Abstract

It is commonly accepted that discomfort sensation(pain) is associated with unpleasant feeling anxiety, fear and helpessness. However, it is not clear why such sensations occur when we feel pain. With the analysis available to us reharding the pain pathway, limbic system, and their realtionship, we have surmised the underlying mechanism for pain is always associated with unplesant feelings. On entering the spinal cord, the pain signals take two pathways to the brain, through the neospinothalamic tract for fast-sharp pain and through the paleospinothalamic tract for a slow-chronic pain. The pain signals excite second-order neuron of the spinothalamic tract. These give rise to long fibers that cross immediately to the opposite side of the cord through the anterior commissure and then pass upward to the brain in the anterolateral column. The most acute painfibers pass all the way to thalamus, terminating in the ventrobasal complex along with the dorsal-medial lemniscal tract for tactile sensation. From these areas, the signals are tranmitted to other basal area of the brain and to the somatic sensory cortex. The majority of slow pain fibers terminate widely in the brain stem, principally in one of the three areas : (1) the reticular nuclei of the brain stem ; (2) the fectal area of the meoencephalon; or (3) the periaquaductal gray region. From the brain stem pain area, multiple short-fiber neurons relay the pain signal upward into the intralaminar and cental nuclei of the thalamus, and into certain portions of the hypothalamus and other adjacent regions of the basal brain. It is already clear that several limbic structures are particularly concerned with the affective nature of sensory sensations - that is, whether the sensations are pleasant or unpleasant. These affective qualities are also called reward of punishment. Electrical stimulation of the certain limbic areas please of satisfies the animal, whereas electrical stimulation of other regions causes terror, pain, fear, defence, escape reaction, and all the other elements of punishment. By using this procedure, the reward centers have been found to be located in the ventromedial nucleus, septum, amygdala, certain areas of the thalamus and extending downward into the basal tegmentum of the meoencephalon. Many afferent connections to the reward and punishment centers of the limbic system from the areas of main pain pathways have been reviewed. Brain stem reticular afferents ascend to the hypothalamus via mammillary peduncle and the dorsal longitudinal fasciculus. The mammillary peduncle arises from the dorsal and vental nuclei of the midbrain and projects mainly to the latreral mammillary nucleus. The ascending component of the dorsal longitudinal fasciculus is formed from cells in the central gray of the midbrain. Fibers in this bundle spread out over caudal and dorsal regions of the hypothalamus where they become part of the periventricular system. Brain stem afferents to the hypothalamus also arise from neurons in the raphe nuclei of the midbrain, the lateral parabrachial nuclei and from the locus ceruleus. From the review in this study, it can be concluded that unpleasant feelings may be evoked by activation of the punishment centers of the limbic system which receive many afferent pain fibers from the brain stem.

• Keywords: pain, unpleasant feeling, neurophysiology