When light is absorbed in a rod, rhodopsin changes its confirmation. This does not result in an action potential, but can be considered as a signal to bipolar cells and horizontal cells which synapse with rods. The most recent models have the hyperpolarization decreasing the release of the neurotransmitter glutamate. Horizontal cells can inhibit the other rods. Bipolar cells synapse with ganglion cells.
Ganglion cells exhibit a spontaneous rate of action potentials in the absence of light.
The frequency of action potentials generated by ganglion cells can either by increased or decreased when light strikes specific rods in specific locations in the retina. In other words, ganglion cells have a steady-state rate frequency of action potentials at rest. Remember in figures such as 8-37, the recordings are coming from ganglion cells that are either excited or inhibited when light strikes rods. There visual field is circular Cells in the primary visual cortex have rectangular visual fields and some also respond to the spatial orientation of an object. The three different cones have the same retinal as rods, but different opsins resulting in their absorbing light of different wavelengths.