The Nerve Messages in the Fibers of the Visual Pathway*

Abstract

A review of the salient features of the fibre response both in the king-crab (Limulus polyphemus) in which there are no synaptic junctures prior to the recording point, and in the vertebrate in which the synaptic layers of the retina are interposed. The relation of the impulse frequency to light intensity is outlined in both cases. In the latter there are 3 different kinds of discharge relative to the onset, duration and cessation of illumination. The differences brought about in the sense-cell discharge under various degrees of dark adaptation are pointed out. The discharge becomes more rapid, more prolonged, and latency is reduced. Each fibre which constitutes the optic nerve is supplied by a retinal field and not by a single sense-cell. This is known as the receptive field and in the frog is about 1 mm. in diam. A point of light anywhere in the field will elicit a response but the center of the field is the most sensitive.