1.17 - Graded Signaling and the Emergence of Multiple Visual Streams in the Outer Retina

With the exception of ganglion and some amacrine cell types, the retina uses graded signals to process visual information. This situation differs from the rest of the CNS where processing utilizes all-or-nothing action potentials. To process graded signals, retinal synapses repurpose transmitters and receptors found elsewhere in the CNS, add new mechanisms, and juxtapose both existing and new mechanisms in unique ways. The idea of repurposing, adding, and juxtaposition is exemplified by the cone synapse. While glutamate is a typical excitatory transmitter, the mechanisms that regulate glutamate release at the terminal, the cleft geometries that distribute glutamate, and the postsynaptic receptors that respond to glutamate are all unique.