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Sensory neurons located here send axons into the dorsal horn of the spinal cord. Axons of dorsal horn neurons cross the midline and ascend the spinal cord in the anterolateral white column.
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Some axons of the spinothalamic pathway terminate in this part of the midbrain. Stimulation of this area of the brain stem produces potent analgesia. Injection of opiates into this region also relieves pain.
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After crossing the midline of the spinal cord, axons enter this and ascend toward the brain.
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Pain information is carried by these, one type of which is myelinated and rapidly conducting and the other type of which is unmyelinated and slowly conducting.
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Pain information is eventually integrated in this structure, and it is much more likely to be activated by a stimulus if people are led to believe that the stimulus will be painful.
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Pain information en route to the cortex maintains its lateral position in this structure, just dorsal to the inferior olivary nucleus.
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One of these in each hemisphere lie in parietal cortex just behind the central sulcus, dividing the parietal lobe from the frontal lobe. They receive touch information from the opposite side of the body.
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Some axons of the spinothalamic tract terminate here. This pain information is then relayed to the cortex.
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Pain information is provided to this (and other) brain stem sites, which control pain-related behavior such as vocalization.
Dorsal root ganglion
Periaqueductal gray
Spinothalamic tract
A? and C fibers
Cingulate cortex
Medulla
Somatosensory cortex (S1)
Thalamic nuclei
Pons
Textbook Reference: Pain: The Body's Emergency Signaling System