To Yagoub Alyami: There is a fairly recent post on science daily which seems to give a basic answer to myofascial pain as determined by the muscle spindle cells. I don't know if this might help you, or if you are more interested in the molecular level of research, - I know there is a lot of research in that area. A Google search on molecular basis of myofascial pain might shake something out.
What I wanted to know was the explanation of the referral patter of the pain. For instant, when press on a tender SCM muscle, the pain can be felt in the ear or orbital area. I've found the central sensitisation theory (Simon's Model) can explain what causes the referral.
The theory of myofascial pain syndrome (MPS) caused by trigger points (TrPs) seeks to explain the phenomena of muscle pain and tenderness in the absence of evidence for local nociception. Although it lacks external validity, many practitioners have uncritically accepted the diagnosis of MPS and its system of treatment.
Maybe you can find an answer in
A critical evaluation of the trigger point phenomenon
John L. Quintner1, Geoffrey M. Bove2 and Milton L. Cohen3