Enkephalin response blocks gate by interfering with which fibers’ transmission?

Enkephalin response blocks gate by interfering with which fibers’ transmission?

• A. A-delta and C-fiber T cells
• B. A-alpha and A-beta T cells
• C. A-delta and A-beta T cells
• D. C-fiber and A-gamma T cells

Answer: (A)

Pain signals are gated at the spinal dorsal horn, and enkephalin modulates that gate by dampening nociceptive input. Enkephalin is released by interneurons in the substantia gelatinosa and acts on opioid receptors to inhibit transmission from the small-diameter nociceptive fibers. Presynaptically, it reduces the release of excitatory neurotransmitters from these fibers, and postsynaptically it makes the dorsal horn neurons less excitable. This dual action lowers the signal that travels to higher brain centers, effectively closing the gate for these inputs. The fibers involved are the A-delta and C fibers, which carry fast and slow pain signals; by contrast, the larger A-beta and A-alpha fibers transmit non-painful touch and proprioception and are not the primary targets of enkephalin in this context.

Pain signals are gated at the spinal dorsal horn, and enkephalin modulates that gate by dampening nociceptive input. Enkephalin is released by interneurons in the substantia gelatinosa and acts on opioid receptors to inhibit transmission from the small-diameter nociceptive fibers. Presynaptically, it reduces the release of excitatory neurotransmitters from these fibers, and postsynaptically it makes the dorsal horn neurons less excitable. This dual action lowers the signal that travels to higher brain centers, effectively closing the gate for these inputs. The fibers involved are the A-delta and C fibers, which carry fast and slow pain signals; by contrast, the larger A-beta and A-alpha fibers transmit non-painful touch and proprioception and are not the primary targets of enkephalin in this context.