Which mechanism explains how heat can offset painful input via the spinal gate?

• A. Endorphin release
• B. Gate Control Theory
• C. Pain amplification
• D. Peripheral sensitization

Answer: (B)

Heat offsets painful input through a spinal gating mechanism. When warmth (non-painful input) activates large-diameter A-beta fibers, these signals stimulate inhibitory interneurons in the dorsal horn of the spinal cord. This inhibitory action reduces the transmission of pain signals carried by small-diameter A-delta and C fibers to the next neurons that project to the brain. In other words, the “gate” at the spinal level closes somewhat due to competing non-painful input, diminishing the brain’s perception of pain. Endorphin release is another way to modulate pain, but the specific mechanism described here is the spinal gate effect. Pain amplification and peripheral sensitization would tend to increase pain rather than offset it.