Page "Pain" Paragraph 29

The pain signal travels from the periphery to the spinal cord along an A-delta or C fiber.

Because the A-delta fiber is thicker than the C fiber, and is thinly sheathed in an electrically insulating material ( myelin ), it carries its signal faster ( 5 – 30 m / s ) than the unmyelinated C fiber ( 0. 5 – 2 m / s ).

Pain evoked by the ( faster ) A-delta fibers is described as sharp and is felt first.

This is followed by a duller pain, often described as burning, carried by the C fibers.

These first order neurons enter the spinal cord via Lissauer's tract.