(i) The structure and function of the meridian (channel and collateral) described by ancient medical doctors may correspond to the blood circulation, nerve control and neurohumoral modulation of modern medicine. (ii) The needling, which can injure the tissue, is a noxious stimulation inducing pain. Acupuncture manipulation, such as lifting and thrusting, twisting and twirling, or electroacupuncture (EA) with the sufferable biggest intensity for patients should be a stronger pain stimulation. The needling sensation of soreness, numbness, distension and heaviness is a deep pain. (id) There is an intrinsic analgesic system in brain, which centers around the periventricular and periaqueductal grey matter, contains endorphins as possible mediators, goes through the descending inhibition system in medulla oblongata, and acts on the gating mechanism in spinal cord. It could be producing analgesia while the system is activated. (iv) NRM might be a supraspinal center modulating pain, and the R-S neurons could form a basic circuit of negative feedback modulating pain. The discovery of excitatory-inhibitory reversible R-S neurons may give a neurophysiological explanation for the double direction modulation of acupuncture at acupoint. (v) Non-noxious stimulation such as massage or stroking could excite type I and II afferent fibers, producing a weaker and transient analgesia through the spinal mechanism. When the acupoint is near the pain area, the afferent information from them could be converged on the same and neighboring spinal segments, the light acupuncture or low intensity of EA also has analgesic effects, showing acupoint specificity. But the acupoint specificity is not limited in a specially designated channel line, and it is closely related to the segment of innervation. (vi) While acupuncture manipulation of lifting and thrusting, twisting and twirling or a high intensity of EA is used, because the intensities of these stimulations exceed the threshold of afferent C fibers, they could fully excite III(A(delta)) and IV(C) afferent fibers, producing a strong and lasting analgesia, mainly through the supraspinal negative feedback mechanism modulating pain, it has curative effects. Therefore, the essence of acupuncture analgesia may chiefly be inhibiting pain with pain.
