A mu-opioid key, cut sharper than the original

Dermorphin binds the mu-opioid receptor, the same receptor morphine uses and the one your own endorphins use. Binding closes calcium channels on the nerve ending, opens potassium channels, and hyperpolarises the cell so it cannot fire, which is how a pain signal is stopped before it travels. Naloxone blocks all of it, which proves the route is the opioid receptor and nothing else. Where it differs from morphine is fit and grip: it holds that receptor far more tightly and more selectively.