The ribbon synapse is a type of neuronal synapse characterized by the presence of an electron-dense structure, the synaptic ribbon, that holds vesicles close to the active zone. It is characterized by a tight vesicle-calcium channel coupling that promotes rapid neurotransmitter release and sustained signal transmission. Ribbon synapses undergo a cycle of exocytosis and endocytosis in response to graded changes of membrane potential. It has been proposed that most ribbon synapses undergo a special type of exocytosis based on coordinated multivesicular release. This interpretation has recently been questioned at the inner hair cell ribbon synapse, where it has been instead proposed that exocytosis is described by uniquantal (i.e., univesicular) release shaped by a flickering vesicle fusion pore. These unique features specialize the ribbon synapse to enable extremely fast, precise and sustained neurotransmission, which is critical for the perception of complex senses such as vision and hearing. Ribbon synapses are found in retinal photoreceptor cells, vestibular organ receptors, cochlear hair cells, retinal bipolar cells, and pinealocytes. The synaptic ribbon is a unique structure at the active zone of the synapse. It is positioned several nanometers away from the pre-synaptic membrane and tethers 100 or more synaptic vesicles. Each pre-synaptic cell can have from 10 to 100 ribbons tethered at the membrane, or a total number of 1000–10000 vesicles in close proximity to active zones. The ribbon synapse was first identified in the retina as a thin, ribbon-like presynaptic projection surrounded by a halo of vesicles using transmission electron microscopy in the 1950s, as the technique was gaining mainstream usage. Source: Wikipedia (en)