Which fiber type has a diameter range of 0.4-1.2 um?

Which fiber type has a diameter range of 0.4-1.2 um?

• A. A fibers
• B. C fibers
• C. D fibers
• D. B fibers

Answer: (B)

Diameter and myelination determine how fast a nerve signal travels. The small-diameter, myelinated fibers fall into a narrow range around 0.4 to 1.2 micrometers, which is the window described for the small, myelinated class. These fibers are autonomic preganglionic fibers—smaller than the large A fibers but faster than unmyelinated options because the myelin sheath speeds conduction even when the diameter is small. The given range lines up most closely with this small, myelinated group, making it the best fit. In contrast, the large A fibers are much bigger, and the unmyelinated C fibers, while also small, lack myelin and conduct more slowly.

Diameter and myelination determine how fast a nerve signal travels. The small-diameter, myelinated fibers fall into a narrow range around 0.4 to 1.2 micrometers, which is the window described for the small, myelinated class. These fibers are autonomic preganglionic fibers—smaller than the large A fibers but faster than unmyelinated options because the myelin sheath speeds conduction even when the diameter is small. The given range lines up most closely with this small, myelinated group, making it the best fit. In contrast, the large A fibers are much bigger, and the unmyelinated C fibers, while also small, lack myelin and conduct more slowly.