First published in 1975. Because of its general importance to a number of related disciplines, students of the modern science of neurophysiology have benefited from time to time from an introductory survey presented at a more elementary level than is usually found in advanced textbooks. The dynamism of the field is such, however, that more up-to-date statements incorporating many of the exciting new findings concerning cellular neurophysiology are required periodically. This text is aimed at filling that need. It is an outgrowth of a part of a course on the neurophysiology of sensory processes taught by the author at The University of Michigan during the last ten years. This book is an attempt to present the subject matter at a level appropriate for advanced undergraduate students and first year graduate students whose knowledge of chemistry, physics, and mathematics is limited to introductory courses.