It is generally recognized that the 'Pain gate' can be shut by stimulating nerves responsible for carrying the touch signal (mechaoreceptors) which enables the relief of pain through massage techniques, rubbing, and also the application of wheat bags and ice packs. The Gate can also be shut by stimulating the release of endogenous opioids which are opioid (pain-relieving) type chemicals released by the body in response to pain stimuli.  Acupuncture and electrical analgesia (TENS) is thought to stimulate their release as a response to stimulation, the opioids then inhibiting the transmission of pain signals in the substantia gelatinosa part of the spinal cord - what is often referred to as the spinal root part of the nerve.