Figure 7.8: Pain receptors in the skin The pain receptors are the sensitive endings of sensory neurons, called free nerve endings. The slower second wave of pain is carried by the very thin C fibers, and the faster first wave is carried by the thicker A-delta fibers. The sense of touch is carried by still thicker (and faster) A fibers, whose endings are not “free” but, rather, are surrounded by a capsule, or end organ, that modifies the pressure stimulus.