Blood supply to the brain

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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 high pressure system? Which is the low pressure 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 oxygen rich 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 • • • MCA ACA PCA ACA Midbrain Branch of internal carotid PCA MCA branches

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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 two thirds of spinal cord • Symptoms –Hemiplegia & loss of pain & temperature – Posterior spinal artery • Supply dorsal surface • of the cord Symptoms –Loss of

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