FIBER GROUPS AND SPINAL PATHWAYS OF CORTICALLY REPRESENTED VISCERAL AFFERENTS

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Abstract
The sympathetic afferent fibers responsible for the cortical pri-mary responses and the localized secondary repetitive waves be-long to the A beta group. Over 95% of these fibers have conduction velocities between 64-35 m./second. The A gamma-fast delta fibers with maximal conduction velocities between 35-21 m./ second are responsible for reflex movement of the body wall, the localized 2d and 3d early waves and the generalized secondary response. The primary responses are dependent on the posterior columns, the distr. of A beta splanchnic afferents being intermediate between arm and leg projections on the ipsilateral side. The generalized secondary response and second early wave near the cruciate sulcus are dependent on the anterolateral columns. The pathway of the A gamma-fast delta sympathetic afferents is in the anterolateral columns close to the central grey matter and is bilateral. Primary responses dependent on an intact splanchnic pathway may be recorded following mechanical stimulation of the mesentery. The fast splanchnic projection to the cortex is apparently derived in part from Pacinian corpuscles. Very little spatial summation is required for the fast splanchnic afferent volleys to reach the cortex. The possible relationships of the fast and slow sympathetic afferent cortical projections to the senses of visceral distention and pain are discussed.