This section will consider the structure and function of muscle receptors, as well as the central nervous system mechanisms with which they are concerned. In volume I of this Handbook, receptor mechanisms are discussed in detail. Also, the crustacean stretch receptor and the frog muscle spindle have been considered. The present section will be concerned with vertebrate muscle receptors with an emphasis on mammals. Muscle receptors provide interesting examples of specialized mechanorecep tors. The muscle spindle is a striking case of a receptor which is regulated in its function by the central...