Beta-endorphin. Polarised light micrograph of crystals of beta-endorphin, an opioid peptide that relieves pain. Endorphins are a group of peptides (small proteins) that occur in the brain. Beta- endorphin is the most active type. Their effects resemble morphine and other opiate drugs, that is, alteration of the perception of pain. Because they are produced by body cells they were named endorphins (endogenous morphines"). Besides the nervous system, they occur at other body sites. Their effects on nerve endings are analgesic (pain killing), while they may also control the body's response to stress as well as determining mood and pleasure. Magnification: x55 at 5x7cm size. x80 at 4x5inch size."