When light strikes the photoreceptor, a molecule of retinal is converted from the 11-cis to the all trans form. This in turn causes a conformational change that activates transducin. When transducin becomes activated, like other G proteins, it activates a cyclic nucleotide phosphodiesterase, which breaks down cyclic GMP present in the cytoplasm. This in turn shuts down cGMP-dependent sodium channels, which are normally open in the rod outer segments. As sodium channels are inactivated, the membrane hyperpolarizes, which leads to a decrease in neurotransmitter release.
Bipolar cells can respond in two general ways to incoming light.
On bipolar cells exhibit different properties, and fire when less glutamate is released in response to light. Several photoreceptors converge upon a single bipolar cell to alter its firing rate. In addition, bipolar cells receive input from horizontal cells, which can also regulate the firing rate of the bipolar cell. In general, the influence of light in the surrounding field is opposite that of the direct effects of photoreceptors. Ganglion cells receive input from bipolar cells and from amacrine cells.