This book was developed from a course of lectures and practicals given to first-and second-year medical students at the University of Leeds. My aim has been to provide a comprehensive account of the nervous system and its functions, which I hope will help the student to attain a better understand­ ing of clinical neurology. For this reason a good deal of attention has been paid to the study of control systems, and emphasis laid on those mechanisms that are frequently deranged by injury or disease. In particu­ lar, a useful coverage has been given to disturbances of the motor and sensory systems that commonly occur in human beings. Throughout the text numerous references have been made to the great pioneers of the past and to present-day investigators whose contributions have added enormously to our knowledge of the subject or who have pointed the way to important advances. Perhaps the most striking change in recent years has been the application of new techniques in neurophysiology for more precise measurement and analysis of experimental results. A biophysical approach is now mandatory and some of its broad outlines have been included. This should present no difficulty to individuals interested in biological methods, especially those who wish to pursue careers in science or to become professional physiologists. With this idea in mind, I have included references to laboratory procedures and many illustrations from original research.