<p>by Shuji Wakatsuki, Toshiyuki Araki</p> Neurodegeneration is frequently associated with oxidative stress, yet the mechanisms that convert reactive oxygen species (ROS) into irreversible degenerative signals remain incompletely understood. Neurons in the central and peripheral nervous systems often differ in their responses to injury, but these differences cannot be reduced to a simple contrast between weak and strong antioxidant capacity. This Essay proposes that neuronal vulnerability is shaped by multilayered signaling thresholds comprising ROS production, antioxidant and thiol buffering, redox-sensitive signal detection, molecular gating, and commitment to degeneration, survival, or repair. This framework may help explain selective neuronal vulnerability in neurodegenerative diseases and identify intervention points downstream of global ROS suppression.