Answer and Explanation:
The retina covers the internal phase of the eye. It characterizes by its complex interaction between many morphologically and functionally different cells, which are located in many layers. The principal processing mechanism in the retina is lateral interactions among cells, and the most common lateral processing is lateral inhibition.
Photoreceptors are those cells that receive the light and translate the luminous signal into an electrical signal. These are the cones and sticks.
The horizontal cells intervene in the lateral spatial interaction between photoreceptors.
Bipolar cells receive information from the photoreceptors and from the horizontal cells and transmit it to the most internal layers in the retina.
The retina is stratified into five layers. One of these is the external plexiform layer, a contact zone between photoreceptors, horizontal cells, bipolar cells, and other cells.
In the vertebrates´ retina, the lateral inhibition is produced for the first time in the external plexiform layer, through the horizontal cells. These cells connect to photoreceptors, other horizontal cells, and bipolar cells. The connection between horizontal cells might reduce or amplify the photoreceptor answer, and this last one is transmitted by the bipolar cells to the interior of the retina. In photoreceptors, there are two connections to horizontal cells, a direct connection, and an indirect one. The connection between photoreceptors, horizontal cells, and bipolar cells is known as lateral inhibition. By this inhibition, photoreceptors allow the contrasting perception in an image. Lateral inhibition allows discriminating one stimulus from other stimuli, by enhancing contrast and definition. The inhibitory modulation is produced by the inhibitor neurotransmitter GABA.The spacial extension of lateral inhibition changes according to the adaptation to light. Gap junction between horizontal cells and between photoreceptors and horizontal cells might vary with the amount of light.
