What is meant by sensitization?
Sensitization is a state in which a peripheral receptor or a central neuron either responds to stimuli in a more intense fashion than it would under baseline conditions, or responds to a stimulus to which it is normally insensitive. Sensitization occurs both at the level of the nociceptor in the periphery and at the level of the second-order neuron in the spinal cord.
In the periphery, tissue injury may convert a high-threshold mechanoreceptor (which normally would respond only to noxious mechanical stimuli) into a receptor that responds to gentle stimuli as though they were noxious. Centrally, the second-order neurons (those on which the primary afferents synapse) also may become hyper-excitable. When spinal cord neurons are hyper-excitable, they may fire spontaneously, giving rise to spontaneous pain. This is typically the case after deafferentation.