Figure 1.

Gate Control Theory. Both small and large fibers from the periphery come into the substantia gelatinosa. Generally, larger fibers carry general somatosensation information while smaller fibers carry nociceptive information. The two fiber types summate in the substantia gelatinosa. If the signal carried by the nociceptive fibers is stronger than the general sensation signal, a pain stimulus can be passed from the substantia gelatinosa toward the brain. Descending modulatory fibers interact with pain signals in the substantia gelatinosa.