As a part of the retina
, the bipolar cell
exists between photoreceptor
and cone cells
) and ganglion cell
. They act, directly or indirectly, to transmit signals from the photoreceptors to the ganglion cells.
Bipolar cells are so-named as they have a central body from which two sets of processes arise. They can synapse with either rods or cones (but not both), and they also accept synapses from horizontal cells
. The bipolar cells then transmit the signals from the photoreceptors or the horizontal cells, and pass it on to the ganglion cells directly or indirectly (via amacrine cells). Unlike most neurons, bipolar cells communicate via graded potentials
, rather than action potentials
Bipolar cells receive synaptic input from either rods or cones, but not both, and they are designated rod bipolar or cone bipolar cells respectively. There are roughly 10 distinct forms of cone bipolar cells, however, only one rod bipolar cell, due to the rod receptor arriving later in the evolutionary history than the cone receptor.
Bipolar cells can be categorized into two different groups, ON and OFF, based on how they react to glutamate
released by photoreceptor cells. When light hits a photoreceptor cell, the photoreceptor hyperpolarizes, and releases less glutamate. An ON bipolar cell will react to this change by depolarizing. An OFF bipolar cell will react to this decrease in glutamate by hyperpolarizing.
Under dark conditions, a photoreceptor cell will... Read More