Fig. 1.6.27. Synapses from outer plexiform layer of the retina. Presynaptic terminals (rod spherules and cone pedicles) are invaginated by fine neurites of bipolar and horizontal cells. No postsynaptic densities are formed but terminals contain a dense lamella called the synaptic ribbon perpendicular to the presynaptic membrane. Synaptic vesicles are clustered around the ribbon (arrows) and they are also present in processes of horizontal cells (asterisks). Scale = 300 nm. (Mouse, retina.) Download the high resolution image (a); Download the high resolution image (b).