Opioids: Endogenous Opioid Pathway
Morphine and related compounds
(opioids) mimic the effects of the endogenous
opioid neurotransmitters—endorphins and enkephalins. Endogenous opioid
receptors are located throughout the pathways that relay the pain signal from
its source to higher CNS centers for processing, evaluation, and response (such
as via the spinoreticular tract [see Figure 325]). Descending pathways,
including endogenous opioids, NE, and 5HT, modulate
the transmission of the incoming pain signal. Thesen pathways can be activated subconsciously or
consciously, which may account for a large analgesic placebo effect. Opioids
alter the perception of pain. Such modulation of the affective component of
pain can improve a patient’s quality of life even in the presence of a continuing sensation of pain.
