Blood supply to the brain
The brain is dependent on cerebral
vasculature
• Blood serves the brain like food serves the
•
body. The brain uses 20% of the blood in
the body. Arterial blood (carried in
arteries, arterioles, capillaries) nourishes
the brain by supplying:
– oxygen: The brain requires 25% of the
body’s oxygen to function maximally
– glucose
– other nutrients
Venous blood (carried in veins) removes
metabolic waste (carbon dioxide, lactic
acid, etc.)
Which is
the highpressure
system?
Which is
the lowpressure
system?
Why?
The brain is highly vulnerable to
disturbance of its blood supply
• Interruption of blood supply lasting only
•
•
second can cause neurological symptoms
Within minutes, interruptions of blood supply
can cause irreversible neuronal damage
Stroke, also called cerebrovascular accident
(CVA) = brain damage cause by vascular
disruptions, either
– Loss of blood supply, when an artery is
blocked (occlusive stroke)
– Bleeding (hemorrhagic stroke)
Overview of arterial blood supply to brain
• Two systems of arteries deliver
•
glucose-, nutrient-, and oxygenrich blood from the heart and
aorta toward the brain
– Internal carotids (L&R)
– Vertebral (L&R)-basilar system
These two systems are the inputs
to a circular arterial loop at the
base of the brain, called the Circle
of Willis
– There is a
in the middle of the
circle
– The interconnections between blood
vessels (anastomoses) in the Circle of
Willis protect the brain when part of
its vascular supply is blocked
– Common locations of blockages are
indicated by the dark areas
Input from the internal
carotids to the Circle of Willis
right
left
• Heart  Aorta 
•
•
– Left common carotid branches directly off the aorta
– Right common carotid branches off of the right subclavian which
branches off the aorta
Each common carotid (L&R) splits into two arteries
– External carotid artery
– Internal carotid artery
The internal carotids (L&R) connect to opposite sides of Circle of
Willis
Input from the vertebral-basilar
system to the Circle of Willis
right
left
• Heart  Aorta 
•
•
•
– Subclavians (L & R)
Vertebral arteries (L&R) branch off of the subclavians
The two vertebrals join to form one basilar artery
The basilar artery connects to posterior portion of Circle of Willis
Note that branches off of the vertebral arteries and the basilar
artery supply the cerebellum, spinal cord, and brain stem
Arterial outputs from the Circle of Willis to the
brain
• Three sets of paired
outputs from the Circle of
Willis deliver glucose-,
nutrient-, and oxygen-rich
blood into the brain
– Middle cerebral arteries
– Posterior cerebral
arteries
– Anterior cerebral arteries
Circle of Willis:
Schematic review of
--the locations of inputs
(green)
Internal carotid
Basilar artery
--the output arteries
(blue)
ACAs
MCAs
PCAs
--communicating arteries
which complete the
circle (pink)
Anterior communicating (1)
Posterior communicating (2)
Arterial blood supply to brain, in situ
Inferior view of brain
anterior
posterior
Two systems of inputs (#s 3; 8 & 10), three systems of outputs
(#s 2, 4, 6), plus two “communicating arteries” (#s 1, 5).
(Note: #s 7, 9, and 11, are branches off of the vertebral and
basilar arteries, and supply the cerebellum.)
Where do MCAs, ACAs, PCAs branch
out after exiting Circle of Willis?
Lateral view
of left
hemisphere
Approx.
location of
Circle of Willis
Medial view
of right
hemisphere
Note location of watershed region (where supply is received from >1 cerebral artery
Small branches of cerebral
arteries supply core areas of
brain
• E.g. MCA
A coronal section, showing how cerebral
arteries supply deep structures and white
matter of brain, as well as cortex
• MCA
• ACA
• PCA
Midbrain
MCA
ACA
PCA
Branch of internal carotid
MCA branches
Strokes disrupt blood supply:
Two types of stroke
• Stroke / cerebrovascular accident (CVA)
– Occlusive (ischemic) stroke:
Thrombosis or embolism
– Hemorrhagic: Hemorrhaged
aneurysm, or bleed of
arteriovenous malformation
Area of infarct
+ surrounding
penumbra
What does blood supply have to do with the brain,
and with practice of SLP?
• Knowing principle that “different structures in brain contribute
to different functions” and using the clinicopathologic method
– SLP can make clinical (diagnostic and therapeutic)
predictions and plans, based on
• the site(s) where arterial blood supply is lost
• knowledge that nervous tissue will be damaged or die at
those sites
• knowledge of the kinds of functional changes associated
with damage in that/those place(s)
– E.g. left side of cerebrum vs. right side of cerebrum
– E.g. cerebellum
– E.g. brainstem
Some clinical applications (a preview)
• The internal carotids supply more blood to cerebrum than
•
•
•
•
•
•
•
vertebral-basilar system
Left MCA supplies the lateral left cortex, which is associated
with the function of ______________
Right MCA supplies the lateral right cortex, associated with the
function of __________________
Proximal branches of both MCAs supply the putamen and
caudate, which are part of ______, important for movement
PCAs supply thalamus, which is a gateway for all neural
pathways going to the cerebral cortex, including those that
arouse (wake up) the cortex. (Remember limbic/olfactory?)
PCAs supply occipital lobe, important for __________
ACAs supply medial cerebrum, important for sensori-motor
functions of _________________
Vertebral-basilar system supplies the brain stem important for
___________ and cerebellum, important for _________
Blood supply to the spinal cord
Spinal cord: Clinico-pathologic
method
– Anterior spinal artery
• Supply anterior twothirds of spinal cord
• Symptoms
–Hemiplegia & loss of
pain & temperature
– Posterior spinal artery
• Supply dorsal surface
of the cord
• Symptoms
–Loss of
discriminative touch
Blood-Brain Barrier
Blood-Brain Barrier
• First Line of Defense
– Functional in only
CNS vessels
– Restriction of
movement of
harmful (infectious
microorganisms)
substances from
blood to brain tissue
– Medical implications
• Exclusion of
antibodies,
making treatment
of cerebral
infections difficult
Venous sinus system of the
brain
VENOUS SINUS SYSTEM
• Functions
– Collection of deoxygenated blood
– Transportation back to heart
•Veins emptying into sinuses
•Dural sinuses
–Separation of periosteal & meningeal
dural layers