Figure 1.

Role of neurons and SCs in regeneration. The peripheral nerve is mainly formed by axons and SCs. SCs have a crucial role in nerve homeostasis and regeneration by supporting axons by several means. SCs myelinate large axons (A). In response to injury, Wallerian degeneration takes place. SCs dedifferentiate, proliferate, and start myelin debris clearance. Macrophages migrate to the local area to take over phagocytosis of myelin and axonal debris and to interact with other cells in the injured microenvironment (B). Differentiated SCs form bands of Büngner and remyelinate the axon. Several neurotrophic factors, cytokines, and exosomes are released from the local cell population interacting with axons. In this sequence, the axon starts outgrowing in an attempt to reinnervate the target organ (C). Successful reinnervation is the final goal of nerve regeneration, but it is seldom achieved because it depends on several factors such as age, severity of injury, and distance from the cell body (D).