Characteristics of Sympathetic Neuroeffectors in Man

¹ From the Department of Physiology and the Department of Otolaryngology, University of Gothenburg, Gothenburg, Sweden

The sympathetic fibers to the pupillary dilator muscle have been directly stimulated at maximal strength and increasing frequencies in anesthetized man during surgical operations on the neck. The normal, tonic discharge of the fibers was first blocked by locally injected xylocaine. Plotting the effector responses against the stimulation frequencies gives a hyperbolic curve similar to that found in animals, with a steep rise of the response up to about 10 impulses/sec., after which little further effect is gained. By comparing the changes of the pupillary size before sympathetic block with the effects obtained on direct sympathetic stimulation it was possible to estimate approximately the physiological discharge range of these autonomic fibers.