axon synapses in cone retinal bipolar cell type 7 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 axon terminal is narrowly stratified and are found just below a calretinin-expressing band in sublamina 4 of the inner plexiform layer. IMB cone bipolar cell sublaminar layer S4