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pathways ascending pathways
source: Purves et. alThe pathways related to pain are complex and numerous and at times can be confused with pathways related to non-nociceptive temperature neurons that follow the same anatomical route although unrelated to the pain system. A basic understanding, however, can be obtained by looking at the spinothalamic system and the trigemino-thalamic tract system.
The central axons of nociceptive nerve cells, which carry information from pain and temperature receptors, enter the spinal cord via the lateral division of the dorsal roots. When reaching the dorsal horn, the projecting axons branch into two pathways – the ascending collateral and the descending collateral, forming the dorsolateral tract of Lissauer. The axons in Lissauer’s tract run through the spinal cord segments before they penetrate the dorsal horn. The two axons cross over to the contralateral side in the spinal cord and then synapse on the caudal medulla.