Neurobiological basis of muscle pain

Mechanisms in the lesioned muscle:The peripheral mechanism underlying the t enderness and pain during movement of a damaged muscle is the sensitization of muscle nociceptors. Ongoing activity of nociceptors causes spontaneous pain in addition to tenderness. Muscle pain (particularly that originating in myofascial trigger points) is often mislocalized because it is referred to other deep somatic tissues. The development of trigger points is a purel y peripheral event, whereas the referral of muscle pain is based on central nervous mechanisms. Mechanisms at the spinal level: The input from muscle nociceptors induces n europlastic changes in the spinal cord and higher centres of the central ne rvous system. These changes are associated with an overexcitability of neur ones (central sensitization) and contribute to hyperalgesia of patients. Re sting activity of spinal neurones (and hence spontaneous pain) is strongly dependent on nitric oxide (NO). A muscle lesion is likely to lead to an inh ibition of the homonymous muscle, it can, however, elicit spasm in another muscle. Supraspinal mechanisms: Spinal neurones that mediate muscle pain are subjec ted to a strong descending inhibitory influence. The inhibitory tracts orig inate in the mesencephalon and medulla oblongata. A dysfunction of this inh ibitory system might be involved in the pathogenesis of fibromyalgia.