tailieunhanh - Chapter 012. Pain: Pathophysiology and Management (Part 4)

Pain transmission and modulatory pathways. A. Transmission system for nociceptive messages. Noxious stimuli activate the sensitive peripheral ending of the primary afferent nociceptor by the process of transduction. The message is then transmitted over the peripheral nerve to the spinal cord, where it synapses with cells of origin of the major ascending pain pathway, the spinothalamic tract. The message is relayed in the thalamus to the anterior cingulate (C), frontal insular (F), and somatosensory cortex (SS). B. Painmodulation network. Inputs from frontal cortex and hypothalamus activate cells in the midbrain that control spinal pain-transmission cells via cells in the. | Chapter 012. Pain Pathophysiology and Management Part 4 Pain transmission and modulatory pathways. A. Transmission system for nociceptive messages. Noxious stimuli activate the sensitive peripheral ending of the primary afferent nociceptor by the process of transduction. The message is then transmitted over the peripheral nerve to the spinal cord where it synapses with cells of origin of the major ascending pain pathway the spinothalamic tract. The message is relayed in the thalamus to the anterior cingulate C frontal insular F and somatosensory cortex SS . B. Painmodulation network. Inputs from frontal cortex and hypothalamus activate cells in the midbrain that control spinal pain-transmission cells via cells in the medulla. Pain Modulation The pain produced by injuries of similar magnitude is remarkably variable in different situations and in different individuals. For example athletes have been known to sustain serious fractures with only minor pain and Beecher s classic World War II survey revealed that many soldiers in battle were unbothered by injuries that would have produced agonizing pain in civilian patients. Furthermore even the suggestion of relief can have a significant analgesic effect placebo . On the other hand many patients find even minor injuries such as venipuncture frightening and unbearable and the expectation of pain has been demonstrated to induce pain without a noxious powerful effect of expectation and other psychological variables on the perceived intensity of pain implies the existence of brain circuits that can modulate the activity of the pain-transmission pathways. One of these circuits has links in the hypothalamus midbrain and medulla and it selectively controls spinal pain-transmission neurons through a descending pathway Fig. 12-4 . Human brain imaging studies have implicated this pain-modulating circuit in the pain-relieving effect of attention suggestion and opioid analgesic medications. Furthermore each of the .