Which statement best describes the mechanism by which TENS reduces pain?

• A. Blockade of nociceptive fibers
• B. Stimulation of mechanoreceptors can override pain impulses
• C. Direct chemical analgesia
• D. Activation of the sympathetic nervous system

Answer: (B)

TENS reduces pain mainly through a gate control mechanism: stimulating large-diameter mechanoreceptors activates fast A-beta fibers, which engage inhibitory interneurons in the dorsal horn of the spinal cord. This inhibition dampens the transmission of nociceptive signals from small-diameter fibers up to the brain, so the perception of pain is lessened. In other words, non-painful input from the TENS stimulation can override the pain impulses by altering how the spinal cord processes those signals. This is different from physically blocking nociceptor signals, producing chemical analgesia, or activating the sympathetic system, which do not capture the primary way TENS modulates pain.