Pain Mechanisms and Pathways

Irrespective of whether chemical, mechanical, or thermal stimuli are involved, they become significantly more effective in the presence of prostaglandins (p.196). 

Chemical stimuli also underlie pain secondary to inflammation or ischemia (angina pectoris, myocardial infarction). The intense pain that occurs during overdistension or spasmodic contraction of smooth muscle abdominal organs may be maintained by local anoxemia developing in the area of spasm (visceral pain). 

Impulse traf c in the neospinothalamic and palaeospinothalamic pathways is subject to modulation by descending projections that originate from the reticular formation and terminate at second-order neurons, at their synapses with first-order neurons or spinal segmental intemeurons (descending antinociceptive system). This system can inhibit substance P-mediated impulse transmission from first- to second-order neurons via release of endogenous opiopeptides (enkephalins) or monoamines (norepinephrine, serotonin). 

All rights reserved. Usage subject to terms and conditions of license. 

---

Mechanism of Action An opioid agonist that binds to opioid receptors in the CNS, reducing stimuli from sensory nerve endings and inhibiting ascending pain pathways. Therapeutic Effect Alters pain reception and increases the pain threshold. Pharmacokinetics ... 

---