Pain transmission can be influenced by several descending pathways. All of the following are involved with the descending influence on nociceptive transmission, EXCEPT:
The ventral lateral nucleus of the thalamus is primarily involved with motor function and does not contribute to descending pathways that influence pain transmission. Neurons in the periaqueductal gray project to the nucleus raphe magnus, the cells of which give rise to raphespinal fibers. These axons utilize serotonin as a neurotransmitter, which they release at their terminals on enkephalinergic interneurons in the substantia gelatinosa of the dorsal horn. The latter neurons then form synapses directly wtih the terminals of incoming primary afferent pain fibers from the dorsal roots.
Ventral lateral thalamic nucleus
Periaqueductal gray
Nucleus raphe magnus
Raphespinal fibers