OCULOMOTOR NERVE AND REFLEX DILATATION OF PUPIL

Abstract

Observations upon the diam. of the pupil in the cat following preganglionic para-sympathectomy, pre- and postganglionic sympathectomy, and combinations of these procedures indicate that inhibition of the third nerve is responsible not only for the reflex dilatation elicited by withdrawal of light and by painful stimulation, but also for the immediate dilatation conditioned by emotional excitement. The sympathetic and parasympathetic are opposed in their action upon the pupil. Under ordinary conditions sympathetic dilator tone is remarkably constant while 3d-nerve constriction is subject to extreme reflex modification. Consequently changes in the size of the pupil depend upon reflex variations in the activity of the oculomotor nerve. That sympathectomy effects a diminution in the extent and rate of reflex dilatation demonstrates that in normal animals the dilatation caused by inhibition of the sphincter pupillae is augmented by the tonic contraction of the dilator muscle. The miotic action of eserine on the pre-ganglionic parasympathecto-mized pupil is shown to be less but more prolonged than on the normal pupil while the constriction it produces in the sympathectomized or sympathectomized-parasympathectomized pupil is greater than in the normal. Nembutal depresses sympathetic activity.