TENS units work by delivering small electrical impulses through electrodes that have adhesive pads to attach them to a person’s skin. These electrical impulses flood the nervous system, reducing its ability to transmit pain signals to the spinal cord and brain. HOW DOES TENS WORK? Pain modulation: For pain to be perceived there is usually a chain whereby peripheral receptors are stimulated by a noxious physical or chemical agent and this stimulus is carried by peripheral nerves to the spinal cord, up to the cord, through the brainstem and so to the cerebral cortex, where the pain is appreciated by the conscious level. This route necessarily involves a number of synapses and the inhibition of impulses on their route to the cortex is the mechanism whereby pain can be modulated. Nociceptive nerve endings may be stimulated by the chemicals released by tissue injury or accumulated as a result of metabolic activity, and thus creating an electrical potential. The degree of stimulation produced is governed by the number of chemicals present. It is postulated that the removal of these chemicals from the area may help reduce the level of nociceptive stimulation and thus the physiotherapeutic agents (ice and heat) affecting the circulation may help achieve this. The nociceptive stimulus is carried to the cord along with either a slow-conducing, non-myelinated C fiber or a faster-myelinated Ad (delta) fiber. Both will eventually enter the cord via the posterior route. It is postulated that as both of these fibers have a maximum frequency at which they can conduct that if a higher frequency of stimulation is applied, a physiological block o conduction might occur. TENS produces this required frequency and so has this effect. A TENS unit has controls that allow people to administer an appropriate level of pain relief

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