axon synapses in cone retinal bipolar cell type 5 cone bipolar cell (sensu Mus) DB4 cone bipolar cell 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 axon terminal is restricted to sublamina 3 of the inner plexiform layer. It is narrowly stratified and branched. The dendritic tree has many delicate branches. sublaminar layer S3