Cannon's law of denervation states that when a tissue is deprived of its nerve supply, it will develop hypersensitivity to its own neurotransmitter(s).
Adult and Pediatric Urology, Volume 2
Lippincott Williams & Wilkins, 2002
An enigma in the past, and today a source of great interest to neurobiologists, the importance of denervation supersensitivity with regard to pain has not been appreciated. The implications of Cannon's Law of denervation are probably far more embracing than the few conditions briefly discussed here. It is possible that many other forms of pain, eg, trigeminal or postherpetic (neuralgic) and even chronic low-back pain, are a postdenervation supersensitivity phenomenon rather than the result of noxious stimuli. Thus, pain may be the central perception of 1) an afferent barrage from noxious stimuli or 2) the abnormal input into the central nervous system from ordinarily non-noxious stimuli rendered excessive through overly sensitive receptors (or a variable combination of both). Consider, therefore, the chronic "low back" patient whose discomfort still persists following resolution of the acute phase. Though not crippled or even in distress, he is unable to cope with any but light activities. Such a patient many not be "hyperalgesic" in that ordinarily non-noxious stimuli, eg, prolonged standing, sitting, or walking, can cause symptoms. "Pain" as a scientific term should preferably be discarded and a distinction made between "nociception" and "hyperalgesia," because different approaches are required in their management.
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