The brain depends on a continuous, high-volume blood supply due to high metabolic demand and minimal energy storage, thus interruption of blood flow for minutes can cause irreversible neuronal injury.
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This lecture focuses first on arterial supply, as arterial pathology is far more common and clinically significant.
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Strokes:
One of the most common causes of neurological disability is a stroke. A stroke is a sudden occlusion/blockage of a cerebral artery leading to death of brain tissue (infarction).
Cerebral haemorrhage:
Cerebral haemorrhage occurs when a blood vessel in the brain ruptures. This is often due to an aneurysm (abnormal balloon-like swelling of an artery which may rupture). If this blood from the ruptured vessel enters the subarachnoid space then it is known as a subarachnoid haemorrhage and if it enters the brain it is known as an intracerebral haemorrhage
As mentioned earlier, the brain is highly metabolically active, has no energy reserves, and depends entirely on continuous arterial blood flow.
Because of this, its blood supply is tightly regulated, and interruption leads to stroke:
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The forebrain is the region most frequently affected by cerebro-vascular accidents.
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The circle of willis
Okay, the first thing you need to understand is the Circle of Willis. The Circle of Willis is a ring-like arterial anastomosis at the base of the brain that connects the anterior (carotid) and posterior (vertebrobasilar) circulations. It’s located in the subarachnoid space and surrounds the optic chiasm, the infundibulum, and hypothalamus.
The Circle of Willis is made up of 7 main arterial components: