In experimental animals, both noxious and innocuous stimulation of somatic afferents have been shown to evoke reflex changes in sympathetic efferent activity and, thereby, effector organ function. These phenomena have been demonstrated in such sites as the gastrointestinal tract, urinary bladder, adrenal medulla, lymphatic tissues, heart and vessels of the brain and peripheral nerves. Most often, reflexes have been elicited experimentally by stimulation of cutaneous afferents, although some work has also been conducted on muscle and articular afferents, including those of spinal tissues. The ultimate responses may represent the integration of multiple tonic and reflex influences and may exhibit laterality and segmental tendencies as well as variable excitability according to the afferents involved. Given the complexity and multiplicity of mechanisms involved in the final expression of the reflex response, attempts to extrapolate to clinical situations should probably be eschewed in favor of further systematic physiological studies.
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