Diagram showing a few of the connections of afferent (sensory) fibers of the posterior root with the efferent fibers from the ventral column and with the various long ascending fasciculi. (Lissauer's fasciculus visible in upper left.)
Diagram of the principal fasciculi of the spinal cord. (Lissauer's fasciculus visible in upper right.)
The posterolateral tract (fasciculus of Lissauer, Lissauer's tract, tract of Lissauer, dorsolateral fasciculus, dorsolateral tract, zone of Lissauer) is a small strand situated in relation to the tip of the posterior column close to the entrance of the posterior nerve roots.
It contains centrally projecting axons carrying discriminative pain and temperature information (location, intensity and quality), which enter the spinal column and ascend or descend one or two spinal segments in this tract before penetrating the grey matter of the dorsal horn, where they synapse on second-order neurons. The axons of these second-order neurons cross the midline and ascend in the anterolateral quadrant of the contralateral half of the spinal cord, where they join the spinothalamic tract. The second-order neurons ultimately synapse on neurons in the ventral posterior lateral nucleus (VPL) of the thalamus.
It 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.