Postganglionic fibers are typically ________ and __________; leading to a ________ conduction velocity.

• A. myelinated and larger; faster
• B. myelinated and smaller; slower
• C. unmyelinated and smaller; slower
• D. unmyelinated and larger; faster

Answer: (C)

Conduction velocity depends on whether the fiber is myelinated and how big its diameter is. Postganglionic autonomic fibers are typically unmyelinated and have a relatively small diameter. Without myelin, conduction cannot jump between nodes, and the small diameter raises internal resistance, both of which slow the speed of transmission. That combination—unmyelinated and small—produces slower conduction velocity, which is why this option is the best description.

In contrast, fibers that are myelinated and larger conduct signals much faster due to saltatory conduction and lower internal resistance, so those descriptions don’t fit postganglionic autonomic fibers.