Damage to stretch-sensitive nerve filaments may contribute to chronic muscle pain

Chronic muscular pain may be linked to a previously unknown principle for how pain signals are transmitted in the human body. This is shown by Umeå University researchers Tuija Athanassiadis and Karl-Gunnar Westberg, in collaboration with Canadian associates, in the scientific journal PLoS One.

Muscles have sensory organs called muscle spindles. Their task is to inform the brain of changes in muscle length. Muscle spindles therefore contain a special type of large diameter nerve filaments that signal stretch of the muscle. The Umeå scientists' studies show that muscle spindles also contain fine nerve filaments with pain receptors. When a muscle is damaged as a result of overloading, these pain receptors are activated by the release of a signal substance from the neighboring stretch-sensitive nerve filaments in the muscle spindle.

It was previously believed that the pain receptors in muscles were exclusively found in the membranes that surround the muscles or in connection with the blood vessels in the muscle. With these new findings the Umeå researchers are drawing attention to a hitherto unknown and interesting mechanism. Damage to the stretch-sensitive nerve filaments of the muscle spindle may contribute to and sustain chronic pain in jaw muscles as well as in other muscles.