Bipolar cells connect them to the photoreceptors. Rods contain the purple pigment rhodopsin . The dissociation causes changes in ionic permeability of the cell and so allows the creation of nerve impulses. In cones, the trichromatic theory of color vision suggests that our color perception dpends on stimulation of only 3 cone types. The fovea centralis is within the macula lutea , and there is the greatest concentration of photoreceptors.
Olfaction involves actively dividing receptor neurons , with receptors linked with G-proteins.
Anosmia can follow head injuries that damage the olfactory nerves or infections that damage the cells, and will contribute to ageusia because of the contribution of smell to taste. The Papez circuit runs among different components of the system. Forgetfulness in Alzheimer's is associated with a loss of neurons in the hippocampal formation.