Session 1 - Blood Supply And Venous Drainage Flashcards
What is the arterial supply to the brain?
two pairs of arteries: the internal carotid arteries, and the vertebral arteries.
ascend in the neck and enter skull, they form the circle of Willis.
The vertebral arteries supply approximately 20% of blood to the brain, mainly the posterior parts such as the occipital lobe, cerebellum and brainstem.
The internal carotid arteries supply the remaining 80% including the rest of the cerebrum and diencephalon.
What is the circle of Willis?
The branches of the circle of Willis wrap around parts of the brain and give off smaller and smaller branches that penetrate the brain tissue.
What is the branches of the circle of Willis?
seen on the inferior surface of the brain lying on the brainstem and frontal lobe:
• Internal carotid arteries (left and right) – ascending upwards from the neck.
• Vertebral arteries (left and right) – ascending upwards through the cervical vertebrae.
• Basilar artery – a singular artery formed by the unison of the two vertebral arteries. It gives off small pontine arteries to supply the brainstem as it travels along its surface.
• Posterior cerebral arteries (left and right) – formed by the bifurcation of the basilar artery, these arteries pass posteriorly after their formation.
• Middle cerebral arteries (left and right) – the continuation of the internal carotid arteries after they have entered the skull. These arteries pass into the lateral sulcus and give off many branches to both superficial and deep brain tissue.
• Anterior cerebral arteries (left and right) – branches of the internal carotid arteries as they enter the skull. These arteries pass anteriorly and then wrap backwards over the corpus callosum.
• Posterior communicating arteries (left and right) – join the posterior cerebral to the middle cerebral arteries.
• Anterior communicating artery – joins the left and right anterior cerebral arteries.
• Cerebellar arteries – there are 3 pairs of cerebellar arteries:
o Anterior inferior cerebellar arteries (AICA).
o Posterior inferior cerebellar arteries (PICA).
o Superior cerebellar arteries (SCA).
What are the vascular territories?
major arteries of the circle of Willis supply a specific area of the brain.
What is the ACA?
Anterior cerebral artery (ACA)
supply the medial aspects of the frontal and parietal lobes, and a strip of cortex on the superior aspect. This includes the motor and somatosensory cortex responsible for the lower limbs.
They also supply some of the anterior structures of the diencephalon.
What is the MCA?
Middle cerebral artery (MCA)
supply the vast majority of the lateral aspects and deep parts of the hemispheres. This includes the parts of the motor and somatosensory cortices responsible for the face, arms and trunk, and a structure called the internal capsule that transmits all fibres to and from the cortices.
The MCA also supplies some of the structures of the diencephalon.
What is the PCA?
Posterior cerebral artery (PCA)
These vessels mainly supply the occipital lobe which contains the visual cortex, but also a small portion of the inferior temporal lobe.
What is the basilar artery?
This large singular vessel carries arterial blood from the vertebral arteries to the circle of Willis.
It gives off small branches to supply the pons. As the pons forms part of the pathway of between the brain and spinal cord, disruption of the basilar artery can potentially threaten the function of all ascending and descending fibres including all motor control and sensation from the neck down.
What are the cerebellar arteries?
Cerebellar arteries (AICA, PICA, SCA)
These vessels mainly supply the cerebellum, but in addition to the basilar artery, they also supply parts of the brainstem.
What is a stroke?
Stroke
A stroke is an interruption to the blood supply of part of the brain leading to a neurological deficit that lasts longer than 24 hours. Strokes may be ischaemic (caused by obstruction of a vessel by a thrombus or embolus and subsequent downstream ischaemia) or haemorrhagic (caused by rupture of a blood vessel leading to compression of nearby structures by the accumulation of blood).
By knowing the function of specific areas of the brain and knowing which areas of the brain are supplied by which artery, a clinician can identify the responsible vessel based on the symptoms alone. Middle cerebral artery strokes, for example, may cause weakness and numbness of the hands and face, whereas an anterior cerebral artery stroke may cause weakness and numbness of the legs. A posterior cerebral artery stroke may cause blindness whereas a basilar stroke may cause complete paralysis.
What are berry aneurysms?
Berry aneurysms
Aneurysms are deformities in arterial vessel walls causing them to balloon and make them prone to rupture. Berry aneurysms, named after their characteristic appearance, may be found in the cerebral circulation on the sides of cerebral arteries. They are often asymptomatic until they rupture. A ruptured berry aneurysm most often causes a subarachnoid haemorrhage, leaking arterial blood into the subarachnoid space. Symptoms include a severe, sudden-onset headache, vomiting or a reduction in a patient’s conscious level.
