Spinomesencephalic tract:

spinomesencephalic tract represented by the purple nerve fiber traveling up from the spinal cord and synapsing in the periaqueductal grey in the midbrain.

aka spinotectal tract, the spinomesencephalic tract is part of the anterolateral system; it terminates in the periaqeductal grey of the midbrain. The periaqueductal grey is thought to be an area that is important to inhibiting or controlling pain sensations and so the spinomesencephalic tract contributes to that role.

Watch this 2-Minute Neuroscience video to learn more about the spinoreticular tract.