evokes appropriate protective reflexes and/or behaviors. An example of an acute, protective, nociceptive reflex is withdrawing your finger from a heated surface you touch unexpectedly. If you analyze the event, you will note that you actually removed your finger from the heated surface before you perceived the event as painful. Another more common type of protective pain is that associated with tissue inflammation and tissue repair. One common example is postsurgical pain, which is longer lasting than the pain produced when one touches a heated surface.

Nonprotective Pain

There is also pain that I consider abnormal because it serves no protective value. Examples of these types of pains in humans are those associated with terminal cancer, nerve injury, and after a stroke. Some of the pain syndromes

Figure 2 Pain that might be considered “normal” typically serves a protective function. Acute noxious stimulation, such as unexpectedly touching a hot surface or pricking a finger with a needle, evokes a nociceptive withdrawal reflex that, for example, prevents us from further burning our finger. After tissue injury associated with inflammation and repair processes, the injured tissue exhibits enhanced sensitivity to stimulation, termed hyperalgesia (see text and Figure 3). The enhanced sensitivity (e.g., to pressure applied to a sprained ankle or at the site of a surgical incision) is also normal and protective, preventing us from further damaging already injured tissue. Pain that might be considered “abnormal” provides no protective function. Nonprotective pains include those associated with cancers, peripheral and central nervous system damage (e.g., following a stroke), and others often classified as chronic. These pains certainly tell us that something is wrong, but they serve no protective function.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement