Fig. 1.

Nociceptive pathways in the dorsal root ganglia (DRG) and central nervous system. Axons of nociceptors transmit information from the periphery to second-order neurons in the dorsal horn of the spinal cord. Neural connections from the dorsal horn to the thalamus and from there to the cortex relay this noxious information to higher centers of the central nervous system. The central axons of primary afferent nociceptive neurons also provide information to polysynaptic spinal cord interneurons, which are essential for the withdrawal reflex. Descending pathways originating in the cortex and/or midbrain provide modulatory feedback signals at the level of the spinal cord. Impulses can also travel back along the peripheral axon toward the distal nerve endings, resulting in neurogenic inflammation