axon synapses in cone retinal bipolar cell type 6 cone bipolar cell (sensu Mus) An ON-bipolar neuron found in the retina and having connections with cone photoreceptors cells and neurons in the inner half of the inner plexiform layer. The cell has a loose, delicate axon terminal that opens in sublamina 3 of the inner plexiform layer and descends into sublamina 4. DB5 cone bipolar cell sublaminar layer S4