Group A nerve fibers are one of the three classes of nerve fiber as generally classified by Erlanger and Gasser. The other two classes are the group B nerve fibers, and the group C nerve fibers. Group A are heavily myelinated, group B are moderately myelinated, and group C are unmyelinated.
The other classification is a sensory grouping that uses the terms type Ia and type Ib, type II, type III, and type IV, sensory fibers.
Group B nerve fibers are one of the three classes of nerve fiber as generally classified by Erlanger and Gasser. They are moderately myelinated, which means less myelinated than group A nerve fibers, and more myelinated than group C nerve fibers. They have a medium conduction velocity of 3 to 14 m/s. They are usually general visceral afferent fibers and preganglionic nerve fibers of the autonomic nervous system. They are used in Bainbridge reflex as afferents.