What spinal cord region is associated with where fast and slow pain fibers synapse?

The substantia gelatinosa plays a crucial role in processing pain signals within the spinal cord. It is located in the dorsal horn of the spinal cord and is specifically involved in the modulation of sensory information, particularly related to pain.

Fast pain fibers, which carry sharp, immediate pain sensations, synapse here along with slow pain fibers responsible for dull, aching pain. The substantia gelatinosa contains various types of neurons that can inhibit or facilitate pain signals, thereby influencing how pain is perceived and processed by the central nervous system. Through its connections, it also communicates with higher brain centers, making it a key region for pain modulation.

Although the gracile and cuneate nuclei are associated with fine touch and proprioception, they do not primarily deal with pain fibers. The internal arcuate fibers are pathways that convey proprioceptive and fine touch information to the thalamus and do not play a significant role in pain perception. Hence, the substantia gelatinosa's involvement with both fast and slow pain fibers makes it the correct answer in this context.