Fig 4.
Schematic diagram showing ascending and descending pathways. Ascending touch pathways include the dorsal column–medial lemniscus. Touch sensation transmits via heavily myelinated Aβ fibers that ascend in the ipsilateral dorsal columns to the gracile or cuneate nuclei in the brain stem. Ascending pain pathways include the anterolateral pathway, which is a combination of the spinothalamic, spinoreticular, and spinomesencephalic pathways. Pain sensation transmits via thinly myelinated Aδ fibers and unmyelinated C primary afferent fibers. Descending fibers modulate touch and pain sensation.54 Red highlights descending pathways from the cortex, blue shows descending modulation from the reticular formation, and green highlights descending modulation from the raphe nuclei. PRF = pontine reticular formation; NRM = nucleus raphe magnus, RVM = rostral ventromedial medulla, MRF = medullary reticular formation. Pathways are drawn according to selected publications.34,53–55