Mr XY aged 74-years, has been taking buprenorphine patches (Norspan transdermal patch) to treat his chronic back pain. What type of agonist is Buprenorphine, and on which receptor it acts to elicit its analgesic effect? Discuss the main characteristics of this type of agonist? Give an example of an analgesic that is acting as a full agonist on the same receptor? (Hint: use the terms affinity & efficacy in your answer; be specific on the subtypes of receptors).