Abstract
Gruber 1 has shown that in the results of both afferent and efferent stimulations, in some instances essentially the same effect is produced by a high frequency and weak intensity of stimulation as by a low frequency of higher intensity, while in other instances an opposite result occurs. In afferent stimulation, spatial and temporal summation might account for the phenomena, which, however, offer more difficulty of interpretation when direct stimulation of efferent nerves show a similar effect. Dr. Gruber suggested that we attempt to correlate his findings with the analysis of fiber types which we have been carrying on by means of the oscillograph.
Results of stimulation of the cervical sympathetic were employed as criteria: dilatation of the pupil and retraction of the nictitating membrane of cat and rabbit; vasoconstriction in the conjunctiva of the cat, and in the ear of the rabbit; and pilometer effects upon the hair between ear and eye of the cat. The nerve was stimulated posterior to the superior ganglion (mostly preganglionic fibers) and observations were made on the peripheral response in the animal, decerebrated or anesthetized, while action potentials were being recorded from the cut central end of the nerve. For the most irritable fibers giving rise to the first wave of the cervical sympathetic action potential picture, no effect can be detected from peripheral stimulation, and these fibers have previously been judged to be afferents (Bishop and Heinbecker 2 ). The second potential component is double, and consists of the main potential of this nerve, arising from small myelinated sympathetic fibers. Stimulation of the first division of this group, giving a distinct wave in the potential picture, elicits the effect on the pupil and nictitating membrane of the eye.
Get full access to this article
View all access options for this article.