Figure 3.

The experience of pain depends on efficient transmission of nociceptive information from peripheral nociceptor neurons to second order interneurons in the spinal cord, and then onto supraspinal structures. First-order primary afferent neurons transmit nociceptive signals from a peripheral stimulus site to the spinal cord via the dorsal root ganglion and synapse with second-order nociceptive projection neurons in the spinal dorsal horn. Secondary order projection neurons ascend in the contralateral spinothalamic and spinoreticular tracts that relay the signal to cortical centers. Descending pathways projecting from the periaqueductal gray (PAG) in the midbrain and the rostral ventromedial medulla (RVM) to the dorsal horn influence pain transmission.