Which nerve fibers primarily transmit slow, dull, burning nociceptive pain?

• A. A-delta fibers
• B. A-beta fibers
• C. C fibers
• D. Interneurons

Answer: (C)

Slow, dull, burning pain is carried mainly by unmyelinated C fibers. These small, non-myelinated fibers conduct slowly (about 0.5–2 m/s), so the pain signal arrives later and lasts longer, producing the characteristic second, lingering pain described as burning or ache. They are polymodal nociceptors, activated by chemical mediators released during tissue injury (like histamine and bradykinin) as well as thermal and mechanical stimuli. The signal travels from peripheral free nerve endings through the dorsal root ganglion into the dorsal horn and then up the spinothalamic pathway to the cortex, where it’s integrated with emotional and motivational aspects, giving diffuse, poorly localized pain that can persist after the initial injury. By contrast, A-delta fibers are fast and convey the initial sharp pain, A-beta fibers handle non-nociceptive touch, and interneurons are CNS cells that modulate transmission rather than serve as the primary conduits for nociceptive signals.