THE PERIPHERAL ORIGIN OF NERVOUS ACTIVITY IN THE VISUAL SYSTEM
Cold Spring Harbor Symposia on Quantitative Biology
69 It is the function of the 3ense organs to reflect, in the nervous activity they generate, the state of the organism's environment, initiating chains of neural events that regulate behavior. The mechanisms whereby environmental influences excile activity in afferent aerve fibers have been discussed by many authors. Nevertheless, it is not yet possible to trace, step by step, the physical and chemical events that intervene between the action of a stimulus on a receptor and the response of the
... he response of the associated afferent fiber. This paper will consider some of the ideas that have been developed, and add new observations that bear on the problem of the origin of nervous activity, with particular reference to the visual system. The activity that is generated in afferent nerve fibers, when their sense organs are stimulated, consists of trains of nerve impulses such as are observed elsewhere in the nervous system. In any one fiber, the frequency of the discharge of impulses depends upon the intensity of the stimulus and upon the sti .c 01 the receptor, as determined by the various factors affecting its responsiveness. These ore now familiar facts of neurophysiology (Adrian, 1935). An example of such neural activity is given in Figure 1 , which shows oscillograms of the action potentials recorded from a single optic nerve fiber from the eye of Limulus. In this case, a visual receptor element, stimulated by light, initiated the activity. As a result of the work of many investigators, beginning with Adrian and his associates, the discharge of impulses in afferent fibers has been recorded for almost all the major types of sense organs. The fact has emerged that, except for differences in the amount of sensory adaptation shown by different types of end organs under continuous stimulation, the patterns of response are essentially alike. Evidently, the various kinds of sensory end-organs with their associated afferent fibers possess certain fundamental properties in common.