Muscle, Skeletal/physiopathology; Myelin Proteins/deficiency; Neural Conduction/physiology; Peripheral Nerves/physiopathology; Action Potentials/physiology; Age Factors; Animals; Biophysics; Disease Models, Animal; Electric Stimulation/methods; Gene Expression Regulation/genetics; Kv1.2 Potassium Channel/metabolism; Luminescent Proteins/genetics; Mice; Mice, Knockout; Microscopy, Electron, Transmission/methods; Myelin Basic Protein/metabolism; Myelin-Associated Glycoprotein/metabolism; Nerve Block/methods; Nerve Fibers/metabolism; Nerve Fibers/pathology; Neural Conduction/genetics; Peripheral Nerves/pathology; Peripheral Nerves/ultrastructure; Peripheral Nervous System Diseases/genetics; Peripheral Nervous System Diseases/pathology; Peripheral Nervous System Diseases/physiopathology; Protein Binding/genetics; Reaction Time/genetics; Saxitoxin/pharmacokinetics; Sodium Channels/metabolism; Tritium/pharmacokinetics