Which nerve fiber type is responsible for fast, sharp, well-localized pain and is typically myelinated?

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

Answer: (B)

Fast, sharp, well-localized pain is transmitted by A-delta fibers. These thinly myelinated nociceptive fibers conduct rapidly, producing the initial, high-quality pain that you can pinpoint to a specific spot right after a damaging stimulus. The quick conduction and precise localization come from their myelin and small diameter, which allow fast signal travel to the spinal cord and up to the somatosensory cortex for pinpoint localization. In contrast, unmyelinated C fibers carry slower, dull, aching pain with diffuse localization, large-diameter A-beta fibers convey non-nociceptive touch and can modulate pain, and B fibers are autonomic preganglionic fibers not primarily involved in nociceptive signaling.