Thecentral nervous system is made of two types oftissue:white matter andgrey matter. Grey matter containsnerve cell bodies, and white matter is made of thenerve fibres.
When a sample is freshly cut, it usually slightly pink in appearance (for both types). Whenpreserved informaldehyde, white matter appears to be almost white. White matter consists mostly ofmyelinatedaxons:. Myelin is alipid tissue (a fat) withcapillaries. It helps to keep the electrical in the nerve fibre. This is important for fast and accurate sending of signals. In thebrain white matter is surrounded by grey matter most of the time. In thespine, white matter is outside, and grey matter inside: the myelin sourrounds the nerve cells, and helps the transmission of nerve signals.
White matter is used to connect different areas of grey matter. If a section of white matter is damaged, the brain may be able to find a different route to replace the lost connection. The brain contains a third kind of tissue, which appears darker. It is calledsubstantia nigra, a part of the brain that is involved inpleasure &reward,addiction andmovement.
