The anterolateral pathways are composed of three tracts: the spinothalamic, spinoreticular, and spinomesencephalic tract. Separate aspects of pain are conveyed through the spinothalamic tract, so we will follow the course of those neurons first. The first-order neuronal cell body of axons forming the spinothalamic tract is located in a spinal ganglion (eFig. 9.52). Axons then enter the spinal cord through the posterior root to reach the posterior horn. From here, axons have two courses: some synapse immediately on second-order neurons in the posterior horn gray matter (lamina I and V), and others have axonal collaterals that ascend or descend one to two spinal cord segments in the posterolateral tract of Lissauer before synapsing with the second-order neurons in the gray matter (eFig. 9.51). Axons of the second-order neurons then cross obliquely over two to three spinal cord segments within the anterior commissure of the spinal cord to join the anterolateral tract on the contralateral side (eFig. 9.52). These second-order axons ascend through the CNS to reach the third-order neuronal cell bodies in the ventral posterior lateral nucleus of the thalamus (eFig. 9.52). Axons from the third-order neurons then project through the posterior limb of the internal capsule to reach the primary somatosensory cortex (eFig. 9.52).