Pain chapters in Neuroscience Online: An Electronic Textbook for the Neurosciences | Department of Neurobiology and Anatomy - The University of Texas Medical School at Houston

http://neuroscience.uth.tmc.edu/s2/chapter06.html

http://neuroscience.uth.tmc.edu/s2/chapter07.html

http://neuroscience.uth.tmc.edu/s2/chapter08.html