Both types of photoreceptors have an outer segment that is composed of membranous disks that contain photopigment and lies adjacent to the pigment epithelial layer, and an inner segment that contains the cell nucleus and gives rise to synaptic terminals that contact bipolar or horizontal cells. There are two types of light-sensitive elements in the retina: rods and cones. A three-neuron chain-photoreceptor, bipolar cell, and ganglion cell-provides the most direct (more.) (B) Diagram of the basic circuitry of the retina. (A) Section of the retina showing overall arrangement of retinal layers. A direct three- neuron chain-photoreceptor cell to bipolar cell to ganglion cell-is the major route of information flow from photoreceptors to the optic nerve. The cell bodies and processes of these neurons are stacked in five alternating layers, with the cell bodies located in the inner nuclear, outer nuclear, and ganglion cell layers, and the processes and synaptic contacts located in the inner plexiform and outer plexiform layers ( Figure 11.4). There are five types of neurons in the retina: photoreceptors, bipolar cells, ganglion cells, horizontal cells, and amacrine cells. Although it has the same types of functional elements and neurotransmitters found in other parts of the central nervous system, the retina comprises only a few classes of neurons, and these are arranged in a manner that has been less difficult to unravel than the circuits in other areas of the brain.
![retina layers retina layers](http://what-when-how.com/wp-content/uploads/2012/04/tmp15F55.jpg)
(C, D) The inner wall of the optic cup becomes the neural retina, while the (more.)Ĭonsistent with its status as a full-fledged part of the central nervous system, the retina comprises complex neural circuitry that converts the graded electrical activity of photoreceptors into action potentials that travel to the brain via axons in the optic nerve. (B) The optic vesicle invaginates to form the optic cup. (A) The retina develops as an outpocketing from the neural tube, called the optic vesicle.