VISUAL SYSTEM: STATE OF THE ART 



73 



61 log at 495 nm 



5 sec 



5mV 



-54 mV 



Figure 19 Bipolar cell responses from the retina of Scyliorhi- 

 nus canicula. Cell responded to long duration (horizontal bars) 

 flashes of 495-nm light. Numbers to the right represent the 

 value of the neutral density filter attenuating the 540-nm 

 diameter circle of light. Electrode penetrated 80 nm from the 

 vitreal surface. (Taken from Ashmore and Falk 1976 by kind 

 permission of the authors and the Journal of Physiology 

 (London) © 1976 Cambridge University Press Limited.) 



Ganglion Cell Responses— Ganglion cells are tertiary neurons whose 

 axons form the optic nerve. Their responses represent the final output of the 

 retina. 



Extracellular recordings show that ganglion cells respond to an increase or 

 decrease in light stimuli with all-or-none nerve action potentials. The recep- 

 tive field of ganglion cells is organized into a center region and a concentric 

 surround whose responses are of opposite sign and are thus antagonistic. 

 Responses obtained by recording in the center of a receptive field differ 

 depending on the type of cell from which the response is being recorded. A 

 small spot of light in the receptive field center that evokes a burst of spikes 

 characterizes the "on-center" cell (Figure 20). This same stimulus applied to 



