Central pain control.

We describe the anatomic and physiological components involved in pain physiology, with the goal of providing readers with the background information needed to understand central pain control mechanisms. These include spinal segmental controls, supraspinal excitatory and inhibitory controls, and diffuse noxious inhibitory controls (DNICs). Pain is a subjective sensation produced by an emotionally unpleasant experience considered to originate in adaptive processes taking place within neuron networks located at various levels of the central nervous system. The intensity of the components of pain is influenced by the stimulus characteristics, patient-related factors, and the setting in which the stimulus occurs. The various components of pain and the psychological and neurophysiological mechanisms that underlie the affective dimension of pain are reviewed. As a conclusion, phantom pain is used to illustrate the role for physiological systems independent from those involved in the physiology of nociception and pain, such as the motor cortex. This example highlights the extreme complexity of pain and pain control systems in humans.