The document discusses opioid analgesics and their mechanism of action in reducing pain. It notes that opioids work by binding to opioid receptors in the brain and spinal cord, which inhibits the transmission of pain signals to the brain. Specifically, opioids promote the opening of potassium ion channels and inhibit calcium ion channels in neurons, reducing neurotransmitter release and nerve signal transmission. This leads to analgesic, or pain-relieving, effects. However, opioids can also cause side effects like respiratory depression and dependence with prolonged use.

3. Reticular formation in brain stem Target area for opioid analgesia

9. Synapses between afferent nociceptive neurons and secondary ascending neurons relay pain signals to the brain. The entry of Ca 2+ into the pre-synaptic primary neuron and the release of K + from the post-synaptic secondary neuron are processes involved in signal transmission across the synapse .

11. Opioids binding to ion channel associated  receptors inhibit the influx of calcium ions into the pre-synaptic terminal and increase the outflow of potassium ions from the post-synaptic membrane. This has the effect of reducing the release of the neurotransmitter glutamate and hyperpolarising the post-synaptic membrane. Synaptic transmission is inhibited.