The posterolateral tract contains centrally projecting
axons from dorsal root
ganglion cells carrying peripheral pain and temperature information (location, intensity and quality). These axons enter the spinal column and penetrate the
grey matter of the dorsal horn, where they synapse on second-order neurons in either the
substantia gelatinosa of Rolando or the
nucleus proprius. Those neurons project their axon to the anterolateral quadrant of the contralateral half of the spinal cord, where they give the
spinothalamic tract. The axons of second-order neurons ultimately synapse on neurons in the
ventral posterior lateral nucleus (VPL) of the
thalamus after coursing in the spinal
lemniscus. After this, the 3rd order neuron fibers traverse the internal capsule and the corona radiata, ultimately synapsing in the post central gyrus (
somatosensory cortex). The location of this synapse is dependent upon the somatotopic organisation of the somatosensory cortex, it can be estimated according to the position on the 'somatosensory homunculus' The posterolateral tract consists of fine fibers which do not receive their myelin sheaths until toward the close of
fetal life. In addition it contains great numbers of fine non-myelinated fibers derived mostly from the
dorsal roots but partly
endogenous in origin. These fibers are intimately related to the
substantia gelatinosa which is probably their terminal nucleus. The non-myelinated fibers ascend or descend for short distances not exceeding one or two segments, but most of them enter the substantia gelatinosa at or near the level of their origin. ==Clinical significance==