Three pairs of major veins return deoxygenated blood from the tissues of the head and neck to the heart. Several major arteries - including the facial, superficial temporal, and occipital arteries - branch off from the external carotid to provide blood to the many superficial structures of the head. In the neck and head exterior to the skull, the external carotid artery provides blood flow to the skin, muscles, and organs. The Circle of Willis provides insurance that the brain will continue to receive blood flow in the event that one of its major arteries is blocked by allowing blood flow between all of the major arteries to all of the regions of the brain. These arteries collectively form a ring of blood vessels known as the Circle of Willis. At the base of the brain, the internal carotid arteries branch off into the left and right anterior cerebral arteries and the left and right middle cerebral arteries that supply blood to the middle and anterior regions of the brain.Īt the base of the brain several communicating arteries form anastomoses, or passages, between the left and right posterior cerebral, left and right internal carotid, and left and right anterior cerebral arteries.

The internal carotid arteries pass into the skull inferior to the brain through the left and right carotid foramina. The left and right carotid arteries each divide in the neck to form the left and right internal carotid as well as the left and right external carotid arteries. From there the basilar artery provides blood to the posterior structures of the brain, including the brain stem, cerebellum, and cerebrum. The vertebral arteries travel through the transverse foramina of the cervical vertebrae before entering the skull at the foramen magnum and joining at the base of the brain to form the basilar artery. Oxygenated blood enters the neck from the trunk through four major arteries: the left and right vertebral arteries and the left and right common carotid arteries.

Any interruption in the blood flow to the brain very quickly results in the decline of mental function, loss of consciousness, and eventually death if not corrected.

Vascular structure of thebrain