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.