text: The ribbon synapse is a special type of synapse found in sensory neurons such as photoreceptor cells, retinal bipolar cells, and hair cells.  Ribbon synapses contain a dense protein structure that tethers an array of vesicles perpendicular to the presynaptic membrane.  In an electron micrograph it appears as a ribbon like structure perpendicular to the membrane. Unlike the traditional synapse, ribbon synapses can maintain a graded release of vesicles.  In other words, the more depolarized a neuron the higher the rate of vesicle fusion.  The Ribbon synapse active zone is separated into two regions, the archiform density and the ribbon.  The archiform density is the site of vesicle fusion and the ribbon stores the releasable pool of vesicles. The ribbon structure is composed primarily of the protein RIBEYE, about 64–69% of the ribbon volume, and is tethered to the archiform density by scaffolding proteins such as Bassoon.