Diagram of signals postulated to control microglial cell migration to lesions. (A) The nerve cord before injury. (B) The cord from injury (on left) to several hours later. Note the presence of the NO and Ca²⁺ gradients, and the opening of the innexon channels. It is during this phase that the microglia become round and move toward the crush in response to ATP. (C) Recovery from injury after microglia have begun to accumulate at the site of injury. MG, microglia; inx, innexon; P2YR, purinergic receptor.