Even though the brain requires large amounts of oxygen and nutrients to function properly, blood flows to it through a surprisingly small number of arteries. These major blood vessels to the brain have a crucial job, and blockages in these vessels can have devastating consequences. The large vessels to the brain include the carotid arteries and the cerebral arteries.
Diseases such as atherosclerosis and diabetes can contribute to the buildup of plaque on the walls of the blood vessels. Plaque can reduce and sometimes even block the flow of blood downstream. Also, blood clots or debris from atherosclerotic plaques can lodge suddenly in a major vessel, preventing blood from reaching the brain tissue downstream of the vessel. Additionally, a blood clot from the heart can travel up to the brain and causes a blockage. This is one of the most common reason for an ischemic stroke.