ipRGCs to the G-proteins G(q), G(11), and G(14), which are all of the G(q)-type. In fact, they can functionally replace each other, as a knocking out only two of them has no phenotypical effect. The G-proteins activate the phospholipase C PLCB4, which causes the TRP-channels TRPC6 and TRPC7 mediate to open so that the cell depolarizes. This is like in the photoreceptor cells of the Drosophila eye, and in contrast to the vertebrate rod and cone cells, where phototransduction eventually makes the cells hyperpolarize. Like other rhabdomeric opsins, Melanopsin has intrinsic photoisomerase activity. Function Melanopsin-containing ganglion cells, like rods and cones, exhibit both light and dark adaptation; they adjust their sensitivity according to the recent history of light exposure. However, while rods and cones are responsible for the reception of images, patterns, motion, and color, melanopsin-containing ipRGCs contribute to various reflexive responses of the brain and body to the presence of light. Evidence for melanopsin's physiological light detection has been tested in mice. A mouse cell line that is not normally photosensitive, Neuro-2a, is rendered light-sensitive by the addition of human melanopsin. The photoresponse is selectively sensitive to short-wavelength light (peak absorption ~479 nm), and has an intrinsic photoisomerase regeneration function that is chromatically shifted to longer wavelengths. Melanopsin photoreceptors are sensitive to a range of wavelengths and reach peak light absorption at blue light wavelengths around 480 nanometers. Other wavelengths of light activate the melanopsin signaling system with decreasing efficiency as they move away from the optimum 480 nm. For example, shorter wavelengths around 445 nm (closer to violet in the visible spectrum) are half as effective for melanopsin photoreceptor stimulation as light at 480 nm. Melanopsin in the iris of some, primarily nocturnal, mammals closes the iris when it is exposed to light. This local pupil light reflex (PLR) is absent from primates, even though their irises express melanopsin. Mechanism When light with an appropriate frequency enters the eye, it activates the melanopsin contained in intrinsically photosensitive retinal ganglion cells (ipRGCs), triggering an action potential. These neuronal electrical signals travel through neuronal axons to specific brain targets, such as the center of pupillary control called the olivary pretectal nucleus (OPN) of the midbrain. Consequently, stimulation of melanopsin in ipRGCs mediates behavioral and physiological responses to light, such as pupil constriction and inhibition of melatonin release from the pineal gland. The ipRGCs in the mammalian retina are one terminus