Needling acupuncture points stimulates the nervous system to release endorphin and serotonin. These natural chemicals change the experience of pain and influence the body’s own internal regulating system. Many of the main points used such as Stomach 36 and Liver 3 are near many nerve endings. This could explain their effectiveness at treating a wide variety of symptoms. Acupuncture is a very old medical art in itself with origins dating back aprrox. 5000 years
Fascia connective tissue is what connects the acupuncture channels and navigates the paths they take from the internal to the external, interweaving through the various channels and organs. This explains how acupuncture can influence the various organs and bodily systems. There are electrial impulses continuously being emitted through our body some theories suggest this is in part how acupuncture works.
MRI imaging as shown a change in the function of the brain and how it perceives pain when one has acupuncture needles in with the change lasting up to a few days. I think it is a combination of these various theories as well as the intention of the practioner and the receptiveness of the patient to heal.