The United States Congress designated the 1990's as the "Decade of the Brain" in recognition of the importance of neuroscience to the health and well-being of Americans. It has been suggested that as many as 20% of all patients seeking medical treatment have neurologic problems, either as the presenting complaint or as an associated condition complicating the primary illness. To this end, it is important that physicians understand basic neuroscience principles and nervous system diseases. Of course, this text is not encyclopedic but instead is an outline of the knowledge required of all medical students. Interested students can consult numerous texts that provide comprehensive coverage of the field, including Greenfield's Neuropathology and the exhaustive 60 + volume Handbook of Clinical Neurology. The information selected for inclusion in this volume of the Oklahoma Notes series remains true to the goal of the whole series-incorporating only that material vital in both the general clinical practice of medicine and to answer questions on the all-important United States Medical Licensing Examination. Roger A. Brumback Richard W. Leech Acknowledgments This text would not have been possible without a great deal of help and support from a number of individuals. We want to thank all those who assisted in our education in neuroscience and neuropathology including: William M. Landau and Philip R. Dodge of the Washington University School of Medicine, Lowell W. Lapham of the University of Rochester Medical Center, and Ellsworth C.