Figure 11.18. Circuitry responsible for generating receptive field center
responses of retinal ganglion cells. In this case, the centers of the on- and offcenter ganglion cell receptive fields are illuminated without illumination of the
surrounds. Light falling on the receptor leads to a reduction in transmitter
release that has opposite effects on the two populations of bipolar cells: oncenter bipolar cells depolarize, and off-center bipolar cells hyperpolarize. This,
in turn, leads to an increase in the firing rate of on-center ganglion cells and a
decrease in the firing rate of off-center ganglion cells.
Figure 11.19. Circuitry responsible for generating the antagonistic surrounds of
retinal ganglion cell receptive fields. In this case, an increase in illumination is
confined to photoreceptors that contribute to the surround of the ganglion cells'
receptive field; there is no change in the illumination of the photoreceptors that
contribute to the center. Onset of light in the receptive field surround causes the
photoreceptors in this location to hyperpolarize, reducing glutamate release
onto horizontal cell processes. Horizontal cells contacting these photoreceptors
hyperpolarize and decrease their rate of transmitter release onto the synaptic
terminals of the photoreceptors that contribute to the receptive field center. The
transmitter utilized by the horizontal cells hyperpolarizes photoreceptor
terminals, and its reduction leads to a net depolarization of the photoreceptor
terminals that contribute to the receptive field center. As a result, these
terminals increase their rate of transmitter release onto the processes of bipolar
cells causing the on-center bipolar cells they contact to hyperpolarize and the
off-center bipolar cells to depolarize. Changes in the release of transmitter from
the bipolar cells then lead to changes in the spike rate of retinal ganglion cells
as shown.
Fuente: Purves D, Augustine G, Fitzpatrick D, Katz L. Neuroscience. 2001; USA