Which of the following are TRUE/FALSE regarding pain suppression ("Analgesia") system in the brain and spinal cord: 1. The raphe magnus nucleus, a thin midline nucleus reticularis paragigantocellularis, is located laterally in the medulla. 2. It consists of two main components. 3. The periaqueductal gray (in midbrain) and periventricular areas of the mesencephalon and upper pons surround the aqueduct of sylvius and poions of the third and fouh ventricles. 4. Enkephalins and serotonin are involved in the analgesia system (brain and spinal cord). 5. A pain inhibitory complex is located in the ventral horns of the spinal cord.

Pain suppression ("Analgesia") system in the Brain and Spinal Cord: It consists of three major components: The periaqueductal gray (in midbrain) and periventricular areas of the mesencephalon and upper pons surround the aqueduct of sylvius and poions of the third and fouh ventricles. Neurons from these areas send signals to The raphe magnus nucleus, a thin midline nucleus reticularis paragigantocellularis, located laterally in the medulla. From these nuclei, second order signals are transmitted down the dorsolateral columns in the spinal cord to A pain inhibitory complex located in the dorsal horns of the spinal cord. At this point, the analgesia signals can block the pain before it is relayed to the brain. Note: "Several transmitter substances are involved in the analgesia system (of brain and spinal cord); especially involved are enkephalin and serotonin" . "Along with the opioid receptor, the component nuclei of this pain modulating circuit contain endogenous opioid peptides such as the enkephalins and B-endorphin". About a dozen such opiate-like substances have now been found at different point of the nervous system ; all are breakdown products of three large protein molecules ; pro-opiomelanocoin, proenkephalin, and prodynorphin. Among the major impoant of these opiate-like substances are B-endorphin, met-enkephalin, leu-enkephalin, and dynorphin. Fibers originating in this area send signal to the dorsal horns of the spinal cord to secrete serotonin at their endings. The serotonin cause local cord neurons to secret enkephalin as well. The enkephalin is believe to cause both presynaptic and postsynaptic inhibition of incoming type C and type A/ pain fibers where they synapse in the dorsal horns. The 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 link in the hypothalamus, midbrain, and medulla, and it selectively controls spinal pain-transmission neurons through a descending pathway. Ref: Harrison 17/e, page 83 ; Guyton 11/e, page 602-03 ; Ganong 23/e, page 177-78 ; Katzung 10/e, page 489.