Modulatory Effects of Descending Systems on Spinal Dorsal Horn Neurons
It is well established that suprasegmental modulation of spinal reflexes and spinal neuronal responses can be demonstrated from widespread areas of the brain, including the brainstem, diencephalon, and cortex. Indeed, many of these spinal reflexes and neurons are tonically modulated from supraspinal sites. Early investigators employed lesions and intracerebral electrical stimulation to locate the site(s) of origin of descending control of flexion reflexes. Although these efforts were directed primarily toward understanding mechanisms of motor control, they also contributed significantly to our knowledge of sensory mechanisms and the suprasegmental modulation of nociception. Focal electrical brain stimulation and intracerebral drug microinjections are widely employed today to examine descending modulatory influences on spinal dorsal horn neurons and nociceptive reflexes, focusing often on “intrinsic” systems of pain control. This chapter considers descending inhibitory modulation of nociceptive transmission in the spinal cord, but it is important to recognize that centrifugal influences on somatosensory pathways can be either inhibitory or excitatory. The substrates for these spinopetal effects have been discussed further in the chapters by Hammond (Chapter 15), Ruda (Chapter 7), and LaMotte (Chapter 5).
KeywordsDorsal Horn Spinal Dorsal Horn Dorsal Horn Neuron Spinal Dorsal Horn Neuron Nucleus Raphe Magnus
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