Which nerve fibers are myelinated and transmit pain signals rapidly?

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

Answer: (C)

Fast, sharp pain is carried by myelinated nerve fibers called A-delta fibers. Their thin myelin sheath and small diameter let them conduct impulses quickly, typically around 5–30 meters per second, so the sudden, well-localized pain you feel right after an injury is transmitted rapidly to the brain. In contrast, C fibers are unmyelinated and convey slow, dull, aching pain that is harder to localize, while A-beta fibers are larger, heavily myelinated fibers that carry touch and proprioception rather than pain. B fibers are autonomic and not primarily involved in rapid pain signaling. Hence, the fast, well-localized pain signal comes from A-delta fibers.