Brain slice. View of a slice through a healthy human brain. The front of the brain is at left, with a ventricle (space) at lower right. The two main types of brain tissue can be seen: the grey matter (light brown) makes up the external layer of the brain, and the paler white matter (yellow) is found in the centre. The brain is made almost exclusively of nerve cells (neurones). The grey matter mainly contains neurone cell bodies, and the white matter consists of nerve fibres linking different areas of grey matter. For a comparison with the brain slice of a person with Alzheimer's disease see images M108/415 or M108/416.