<P> The basic circuitry of the retina incorporates a three - neuron chain consisting of the photoreceptor (either a rod or cone), bipolar cell, and the ganglion cell . </P> <P> The first action potential occurs in the retinal ganglion cell . This pathway is the most direct way for transmitting visual information to the brain . </P> <P> There are three primary types of photoreceptors: Cones are photoreceptors that respond significantly to color . In humans the three different types of cones correspond with a primary response to short wavelength (blue), medium wavelength (green), and long wavelength (yellow / red). Rods are photoreceptors that are very sensitive to the intensity of light, allowing for vision in dim lighting . The concentrations and ratio of rods to cones is strongly correlated with whether an animal is diurnal or nocturnal . In humans, rods outnumber cones by approximately 20: 1, while in nocturnal animals, such as the tawny owl, the ratio is closer to 1000: 1 . Retinal ganglion cells are involved in the sympathetic response . Of the ~ 1.3 million ganglion cells present in the retina, 1 - 2% are believed to be photosensitive . </P> <P> Problems and decay of sensory neurons associated with vision lead to disorders such as: </P>

Where are the sensory receptors located on a neuron