Category B -full version without watermark 720x576 (check terms and conditions at www.teledesign.de) The version with watermark is for free to embed. - How is pain generated? Stimuli are detected by receptors and converted into electrical impulses. These signals reach the spinal cord and are transmitted to the brain. Via the brain stem they get to the "gate of consciousness" -- the thalamus. Here they are filtered and conveyed to brain regions that are responsible for the location, pain severity and its emotional impact. All pain related sites show a high density of opiate receptors. This means endogenous substances with opiod like effects are involved in pain perception. In the development of chronic pain, above all biological and psychological phenomena are involved. They can lead to pain without an apparent trigger. Analgesics act by various mechanisms. Anti-inflammatory drugs act directly at the site of pain. Local anesthetics transiently block the transmission to the nerve tract. Other medications inhibit the signal transduction between the neurons on the way to the brain. Opiates act on all steps of pain perception.