Anterolateral pathways

The Anterolateral pathways convey temperature and pain sensations, and poorly discriminated touch sensation as shown in figure. The primary afferents are small diameter high threshold dorsal root ganglion (DRG) cells driven by nociceptors and low threshold DRG cells excited by thermoreceptor or mechanoreceptor input.

The small diameter fibers, situated laterally in the dorsal roots, enter Lissauer’s tract, where they divide into ascending and descending branches that enter the dorsal horn within a couple of segments. Nociceptive Aδ afferents synapse with projection neurons in laminae I and II, and with the distal dendrites of lamina V cells, although visceral and muscle nociceptors do not project to lamina II. Nociceptive C fibers synapse with other laminae I and II neurons. Large diameter fibers from mechanoreceptors enter the dorsal horn medially and synapse with neurons in deeper Rexed laminae (IV–VIII). Axons of dorsal horn cells either cross the midline within 1 or 2 segments, or remain ipsilateral, to ascend in the anterolateral columns.