In this mouse lung, pain fibers
catch a whiff of the spicy chemical in hot peppers and recruit immune cells (green), which can crank up inflammation.
"Thermocoagulation"which uses heat supplied by an electrical current to destroy nerve cells-has the advantage that pain fibers
are more sensitive to the treatment resulting in less destruction of other sensations (touch and temperature).
The pain message starts with the stimulation of special pain fibers
in the nerve endings embedded in the skin.
Because the histamine-sensing itch fibers could not detect itchy mechanical stimuli, like a scratchywool sweater, the researchers turned to another likely culprit: pain fibers.
Pain fibers (green) of the same class follow a similar pathway.
Indeed, in animal models of chronic pain, neuronal connections are altered in the spinal cord such that touch and pressure excite true central pain fibers. New evidence suggests that changes in innervation associated with chronic pain may also affect peripheral organs (FIGURE).
Women undergoing surgery for painless conditions had a low density of pain fibers in the lower uterine segment compared with women who had chronic pain before surgery, who had a higher density of pain fibers.
Paul Ranalli, writing in NRL News, has observed, "Careful anatomical studies reveal, in fact, that the ascending pain fibers
reach the cortex by 20 weeks.
The descending pain modulation system runs parallel to the pain fibers, involving the cortical and diencephalic systems, mesencephalic systems (periaquaductal gray) to the nucleus rapine magnus which exerts an effect on the dorsal horn.
In the wake of prolonged stimuli and sensitization, an intracellular build-up of calcium ions further increases sensitivity, while stimulating protein synthesis which initiates the process of nerve growth in the affected and surrounding neurons. As the pain fibers grow and make new connections, the pain spreads and persists while the inhibitory nerves which serve to dampen messages of pain are slowly destroyed and the neurochemical systems related to control of EAAs, serotonin, norepinepherine, opiates and GABA become dysfunctional.[4,10] When unpleasant stimuli persists for longer than 24 hours, this process begins, particularly with the small, unmyelinated C-fibers that are associated with the more bothersome type of pain.
Vulvar vestibulitis is now often viewed as neuropathic pain--that is, the activation of local pain fibers
that appears to be strikingly out of proportion to any demonstrable tissue damage.
not only transmit pain but also promote inflammation in the blood vessels and other tissues they innervate.