**7. Effects and uses**

Effect of TENS is based on gate control theory and pain modulation.

TENS stimulates thick, myelinated, sensory fibres (A-fibres), which in turn blocks the impulses of pain-modulating fibres (C-fibres) and closes the gate to pain signals at the level of their entry into the spinal cord. In TENS, low-frequency and high-intensity or high-frequency and low-intensity electrical stimulation is applied, it gives sharp stimulus carried towards cerebellum, and its passage through the midbrain will cause the periaqueductal area of grey matter and raphe nuclei to interact to release opiate-like substance at cord level. The enkephalins and endorphins released have the effect of blocking forward transmission in the pain circuit. TENS treatment also relaxes the jaw muscles, lesser the degree of stress, and reduces the pain [21].

According to the gate control theory, when the large diameter, low-threshold mechanoreceptors are stimulated by simple mechanical stimulation of the receptors in the skin, muscle or joints or by electrical stimulation, the SG cells are stimulated through an excitatory synapse. The SG cells, receiving inputs from nociceptors and mechanoreceptors, integrates and modulates the pain fiber activity and prevents transmission of nociceptive information to higher centers.
