Peripheral Mechaniism of Muscle Nociception and Local Muscle Pain

Abstract

Objectives: In medical practice muscle pain is by far more frequent and important than is cutaneous pain. However, the bulk of experimental data on pain mechanisms has been obtained in studies dealing with cutaneous nociception. The present report gives an overview of the neuroanatomical and neurophysiological literature on muscle pain and tries to draw parallels between experimental data and symptoms in patients. Findings: The neurophysiological basis of local muscle pain is an increased impulse activity in muscle nociceptors. histologically, muscle nocicpetors are probably free nerve endings that are connected to the spinal cord by fine afferent fibers. Nociceptors can be excited by tissue-threatening stimuli and are not or only liminally activated during phsyiological muscle activity. Endogenous substances such as bradykinin have a sensitizing action on nociceptors. The tenderness of a lesioned muscle can be explained by an activation of sensitized nociceptors by weak mechanical stimuli. Ischemia [hypoxia] and adrenaline sensitize and activate muscle nociceptors, particularly if they are irritated by an additional lesion. Local vicious cycles are discussed as a possible cause of the formation of trigger points. Conclusions: The data show that at least some symptoms of muscle pain in patients can be explained by results obtained in animal experiemtns. One example is the tenderness of lesioned muscle caused by sensitization of muscle nociceptors.

KEYWORDS:

• Muscle nociceptor
• free nerve ending
• sensitization