Spinal Pathways for Somatocardiac Reflexes.Small, somatic afferent fibers, among which mediate painful responses, have important influences on the functions of the heart and vasculature by reflexly controlling autonomic nervous system activity. These reflexes are largely conducted by ascending spinal pathways to the brainstem. The spinal pathways mediating somatosympathetic reflexes are reviewed and compared to those involved in somatovagal reflexes controlling the heart. In seven chloralose anesthetized cats, single unit activity was recorded from cardiac vagal preganglionic fibers. Supramaximal, electrical stimulation of the peroneal nerve inhibited the excitatory influences from electrical stimulation of the carotid sinus nerve. From spinal lesion studies, these inhibitory influences are conducted through ascending, bilateral, spinal pathways in the dorsolateral sulcus area near the dorsal root entry zone. Following these lesions, peroneal nerve stimulation produces vagoexcitatory responses. Thus, similar to reflex effects on sympathetic activity to the heart and vasculature, somatic afferents can excite or inhibit vagal control of the heart, although the directional changes are the reciprocal to those of the sympathetic responses. These somatoautonomic reflex responses involve pathways that ascend in the dorsolateral funiculus and sulcus areas of the cat spinal cord.