FIGURE 2-1. Anatomical distribution of nociception and pain.

FIGURE 2-1Anatomical distribution of nociception and pain

This figure schematizes the major neuroanatomical structures that differentiate nociception and pain, an understanding of which is essential for studies in which the animals may experience pain. Nociception refers to the process through which information about peripheral stimuli is transmitted by primary afferent nociceptors to the spinal cord, brainstem, thalamus, and subcortical structures. In contrast, the experience of pain can result only when there is activity of thalamocortical networks (represented in the dark shaded box at the top) that process the information conveyed by pathways of nociception. The magnitude of pain is determined to a great extent by the strength of descending inhibitory and facilitatory controls (in the lighter shaded boxes) that originate throughout the neuraxis and regulate the processing of ascending nociceptive messages. The figure also illustrates several important surgical preparations used to study nociceptive processing under conditions in which different parts of the brain are disconnected from afferent nociceptive input. Thus, transection of the spinal cord produces a “spinal” preparation. Decerebrate preparation entails transection of the brain between the midbrain (at the level of the colliculi) and the thalamus. In the decorticate preparation, connections from the thalamus to the cortex are severed. In all of these conditions, information generated by the activity of nociceptors located below the level of transection is unlikely to reach structures above the transection. No evidence exists at present that hormonal or other nonneural mechanisms are able to “bypass” the transection to access the brain and evoke a pain perception.

From: 2, Mechanisms of Pain

Cover of Recognition and Alleviation of Pain in Laboratory Animals
Recognition and Alleviation of Pain in Laboratory Animals.
National Research Council (US) Committee on Recognition and Alleviation of Pain in Laboratory Animals.
Washington (DC): National Academies Press (US); 2009.
Copyright © 2009, National Academy of Sciences.

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