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.
James P. Lund, Somayeh Sadeghi, Tuija Athanassiadis, Nadia Caram Salas, François Auclair, Benoît Thivierge, Isabel Arsenault, Pierre Rompré, Karl-Gunnar Westberg, Arlette Kolta: Assessment of the Potential Role of Muscle Spindle Mechanoreceptor Afferents in Chronic Muscle Pain in the Rat Masseter Muscle PLoS One June 2010; volume 5, issue 6, e11131.
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