Primary afferent nociceptors

Published on January 26, 2009   43 min

A selection of talks on Clinical Practice

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The development of the nociceptor concept. As many scientists in the previous centuries, the famous philosopher Rene Descartes believed that pain can be caused by the stimulation of any nerve in our body. The often recorded drawing from his book on the functioning of the human body may illustrate this. According to his assumption, pain is induced by noxious stimuli which over-excite all kinds of nerves. Any nerve will transmit an alarm signal into the brain, which leads to pain. This assumption has been called intensity hypothesis.
In the late 19th century, the German physiologist, Max von Frey, challenged this assumption. Nowadays, he's best known for the development of the Von Frey hairs, which allow application of graded mechanical stimulation to the body surfaces. The figure in blue shows an original depiction of this device in a paper of Von Frey published in 1897. The pointed stiff hair, nowadays, usually a nylon filament of defined diameter is used, attached to a handle, is pressed against the skin so that it slightly bends. The exerted pressure defines the strengths of this stimulus. With this simple device, Von Frey made the discovery which made him famous, the pain points in the skin. He writes in one of his papers: "It is possible to stimulate the skin in such a way as to produce a painful sensation with no proceeding or accompanying pressure sensation. That this can be done leads to the conclusion that pain is the result of exciting special organs. The pain points are a sign of the irregular distribution of specifically pain sensitive organs over this skin." The characteristic features of the pain points are: they can be distinguished from touch, warmth and cold points. The stimulation induces a sustained, often increasing pain sensation. And they require stronger deformation than touch points.