False-colour nuclear magnetic resonance (NMR) image of a mid-sagittal section through a human head, showing structures of a normal brain, airways (dark blue) & facial tissues. The heavily- folded cerebral cortex (the brain's grey matter), which forms the outer part of the cerebrum, appears green & light blue. Beneath it at right is the feathery outline of the cerebellum. Immediately to the left of the cerebellum in green are the structures of the brainstem, an enlarged extension of the spinal cord. The uppermost bones of the neck are seen to the left of the spinal cord. Cerebro-spinal fluid, which bathes the brain and surrounds the spinal cord, appears dark blue.