sentences:  During the development of the central nervous system Eph/ephrin signaling plays a critical role in the cell-cell mediated migration of several types of neuronal axons to their target destinations.Eph/ephrin signaling controls the guidance of neuronal axons through their ability to inhibit the survival of axonal growth cones, which repels the migrating axon away from the site of Eph/ephrin activation.The growth cones of migrating axons do not simply respond to absolute levels of Ephs or ephrins in cells that they contact, but rather respond to relative levels of Eph and ephrin expression, which allows migrating axons that express either Ephs or ephrins to be directed along gradients of Eph or ephrin expressing cells towards a destination where axonal growth cone survival is no longer completely inhibited.