Ca ion flow regulates several secondary messenger systems in neural adaptation for visual, auditory, and the olfactory system. It may often be bound to calmodulin such as in the olfactory system to either enhance or repress cation channels. Other times the calcium level change can actually release guanylyl cyclase from inhibition, like in the photoreception system. Ca ion can also determine the speed of adaptation in a neural system depending on the receptors and proteins that have varied affinity for detecting levels of calcium to open or close channels at high concentration and low concentration of calcium in the cell at that time.