Acupuncture needles stimulate the central nervous system via peripheral receptors to give the brain information. Thermoreceptors, mechanoreceptors, chemoreceptors, and photoreceptors all tell the brain-specific information so it can act on the stimulus. Local insertion of an Acupuncture needle causes light inflammation so that the body can bring in more white blood cells, increase blood flow and stimulate the immune system to bring in macrophages to clean the area up. For example, working on arthritis with local needling would produce an effect on healing the area. A more robust and farther-reaching effect of Acupuncture is systemic. Acupuncture releases enkephalins, endorphins, serotonin, etc. These neurotransmitters and hormones are why acupuncture is so effective for pain and balances the endocrine system. Releasing these substances helps to down-regulate pain signals in the midbrain and is quite effective for chronic pain syndromes with no known functional cause.