Central Nervous System/metabolism; Evolution, Molecular; Myelin P0 Protein/genetics; Myelin Proteolipid Protein/genetics; Myelin Sheath/metabolism; 2',3'-Cyclic Nucleotide 3'-Phosphodiesterase; Amyloid beta-Protein Precursor/metabolism; Animals; Axons/metabolism; Axons/pathology; Cell Adhesion Molecules, Neuronal/metabolism; Central Nervous System/pathology; Central Nervous System/physiopathology; Exercise Test; Gene Expression/genetics; Longevity/genetics; Mice; Mice, Knockout; Mice, Transgenic; Microscopy, Electron; Motor Activity/genetics; Myelin Basic Protein/genetics; Myelin Basic Protein/metabolism; Myelin P0 Protein/metabolism; Myelin Proteolipid Protein/metabolism; Myelin Sheath/pathology; Myelin Sheath/ultrastructure; Myelin-Associated Glycoprotein; Oligodendroglia/metabolism; Optic Nerve/chemistry; Phosphoric Diester Hydrolases/metabolism; Promoter Regions, Genetic/genetics; Receptors, Cell Surface/metabolism; Sodium Channels/metabolism; Spinal Cord/metabolism; Spinal Cord/pathology; Survival Analysis; X-Ray Diffraction