The Pain Truth: What is Pain?

How is the nebulous and murky nature of pain explained?

| July 2016

In The Sting of the Wild, (Johns Hopkins University Press, 2016) the colorful Dr. Justin O. Schmidt takes us on a journey inside the lives of stinging insects, seeing the world through their eyes as well as his own. He explains how and why they attack and reveals the powerful punch they can deliver with a small venom gland and a "sting," the name for the apparatus that delivers the venom. We learn which insects are the worst to encounter and why some are barely worth considering. With colorful descriptions of each venom’s sensation and a story that leaves you tingling with awe, Dr. Schmidt’s one-of-a-kind style will fire your imagination.

To find more books that pique our interest, visit the Utne Reader Bookshelf.

What is Pain?

Everybody knows what pain is. It is the sensation felt when a knee is scraped in a fall, the skin is overexposed to the sun, or a bare foot steps on a bee. Pain is familiar, yet mysterious. We know pain when we sense it. Pain is clearly recognizable. Warmth is not pain, though it can become pain if too much heat is experienced. Likewise, chills caused by cold temperatures are clearly unpleasant, but they are not pain. Cold, like warmth, can produce elements of pain but is not classic pain. As the tobogganing kid knows, toes get wet, cold, and unpleasant but not usually truly painful like a stubbed toe. But, oh wait until the true pain comes as the toes warm before a toasty fireplace. Though we might call stomach upset and nausea painful, is it really pain? We call nausea “pain” for lack of a proper descriptive word, but everybody knows nausea pain is different and, I would argue, far more unpleasant than the pain of a runner’s stitch caused by the spleen contracting to squeeze more red blood cells into the bloodstream to provide acutely needed oxygen to muscles.

We know pain when we feel it. Do we know physiologically and medically what pain really is? The response gets murky. Describing actions that cause pain — slamming one’s finger in a door, for example — is simple. Distinguishing pain from nonpain is generally easy. Hunger, though often called pain, is certainly different from the pain of a stomach ulcer caused as acids eat into and destroy stomach tissues. Again, we lack a common, distinguishing word for hunger pain, though perhaps “hunger pangs” is a proper phrase that when spoken sounds the same as “hunger pains.”

There may be no universal consensus on what is and what is not pain. We generally recognize pain as a distinct experience, one that presents in a variety of flavors. Common pain is the sensation felt when skin is damaged, a tooth injured, a bone broken, a muscle pulled, the spleen makes a stitch, or a variety of other mostly dermal or skeletal-muscular problems. Another broad category, visceral pain, is experienced when visceral organs signal damage or potential damage. The visceral pain resultant from tonsillectomy in adults, hemorrhoid surgery, childbirth (I am told), or other sources one hopes to rarely experience is distinctly different from common pain and a considerably less pleasant form of pain. Headache pain is another category of pain. The point of this discussion is not to define pain concretely, to make a pain phylogenetic “family” tree, or even to claim that all the separations above are clear-cut (they are not); the point is to illustrate just how complicated and murky pain is.

How is the nebulous and murky nature of pain explained? What is the cause of this lack of tidiness, both in descriptive language and in real-life sensation? Several poorly defined explanations can be offered. A medical explanation might focus on the separate pathways of nerves and distal structures between the motor and autonomic nervous systems and the sensory nervous system. Action potentials sent from the brain to muscles travel down different nerve axon pathways than pain signals generated when the tongue is bitten. Signals to the brain originate from receptors located throughout the body. Many of these receptors are sensory receptors that detect temperature, pressure, stretch, chemicals, itch, or a variety of other sensations, including pain. The signals from these receptors are transmitted to higher nervous centers in the spinal cord and brain through fine nerves of the separate sensory nervous system. Matters become more subtle. Pain and itch, for example, are separate sensations.1 Are they related, that is, is one just a smaller degree than the other? No, they are not simply degrees of difference, and, unfortunately, how they relate is unclear and an active topic of research. Is the tickle sensation related to the pain and/or itch sensation? Again no tidy answer is forthcoming. Complicating the issue further is the feature that tickling can be a pleasant sensation, especially in social situations, or it can be an excruciatingly unpleasant experience. How are the two tickle responses related? In degrees of stimulus? The difference is unclear.