Complex sentence: They are considered to be part of the autonomic nervous system, however unlike the efferent fibers of the autonomic nervous system, the afferent fibers are not classified as either sympathetic or parasympathetic.
Split into simpler sentences: They are considered to be part of the autonomic nervous system. However, unlike the efferent fibers of the autonomic nervous system, the afferent fibers are not classified as either sympathetic or parasympathetic.