Describe the circle of Willis. Mention about the origin of the major vessels which supply the cranium.
Blood Supply to The Brain
Main vessels that supply the brain
Arterial supply
Brain is supplied by Right and left main systems of blood vessels
1. Carotid system - consisting of the right and left internal carotids which take origin from respective common carotids.
2. Vertebral system - consisting of the right and left vertebral arteries which take origin from the respetive subclavian arteries.They pass into the cranium travelling through the foramina in the transverse processes of the cervical vertebrae
The above mentioned arteries form a circle at the base of the brain called Circle of Willis
Parts of the Circle of Willis are:-
Right and left anterior cerebral arteries
One anterior communicating artery - connecting the Right and left anterior cerebral arteries
Right and left posterior communicating arteries - which connect the carotid system and the vertebral system
Right and left posterior cerebral arteries
Basilar artery formed by the union of the right and left vertebral arteries - basilar gives off branches to the right and left.
(anterior, middle and posterior cerebral arteries, anterior and posterior communicating arteries and basilar artery)
Right and left middle cerebral arteries
The basilar artery and middle cerebral arteries, though they supply the brain, are not considered part of the circle.
Venous drainage
By dural venous sinuses of the brain - formed by the layers of the dura mater lined with endothelium
They are:-
One superior sagittal sinus
One inferior sagittal sinus
One straight sinus
Two transverse or lateral sinuses
Two sigmoid sinuses
All blood comes to sigmoid sinuses and the sigmoid sinuses continue downwards as the right and left internal jugular veins.
The origin of the major vessels which supply the cranium.
Cranium = skull minus mandible
The major vessels that supply the cranium and their origin : -
