a primitive type of skin sensitivity that perceives only strong mechanical and temperature stimuli. It contrasts with the more refined and discriminating epicritic sensibility.

In protopathic sensibility, the sensations perceived are not distinctly localized but are diffuse, strong, and painful. Protopathic sensibility does not normally occur in pure form because it is closely associated with epicritic sensibility. When an injured sensory nerve is regenerated, protopathic sensibility is first to appear. This phase of functional regeneration is marked by high thresholds of perception and strong emotional reactions to supraliminal stimuli.

Protopathic sensibility is transmitted principally along the thinnest nerve fibers, which lack a myelin sheath and conduct nerve impulses slowly; it is related chiefly to the spinothalamic system, whose receptive neuron fields are often nonspecific and very large, covering the entire body. This system produces generalized forms of sensation and ensures the transmission of information concerning chiefly qualitative peripheral influences.

The terms “protopathic sensibility” and “epicritic sensibility” are becoming obsolete in medical literature in view of recent studies of the skin’s tactile, temperature, and pain sensitivity.