Each part of the body is governed by a specific area of the brain. If either the part of the brain or its corresponding body part is damaged, the related part also suffers. The answer lies in the way the two are connected. How are they connected, by the way? The nervous system. That’s right, when one node — the brain or the limb it governs — is damaged, the other atrophies either because it’s deprived of vital growth energy or it no longer has any work to do. In the case of brain damage, it is no longer able to govern the related body part because the neurons themselves are damaged. In the case of a damaged limb, the brain simply shuts down that part of itself because it no longer has to use the particular neurons to control a limb that can no longer function.