What properties characterize A delta and C fibers?
A delta fibers are small-diameter (1 to 6 µm), myelinated primary afferent fibers; C fibers are smaller-diameter (1.0 µm) unmyelinated primary afferents. The A delta fibers conduct at velocities between 5 and 25 milliseconds; C fibers conduct at 1.0 µm/sec. Many C fiber nociceptors are polymodal and respond to thermal, mechanical, and chemical noxious stimulation. Other primary afferent nociceptors respond more selectively to noxious thermal or mechanical stimulation. It is unclear whether there are specific neurotransmitters associated with the modality subtypes of A delta and C fibers.
