Biology 30 – Nervous System Practice Exam

Pain signals come from two main types of nerve fibers that differ in speed and the quality of pain they carry. A-delta fibers are myelinated and larger, so they conduct impulses quickly. This rapid transmission produces the initial, well-localized, sharp pain you feel right after an injury—the first pain. In contrast, C fibers are unmyelinated and smaller, so they conduct more slowly and relay a dull, burning, aching pain that lasts longer and is less easy to pinpoint—the second pain.

So the best description is that A-delta fibers carry fast, sharp pain, while C fibers carry slow, dull pain. This difference in conduction speed and pain quality stems from their myelination and axon diameter.