Structure and function of a complex sensory synapse.

Vision is the most important of the senses for humans, and the retina is the first stage in the processing of light signals in the visual system. In the retina, highly specialized light-sensing neurons, the rod and cone photoreceptors, convert light into neural signals. These signals are extensively processed and filtered in the subsequent retinal network before transmitted to the higher visual centres in the brain, where the perception of viewed objects and scenes is finally constructed. A key feature of signal processing in the mammalian retina is parallel processing. Visual information is segregated in parallel pathways already at the rod and cone photoreceptor terminals, which provide multiple output synapses for the faithful encoding and transfer of the visual signals to the post-receptoral retinal network. This review aims at highlighting the current knowledge about the structural and functional pre- and post-synaptic specializations of rod and cone photoreceptor ribbon synapses, which belong to the most complex chemical synapses in the central nervous system.