The brain.
D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology*; D002531:Cerebellum / Q000502:physiology; D006801:Humans; D009132:Muscles / Q000294:innervation; D009474:Neurons / Q000502:physiology / Q000648:ultrastructure