Final answer:
Opioids and endorphins both affect the transmission of pain by binding to opioid receptors and reducing pain signals in the nervous system.
Step-by-step explanation:
Opioids, such as morphine and codeine, and endorphins are both involved in the transmission of pain. Opioids are a category of drugs that mimic the body's natural opioids and bind to opioid receptors to reduce pain. Endorphins, which are naturally produced by the body, also bind to these receptors and contribute to pain reduction. By activating these receptors, opioids and endorphins can inhibit the transmission of pain signals in the nervous system.