Light rays enter the eye through an opening in the center of the iris called the pupil. Light is then focused by muscles in the eyes like the lens and the cornea onto the rear surface of the eye known as the retina. The retina is lined with visual receptors. Bipolar and amacrine cells within the retina receive messages from the visual receptors and send them to the ganglion cells. Axons of the ganglion cells form the optic nerve that travels to the brain. Bipolar cells in the retina are divided into cones and rods. Cones are a type of receptors that are most abundant around the fovea and are essential for color vision and are more useful in bright light. Rods are most abundant in the periphery of the eye and respond to faint light. Cones and rods absorb different wavelengths of light. Photopigments are chemicals released by cones and rods when hit by light. These chemicals activate second messengers within the cell. These signals are then passed from one neuron to …show more content…
The optic nerve transports information to the lateral geniculate nucleus in the thalamus. The primary visual cortex receives information from the lateral geniculate nucleus. The primary visual cortex consists of three types of cells. Simple cells that respond more in the light, complex cells that responds to a moving stimulus and hypercomplex cells that respond to bar-shaped patter of light in a large receptive field. The response of these different types of cells is what causes vision to occur. Cell arrangement in the eyes and the brain contributes to the path of visual input. Our vision is dominated by what we see in the fovea, which affects the placement of receptors on the retina. Receptors may be denser in some areas of the eye than others for different reasons. For instance, predatory birds have greater density of receptors on top of the eye to help them see better what is on land. Rats have a greater density on the bottom of the eye so they can watch out for predators flying above