Download TSM61 - Blood Supply to the Brain

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Describe the blood supply of the brain
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)
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) 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
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
See TSM39 - CSF and Ventricles