The fourth edition of this highly successful text has been extensively revised and restructured to take account of the many recent advances in the subject and bring it right up to date. The classic observations of recent years can now be interpreted with the powerful new techniques of molecular biology. Consequently there is much new material throughout the book, including many new illustrations and extensive references to recent work. Its essential philosophy remains the same, though: fundamental concepts are clearly explained, and key experiments are examined in some detail. This textbook will be used by students of physiology, neuroscience, cell biology and biophysics. Specializing undergraduates and graduates as well as lecturers and researchers will find the text thorough and clearly written.