Download TSM61 - Blood Supply to the Brain

TSM61: BLOOD SUPPLY TO THE BRAIN
04/11/08
LEARNING OUTCOMES
Describe the blood supply of the brain
ROOT ARTERIES
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The brain receives its blood supply from branches of the internal carotid artery and vertebral artery
The vertebral artery is a branch of the subclavian artery passing through the foramen magnum
o Gives branches to the cerebellum and medulla
o The two arteries join at the pontomedullary junction to form the basilar artery
o Ascends the ventral pons giving numerous pontine and cerebellar branches
o Bifurcates at the midbrain to form the posterior cerebral arteries
The internal carotid artery ascends into the skull through the carotid canal of the temporal bone
o Gives three key branches:
 Ophthalmic – supplies the eye (including the retina) and orbit via the optic canal
 Posterior communicating – supplies the optic tract, (hypo)thalamus and midbrain
 Anterior choroidal – supplies the choroid plexus, internal capsule, basal ganglia
o Terminates as the anterior and middle cerebral arteries (80% blood flow to middle)
CEREBRAL ARTERIES
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The anterior, middle and posterior cerebral arteries together supply all parts of the brain
The anterior cerebral artery runs posteriorly along the medial surface of the hemisphere
o Arches along the corpus callosum
o Supplies the area of the motor cortex associated with the lower limbs (amongst others)
The middle cerebral artery runs laterally and supplies almost the whole lateral hemisphere
o Supplies the primary somatosensory cortex (amongst others)
o Supplies all motor areas except those of the lower limbs
The posterior cerebral artery runs inferiorly to the occipital lobes
o Supplies the posterior parietal cortex and inferior parts of the temporal lobe
o Also supplies the hippocampus
Communicating arteries join the cerebral arteries to form the Circle of Willis
o The anterior cerebral arteries are joined together (ant. communicating)
o The internal carotid and posterior cerebral arteries are joined (post. communicating)
CEREBRAL BLOOD FLOW (CBF) REGULATION
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Cerebral blood flow (CBF) normally takes around 15% of cardiac output
o Majority supplies grey matter
o Overall CBF can increase up to 60% of CO if needed
o Chronic systemic hypertension can disturb autoregulation
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Most regulation of CBF is through local control of focal vessels
o Increased neuronal activity in a functional area elicits local vasodilatation
o Mediated by metabolic factors including potassium and hydrogen ions and adenosine
o Sympathetic activity (neurogenic) has relatively little effect
Describe the main types of intracranial haemorrhage
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See TSM39 - CSF and Ventricles