The two layers that comprise the retina are an outer pigmented layer called the pigment epithelium, which adheres to the choroid, and an inner layer of nerve tissue called the sensory (or neural) retina. The inner layer of nerve tissue consists of three separate layers of neurons. The first and closest to the choroid is a layer of sensory receptors, the photoreceptors cells called rods and cones, and various other neurons. Next is a layer of bipolar neurons, the nerve cells that receive impulses generated by the rod and cone cells. The third or inner layer consists of ganglionic neurons attached directly to the optic nerve.