Figure 1.

Descending pain pathways and central sensitization. Descending pain pathways and central sensitization modulate the pain response in the dorsal horn of the spinal cord. Descending analgesic pathways include the serotonin-norepinephrine and opioidergic descending pathways, which dampen pain sensitivity response. Loss of descending analgesia leads to hyperalgesia and allodynia. Central sensitization occurs through the action of glutamate on the N-methyl-D-aspartate (NMDA) receptor, resulting in an increase in intracellular calcium levels and kinase activation, leading to hyperalgesia and allodynia.