Arterial Supply to the Brain Flashcards
What proportion of the bodys total oxygen consumption is due to the brain?
Approxiamately 1/5.
What are the main arteries that supply the brain?
The internal carotids and vertebral arteries. Within the cranium, the branches of an anostomotic circle, the Circle of Willis supplies the majority of the cerebrum.
Other smaller branches of the vertebral arteries supply the pons and spinal cord.
What is the pathway of the internal carotid artery?
Originates at the bifurcation of the left and right common carotid arteries, at the level of C4 vertebra.
They move superiorly within the carotid sheath, and enter the brain via the carotid canal of the temporal bone.
They do not supply branches to the face or neck. Once in the cranial cavity, the internal carotids pass anteriorly through the cavernous sinus.
Distal to the cavernous sinus, what branches does the ICA give off?
What does the ICA continue as?
1) Ophthalmic artery - supplies the structure of the orbit.
2) Posterior communicating artery - acts as an anostomotic ‘connecting vessel’ in the circle of Willis.
3) Anterior choroidal artery - supplies structures in the brain important for motor control and vision.
4) Anterior cerebral artery - supplies part of the cerebrum. The
The ICA continues as the middle cerebral artery.
What is the pathway of the vertebral arteries?
The vertebral arteries arise from the subclavian arteries, medial to the anterior scalene muscle.
They then ascend the posterior aspect of the neck and through the transverse foramina of the cervical vertebrae.
These vertebral arteries enter through the foramen magnum. These arteries converge to form the basilar artery.
What branches does the vertebral artery give off within the cranial vault?
1) Meningeal branches - supplies the falx cerebelli, a sheet of dura mater.
2) Anterior and posterior spinal arteries - supplies the spinal cord, spanning its entire length.
3) Posterior inferior cerebellar artery - supplies the cerebellum.
What arteries form the Circle of Willis?
Anterior cerebral arteries
Internal carotid arteries
Posterior cerebral arteries
Posterior communicating arteries
Anterior communicating artery
What is the arterial supply to the cerebrum?
1) Anterior cerebral artery - supplies anteromedial aspect of the cerebrum.
2) Middle cerebral artery - supplies the lateral aspect of the cerebrum.
3) Posterior cerebral artery - supplies the medial and lateral aspects of the posterior cerebrum.
What is the arterial supply to the spinal cord?
Supplied by three longitudinal arteries. These arteries descend from the brainstem to the conus medullaris:
1) Anterior spinal artery - branch of the vertebral arteries, travelling in the anterior median fissure. Gives rise to sulcal arteries that enter the spinal cord.
2) Two posterior spinal arteries - originate from the vertebral arteries or the posterior inferior cerebellar artery, anastomosing with one another in the pia mater.
However, below the cervical level supply, these longitudinal arteries are insufficient. There is support via anastomosis with the segmental medullary and radicular arteries.
The anterior and posterior segmental medullary arteries are derived from a number of arteries, before entering the intervertebral foramen.
The great anterior segmental artery of Adamkiewicz reinforces circulation to the inferior 2/3 of the spinal cord, and is found on the left in the majority of individuals.
Clinical relevance: Intracerebral aneurysms
Symptoms?
Prognosis?
Treatment?
An aneurysm is a dilation of an artery, which is greater than 50% of the normal diameter.
Most likely to occur is vessels contributing to the Circle of Willis. These are particularly dangerous. Produce few symptoms until they rupture.
Upon rupture, blood pools in the subarachnoid space - with a subsequent increase in intracranial pressure. Treatment is surgical and urgent.
Clinical relevance: spinal cord infarction
Symptoms?
Aetiology?
Treatment?
Also called a spinal stroke - refers to death of nervous tissue, resulting from an interruption of the arterial supply.
Results in muscle weakness and paralysis with a loss of reflexes.
This may be caused by vertebral fractures or dislocations, vasculitic disease, atheromatous disease, or external compression (e.g. abdominal tumours. 95% of spinal cord ischaemic events occur anterior to the spinal cord with the posterior column preserved.
Treatment is by reversal of known cause.
