Acupuncture is a specialised sensory stimulation that is analysed through sensory neural pathways. Therefore to understand its action we have to analyse the anatomy, physiology and pharmacology of the nervous system, aided with a knowledge of neuroendocrinology and the chemoarchitecture of the brain. Various neural theories have been developed to explain the mechanisms of acupuncture. It is now evident that acupuncture reacts at local, regional (spinal cord) and general (brain) levels. Therefore, inserting one or more needles at particular points (or areas) of the body activates neural pathways on three different levels, provoking local, regional, and general reactions.
The local reaction is a multifactorial phenomenon. The electric injury potential due to the needle, the presence and synthesis of opioid peptides at the site of injury, and substance P, histamine like substances, bradikinin, serotonin and proteolitic enzyme release around the needle, all occur during needling.
The regional reaction concerns the activation of a larger area (2–3 dermatomes) via reflex arches. We can analyse the viscero-cutaneous, cutaneo-visceral, cutaneo-muscular and viscero-muscular reflexes and also the vegetative, stretch and polysynaptic segmental reflexes.
The general reaction mainly activates the brain central mechanism of internal homoeostasis. We can explain the action of acupuncture in acute and chronic pain syndromes, in addiction and in psychiatric disease through the role of central neurotransmitters and the modulatory systems that are activated by acupoints: opioid, non-opioid and central sympathetic inhibitory mechanisms.