A family of endogenous, morphinelike peptides present within the central nervous system. The enkephalins, the first members of the endorphin family, were discovered by John Hughes and Hans Kosterlitz in 1975 and opened research into a wide number of centrally active neuropeptides. The term endorphin is generic, referring to all the opioid peptides, while specific peptides are given individual names, such as the enkephalins, dynorphins, and β-endorphin. Their isolation, shortly after the identification of the opioid receptors, brought together the concept of endogenous opioid peptide systems within the central nervous system which can modulate pain perception and through which opioids act.