Which mechanism does gate control theory propose to reduce pain transmission in the spinal cord?

Which mechanism does gate control theory propose to reduce pain transmission in the spinal cord?

• A. Input from large-diameter fibers can inhibit dorsal horn transmission.
• B. Small-diameter fiber input inhibits transmission.
• C. Descending pathways have no effect on dorsal horn.
• D. Gate control theory does not involve spinal mechanisms.

Answer: (A)

The key idea is a gating mechanism in the dorsal horn of the spinal cord. When large-diameter, non-nociceptive fibers are activated, they engage inhibitory interneurons in the dorsal horn, which suppress the transmission of pain signals carried by small-diameter nociceptive fibers. This inhibition effectively “closes the gate,” reducing pain transmission to higher brain centers. That’s why the mechanism described—input from large-diameter fibers inhibiting dorsal horn transmission—is the best fit. Descending pathways can modulate this gate, so saying they have no effect would be incorrect. Conversely, small-diameter fibers are the carriers of pain signals, so their input tends to promote transmission rather than inhibit, and the idea that gate theory involves no spinal mechanisms is inaccurate.

The key idea is a gating mechanism in the dorsal horn of the spinal cord. When large-diameter, non-nociceptive fibers are activated, they engage inhibitory interneurons in the dorsal horn, which suppress the transmission of pain signals carried by small-diameter nociceptive fibers. This inhibition effectively “closes the gate,” reducing pain transmission to higher brain centers.

That’s why the mechanism described—input from large-diameter fibers inhibiting dorsal horn transmission—is the best fit. Descending pathways can modulate this gate, so saying they have no effect would be incorrect. Conversely, small-diameter fibers are the carriers of pain signals, so their input tends to promote transmission rather than inhibit, and the idea that gate theory involves no spinal mechanisms is inaccurate.