Opioid analgesics : agonists of opioid receptors and antinociceptive system

Opioid analgesics provide analgesic effects without loss of consciousness, or dive into a dream and the oppression of other kinds of sensitivity.
The main mechanism of analgesic action of opioid analgesics are: 1) inhibition of pain impulses in the afferent paths of the CNS (violation of impulse transmission from the end of the primary afferents to neurons of spinal cord), 2) increased the inhibitory effect of descending antinociceptive system to conduct pain impulses in the afferent paths of the CNS; 3) change in emotional pain assessment.
The action of narcotic analgesics is mediated through opioid receptors.
1. As a result, the excitation of presynaptic opioid receptors located on terminals of primary afferents, reduced the allocation of substance P from primary afferent endings, with broken transmission of pain impulses to the neurons posterior horns of the spinal cord. Due to stimulation of postsynaptic opioid receptors and is disruptive to the depolarization of the postsynaptic membrane and inhibited the activation of neurons under the influence of a mediator. All this leads to disruption of transmission of pain impulses at the level of the spinal cord (spinal action).
2. With stimulation of opioid receptors in the gray matter okolovodoprovodnom and some other parts of the brain stem are activated descending antinociceptive systems that have a braking effect on the transmission of pain impulses along the afferent paths of spinal cord (supraspinal action). Descending inhibitory influences carried out with the participation of serotonin and noradrenaline
3. As a result of narcotic/opioid analgesics on the higher parts of the central nervous system changes the emotional evaluation of pain, decrease the perception (even if feeling the pain persists, it is less concerned about the patient).
Among the substances that stimulate opioid receptors, produce full agonist of opioid receptors (substances that can cause the maximum effect for this system), a partial opioid receptor agonists (substances that cause the effect is always smaller than the maximum) and antagonisty opioid receptors (receptors stimulates one subtype and blocking receptors of another subtype).