What documents do I need to present to reenter the United States? If seeking to enter the United States after temporary travel abroad, you will need to present a valid, unexpired âgreen cardâ (Form I-551, Permanent Resident Card).
Brain Tour. 2. Supply lines. Your brain is nourished by one of your body's richest networks of blood vessels. With each heartbeat, arteries carry about 20 to 25 percent of your blood to your brain, where billions of cells use about 20 percent of the oxygen and fuel your blood carries. When you are thinking hard, your brain may use up to 50 percent of the fuel and oxygen.
Normal function of the brainâs control centers is dependent upon adequate supply of oxygen and nutrients through a dense network of blood vessels. Blood is supplied to the brain, face, and scalp via two major sets of vessels: the right and left common carotid arteries and the right and left vertebral arteries. The common carotid arteries have two divisions. The external carotid arteries supply the face and scalp with blood. The internal carotid arteries supply blood to most of the anterior portion of the cerebrum. The vertebrobasilar arteries supply the posterior two-fifths of the cerebrum, part of the cerebellum, and the brain stem.