The distinction between nociception and pain was discussed and the identification criteria presented. Peripheral nociceptors have been identified in avian peripheral tissues and on the basis of their physiological properties were divided into high threshold mechanical, mechano-thermal, thermal and articular group III and IV nociceptors. These receptors relay information from noxious stimulation to lamina I/II of the dorsal horm of the spinal cord and from there to the medullary reticular formation and thalamus. Nociceptive peripheral stimulation results in either escape responses or crouching; immobility depending on the stimulus and persistent stimulation can result in learned helplessness.