After peripheral nerve injury, axons must regrow across gaps of centimeters to reconnect with targets. This process takes months, and many regenerating axons never make it. The limiting factor is not just the distance—it is the signaling environment that guides and sustains growth.

Neurotrophins (NGF, BDNF, NT-3) are the critical signaling molecules. But their role is more precise than simple growth factors. Each neurotrophin binds specific Trk receptors on axons, creating distinct signaling programs that coordinate different phases of regeneration.