The Response of the Photoreceptor to Light Is SynapticaIIyTransmitted to the Ganglion Cells by the Bipolar Cells

The hyperpolarizing response of the rods and cones to light influences bipolar cells by a chemical synapse. In turn, the bipolar cell influences action potential frequencies in the gan­glion cell axons on their way to the brain.

Considerable pro­cessing of the visual image occurs in the retina, such as the initial stages of color discrimination, contrast enhancement, and directional sensitivity, in addition to light-dark dis­crimination and detection of large changes in luminance. The synaptic interactions among photoreceptors, bipolar cells, and horizontal cells (see Figure 14-4) play a significant role in contrast enhancement and directional sensitivity. The inter­actions of amacrine cells with bipolar cells and ganglion cells appear to play a role in processes such as the ability to detect changes in the rate of alternation between light and dark. A more detailed description of the synaptic and membrane changes in the chain of transmission within the retina, account­ing for these types of retinal image processing, is beyond the scope of this book. To learn more about the many interesting and unusual phenomena occurring in the retina, the reader should refer to the Bibliography.

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