curare (kyŏrärˈē) [key], any of a variety of substances originally used as arrow poisons by Native South Americans in hunting and in warfare. The main active substance of curare, tubocurarine, is an alkaloid extracted from Chondodendron tomentosum, Strychnos toxifera, and other plant species. The poison produces muscle paralysis by interfering with the transmission of nerve impulses at the receptor sites of all skeletal muscle. Muscles with many nerves, such as eye muscles, are affected first. In recent years curare has been put to medical use. When given in small quantities with general anesthesia, especially in abdominal surgery, curare ensures the desired relaxation of muscle tissue with a minimal concentration of the anesthetic, lessening the possibilities of anesthesia-induced complications. Curare is also used to relieve spastic paralysis, to treat some mental disorders, and to induce muscle relaxation for the setting of fractures.