and protein antibodies from accessing the brain (dopamine)

BBB

oxygen consumption increases from the brainstem to the cerebral cortex, leaving the cerebral cortex

more vulnerable to hypoxia than vital structures in the lower brainstem

cerebral arteries auto regulate local blood flow, primarily depending on 2 factors:

bp and metabolites

is vitally important to ensure adequate BF and to prevent brain edema

autoregulation

accumulation of excess tissue fluid in brain

edema

edema causes include:

-concussion

-cardiac arrest

-high altitude: fluid pressure results in ischemia, causing arterioles to dilate, increasing the capillary pressure, and producing more edema

pressure w/in skull

ICP

normal ICP

5-15 mm Hg

ICP above 20 is

pathologic

potential causes of ICP include

edema, hydrocephalus, tumor, hemorrhage, and other space-occupying lesions

increased ICP symptoms

vomiting, nausea, headache, drowsiness, frontal lobe gait ataxia, and visual and eye movement problems

BF to brain can be evaluated by

PET scan or angiography

based on metabolism of injected radioactively labeled substances

PET scan

major venous system of the brain consists of

cerebral veins

veins drain into

dural sinuses and the internal jugular vein

2 sets of veins drain the cerebrum:

superficial and deep

drain cortex and the adjacent white matter then empty into the superior sagittal sinus or one of the sinuses around the inferior cerebrum

superficial veins