pain and modulation processes

pain is one of the most important and sometimes difficult problems, that patients and physicians are encountered. it may be clinically acute or chronic, acute pain has usually definite cause and favourable response to treatment. on the other hand there are difficulties in diagnosis and management of chronic pain. peripheral and cranial nerves convey pain impulses toward central nervous system, and modulations take place at several levels. diagnosis of different pains, including nociceptive, nerve trunk pain and deafferentation types is essential to acceptable management. in this article we review pain pathway, neurotransmitters and modulation.