Activation of which of the following fiber result in first pain which help to localize the site and intensity of the noxious stimulus:

Activation of A delta fiber releases glutamate, and is responsible for first pain (also called fast pain or epicritic pain) which is a rapid response and mediates the discriminative aspect of pain or the ability to localize the site and intensity of the noxious stimulus. Adelta fibers are thinly myelinated, 2-5 microns in diameter and conduct at rates of 12-35 m/s. Activation of C fibers releases a combination of glutamate and substance P, and is responsible for the delayed second pain (also called slow pain or protopathic pain) which is the dull, intense, diffuse, and unpleasant feeling associated with a noxious stimulus. Unmyelinated C fibers are 0.4 -1.2 m in diameter and they conduct at low rates of 0.5-2 m/s. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 8. Somatosensory Neurotransmission: Touch, Pain, and Temperature. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.