The neuronal components of the optic nerve of the crayfish as studied by single unit analysis

Abstract

Abstract Unit responses were obtained from the optic nerve of the crayfish, Procambarus clarki (Girard) with steel needles. Eighty‐three repeatedly recognized elements are described. They range from bundles of primary sensory fiber to complexly reacting multimodal interneurons. Visually reacting fibers fall into two main classes, one class reacts tonically to overall illumination, the other responds to moving objects. Sustaining fibers react to increased light with increased output, dimming fibers are active in the dark and inhibited by light. Fourteen sustaining and four dimming fibers are described. The main movement fiber type, of which eleven have been found, responds to shadows. They “habituate” quickly and react best to movement of small black objects. All these fibers, and some others, are present as centrifugal elements from the other eye. All these fibers, and some others, are present as centrifugal elements from the other eye. Four fibers, two sustaining and two movement ones, change their fields with positions of the animal. These “space‐constant” fibers “look” at the sky from all positions for which possible and are otherwise “blind.” Mechanoreceptive interneurons form a bundle between the first and second classes of optical fibers. Seventeen members are described. Five multimodal fibers, with combined visual and mechanoreceptor input are described. Maps of the approximate locations of the units in the cross‐section of the optic nerve are presented. The number of times specific fibers were found exceeded 50 for 28.