Which statement about nerve fibers is true?

• A. A fibers are the largest diameter fibers and include both sensory and motor types.
• B. B fibers are larger.
• C. C fibers are larger and faster.
• D. A fibers have only motor functions.

Answer: (A)

The main idea is how nerve fibers differ by diameter and myelination, which determines how fast they conduct signals and what they carry. The largest diameter, myelinated fibers are the A fibers, and they handle both directions of information: they include motor fibers that travel from the CNS to skeletal muscle and sensory fibers that carry touch and proprioceptive information from the periphery. That combination of large size, fast conduction, and mixed sensory–motor roles is what makes the statement true. In contrast, other fibers are smaller or unmyelinated and tend to be more limited in function (for example, autonomic fibers or slow, dull pain fibers), and A fibers are not restricted to motor functions alone.