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Descending analgesia systems. Two projection neurons in the spinal cord dorsal horn that receive descending inhibitory synapses (minus signs) from brainstem neurons are shown. The descending axons originate in the nucleus raphe magnus (NRM) and the locus ceruleus (LC) and adjacent nuclei of the parabrachial region. The periaqueductal gray (PAG) is shown to have excitatory connections (plus signs) to the NRM and LC.
