a major somatosensory system consisting of nerve fibers that originate mostly from dorsal horn cells and ascend in the white matter of the spinal cord, conveying information about pain, temperature, and touch to higher centers. It includes the spinothalamic tract; the spinoreticular tract, traveling through the spinal cord to the reticular formation of the brainstem; and the spinomesencephalic tract, traveling through the spinal cord to the mesencephalon (midbrain).